CA1222884A - Static bending apparatus for grading wood panels - Google Patents

Abstract

"STATIC BENDING APPARATUS FOR GRADING WOOD PANELS" A non-destructive method and apparatus is provided for testing a wood panel, such as a sheet of plywood, to establish values which may be used in calculating a measure of the modulus of elasticity (MOE) for the panel. The invention involves supporting the bottom surface of the panel horizontally with two spaced parallel rollers and contacting the top surface of the panel with a pivotally mounted loading bar which is adapted to apply linear loading to the panel substantially uniformly across its width, even though the panel may be warped or bent. The loading bar is biased by a double-acting cylinder so as to apply a first load and then, in quick succession, a second incremental load. The two loads are selected so as to fall on the substantially linear portion of the load deflection curve for the panel. The magnitudes of the two loads are measured with suitable means, such as a load cell. The extension or distance moved by the cylinder in applying the incremental load is known or measured. With the two loadings and the incremental deflection established, one can calculate,using standard formulae, a value which is found to closely approximate the MOE.

Description

1 Field o~ the_ nvent on

2 The inverltion relates to a methocl and apparatus fvr the non-

3 destructive testing of a reconstitu~ed wood panel, such as a sheek o~
plywood.

BACKGROUND OE THE INVENTION
6 Wood panels, generically termed "reconstituted wood panels", 7 include such fabricated produc-ts as plywood, Flakeboard, hardboard, particleboard, 8 waferboard, oriented strand board and -the like. Such panels are manufactured g in the form of large relativel~y thin sheets. Typically, such a panel might be about four feet in width and eight feet in length.
11 As a consequence of the process of manufacture, such panels 12 display a greater propensity to warpage and sagging than a natural wood 13 product~
14 It is desirable to be able to establish, at a relatively high speed and in a non-destructive fashion, values for the panel which can be 16 used to calculate a measure of the stiffness of the panel. ~e have found 17 that the stiffness of a panel correlates with the modulus of elasticity 18 (MOE), and, as a result, with the modulus of rupture (MOR) of the panel.
19 At this time, to our knowledge, there is no machine available which can, in a matter of seconds, grade a panel by yielding such values.
21 There is, in oommon use in the industry~ a machine known as the Post Flexure 22 machine. In the use of this machine, the panel is threaded on edge into two 23 spaced vertical frames, which frames are then ro-tated in opposite directions 24 to flex the central part of the panel. The values for the force used to effect rotation, and the extent of deflection effected are used in suitable 26 equations to calculate a value representative of MOE. Howe~er, this machine 27 is not suitable for grading on a production line~ as it takes several minutes 28 to test a panel with it.

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1 We evolvecl the fqllowing cirteria for a machine that could be 2 used to 9rade wood panels:
3 (1) itrnust accommodate the larye panels;
(2) it must distribute the deflect1ng load substantially uniformly and linearly across the ~ull width of the panel, 6 in spite of the warped or sagging nature of said panel;
7 (3) it must cope with the fact that the load deflection (or 8 momerlt vs. deflection) curve for a wood panel is not, 9 typically, linear in the proximity of the zero point; and 11 (~) it must be relativèly fast in operation and capable of 12 being upgraded to production line speeds.
~ ' 13 SUMMARY OF T~E INYENTION
14 The invention involves applying a first linear load to one major surface of the panel while supporting it on the opposite side with two 16 spaced apart linear supports which bracket the loading member. The load is 17 applied with a loading menlber which can pivot in a plane perpendicular to 18 the main surface of the panel, to permit the loading member to conform to 19 the warped or sagging surface of the panel. The load which is applied is selected so as to fall on the substantially linear portion of the load 21 deflection curve for the panel. Once the panel has been deflected in this 22 manner, the loading is then incrementally increased, causing further deflection.
23 The two loadings and the incremental deflection distance are noted or measured.
24 These three measurements can then be used to compute a reasonably accurate estimate of the MOE and MOR.
26 Broadly stated~ the invention in one aspect comprises an 27 apparatus, for non-destructive testing of a reconstituted wood panel, 28 comprising: a support frame, means, associated with the support fram~, . . ~ . ~

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1 for bearing against one major surFace q~ the panel along two spac~d apart 2 parallel lines ex~ending subs~antjally across -the width oF the panel; means, 3 associated with the support frame, for bearing against the other major

4 surface of the panel along a line extending substantially across the width of the panel between the aforesaid spaced.lines of con-tact; one of said bearing means being pivotally mounted on said support frame for pivoting 8 in a plane generally perpendicular to the main plane of the panel, whereby it may conform closely with the panel surface to apply a substantially linear and uniForm load across substan-tially the width of the panel, means for biasing the load-applying bearing means to apply a first load to the 11 panel, said first load being selected to fall on the substantially linear 12 portion of the load deflection curve for the panel, to thereby deflect the 13 panel across its width a first distance; and means for further biasing the 14 load-applying bearing means to apply an incremental load to the panel to thereby ~urther deflect the panel a second distance; whereby the loadings 16 and second distance may be noted and the v.alues used to calculate a measure 17 of the stiffness of the panel.
18 In another aspect, the invention comprises a method for 19 testing the s-tif-Fness of a reconstituted wood panel, comprising: con-tacting one major surface of.the panel substantially across its ~idth ~lith 21 a loading member and biasing said member to apply a substanti~lly linear 22 and uniform first load to the panel while supporting the other major surface 23 of the panel along two spaced lines:bracketing and parallel to the line of 24 application of said first load, to thereby deflect the panel, said load being of a magnitude to fall on the substantially linear portion of the 26 load deFlection curve for the panel; determining the magnitude of the first27 load; further biasing the loading member in quick succession to apply an 28 incremental load to the panel and further deflect said panel through a 29 pre-determined distance; and determining the magnitude of the first load;
whereby the loadings and deflection distance obtained by applying the 31 incremental load may be used to obtain a measure of the stiffness of the panel.

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1 ~p DESCRIPTI~N.~F T!.. IE.D~Q~INGS.
2 Fiyure l is a perSpective view of the apparatus~ showing a 3 panel undergoing deflection;
4 Figure 2 is a 3 part sec~ional schematic view ~f the lqading bar, doubl.e-acting cylinder, load cell, and universal pivot, which together 6 make up the deflecting assembly~-with the cylinder shown in the beginning 7 mode (Figure 2a), first loading mode (Figure 2b), an~ second loading mode 8 (Figure 2c);
9 Figure 3 is a schemat;c YieW showing the pneumatic-hydraulic actuating.circuit, the deflecting assembly, the panel, and the support 1l means; and 12 Figure 4 is a typical load deflection curve for a wood 3 panel, developed using a Post flexure machine - the non-linear and linear 4 portions of the curve are identified. -~ _ _ . _--_ . _ _ . ~ _ . . . _ _ _ _ .... _ _ .. .... .. . _ . .. .

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1 DESCRIPrION;OF'T~E'~EFERR~D'EMBODIMENT
2 In Gen~ral 3 The static bend~ng apparatus 1 comprises, in gen~al, a 4 frame 2, a pair of support rollers 3,'a pivoted load-aPplying two-stage cylinder assembly 4, and a load cell S.' The rollers 3'support the wood 6 panel 6 to be tested. The cylinder assembly 4 applies two diFferent and 7 sequential loadings, to pre-load and then incrementally load the panel to 8 deflect the latter through a pre-determined distance. The load cell 5 9 provides a measure of the loading applied. And the frame 2 carries the aforementioned components.

11 The Support Frame 12 The support frame 2'comprises a horizontal, rectangular 3 section 7. A pair of vertically extending posts'8 project upwardly from 4 the side members 7a of the section 7, substantially at their mid-points.
A horizontal beam 9 extends between the posts 8 and is supported thereby.
16 The beam 9 is therefore positioned to extend transversely across the 17 rectangular section 7, substantially at its mid-point, and in vertically 18 spaced relation thereabove. The rectangular section 7 is of sufficient 19 width and length so as to accommodate the wood panel 6.

20 The Supports 21 A pair of parallel, spaced apart, elongate support rollers 22 3 are each supported by a pair of pillow blocks ll, which pillow blocks 23 are mounted on the rectangular-section side members 7a adjacent the 24 latters' ends. The wood panel 6 may thus be supported by the rollers 3 25 from below and across its width, at poin-ts adjacent each of its ends.

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1 There is thus.prqvided'n1e~ns. associated with th~ support 2 Frame, For bear~ng against'orle major surfa,ce oF the panel:along.two 3 spaced,parall,el.lines extending su~s~antiall~ across the wi~lth ~f ~he 4 panel. ' The rollers 3 are.utilize'd to provide the desired two 6 spaced end supports fo,r the panel, w~ile ~fering no frictional resistance 7 ,to panel movement which arises from central deflection thereof.

8 The Load Cell and Cylinder Assembly .
9 The load cell 5 is mounted to the underside of the beam 9 by a universal joint 13. The load cell 5 is connected to the piston rod 11 14 of the two-stage cylinder assembly'4. At its lower end, the cylinder 12 assembly 4 includes an attached loading bar.l5, which may be biased to 13 press against the wood panel 6, to deflect the latter.
14 The cylinder assembly 4 comprises a cylinder body 17 which forms upper and lower chambers 18, 19 separated by a divider 20.
16 A piston 21 is disposed in upper chamber 18 and, as previously mentioned, 17 its piston rod 14 is connected to the load cell 15. A second piston 22 18 is disposed in the lower chamber 19 and its piston rod 23 is connected to 19 the loading bar 15.
.20 A port 24, fo,r adm;tting and exhausting of pressurized 21 air, communicates through the cylinder body wall with the bottom end 22 of the upper chamber 18. A port 25, for admitting and exhausting of oil, 23 communicates with the top end of the upper chamber 18.
24 Turning now to the lower,chamber 19, a port, 26 for admitting and exhausting of oil, communicates with the top end of said 26 lower chamber. And a port 27', for admitt;ng and exhausting of.pressurized 27 air, communicates with the lower end'of the lower chamber,l9.:
28 Ha~ing reference to the pneumatic-hydraulic circuit shown 29 in Figure 3, a source A of pressurized air supplies air'through line 28 to a 4-way pneumatic valve 29.

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1 The air can move frolll this valve 29 through either line 30 2 or 31. Line 30 connects with the upper end of the pre-load oil reservoir 3 cylinder 32. This pre-load reservoir cylinder 32 connects a-t its base 4 with a line 33. The line 33 is controlled by a 2-way norm~lly closed valve 34 and connects with the port 25 at the top end of the upper chamber 6 18. Line 31 connects with the port 24 at the lower end of the upper 7 chamber 18.
8 The air source A is also connected through line 35 with 9 4-way pneumatic valve 36. A line 37 connects the valve 36 with the upper end of the final load reservoir cylinder 38. The lower end of cylinder 38 11 is connected by line 39 with the port 26 leading into the upper end of the 12 lower chamber 19. The valve 36 is also connected by a line 40 with the 13 port 27 leading into the lower end of the lower chamber lg.
4 By means of this arrangement, one can first open the valve 29 and admit pressurized air from source A through lines 28 and 30 into the pre-16 load reservoir cylinder 32. Upon opening the valve 34, oil is forced by 17 the air from cylinder 32 through line 33 and valve 34, to fill the upper 18 end of the upper chamber 18. Valve 34 is then closed and the oil in chamber 19 18 is 'locked' in place. Valve 36 can also be opened to admit air through line 37 into the final load reservoir cylinder 38 and force oil through line 21 39 to the upper end o-f lower chamber 19. Valve 36 can then be switched to 22 introduce air through line 40 to the lower end of chamber 19. At this 23 point, the system is ready for use. Both pistons 22 and 21 are adjacent the 24 divider 20 and piston rod 23 is ~ully retracted.

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To ini-tiate testing QF ~.panel ~ the valve 2~' is opened to 2 admit air through line 3'1 and port 2~ intQ.the lower end oF upper chamber 3 18. At the same time, va'lve 34 'is opened to allow oil to be exhausted 4 from chamber 18 into reservoir cylinder' ~2.. ~s a result, the cyl;nder body 17 is forced clownward and the piston rod 23 and loading bar 15 6 press downwardly against the panel. The fo.rce being applied by the loading 7 bar 15 is monitored on the load cell S., until it reaches a pre-determined 8 value. This value is selected to correspond with a point that is saFely 9 on the linear portion of the Inoment vs deflection curve for a panel of the 10 type being tested. A typical example of'such a curve is shown in Figure 4.
1l At this stage, valve 34 is closed, so that the pre-load force being 12 applied to the panel is maintained.
13 The valve 36 is then opened to apply air pressure through 14 line 37 to force oil from cylinder 38 into the upper end of the lower chamber 19. This causes the piston 22 and rod 23 to move downwardly 16 through a known travel, being the fu.ll stroke of -the.piston 22. When 17 this stroke is complete, the force being exerted by the loading bar 15 18 is noted from the load cell 5.
19 The circuit is then returned to the starting condition by opening line 37 through valve 36, admit~ing air through valve 36 and 21 line 40 to retract the piston 22, and opening valve 34 and admitting air 22 through valve 29 and line 30 to depress piston 21.
23 By vir-tue of this arrangement~ the fo.llowing steps occur:
24 (1) the panel is de-Flected tu a limited.extent by applying a load of pre-determined magnitudei 26 (2) the panel is then -Further deflected through a known 27 distance and ~he Inagnitude of the incrernental. load 28 required to achieve this is ~measured.

_ g _ ~L~ 2~3~3~l 1 From the v,alues Fo,r,the pre-load, the incremental, load ,2 the deflecting arising from -the incrementa'l, load and the known span and3 width of the panel, the st-iffness of the panel can be calculated. A
4 close approximation of the MOE can be calculated if the thickness of the pane'l is known.
6 Loading bar 15 contacts the mid-point of panel 6 from above, 7 transmitting the loads supplied by cy'linder assembly ~ to said panel.
8 Loading bar l5 consists of an elongate rod 41 having a sheaved wheel 42 9 at each end thereof., The bar 15 is operatiYe to distribute the applied loads'substantially uniformly across the panel width as a line load.
11 The loading bar l5 is threadably engaged to the lower end of lower pis-ton12 r~d 23 and is operative to move concomitantly therewi~h. Sheaved ~heels 13 42 engage guides 43 mounted on posts 8 and fu,nc~ion to maintain -the 14 bar l5 in longitudinal alignment. Provision of universal joint l3 ensures good contact between bar 15 and panel 6, irrespective of warping, sagging, 16 or surface irregularities thereof., 17 Stated otherwise, there is provided means for bearing against 18 the upper major surface of the panel along a line extending substantially 19 across the width of the panel, which means are piyotally mounted on the support frame fo,r pivoting in a plane generally perpendicular to the 21 main plane of the panel, whereby said bear;ng means may conform closely 22 with the panel surface to apply a substantially linear and uniform load 23 across substantially the width of the panel.

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1 Example 2 This example shaws the clos~ correlation, in t~le calculated 3 MOE results, which is o~ained by the use of the present appara-tus ~nd 4 the industry-accepted Post Flexure apparatus.
Testing was conducted ~o,llowing the requirements ~f ASTM D
6 3043-76 (1981) Method C for the Post flexure apparatus.
7 The present apparatus was operated in accordance With the 8 fo,llowing specific conditions:
9 The support rollers for plyw~Qd sa~ple'M~ ,were chosen to be spaced 1118mm and the initi.al pre-determined stress 11 , l.evel for preload was 3.5 MPa. This sample Was 1,219mm 12 wide and had a thickness of 9.44mm . The incremental de-13 flection Following preloading was chosen to be 12.75mm.
14 The materials tested were nominally 1220 x'2440 x 9.5mm panels of softwood plywood and 1220 x 2~40 x ll.lmm panels of waferboard.
16 The test procedure followed with respect to using both 17 machines was as follows:
18 1. Each 1220 x 2440 mm sheet was cut into two 1220 x 1220 mm 19 samples. Half were designated as A'-- -for testing parallel to the grain direction (or along the length 21 in the case of undirectional boards) and half were 22 designated B -- for testing across the grain direction 23 (or along the width) ;
24 2. Parallel and cross dimensions were measured at mid-span;
3. Thickness was measured at the middle of each edge and 26 the average of the fQur ualues recorded;
27 4. All of the A panels, then all of the B panels were 28 tested on the present'(MSR) machine;

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1 5. A check was made to ensure tha-t -the two load ~evels Froln 2 the MSR machine testiny (preload and Fi,nal l~ad) h~th 3 fell on the straight.line portion of the load deflectlon 4 plot from the Post,~lexure machine testing, shown in Figure 4 ; and 7 6. All of the A panels and then all of the B panels were 8 tested to fa,ilure on the Post flexure machine (per ASTM D
9 3043C-76).

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1 The data.deri~ed ~'r,om testiny the MSR machine was.used to 2 compute MOE using the fo'llowing equation:
3 MOE = -4 - b .~ Y

4 where: b = wi~th o.f specimen in millimetres d = averaye'thickness of specimen in millimetres 6 - L - length of span in millimetres 7 ''~ = s'lope of.the load deflection curve derived QY
7 using two points established by the pre-load 9 and incremental load.

The MOE from the Post -flexure-testing was calculated using 11 the computations required by the afo.resaid ASTM standard.
12 The results from the testing were as follows:
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1 ABLE A-l 2SUMMARY OF rESrlNG - MSR*AND POST FLEXURE

3 MSR Post Flexure 4 Sample Thick. MOE MOE
Number mm MPa MPa 6 M~l-A 9.44 8,580 8,810 7 M-2-A 9.31 8,910 9,130 8 M-3-A 9.38 8,870 9,620 g M-4-A 9.20 10,190 10,780 M-S-A 9.16 9,210 9,860 11 M-6-A 9.34 8,530 8,540 12 M-7-A 9.14 8,990 10,000 13 M-8-A 9.81 8,650 8,610 14 M-9-A 9.18 10,350 10,700 M-10-A 9.29 9,390 9,250 16 M-ll-A 9.52 8,690 9,060 17 M-12-A 9.31 9,410 9,380 18 M-l3-A 9.31 8,890 8,840 19 M-14-A 8.87 11,570 11,410 M-15-A 9.38 10,320 10,750 21 M-16-A 9.14 10,850 11,360 22 M-17-A 9.16 10,210 10,070 23 M-18-A 9.23 9,670 9,630 24 M-l9-A 9.16 10,720 10,530 M-20-A 9.13 10,380 10,400 26 Average 9.27 9,620 9,840 27 Test Material - 9.5 mm Spruce Plywood 28 Test Direction - Machine or Parallel Direction 29 Conditioning - As Received Predeter~ined Initial Stress Leyel - 3.5 MP~

31 Str~ke ~f Final Load Cyiinder - 12.75 mm* MSR designates the 32 Tes~ Span - 1118 mm present machine ~2~8~3~
1 TABLE A-?

2 SUMMARY OF rESrIN~ - MSR AND POST FLEXURE

3 MSR Pos-t Flexure 4 Sample Thick. MOE MOE
Number mm MPa MPa 6 T-l-B 9,54 700 740 7 T-2-B 9.39 540 520 8 T-3-B 9.50 790 800 9 T-4-B 9.26 590 640 T-5-B 9.18 580 620 11 T-6-B 9.54 610 580 12 T-7-B 9.40 780 720 13 T-8-B 9.84 540 560 14 T-9-B 9.12 700 710 T-10-B 9.28 620 670 16 T-ll-B 9.59 710 760 17 T-12-B 9.30 660 730 18 T-13-B 9.42 920 1,060 19 T-14-B 9.07 560 700 T-15-B 9.41 620 740 ~1 T-16-B 9.33 580 --22 T-17-B 9.09 660 850 23 T-18-B 9.02 550 --24 T-l9-B 9.14 550 790 T-20-B 8.98 580 760 26 Average 9.32 650 720 27 Test Material - 9.5 mm Spruce Plywood 28 Test Direction - Transverse Direction 29 Conditionin~ - As Received Predeterming Initial Stress Level - 0.8 MPa 31 Stroke of Final Load Cylinder - 12.75 mm 32 Test Span - 1118 mm _ _ _ _ _ . ... _ _ . _ .. . ... . _ _ _ ) 3 _ 4 MSR Post Flexure Sample Thick. MOE MOE
6 Number _mm MPa MPa 7 UlA 11.094,360 4,260 8 U2A 11.204,460 4,630 9 U3A 11.284,280 4,430 U4A 10.443,920 3,890 11 U5A 12.173,860 4,040 12 U6A 11.454,320 4,370 13 U7A 10.864,040 4,020 14 U8A 11.764,420 4,530 U9A 11.994,380 4,520 16 UlOA 11.574,710 5,020 17 UllA 11.714,470 4,690 18 U12A 11.304,760 5,140 19 U13A 11.904,310 4,560 U14A 11.194,930 5,390 21 U15A 11.834,320 4,480 22 U16A 11.474,570 4,700 23 U17A 11.224,850 4,890 24 U18A 12.093,880 3,820 U19A 11.215,150 5,310 26 U20A 12.004,210 4,170 27 Average 11.494,410 4,540 28 Test Run - Wa-ferboard 29 Nominal Thickness - 11.1 mm Test Direction - Parallel to Machine Direction 31 Predetermined Initial Stress Level - 2.758 MPa 32 Stroke of Final Cylinder - 12.75 mm 33 Test Span - 1118 mm 4 MSR Pos t Fl exure Sample Thick. MOE MOE
Number mnl MPa _ _ _ MPa_ _ _ 7 UlB 11.13 3,920 3,980 8 U2B 10.82 3,750 3,930 9 U3B 11.34 4,300 4,470 U4B 10.74 4,070 4,360 11 U5B 11.50 4,020 4,390 12 U6B 11.81 37700 3,870 13 U7B 10.90 4,360 4,430 14 U8B 12.02 3,680 3,900 U9B 11.49 49150 4,500 16 UlOB 11.62 3,900 4~160 17 UllB 11.61 3,900 4,090 18 U12B 11.56 3,780 3~830 19 U13B 11.67 4,380 4,700 U14B 11.36 4,610 4,820 21 U15B 11.68 4,270 4,650 22 U16B 11.90 3,940 4,240 23 U17B 11.69 4,300 4,570 24 U18B 11.26 4,680 4,950 U19B 11.43 4,480 4,640 26 U20B 11.27 4,660 5,020 27 Average 11.44 4,140 4,380 28 Test Run - Waferboard 29 Nominal Thickness - 11.1 mm 30 Test Direction - Waferboard Across Machlne Direction 31 Predetermined Initial Initial Stress Level. - 2.758 MPa 32 Stroke of Final Cylinder - 12.75 mm 33 Test Span - 1118 mm , _ . _ . .. .. _ . ..
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Claims (6)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for non-destructive testing of a reconstituted wood panel, comprising:
a support frame;
means, associated with the support frame, for bearing against one major surface of the panel along two spaced parallel lines extending substantially across the width of the panel;
means, associated with the support frame, for bearing against the other major surface of the panel along a line extending substantially across the width of the panel between the aforesaid spaced lines of contact;
one of said bearing means being pivotally mounted on said support frame for pivoting in a plane generally perpendicular to the main plane of the panel, whereby it may conform closely with the panel surface to apply a substantially linear and uniform load across substantially the width of the panel;
means for biasing the load-applying bearing means to apply a first load to the panel, said first load being selected to fall on the substantially linear portion of the load deflection curve for the panel, to thereby deflect the panel across its width a first distance; and means for further biasing the load-applying bearing means to apply an incremental load to the panel to thereby further deflect the panel a second distance;
whereby the loadings and second distance may be noted and the values used to calculate a measure of the stiffness of the panel.

2. An apparatus for non-destructive testing of a reconstituted wood panel, comprising:
a support frame;
first means. associated With the support frame, for bearing against the bottom surface of the panel along two spaced parallel lines extending substantially across the width of the panel;
second means, associated With the support frame, for bearing against the top surface of the panel along a line extending substantially across the width of the panel between the aforesaid spaced lines of contact, said second means being pivotally mounted on said support frame for pivoting in a plane generally perpendicular to the main plane of the panel, whereby it may conform closely with the panel surface to apply a substantially linear and uniform load across substantially the width of the panel;
third means, associated with the support frame, for biasing the second means to apply a first load to the panel, said first load being of a magnitude to fall on the substantially linear portion of the load deflection curve for the panel, to thereby deflect the panel across its width a first distance; and fourth means, associated with the support frame, for further biasing the second means to apply an incremental load to the panel to thereby further deflect the panel a second distance;
whereby the loadings and second distance may be noted and the values used to calculate a measure of the stiffness of the panel.

3. The apparatus as set forth in claim 2 wherein:
the first means comprises a pair of horizontally aligned rotatable members mounted on the support frame.

4. The apparatus as set forth in claim 2 wherein:
the third and fourth means comprises a double-acting cylinder connected at one end with the support frame and at the other end with the second means, whereby extension of one end of the cylinder through a pre-determined travel applies said first load and extension of the other end of the cylinder through a pre-determined travel applies said incremental load and establishes the deflection undergone by the panel when the incremental load is applied.

5. The apparatus as set forth in claim 3 wherein:
the third and fourth means comprises a double-acting cylinder connected at one end with the support frame and at the other end with the second means, whereby extension of one end of the cylinder through a pre-determined travel applies said first load and extension of the other end of the cylinder through a pre-determined travel applies said incremental load and establishes the deflection undergone by the panel when the incremental load is applied.

6. A method for testing the stiffness of a reconstituted wood panel, comprising:
contacting one major surface of the panel substantially across its width with a loading member and biasing said member to apply a substantially linear and uniform first load to the panel while supporting the other major surface of the panel along two spaced lines bracketing and parallel to the line of application of said first load, to thereby deflect the panel, said load being of a magnitude to Fall on the substantially linear portion of the load deflection curve for the panel;

determining the magnitude of the first load;
further biasing the loading member in quick succession to apply an incremental load to the panel and further deflect said panel through a pre-determined distance; and determining the magnitude of the first load, whereby the loadings and deflection distance obtained by applying the incremental load may be used to obtain a measure of the stiff-ness of the panel.