DE202019006018U1 - Device for modeling and strength assessment of welds between mechanical components - Google Patents

Abstract

Computer-implemented device (100) for modeling and strength assessment of weld seams (4a, 4b) between mechanical components (2, 3) of an assembly using a finite element method, characterized by:
a first unit (101) for providing a finite element model (40, 50, 60) for the assembly, in which a first finite element mesh for a first component (2), a separate second finite element mesh for a second component (3) and a third finite element mesh for a weld seam (4a, 4b) connecting the first (2) and the second component (3) having a number of notches (5a, 5b, 5c) are generated, wherein the third finite element mesh has a number of less than 20 finite elements (6a, 6b, 6c) in cross-section, the notches (5a, 5b, 5c) of the weld seam (4a, 4b) are modeled with sharp edges and the distribution of the finite elements follows a defined mesh pattern (8a, 8b, 8c),
a second unit (102) for calculating the finite element model (40, 50, 60), wherein result variables of the finite elements and nodes are provided by the defined mesh pattern (8a, 8b, 8c) of the third finite element mesh for the weld seam (4a, 4b), and
a third unit (103) for applying a notch stress prediction algorithm adapted to the defined mesh pattern (8a, 8b, 8c) of the third finite element mesh for predicting notch stresses occurring in the notches (5a, 5b, 5c) using the provided result variables as input parameters.

Description

The present invention relates to a computer-implemented device for modeling and strength assessment of weld seams between mechanical components of an assembly using a finite element method.

The technical field of the invention relates to the modeling and strength assessment of weld seams between mechanical components of an assembly using a finite element method.

CAE analyses (CAE, computer-aided engineering), which are carried out by a computer, are widely used to simulate and assess the usability of technical structures. A common method of CAE analyses is finite element analysis. In this method, mechanical components are networked with finite elements and thus, for example, deformations or mechanical stresses under given loads are calculated. This can also be used, for example, to assess the strength of a structure.

If finite element models (FE models) are calculated that contain welds, the calculated stresses in the welds do not provide a direct statement about their load-bearing capacity. On the one hand, the FE models usually form the notches (see 1 ) of the respective weld seam is not measured accurately enough, on the other hand the material structure in the weld seam is changed after melting and cooling and cannot be evaluated like the base material.

The 1 a cross-section of a welded assembly 10. The components 2 and 3 of the assembly 10 are connected by the weld seams 4a and 4b. For the strength assessment of the weld seams 4a, 4b using notch stress concepts, the notches 5a, 5b, 5c are rounded with a radius defined in the corresponding regulations.

• Gruppe A: Bei Nennspannungsmethoden werden Kräfte und Momente an der Schweißnaht ausgewertet und damit Nennspannungen für einen Schweißnahtquerschnitt berechnet. Diese Nennspannungen müssen anschließend mit zulässigen Werten entsprechend einer Kerbfall-Klasse (FAT-Klasse) verglichen werden, welche der Anwender manuell wählen muss. Das erfordert gewisses Know-How und lässt fallweise Interpretationsspielraum, der zu Diskussionen und schwankenden Ergebnissen führt. Sonderfälle von Schweißnahtkonstellationen sind oft nicht in Standard-Kerbfall-Kathalogen enthalten.
• Gruppe B: 2 zeigt Strukturspannungskonzepte. Dafür werden die Schweißnähte ausmodelliert und durchgängig (ohne Kontakt) vernetzt. Für die Bewertung werden Spannungen von Stützstellen im Grundmaterial (also neben der Schweißnaht) ausgewertet und in die Schweißnaht-Kerbe extrapoliert. Diese Spannungen werden dann wieder je nach Art der Schweißnaht mit Kerbfall- oder FAT-Klassen verglichen. Das bedeutet erheblichen Aufwand in der Modellerstellung und Auswertung. Und es erfordert wieder gewisses Know-How vom Anwender und lässt teilweise Interpretationsspielraum bei der Wahl der richtigen Kerbfall-Klasse. Die Abbildungen der 2 sind der IIW-Richtlinie gemäß Referenz [1] entnommen.
• Gruppe C: Am genauesten und allgemein gültigsten sind Kerbspannungsmethoden, wie in 3 dargestellt. In 3 zeigt Bezugszeichen 30 ein fein vernetztes FE-Modell einer Baugruppe mit zwei geschweißten Bauteilen 2, 3, wobei die jeweilige Schweißnaht 4a, 4b verrundete Kerben 5a, 5b, 5c aufweist. Aus Gründen der Übersichtlichkeit sind die Kerben nur für die rechte Schweißnaht 4a mit dem Bezugszeichen 5a, 5b, 5c versehen. Dabei müssen die Kerben 5a, 5b, 5c mit einem normierten Radius modelliert und sehr fein vernetzt werden. Auch das bedeutet erheblichen Modellierung- und Berechnungsaufwand. Die Bewertung läuft hier etwas einfacher, da die Kerbspannungen mit fixen normierten zulässigen Werten (z.B. FAT 225) verglichen werden. Diese Methode ist zwar für jede beliebige Schweißnahtkonstellation geeignet, lässt wenig Interpretationsspielraum und ist daher einfacher in der Anwendung. Aber da eine sehr feine Vernetzung und damit großer Rechenaufwand notwendig ist, wird die Kerbspannungsmethode typischerweise nur für kleine, sehr lokale Geometriedetails in sogenannten Submodellen verwendet. Für große Modelle mit vielen Schweißnähten kann die Kerbspannungsmethode wirtschaftlich nicht flächendeckend angewendet werden.

There are a number of regulations that describe additional methods for carrying out weld evaluations based on FE results. The methods are divided into the following three groups: A, B and C:

• Group A: With nominal stress methods, forces and moments on the weld seam are evaluated and nominal stresses are calculated for a weld seam cross-section. These nominal stresses must then be compared with permissible values according to a notch case class (FAT class), which the user must select manually. This requires a certain amount of know-how and leaves room for interpretation in certain cases, which leads to discussions and fluctuating results. Special cases of weld seam constellations are often not included in standard notch case catalogs.
• Group B: 2 shows structural stress concepts. For this, the welds are modeled and networked continuously (without contact). For the evaluation, stresses from support points in the base material (i.e. next to the weld) are evaluated and extrapolated into the weld notch. These stresses are then compared with notch case or FAT classes depending on the type of weld. This means considerable effort in model creation and evaluation. And it again requires a certain amount of know-how from the user and sometimes leaves room for interpretation when choosing the right notch case class. The images of the 2 are taken from the IIW guideline according to reference [1].
• Group C: The most accurate and generally valid are notch stress methods, as in 3 shown. In 3 Reference number 30 shows a finely meshed FE model of an assembly with two welded components 2, 3, where the respective weld seam 4a, 4b has rounded notches 5a, 5b, 5c. For reasons of clarity, the notches are only provided with the reference number 5a, 5b, 5c for the right weld seam 4a. The notches 5a, 5b, 5c must be modeled with a standardized radius and meshed very finely. This also means considerable modeling and calculation effort. The evaluation is somewhat simpler here, since the notch stresses are compared with fixed standardized permissible values (e.g. FAT 225). Although this method is suitable for any weld seam constellation, it leaves little room for interpretation and is therefore easier to use. However, since very fine meshing and thus a large amount of calculation effort is necessary, the notch stress method is typically only used for small, very local geometric details in so-called submodels. For large models with many weld seams, the stress concentration method cannot be applied economically across the board.

Notch stress assessment methods are the most universally applicable and most accurate, but they also require the most computational effort. In addition, notch stress methods require less experience and know-how from the user, since no weld notch cases or fatigue classes have to be selected from catalogs.

All conventional methods require appropriately targeted modeling and meshing. Nominal and structural stress methods use FE models with fewer nodes and thus less computational effort, but require more user input and experience and are less accurate in terms of results than notch stress methods. The latter are very precise and unambiguous in application, but also very computationally intensive.

Information on conventional methods for modeling and strength assessment of welds between mechanical components of an assembly can be found in references [1] to [9].

Against this background, one object of the present invention is to improve the modeling and strength assessment of weld seams between mechanical components of an assembly.

1. a) Bereitstellen eines Finite-Elemente-Modells für die Baugruppe, bei welchem ein erstes Finite-Elemente-Netz für ein erstes Bauteil, ein getrenntes zweites Finite-Elemente-Netz für ein zweites Bauteil und ein drittes Finite-Elemente-Netz für eine das erste und das zweite Bauteil verbindende Schweißnaht aufweisend eine Anzahl von Kerben erzeugt werden, wobei das dritte Finite-Elemente-Netz eine Anzahl von weniger als 20 finiten Elementen im Querschnitt aufweist, die Kerben der Schweißnaht dabei scharfkantig modelliert sind und die Aufteilung der finiten Elemente einem definierten Netzmuster folgt,
2. b) Berechnen des Finite-Elemente-Modells, wobei von dem definierten Netzmuster des dritten Finite-Elemente-Netzes für die Schweißnaht Ergebnisgrößen der finiten Elemente und Knoten bereitgestellt werden, und
3. c) Anwenden eines auf das definierte Netzmuster des dritten Finite-Elemente-Netzes abgestimmten Kerbspannungs-Prognosealgorithmus zur Prognose auftretender Kerbspannungen in den Kerben (in einem verrundeten Zustand) unter Verwendung der bereitgestellten Ergebnisgrößen als Eingabeparameter.

A computer-implemented method for modelling and strength assessment of welds between mechanical components of an assembly using a finite element method is proposed. The method comprises the following steps:

1. a) providing a finite element model for the assembly, in which a first finite element mesh for a first component, a separate second finite element mesh for a second component and a third finite element mesh for a weld seam connecting the first and the second component having a number of notches are generated, wherein the third finite element mesh has a number of less than 20 finite elements in the cross-section, the notches of the weld seam are modeled with sharp edges and the distribution of the finite elements follows a defined mesh pattern,
2. b) calculating the finite element model, whereby result quantities of the finite elements and nodes are provided by the defined mesh pattern of the third finite element mesh for the weld, and
3. c) Applying a notch stress prediction algorithm tailored to the defined mesh pattern of the third finite element mesh to predict notch stresses occurring in the notches (in a rounded state) using the provided result variables as input parameters.

• eine erste Einheit zum Bereitstellen eines Finite-Elemente-Modells für die Baugruppe, bei welchem ein erstes Finite-Elemente-Netz für ein erstes Bauteil, ein getrenntes zweites Finite-Elemente-Netz für ein zweites Bauteil und ein drittes Finite-Elemente-Netz für eine das erste und das zweite Bauteil verbindende Schweißnaht aufweisend eine Anzahl von Kerben erzeugt werden, wobei das dritte Finite-Elemente-Netz eine Anzahl von weniger als 20 finiten Elementen im Querschnitt aufweist, die Kerben der Schweißnaht dabei scharfkantig modelliert sind und die Aufteilung der finiten Elemente einem definierten Netzmuster folgt,
• eine zweite Einheit zum Berechnen des Finite-Elemente-Modells, wobei von dem definierten Netzmuster des dritten Finite-Elemente-Netzes für die Schweißnaht Ergebnisgrößen der finiten Elemente und Knoten bereitgestellt werden und
• eine dritte Einheit zum Anwenden eines auf das definierte Netzmuster des dritten Finite-Elemente-Netzes abgestimmten Kerbspannungs-Prognosealgorithmus zur Prognose auftretender Kerbspannungen in den Kerben unter Verwendung der bereitgestellten Ergebnisgrößen als Eingabeparameter.

According to a first aspect, a computer-implemented device for modeling and strength assessment of weld seams between mechanical components of an assembly using a finite element method is proposed. The device comprises:

• a first unit for providing a finite element model for the assembly, in which a first finite element mesh for a first component, a separate second finite element mesh for a second component and a third finite element mesh for a weld seam connecting the first and the second component having a number of notches are generated, wherein the third finite element mesh has a number of less than 20 finite elements in the cross section, the notches of the weld seam are modeled with sharp edges and the distribution of the finite elements follows a defined mesh pattern,
• a second unit for calculating the finite element model, whereby result variables of the finite elements and nodes are provided by the defined mesh pattern of the third finite element mesh for the weld seam and
• a third unit for applying a notch stress prediction algorithm adapted to the defined mesh pattern of the third finite element mesh to predict notch stresses occurring in the notches using the provided result variables as input parameters.

The respective unit can be implemented in hardware and/or software. In a hardware implementation, the unit can be designed as a device or as part of a device, for example as a computer or as a microprocessor. In a software implementation, the unit can be designed as a computer program product, as a function, as a routine, as part of a program code or as an executable object.

This makes the calculations and strength assessment of weld seams in finite element models easier and faster using stress-prediction algorithms. This makes it possible to model the weld seams with sharp edges and mesh them relatively roughly, while still obtaining a good forecast for the stress-prediction, which can then be used to carry out a strength assessment. This speeds up the calculation and assessment process considerably and also makes it possible to use a stress-prediction algorithm even for FE models with a large number of weld seams. The modeling and evaluation of the weld seams can advantageously be easily automated and carried out by software programs.

Since the notch chip method can also be used with complex FE models using the computer-implemented method, the user needs less know-how than with conventional methods that require the selection of a notch case class. Furthermore, the user can intuitively check the exact type and geometric dimensions of the weld seams using the volume meshing and thus avoid errors. Because the notch chip concept is used as a basis, the method is not limited to a restricted group of weld seam types from a notch case catalog, but can analyze any welding constellation.

If one wants to categorize weld evaluation methods, the proposed method can be placed between the existing structural stress and notch stress methods. The proposed method combines the lower calculation effort of the structural stress methods with the more general applicability and the more precise geometric representation and easier evaluation of the notch stress methods due to the smaller number of nodes.

According to the invention, the third finite element mesh has a number of 1 to 20 finite elements in the cross-section. A small number of elements leads to lower calculation accuracy, but also advantageously to shorter calculation times. A larger number of elements and especially smaller elements near the weld seam notches lead to more accurate results with greater calculation effort and time. The method can therefore be trimmed more towards shorter calculation times or higher accuracy as required.

The finite element is in particular a volume element. The finite elements of the weld seams are designed in particular as 3D volume elements in 3D models and as 2D elements in 2D models and complement the FE model of the unwelded components.

Examples of mechanical components include thin-walled parts, such as sheet metal or profiles, or thick-walled or voluminous parts, such as castings.

According to one embodiment, the first finite element mesh and the third finite element mesh are coupled by means of a first number of coupling elements and the second finite element mesh and the third finite element mesh are coupled by means of a second number of coupling elements.

By using the coupling elements, no common continuous networking is necessary between the third finite element mesh for the weld seam and the first finite element mesh for the first component. Accordingly, no common continuous networking is necessary between the third finite element mesh for the weld seam and the second finite element mesh for the second component. Consequently, the third finite element mesh can be subsequently added to an existing and unwelded component mesh comprising the first finite element mesh and the second finite element mesh. Advantageously, no common nodes are necessary between the finite element meshes for the weld seam and for the components. This advantageously reduces the effort required for networking. The third finite element mesh for the weld seam can also be subsequently integrated.

• b1) Berechnen des Finite-Elemente-Modells, und
• b2) Auswerten der Ergebnisgrößen der finiten Elemente und der Knoten des definierten Netzmusters für die Schweißnaht auf der Basis des berechneten Finite-Elemente-Modells.

According to a further embodiment, step b) is formed by:

• b1) Calculating the finite element model, and
• b2) Evaluating the result quantities of the finite elements and the nodes of the defined mesh pattern for the weld on the basis of the calculated finite element model.

According to a further embodiment, in step b2) result variables are evaluated exclusively within the finite elements and the nodes of the third finite element mesh for the weld seam.

• - Spannungsergebnisse,
• - Reaktionskraftergebnisse,
• - Geometrieparameter, und/oder
• - Materialparameter.

According to a further embodiment, the result variables evaluated in step b2) include:

• - Voltage results,
• - Reaction force results,
• - geometry parameters, and/or
• - Material parameters.

• - Spannungsergebnisse,
• - Reaktionskraftergebnisse,
• - Geometrieparameter, und
• - Materialparameter.

According to a further embodiment, the result variables evaluated in step b2) consist of:

• - Voltage results,
• - Reaction force results,
• - geometry parameters, and
• - Material parameters.

According to a further embodiment, the stress notch prediction algorithm is tested with a plurality of Weld seam constellations are trained using the defined mesh pattern.

Each weld configuration preferably has different geometric dimensions (parameters) of the components and the weld as well as different loads (parameters) and represents a design point in the parameter space. For each design point, firstly the existing modelling method and secondly a variant with standard notch fillet radius and very fine meshing as in 3 calculated. The second model provides the reference results (target values) of the weld seam notch stresses and the first model provides the input data for the notch stress prediction algorithm. The notch stress prediction algorithm is thus fitted (trained) to the existing mesh pattern, the given notch radius and the existing modeling method of the first model. The algorithm trained in this way can then be applied to productive calculation models to predict weld seam notch stresses.

Although the notch stress prediction algorithm requires a certain amount of effort to create (when fitting or training), it is very efficient in subsequent use and requires very little computing time. According to a further embodiment, in step c) a plurality of parameters of the notches are predicted using the notch stress prediction algorithm.

• - Hauptnormalspannungen,
• - Schubspannungen,
• - Von-Mises-Vergleichsspannungen, und/oder
• - Radial-, Tangential- und/oder Axial-Spannungskomponenten im Kerbradius der jeweiligen Kerbe.

According to a further embodiment, these parameters include:

• - principal normal stresses,
• - shear stresses,
• - Von Mises equivalent stresses, and/or
• - Radial, tangential and/or axial stress components in the notch radius of the respective notch.

According to a further embodiment, strength assessments of the assembly are subsequently carried out using the predicted stress concentrations.

According to a second aspect, a computer program product is proposed which causes the method as explained above to be carried out on a program-controlled device.

A computer program product, such as a computer program means, can be provided or delivered, for example, as a storage medium, such as a memory card, USB stick, CD-ROM, DVD, or in the form of a downloadable file from a server in a network. This can be done, for example, in a wireless communications network by transmitting a corresponding file with the computer program product or the computer program means.

Further possible implementations of the invention also include combinations of features or embodiments described above or below with respect to the exemplary embodiments that are not explicitly mentioned. The person skilled in the art will also add individual aspects as improvements or additions to the respective basic form of the invention.

• 1 zeigt einen Querschnitt einer geschweißten Baugruppe;
• 2 zeigt als erstes Beispiel für den Stand der Technik die Strukturspannungsmethode;
• 3 zeigt als zweites Beispiel für den Stand der Technik das Kerbspannungskonzept;
• 4 zeigt den Querschnitt eines FE-Modells einer Baugruppe mit erfindungsgemäß modellierter Schweißnaht;
• 5 zeigt den Querschnitt eines FE-Modells einer Baugruppe mit einer Variante einer erfindungsgemäß modellierten Schweißnaht;
• 6 zeigt den Querschnitt eines FE-Modells einer Baugruppe mit einer weiteren Variante einer erfindungsgemäß modellierten Schweißnaht;
• 7 zeigt Querschnitte von FE-Modellen von Baugruppen mit verschiedenen Varianten von erfindungsgemäß modellierten Schweißnähten;
• 8 zeigt verschiedene Anwendungsfälle von erfindungsgemäß modellierten Schweißnähten;
• 9 zeigt ein schematisches Ablaufdiagramm eines Beispiels eines computerimplementierten Verfahrens zur Modellerstellung und Festigkeitsbewertung von Schweißnähten zwischen mechanischen Bauteilen einer Baugruppe unter Zuhilfenahme einer Finite-Elemente-Methode; und
• 10 zeigt ein schematisches Blockschaltbild eines Ausführungsbeispiels einer computerimplementierten Vorrichtung zur Modellerstellung und Festigkeitsbewertung von Schweißnähten zwischen mechanischen Bauteilen einer Baugruppe unter Zuhilfenahme einer Finite-Elemente-Methode.

Further advantageous embodiments and aspects of the invention are the subject of the dependent claims and the embodiments of the invention described below. The invention is explained in more detail below using preferred embodiments with reference to the attached figures.

• 1 shows a cross-section of a welded assembly;
• 2 shows the structural stress method as a first example of the state of the art;
• 3 shows the notch stress concept as a second example of the state of the art;
• 4 shows the cross-section of an FE model of an assembly with a weld seam modelled according to the invention;
• 5 shows the cross-section of an FE model of an assembly with a variant of a weld seam modelled according to the invention;
• 6 shows the cross-section of an FE model of an assembly with another variant of a weld seam modelled according to the invention;
• 7 shows cross-sections of FE models of assemblies with different variants of weld seams modelled according to the invention;
• 8th shows various application cases of weld seams modelled according to the invention;
• 9 shows a schematic flow diagram of an example of a computer-implemented method for modeling and strength assessment of welds between mechanical components of an assembly using a finite element method; and
• 10 shows a schematic block diagram of an embodiment of a computer-im implemented device for modeling and strength assessment of welds between mechanical components of an assembly using a finite element method.

In the figures, identical or functionally equivalent elements have been given the same reference numerals unless otherwise stated.

Examples of implementation for model creation and strength assessment of weld seams 4a, 4b between mechanical components 2, 3 of an assembly are described with common reference to the 4 to 9 explained. The 4 to 7 Examples of FE models of an assembly with a weld seam according to the invention. Furthermore, the 8th Applications of weld seams modulated according to the invention. Furthermore, the 9 an example of a computer-implemented method for modeling and strength assessment of weld seams 4a, 4b between mechanical components 2, 3 of an assembly using a finite element method.

Starting with 4 This shows an FE model 40 of a welded assembly. A first component 2 and a second component 3 of the assembly are welded by means of two weld seams 4a, 4b. The notches of the weld seam 4a are provided with the reference symbols 5a, 5b, 5c and the finite elements which represent the weld seam 4a are provided with the reference symbols 6a, 6b, 6c. For reasons of clarity, only the notches and the finite elements of the weld seam 4a are provided with reference symbols, but not the notches and the finite elements of the weld seam 4b.

The finite elements 6a, 6b, 6c are designed as 3D volume elements in 3D models and as 2D elements in 2D models and complement the FE model 40 of the welded component. The components 2, 3 and the weld seams 4a, 4b can be networked either with common nodes or independently of each other with separate nodes. A separate, independent network has the advantage that the variation of the weld seam geometry is easier and no change to the basic model of the components 2, 3 is necessary.

In the case of independent networking, the weld elements 6a, 6b, 6c are connected to the components 2, 3 using coupling elements 7a, 7b (see also 5 ). Examples of coupling elements 7a, 7b include contact elements, coupling beams or coupling equations.

The independent networking and connection with coupling elements 7a, 7b is made possible because result variables are preferably evaluated only from within the weld elements or nodes.

The weld seams 4a, 4b are meshed with a defined mesh pattern, whereby these mesh patterns are coordinated with a notch stress prediction algorithm used subsequently. The weld seam elements 6a, 6b, 6c preferably have a predefined number, a predefined distribution and a predefined position within the weld seam 4a, 4b. The notches 5a, 5b, 5c of the weld seam 4a are not rounded, but are modeled with sharp edges. This allows a relatively coarse mesh and thus saves considerable calculation effort and calculation time. The geometry, dimensions and position of the respective weld seam 4a, 4b are preferably modeled realistically, which is why the stiffness is represented with good accuracy and the defined mesh pattern is proportionally adapted to the given weld seam geometry. The 7 some examples of structured mesh patterns 8a, 8b, 8c for weld seams 4a, 4b. It should be noted that the stress notch prediction algorithm used below is tailored to the mesh pattern 8a, 8b, 8c used. The creation of a weld seam mesh with a defined mesh pattern 8a, 8b, 8c can be done automatically using software routines (see process step S1 of the 9 ).

The FE model of the assembly prepared in this way, including the weld seams 4a, 4b, is then solved using a calculation method and the results are evaluated (see process step S2 of the 9 ).

A number of parameters are evaluated from the welds 4a, 4b and made available to the notch stress prediction algorithm as input data. The parameters can be stresses, strains and/or reaction forces of the weld elements 6a, 6b, 6c and nodes. In addition, material and/or geometry parameters, such as the dimensions of the weld cross-section, relative position coordinates of individual nodes within the weld cross-section or connection angles of the connection geometry in the individual weld cross-sections and notches, can be used.

• - Globale Polynome
• - Moving least squares
• - Kriging
• - Radial basis functions
• - Neuronale Netze

The stress prediction algorithm includes in particular metamodels or response surface methods, such as:

• - Global polynomials
• - Moving least squares
• - Kriging
• - Radial basis functions
• - Neural Networks

• - Regression
• - Interpolation
• - Extrapolation

These models are created (fitted or trained) using, for example:

• - Regression
• - Interpolation
• - Extrapolation

The notch stress prediction algorithms are each fitted (trained) to a given weld modeling method with a given mesh pattern. Input data of the notch stress prediction algorithm are a relevant subset of the parameters mentioned above. Output data are notch stresses and notch stress components for each weld notch per weld cross-section.

In order to be able to fit (train) the notch stress prediction algorithm, a sufficient number of weld seam constellations are preferably calculated. Each weld seam constellation has different geometric dimensions (parameters) of the components and the weld seam as well as different loads (parameters) and represents a design point in the parameter space. For each design point, firstly the existing modeling method and secondly a variant with standard notch fillet radius and very fine meshing as in 3 calculated. The second model provides the reference results (target values) of the weld seam notch stresses and the first model provides the input data for the notch stress prediction algorithm. The notch stress prediction algorithm is thus fitted (trained) to the existing mesh pattern, the given notch radius and the existing modeling method of the first model. The algorithm trained in this way can then be used in productive calculation models to predict weld seam notch stresses. Even if the forecast accuracy can be somewhat worse than with the classic rounded and finely meshed notch stress calculation method, the method according to the invention still offers an enormous advantage, since significantly shorter calculation times are achieved with significantly fewer nodes and it is only possible for notch stress evaluation methods to be used economically on complex finite element models with many welds. Without the present method, the number of elements and nodes for notch stress calculation in complex models would be too large to be economically calculated.

The notch stresses and notch stress components thus predicted can subsequently be used to carry out an operational or fatigue strength assessment of the weld.

This notch stress evaluation method is applied to a cross-section of a weld seam, i.e. new local notch stresses can be predicted at defined intervals in the longitudinal direction of the weld seam.

The modeling method can be used in the same way for different weld seam application cases. 8th shows the possible application for T-joints 9a, butt joints 9b and lap joints 9c. For two-sided welded joints, a weld seam model is preferably used on each side. The notch stress prediction algorithm can preferably be fitted so that it can be used unchanged for all of these applications. However, for greater forecast accuracy, specialised notch stress prediction algorithms can also be fitted for individual applications.

For example, in 7 with the reference symbols 8b and 8c, in the case of simple fillet welds, components are welded without geometric weld preparation. In order to obtain a better and continuous connection, the components are often bevelled, as shown by reference symbol 8a, and thus provided with geometric weld preparation. 4 shows a weld seam modelled according to the invention in which the weld seam preparation on the component is fully modelled and networked. As in 5 represented, but the components can also be modeled without weld seam preparation. This is made possible by the independent weld seam meshing and the connection of the weld seams with the components via coupling elements or coupling equations 7a. This facilitates the variation of the weld seam geometry without having to change the finite element model of the components themselves.

The present modelling method also allows, as in 6 shown, in the same way the application to shell models 60. The components 2, 3 are meshed with finite shell elements in the middle plane of the components 2, 3 and the weld seams 4a, 4b with the defined mesh pattern and the real weld seam geometry. The connection is again made with coupling elements or coupling equations 7a, 7b. The present modeling and stress notch prediction method can therefore be used in many different applications ( 4 , 5 , 6 , 8th ) be used.

• In Schritt S1 wird ein Finite-Elemente-Modell 40 (siehe 4), 50 (siehe 5), 60 (siehe 6) für die Baugruppe bereitgestellt. Bei diesem Finite-Elemente-Modell 40, 50, 60 wird ein erstes Finite-Elemente-Netz für ein erstes Bauteil 2, ein getrenntes Finite-Elemente-Netz für ein zweites Bauteil 3 und ein drittes Finite-Elemente-Netz für eine das erste Bauteil 2 und das zweite Bauteil 3 verbindende Schweißnaht 4a, 4b aufweisend eine Anzahl von Kerben 5a, 5b, 5c erzeugt. Dabei weist das dritte Finite-Elemente-Netz eine Anzahl von weniger als 20 finiten Elementen 6a, 6b, 6c im Querschnitt auf. Die Kerben 5a, 5b, 5c der Schweißnaht 4a, 4b werden dabei scharfkantig modelliert. Die Aufteilung der finiten Elemente folgt dabei einem definierten Netzmuster 8a, 8b, 8c (siehe 8). Beispielsweise werden das erste Finite-Elemente-Netz und das dritte Finite-Elemente-Netz mittels einer Anzahl von Koppelelementen 7a, 7b, 7c gekoppelt und das zweite Finite-Elemente-Netz und das dritte Finite-Elemente-Netz werden mittels einer zweiten Anzahl von Koppelelementen 7a, 7b, 7c gekoppelt.

9 shows a schematic flow diagram of an example of a computer-implemented method for modeling and strength assessment of weld seams 4a, 4b between mechanical components 2, 3 of an assembly using a finite element method. The method of 9 comprises the method steps S1 to S3 and is described with reference to the 4 to 8 explains:

• In step S1, a finite element model 40 (see 4 ), 50 (see 5 ), 60 (see 6 ) for the assembly. In this finite element model 40, 50, 60, a first finite element mesh for a first component 2, a separate finite element mesh for a second component 3 and a third finite element mesh for a weld seam 4a, 4b connecting the first component 2 and the second component 3 and having a number of notches 5a, 5b, 5c are generated. The third finite element mesh has a number of less than 20 finite elements 6a, 6b, 6c in the cross section. The notches 5a, 5b, 5c of the weld seam 4a, 4b are modeled with sharp edges. The distribution of the finite elements follows a defined mesh pattern 8a, 8b, 8c (see 8th ). For example, the first finite element mesh and the third finite element mesh are coupled by means of a number of coupling elements 7a, 7b, 7c and the second finite element mesh and the third finite element mesh are coupled by means of a second number of coupling elements 7a, 7b, 7c.

In step S2, the finite element model 40, 50, 60 is calculated, whereby result quantities of the defined elements and nodes are provided from the defined mesh pattern 8a, 8b, 8c of the third finite element mesh for the weld seam 4a, 4b.

• - Berechnen des Finite-Elemente-Modells 40, 50, 60, und
• - Auswerten der Ergebnisgrößen der finiten Elemente und der Knoten des definierten Netzmusters 8a, 8b, 8c für die Schweißnaht 4a, 4b auf der Basis des berechneten Finite-Elemente-Modells 40, 50, 60.

For example, step S2 comprises the following substeps:

• - Calculate the finite element model 40, 50, 60, and
• - Evaluation of the result quantities of the finite elements and the nodes of the defined mesh pattern 8a, 8b, 8c for the weld seam 4a, 4b on the basis of the calculated finite element model 40, 50, 60.

In this case, result variables are preferably evaluated exclusively within the finite elements and the nodes of the third finite element mesh for the weld seam 4a, 4b. The result variables preferably include and consist of: stress results, reaction force results, geometry parameters, and/or material parameters.

In step S3, a notch stress prediction algorithm is applied to predict notch stress occurring in the notches 5a, 5b, 5c using the provided result variables as input parameters. The notch stress prediction algorithm predicts the notch stresses occurring in the notches 5a, 5b, 5c in their rounded state. The notch stress prediction algorithm applied is tailored to the defined mesh pattern 8a, 8b, 8c of the third finite element mesh.

The notch stress prediction algorithm is preferably trained before its application with a plurality of weld parameter variants for the weld 4a, 4b using the defined mesh pattern 8a, 8b, 8c. A plurality of parameters are predicted by means of the notch stress prediction algorithm. This plurality of parameters includes: principal normal stresses, shear stresses, Von Mises equivalent stresses, radial-tangential stress components and/or axial stress components in the notch radius of the respective notch 5a, 5b, 5c.

The predicted stress concentrations can then be used to perform strength assessments of the assembly.

In 10 is a schematic block diagram of an embodiment of a computer-implemented device 100 for modeling and strength assessment of weld seams 4a, 4b between mechanical components 2, 3 of an assembly with the aid of a finite element method.

The device 100 comprises a first unit 101, a second unit 102 and a third unit 103.

The first unit 101 is set up to provide a finite element model 40, 50, 60 for the assembly, in which a first finite element mesh for a first component 2, a separate second finite element mesh for a second component 3 and a third finite element mesh for a weld seam 4a, 4b connecting the first component 2 and the second component 3 and having a number of notches 5a, 5b, 5c are generated. The third finite element mesh has a number of less than 20 finite elements 6a, 6b, 6c in the cross section, the notches 5a, 5b, 5c of the weld seam 4a, 4b are modeled with sharp edges and the distribution of the finite elements follows a defined mesh pattern 8a, 8b, 8c.

The second unit 102 is set up to calculate the finite element model 40, 50, 60, wherein result quantities of the finite elements and nodes are provided by the defined mesh pattern 8a, 8b, 8c of the third finite element mesh for the weld seam 4a, 4b.

The third unit 103 is configured to apply a notch stress prediction algorithm tailored to the defined mesh pattern 8a, 8b, 8c of the third finite element mesh to predict notch stresses occurring in the notches 5a, 5b, 5c using the provided result variables as input parameters.

Although the present invention has been described using exemplary embodiments, it can be modified in many ways.

LIST OF REFERENCE SYMBOLS

2

Component

3

Component

4

Weld

4a

Weld

4b

Weld

5a

score

5b

score

5c

score

6a

finite element

6b

finite element

6c

finite element

30

Finite element model

7a

Coupling element

7b

Coupling element

7c

Coupling element

8a

Net pattern

8b

Net pattern

8c

Net pattern

9a

T-joints

9b

Stump impacts

9c

Lap joints

10

module

40

Finite element model

50

Finite element model

60

Finite element model

100

contraption

101

first unit

102

second unit

103

third unit

S1

Process step

S2

Process step

S3

Process step

CREDENTIALS:

• [1] IIW Guideline ^: “Recommendations for Fatigue Design of Welded Joints and Components” by the International Institute of Welding (IIW) or AF Hobbacher
• [2] FKM guideline: “Calculated strength verification for machine components” from the Research Committee for Mechanical Engineering (FKM) (publisher)
• [3] CN103838975A
• [4] DE102012023670A1
• [5] DE102014224129A1
• [6] EP1337942B1
• [7] EP3267338A1
• [8th] JP2003080393A
• [9] US2013325417A1

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions.

Cited patent literature

• CN103838975A [0065]
• DE 102012023670 A1 [0065]
• DE 102014224129 A1 [0065]
• EP 1337942 B1 [0065]
• EP 3267338 A1 [0065]
• JP 2003080393 A [0065]
• US 2013325417 A1 [0065]

Claims (10)

Computer-implemented device (100) for modeling and strength assessment of weld seams (4a, 4b) between mechanical components (2, 3) of an assembly with the aid of a finite element method, characterized by : a first unit (101) for providing a finite element model (40, 50, 60) for the assembly, in which a first finite element mesh for a first component (2), a separate second finite element mesh for a second component (3) and a third finite element mesh for a weld seam (4a, 4b) connecting the first (2) and the second component (3) having a number of notches (5a, 5b, 5c) are generated, wherein the third finite element mesh has a number of less than 20 finite elements (6a, 6b, 6c) in cross-section, the notches (5a, 5b, 5c) of the weld seam (4a, 4b) are modeled with sharp edges and the division of the finite elements follows a defined mesh pattern (8a, 8b, 8c), a second unit (102) for calculating the finite element model (40, 50, 60), wherein result variables of the finite elements and nodes are provided by the defined mesh pattern (8a, 8b, 8c) of the third finite element mesh for the weld seam (4a, 4b), and a third unit (103) for applying a notch stress prediction algorithm matched to the defined mesh pattern (8a, 8b, 8c) of the third finite element mesh to predict notch stresses occurring in the notches (5a, 5b, 5c) using the provided result variables as input parameters. Device according to Claim 1 , characterized in that the first unit (101) is configured to couple the first finite element network and the third finite element network by means of a first number of coupling elements (7a, 7b, 7c) and to couple the second finite element network and the third finite element network by means of a second number of coupling elements (7a, 7b, 7c). Device according to Claim 1 or 2 , characterized in that the second unit (102) is arranged to: b1) calculate the finite element model (40, 50, 60), and b2) evaluate the result variables of the finite elements and the nodes of the defined mesh pattern (8a, 8b, 8c) for the weld seam (4a, 4b) on the basis of the calculated finite element model (40, 50, 60). Device according to Claim 3 , characterized in that the second unit (102) is arranged to evaluate result variables exclusively within the finite elements and the nodes of the third finite element mesh for the weld seam (4a, 4b). Device according to Claim 3 or 4 , characterized in that the result variables comprise: - stress results, - reaction force results, - geometry parameters, and/or - material parameters. Device according to Claim 3 or 4 , characterized in that the result quantities consist of: - stress results, - reaction force results, - geometry parameters, and - material parameters. Device according to one of the Claims 1 until 6 , characterized in that the third unit (103) is designed to train the notch stress prediction algorithm with a plurality of weld parameter variants using the defined mesh pattern (8a, 8b, 8c) before predicting occurring notch stresses. Device according to one of the Claims 1 until 7 , characterized in that the third unit (103) is arranged to predict a plurality of parameters of the notches (5a, 5b, 5c) by means of the notch stress prediction algorithm. Device according to Claim 8 , characterized in that the parameters comprise: - principal normal stresses, - shear stresses, - Von Mises equivalent stresses, - radial-tangential stress components, and/or - axial stress components in the notch radius of the respective notch (5a, 5b, 5c). Device according to one of the Claims 1 until 9 , characterized in that the third unit (103) is adapted to carry out strength assessments of the assembly using the predicted stress concentrations.

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