CN102169065A - Method for measuring normal rigidity of large contact interface by completely considering plastic influence - Google Patents

Abstract

The invention discloses a method for measuring the normal stiffness of a large contact interface which fully takes into account the influence of plasticity. The method adopts the contact system of two rough bodies as the measurement object, and uses laser light on the two rough bodies on the principle of complete equivalence of the systems. Mark three straight lines that meet the measurement requirements, and obtain the normal stiffness of the contact interface by examining the normal displacement of these three lines during the loading process. On the basis of the existing method, the present invention considers the influence of the shape degree of the contact interface on the normal contact stiffness, and uses a simple and easy laser marking method, so that it is not affected by the contact area and can measure the normal direction of the large contact interface Rigidity; the present invention breaks through the use limitation of the existing method, not only can be used in the laboratory, but also can be conveniently used in engineering practice.

Description

A Method for Measuring the Normal Stiffness of a Large Contact Interface Fully Considering the Effect of Plasticity

technical field

The invention belongs to the technical field of laser scanning and measurement, relates to the dynamic equivalence of a system and the friction characteristics of a material, and in particular to a method for measuring the normal stiffness of a large contact interface which fully takes into account the influence of plasticity.

Background technique

With the rapid development of large-scale mechanical equipment such as high-precision machine tools, heavy-duty gas turbines, and launch vehicles, more and more attention has been paid to the accurate measurement of the stiffness of the contact interface in the structure, because the stiffness of the contact interface will affect the dynamic characteristics of these large-scale mechanical equipment. Significant impact. If the effect of damping is ignored, the contact interface can be equivalent to a homogeneous spring in essence, so the accurate equivalence of the contact system is the basis for accurate measurement of the contact interface stiffness.

The existing equivalent methods for the normal stiffness of the contact interface are all based on the calculation formula proposed by T.R.Thomas&R.S.Sayles (see the literature THOMAS T R, SAYLES R S. Stiffness of machine tool joints: A random-process approach[J]. ASME J.Eng.Ind, 1977, 99: 250-256), which essentially obtains the normal equivalent of this area by examining the displacement variation between the mean line of the rough surface and the rigid surface under different normal loads. Stiffness, which is defined as the normal stiffness of this contact interface.

Since the investigation area of this method does not include all the plastic ranges, it is difficult to realize the complete dynamic equivalence of the elastic-plastic contact system. Therefore, two types of measurement experiments based on the existing equivalent methods, namely direct loading experiments and ultrasonic testing experiments, None of them can accurately measure the normal stiffness of the contact interface. At the same time, the existing measurement methods only consider the influence of the roughness and waviness of the contact interface on the normal contact stiffness, and do not consider the influence of the shape degree. In addition, the mean line of the rough surface investigated by the direct loading experiment is imaginary and will change with the change of the contact state, so it cannot be accurately marked; due to the focus of the ultrasonic experiment, the measurement area is limited, and a large contact interface cannot be obtained. normal stiffness. Therefore, a measurement method that can fully include the influence of material plasticity and facilitate large contact interfaces is necessary.

Contents of the invention

The purpose of the present invention is to overcome the above-mentioned shortcoming of prior art, provide a kind of large contact interface normal stiffness measurement method that fully considers the influence of plasticity, this method adopts two rough body contact systems as measurement object, with the complete equivalent of this system In principle, the laser marks three straight lines that meet the measurement requirements on the two rough bodies, and the normal stiffness of the contact interface is obtained by examining the normal displacement of these three lines during the loading process. This method can not only fully include the influence of material plasticity but also measure the large contact interface.

The purpose of the present invention is solved by the following technical solutions:

This method of measuring the normal stiffness of a large contact interface that fully takes into account the influence of plasticity is characterized in that it includes the following steps:

(1) For the two rough bodies A and B used in the normal stiffness measurement, use the finite element method to establish a contact model that is completely consistent with its parameters;

(2) Through finite element contact analysis, the plastic region range of the contact model of the two rough bodies in the contact process under pressure is obtained, and the maximum value of the plastic region thickness in the full load range is set as u _cl ;

(3) When placing two rough bodies A and B, make the two rough surfaces contact each other, mark a straight line L ₁ and L ₂ parallel to the contact interface on the two rough bodies A and B with laser, so that the straight lines L ₁ and L ₂ The part between can completely contain the plastic region, measure the distance from the straight line L ₁ to the straight line L ₂ and set it as h ₁ ; mark another straight line L ₃ parallel to the contact interface on the rough body A, the straight line L ₃ and the straight line L ₁ Not coincident, measure the distance from straight line L ₁ to straight line L ₃ and set it as h ₂ ;

(4) Apply a normal pressure load P _nom to the rough body A, measure the normal displacements of the three straight lines L ₁ , L ₂ and L ₃ and set them as δ ₁ , δ ₂ and δ ₃ ;

(5) The normal stiffness K _c of the contact interface can be obtained from the measured values of the normal displacements δ ₁ , δ ₂ and δ ₃ of the three straight lines and the pressure load P _nom :

${\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">h</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="P\; nom\; h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">P</figure-callout></span><figure-callout\; id="2"\; label="P\; nom\; h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; nom</span>}}}{{}_{}}<span\; class="notranslate">\; .</span>$

The line widths of the above three straight lines L ₁ , L ₂ and L ₃ are all less than 1 micron.

Compared with the prior art, the present invention has the following beneficial effects:

First, the present invention makes the inspection range h1 of the normal contact stiffness larger than the plastic range ucl, thereby including all the plastic effects of the material during the loading process, making the measurement results closer to reality;

Second, the present invention utilizes a simple and easy laser marking method, so that it is not affected by the contact area and can measure the normal stiffness of the large contact interface;

Third, the present invention considers the impact of the shape of the contact interface on the normal contact stiffness on the basis of the existing method;

Fourth, the present invention breaks through the limitations of the existing methods, not only can be used in laboratories, but also can be conveniently used in engineering practice.

Description of drawings

Figure 1 is a schematic diagram of the contact model of two rough bodies established, where A is the left rough body, C is the contact model of two rough bodies, and B is the right rough body;

Figure 2 is a schematic diagram of the plastic region under a certain load pressure, E is the plastic region;

Figure 3 is a schematic diagram of the change law of the plastic area in the full load range;

Fig. 4 is a schematic diagram of two straight lines marked on a rough body with a laser;

Figure 5 is a schematic diagram of the normal displacement of three straight lines that need to be measured;

Fig. 6 is a comparison between the method of the present invention and the existing method for measuring the normal stiffness of the contact interface.

Detailed ways

The method for measuring the normal stiffness of a large contact interface that fully takes into account the influence of plasticity in the present invention specifically includes the following steps:

(1) For the two rough bodies A and B used in the normal stiffness measurement, use the finite element method to establish a contact model that is completely consistent with its parameters;

(2) Through finite element contact analysis, the plastic region range of the contact model of the two rough bodies in the contact process under pressure is obtained, and the maximum value of the plastic region thickness in the full load range is set as u _cl ;

(3) When placing two rough bodies A and B, make the two rough surfaces contact each other, mark a straight line L ₁ and L ₂ parallel to the contact interface on the two rough bodies A and B with laser, so that the straight lines L ₁ and L ₂ The part between can completely contain the plastic region, measure the distance from the straight line L ₁ to the straight line L ₂ and set it as h ₁ ; mark another straight line L ₃ parallel to the contact interface on the rough body A, the straight line L ₃ and the straight line L ₁ Not coincident, measure the distance from straight line L ₁ to straight line L ₃ and set it as h ₂ ;

(4) Apply a normal pressure load P _nom to the rough body A, measure the normal displacements of the three straight lines L ₁ , L ₂ and L ₃ and set them as δ ₁ , δ ₂ and δ ₃ ;

(5) The normal stiffness K _c of the contact interface can be obtained from the measured values of the normal displacements δ ₁ , δ ₂ and δ ₃ of the three straight lines and the pressure load P _nom :

${\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">h</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="P\; nom\; h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">P</figure-callout></span><figure-callout\; id="2"\; label="P\; nom\; h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; nom</span>}}}{{}_{}}<span\; class="notranslate">\; .</span>$

The present invention is described in further detail below in conjunction with accompanying drawing:

Referring to shown in Fig. 1, establish a model according to the rough body related parameters used in the method of the present invention, these parameters comprise length L, width W, height H of two rough bodies, modulus of elasticity E, material yield limit σ, Poisson's ratio v, density ρ, surface roughness _Ra , peak density D _s and load pressure P _nom etc.

As shown in Figure 2, the plastic region of the rough body under a certain load pressure is obtained through contact analysis.

Referring to Fig. 3, changing the size of the load P _nom can obtain the change law of the plastic region in the full load range, and set its maximum value as u _cl .

As shown in Figure 4, when placing two rough bodies A and B, make the two rough surfaces contact each other, and mark a straight line L ₁ and L ₂ parallel to the contact interface on the rough bodies A and B with a laser (the line width is less than 1 micron ), so that the part between them can completely contain the plastic region, measure the distance from L ₁ to L ₂ and set it as h ₁ , obviously h ₁ is greater than u _cl ; mark another straight line L parallel to the contact interface on rough body A ₃ (L ₃ and L ₁ do not coincide), measure the distance from L ₁ to L ₃ and set it as h ₂ . The normal stiffness of the part between L ₁ and L ₂ is K _cl , and the normal stiffness of the part between L ₁ and L ₃ is K _l .

Referring to Fig. 5, the normal pressure load P _nom is applied to the rough body A, and the normal displacements of the three straight lines L ₁ , L ₂ and L ₃ are measured and set as δ ₁ , δ ₂ and δ ₃ .

According to the relationship between force and deformation, the normal stiffness K _cl of the part between L ₁ and L ₂ can be obtained by δ ₁ , δ ₂ and the normal load P _nom :

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; cl</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; nom</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; |</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

Similarly, the normal stiffness K _l of the part between L ₁ and L ₃ can be obtained through δ ₁ , δ ₃ and the normal load P _nom :

${\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; nom</span>}}}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&delta;</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; |</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

K _cl is the normal stiffness of a block with an interface, h ₂ */K _l /h ₁ is the normal stiffness of a block without an interface of the same length, the difference between the two is caused by the contact interface, so K _cl , h ₂ */K _l /h ₁ and K _c satisfy the following relationship:

$\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; cl</span>}}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}}<span\; class="notranslate">\; +</span>\frac{{\mathrm{<span\; class="notranslate">\; h</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}}{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">h</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; l</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

By substituting (2) and (3) into (4), the normal stiffness K _c of the contact interface can be obtained:

${\mathrm{<span\; class="notranslate">\; K</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">h</figure-callout></span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; <figure-callout\; id="2"\; label="P\; nom\; h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">P</figure-callout></span><figure-callout\; id="2"\; label="P\; nom\; h"\; filenames="HDA0000044397930000023.png"\; state="\{\{state\}\}">\; </figure-callout>}}_{\mathrm{<span\; class="notranslate">\; nom</span>}}}{{}_{}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

Implementation example:

In order to verify the method of the present invention: the method of measuring the normal stiffness of the large contact interface that fully takes into account the influence of plasticity, the existing direct loading measurement method and ultrasonic measurement method are used as comparison objects. Wherein, the numerical value of ultrasonic measurement method is obtained by the experiment that people such as Gonzalez-Valadez M, Baltazar A, Dwyer-Joyce R S.Study of interfacialstiffness ratio of a rough surface in contact suing a spring model[ J]. Wear, 2010, 268: 373-379); the numerical values of the direct loading measurement method and the method of the present invention are obtained by finite element simulation, and its model is shown in Fig. 1 . In order to make an effective comparison with the ultrasonic measurement method, the size and material of the two rough bodies are consistent, and one of the contact surfaces is a smooth plane. The relevant parameters are shown in Table 1.

Simulation model related parameters value (unit) Length L 0.2mm Width W 0.2mm Height H 0.6mm Elastic modulus E 200GPa Yield limit σ 835MPa Poisson's ratio v 0.3 Density ρ 7800Kg/ ^m3 Surface roughness _Ra 1.58μm Peak density D _s 7813/ ^mm2 Load pressure P _nom 0～400MPa

Table 1

Referring to shown in Fig. 6, since the ultrasonic method hardly accounts for the influence of material plasticity, the direct loading method partially accounts for the plastic influence, and the method of the present invention fully accounts for the plastic influence, therefore, in the full load range, the ultrasonic method obtains The normal contact stiffness value is the largest, followed by the direct loading method, and the method of the present invention is the smallest, and the difference between the three increases with the increase of the load. This shows that the method of the present invention has more accurate measurement values due to fully accounting for the influence of material plasticity.

The above examples are obtained for a certain contact area, but the present invention is not limited by the size of the contact area. Therefore, all equivalents or modifications that do not deviate from the spirit disclosed in the present invention fall within the protection scope of the present invention.

Claims (2)

1. a big contact interface normal stiffness measuring method of taking into account the plasticity influence fully is characterized in that, comprises following steps:

(1), utilize Finite Element Method to set up and the on all four contact model of its parameter at two asperities A and the B that adopted in the normal stiffness measurement;

(2), draw the plastic region scope of contact model in the pressurized contact process of two asperities, and the maximal value of plastic region thickness in the full load range is made as u by finite element contact analysis _Cl

When (3) placing two asperities A, B, make the contact of two uneven surfaces, with laser straight line L parallel of difference mark on two asperities A, B with contact interface ₁And L ₂, make straight line L ₁, L ₂Between part can comprise plastic region fully, measure straight line L ₁To straight line L ₂Distance and be made as h ₁Another straight line L parallel of mark on asperities A with contact interface ₃, straight line L ₃With straight line L ₁Do not overlap, measure straight line L ₁To straight line L ₃Distance and be made as h ₂

(4) asperities A is applied the normal pressure load p _Nom, measure three straight line L ₁, L ₂And L ₃The normal direction displacement and be made as δ ₁, δ ₂And δ ₃

(5) the normal direction displacement δ by three straight lines ₁, δ ₂And δ ₃Measured value and pressure load P _NomJust can obtain contact interface normal stiffness K _c:

$K_c=\frac{h_2\&CenterDot;P_{\mathrm{nom}}}{h_2\&CenterDot;|{\mathrm{\&delta;}}_1-{\mathrm{\&delta;}}_2|-h_1\&CenterDot;|{\mathrm{\&delta;}}_1-{\mathrm{\&delta;}}_3|}.$

2. the big contact interface normal stiffness measuring method of taking into account the plasticity influence fully according to claim 1 is characterized in that described three straight line L ₁, L ₂And L ₃Live width is all less than 1 micron.

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