Factors affecting the strength of block-shear specimens

Transcription

1 Fctors ffecting the strength of lock-sher specimens E. Arnold Okkonen Bryn H. River Astrct The ASTM D 143 nd D 905 lock-sher tests re commonly used for mesuring the sher strength of solid wood nd dhesivelyonded joints. The test methods re similr, ut they result in different pprent strengths. Two fctors tht contriute to this difference re specimen shpe nd sher tool design. ASTM D 143 uses single-notched specimens nd sher tool with 1/8 inch offset;astm D 905 uses doule-notched specimens nd sher tool without n offset. This report compres the effects of specimen form (solid or onded with phenol-resorcinol formldehyde dhesive), specimen shpe (single- or doule-notched),sher tool (with or without offset), specimen size (full or reduced), nd grin orienttion (tngentil or rdil) on the pprent strength of southern pine, Dougls-fir, white ok, nd hrd mple lock-sher specimens. The ASTM D 905 sher tool (no offset) produced higher strengths thn the ASTM D 143 sher tool (offset). -size doule-notched specimens hd higher sher strengths thn full-size single-notched specimenswhen other fctors were the sme. When other fctorswere pooled, solid nd dhesively onded specimens hd the sme strength regrdless of shpe (singleor doule-notched).-size specimensconsistently hd higher sher strengths thn full-size specimens when tested in the D 905 sher tool. Tngentil grin in the sher plne produced higher sher strengths thn rdil grin in mple nd ok specimens. Rdil grin produced higher sher strengths thn tngentil grin in Dougls-fir nd southern pine specimens. All fctors hd sttisticlly significnt effects on strength nd there were significnt interctions mong the fctors. Therefore, comprisons of the strength of solid wood nd dhesivelyonded joints should e pproched with cution. species. Our gol ws to find out if lock-sher test methods ffect strength mesurements of specimens in which these fctors vry. The lock-sher test is the test most commonly used y oth the reserch community nd the wood industry to mesure the sher strength of oth solid wood (2) nd dhesively onded joints (1). The results re used in dhesive development, performnce specifictions, ond qulity control, nd in the estlishment of wood strength nd llowle design stresses, mong mny other uses. Both methods hve their roots in erly test methods for the sher strength of wood (4,12). Not coincidentlly, oth tests re similr, lthough not identicl. They differ in the construction of the sher tool (offset or no offset), specimen shpe (single- or doulenotched), nd specimen form (solid or onded wood) (Fig.1). In view of the similrities etween the test methods, the strength of good onded specimen tested ccording to stndrd method D 905 presumly should e the sme s the strength of solid wood specimen tested ccording to stndrd method D 143. Unfortuntely, the comprison of the strengths otined y different locksher tests is not lwys simple or strightforwrd. Vrious reserchers hve noted tht specimen shpe, ond re, grin orienttion, nd fctors such s sher tool design my ffect the pprent strength mesured ylock-sher tests(3,5,7,15). Yvorskyetl.(15)found tht reducing specimen length resulted in n pprent strength increse of 66 percent. McLeod et l. (5) found tht the stndrd D 905 sher tool produced strengths 13 to 60 percent higher thn the stndrd D 143 sher tool, with greter increses for softwoods thn for hrd- In this report we compre the effects of sher tool design nd specimen form, shpe, size, nd grin direction on the pprent strength of solid wood nd dhesively onded lock-sher specimens of four different The uthors re, respectively,physicl Science Technicin nd Forest Products Technologist,USDA Forest Serv.,Forest Products Lortory, One Gifford Pinchot Dr., Mdison, WI This pper ws received for puliction in April Forest Products Reserch Society Forest Prod. J. 39(1): FOREST PRODUCTS JOURNAL Vl. 39. No. 1 43

2 Figure 1. - (A) Schemtic shering of the stndrd ASTM D 905 lock-sher specimen in the stndrd D 905 sher tool (no offset). (B) Schemtic shering of the stndrd ASTM D 143 lock-sher specimen in the stndrd D 143 sher tool (1/84-in.offset). woods. They concluded the increse is due to differences in the construction of the D 905 nd D 143 sher tools. The D 143 tool hs 1/8-inch offset in the verticl plne etween the edges of the loding rm nd the specimen support (Fig. 1B). This offset llows filure to occur through the wekest plne within firly thick region. The D 905 tool hs no verticl offset, forcing filure to occur in more restricted region. Hilrnd (3) found tht differences in the sher tool ffected the pprent sher strength of solid pine nd ok, nd tht interctions occurred etween the sher tool nd the specimen shpe. The pprent strength of single-notched specimen loded in the D 143 offset sher tool is out 33 percent (verge of tngentil nd rdil orienttion) higher thn its strength when loded in the British stndrd 373 sher tool (3). The British stndrd sher tool is similr in principle to the offset sher tool, ut it hs rollers to reduce the force required to overcome friction. Norris (7) showed tht the dded force required to overcome friction in the ASTM D 143 offset tool pprently compenstes for stress concentrtions in the specimen tht decrese the force needed to rek the specimen. The fortuitous result is tht the verge sher strength, mesured with the ASTM D 143 offset sher tool, is very close to the true sher strength otined y plte sher method tht lods the wood in pure sher. The strength of dhesively onded lock-sher specimens lso vries with mny other fctors, including wood species, onding preprtion, onding conditions, nd test method. Reports descriing the effects of mny of these fctors re numerous nd will not e covered here. We tried to eliminte or minimize the vrition of strength cused y fctors other thn the test method in this study. Figure 2. - Dimensions of the (A) full- nd (B) reduced-size ASTM D 143 lock-sher specimens. Dimensions of the (C) full- nd (D) reduced-size ASTM D 905 lock-sher specimens. Mterils Four species of wood were used for the study: southern yellow pine (Pinus spp); Dougls-fir (Pseudotsug menziesii (Mir.) Frnco); white ok (Quercus l); nd hrd mple (Acer scchrum). One cler, stright-grined plnk ws selected for cutting ll the specimens of given species to minimize the effects of tree-to-tree nd within-tree wood vrition. The verge specific grvities of the plnks determined on the sis of volume t pproximtely 12 percent moisture content (MC) nd ovendry weight were 0.55, 0.42, 0.74, nd 0.76 for southern pine, Dougls-fir, white ok, nd hrd mple, respectively. These compre to the respective pulished species verges of 0.54, 0.48, 0.68, nd 0.63 (13). A room-temperture-curing phenol-resorcinol formldehyde resin dhesive ws used for onding. Methods Experimentl design This experiment ws completely rndomized design with fctoril rrngement of 5 experimentl fctors into = 96 tretment comintions, s follows: Experimentl fctors Fctor levels Wood species 1. Southern pine 44 JANUARY 1989

3 Specimen type Grin orienttion of wood in the sher plne Specimen size Sher tool 2. Dougls-fir 3. White ok 4. Hrd mple 1. Solid wood, singlenotched (Fig. 2A) 2. Solid wood, doulenotched (Fig. 2C) 3. Bonded wood, doulenotched (Fig. 2C) 1. Rdil (growth rings perpendiculr to sher tool) 2. Tngentil (growth rings prllel to sher tool) 1. (Fig. 2A & 2C) 2. (Fig. 2B & 2D) 1. No offset (Fig. 1A) 2. 1/8-inch offset (Fig. 1B) Five lock-sher specimens were tested for ech tretment comintion, mking totl of 480 specimens for the entire study. Sttisticl nlysis Four levels of nlyses were conducted using the Sttisticl Anlysis System Generl Liner Models Procedure (10): Anlysis I - ll vriles nd interctions; Anlysis II - y species for remining vriles nd their interctions; Anlysis III - y species for specific test method nd grin orienttion nd their interctions; Anlysis IV - y species nd grin orienttion for significnt effects of test method, using Tukey s multiple comprisons procedure; nd Anlysis IV - y species nd test method for significnt effects of grin orienttion, using Tukey s multiple comprisons procedure. Specimen preprtion The selected plnks were conditioned t 80 F nd 65 percent reltive humidity (RH) to n equilirium MC of pproximtely 12 percent. After conditioning, ll the solid wood specimens were cut nd returned to the conditioning room. The remining portion of ech plnk ws ripped into illets for mking the onded specimens. Four stndrd-size illets (2-1/2 y 12 y 7/8 in.) nd two nonstndrd-size illets (2-1/2 y 12 y 5/8 in.) were cut for ech grin orienttion. The illets were llowed to reequilirte t 80 F nd 65 percent RH efore onding. Just efore onding, the illets were jointed on one surfce with hndfed, three-lded jointer nd then plned to thickness (either the stndrd 3/4 in. or reduced 5/16 in. thickness) on the opposite surfce. Adhesive ws spred t the equivlent of 60 l./mft. 2 of ondline. Bonding conditions were s follows: hrdwoods - ssemly time (30 min. closed),pressure (175 psi), clmp time (24 hr.), temperture (72 F); softwoods - ssemly time (15 min. closed), pressure (150 psi), clmp time (24 hr.); temperture (72 F). After removl from the clmps, the onded ssemlies were llowed to recondition in the 80 F nd 65 percent RH environment efore the specimens were cut. Five stndrd D 905 specimens were cut from ech of the thicker ssemlies, providing 10 specimens of ech grin orienttion. Fourteen reduced-size doule-notched specimens were cut from ech of the thinner ssemlies, providing 10 of ech grin orienttion for testing, with 4 extr specimens. Testing All specimens were tested fter conditioning to equilirium MC t 80 F nd 65 percent RH. The height nd width of the ond or sher re were mesured with digitl micrometer. The lrgest nd smllest dimension in ech direction were verged nd recorded to the TABLE 1. - Apprent sher strength nd stndrd devition of lock-sher specimens. Apprent sher strength Specimen Southern pine Dougls-fir White ok Hrd mple Grin Stndrd Stndrd Stndrd Stndrd Type orienttion Size Sher tool Men devition Men devition Men devition Men devition Solid/single-notched Tngentil Rdil Solid/doule-notched c Tngentil Rdil Bond/doule-notched c Tngentil Rdil Men of five tests. Test method ASTM D 143. c Test method ASTM D 905. No offset 1, , , , Offset 1, , , No offset 1, , , , Offset 1, , , , No offset 1, , , , Offset 1, , , , No offset 1, , , , Offset 1, , , , No offset 1, , , , Offset 1, , , , No offset 1, , , , Offset 1, , , , No offset 1, , , , Offset 1, , , , No offset 2, , , , offset 1, , , , No offset 1, , , , Offset 1, , , , No offset 2, , , , Offset 1, , , , No offset 1, , , , Offset , , No offset 2, , , , offset 1, , , , FOREST PRODUCTS JOURNAL Vol 39, No 1 45

4 Figure 3. - Block-sher strength of southern pine nd Dougls-fir specimens in reltion to four fctors, including specimen type, size, grin orienttion (tngentil nd rdil), nd sher tool (with or without offset). Differences etween slopes nd distnce etween lines of vrious comintions of fctors indicte interctions etween fctors. nerest inch. The verge dimensions were used to clculte the sher re. Testing ws done on universl testing mchine t crosshed speed of 0.25 in./min. The sher force t filure ws recorded nd the verge sher stress t filure ws clculted lter. In the following results nd discussion section, we refer to the verge sher stress t filure s the pprent sher strength or just sher strength. In either cse, it is noted tht these numers most proly do not represent the true sher strength of the wood or of the dhesive ond. The verge wood filure of the specimens ws estimted fter testing. Results nd discussion In the following discussion, the four species of wood descried in the methods re simply referred to s pine, Dougls-fir, ok, nd mple. The mens of the pprent sher strength nd the stndrd devitions for ech group of five specimens with the sme chrcteristics re given in Tle 1 nd plotted in Figures 3 nd 4. The full fctoril nlysis (Anlysis I) reveled mny interctions mong the fctors under investigtion (Tle 2). Species hd n especilly strong effect, nd every interction involving species ws significnt. The nlysis y individul species (Anlysis II, Tle 2) showed tht the remining fctors ll contriuted significntly to sher strength vriility nd tht there were mny significnt interctions etween these fctors. Eleven of the 24 possile second-order interctions, 5 of 16 possile third-order interctions, nd 1 of 4 possile fourthorder interctions were significnt (Tle 2). Every fc- Figure 4. - Block-sher strength of white ok nd hrd mple specimens in reltion to four fctors, including specimen type, size, grin orienttion (tngentil nd rdil), nd sher tool (with or without offset). Differences etween slopes nd distnce etween lines of vrious comintions of fctors indicte interctions etween fctors. tor ws involved in significnt interctions. Consequently, chnging the level of one fctor while holding nother fctor constnt chnged the effect of the other fctor. This cn e seen in Figures 3 nd 4. Interctions etween fctors re indicted where given pir of lines differs in slope or position, or where the pirs of lines form different ptterns for different species or specimen types. Tests for the independent effects of the fctors were not meningful ecuse of these interctions. Lter in this section, we will further restrict the nlysis to gin etter sttisticl informtion out certin fctors. Menwhile, we cn gin prcticl informtion from simple numericl comprisons mong the individul group mens reported in Tle 1 nd shown in Figures 3 nd 4. Specimen size nd shpe nd sher tool design The men sher strengths listed in Tle 1 nd plotted in Figures 3 nd 4 reveled tht in 47 of 48 comprisons, specimens tested in the sher tool without offset were s strong s or stronger thn those tested in the sher tool with offset. The mximum increses in strength under otherwise like conditions were 49 percent for pine, 33 percent for Dougls-fir, 33 percent for ok, nd 61 percent for mple. Similrly, Tle 1 revels tht in 23 of 24 comprisons, reduced-size specimens tested in the sher tool without offset were stronger thn the full-size specimens. The mximum increses in strength under other 46 JANUARY 1989

5 wise like conditions were 41 percent for pine, 30 percent for Dougls-fir, 58 percent for ok, nd 23 percent for mple. The increse in the pprent sher strength cused y reducing specimen size ws due to lower stress concentrtions t the ends of the shortened joint (15). The effect of size ws much less nd quite inconsistent when the specimens were tested in the sher tool with offset. This cn e seen y the slnt of the lines leled offset in Figures 3 nd 4. Yvorsky nd Cunninghm (14) showed tht most of the shering force pplied to the full-size specimen is crried y the 5/16-inch-thick lyer of wood nerest to the sher plne. Since the reducedsize specimen is only 5/16 inch thick on either side of the ondline, 1/8-inch offset drsticlly reduces the ering re. The reduced ering re llows crushing nd worsens the criticl tension stresses t the ends of the joint. Specimen shpe ( suelement ofspecimen type) ws strong nd consistent fctor. Tests with doule-notched specimens resulted in higher pprent sher strengths thn tests with single-notched specimens in 31 of 32 comprisons of specimens with otherwise like chrcteristics. The strength increses rnged from little more thn zero up to 25 to 28 percent without much difference etween species. The effects of grin orienttion nd specimen form (lso suelements of specimen type) were more oscured y interctions, ut some oservtions out these fctors re worth discussing. Specimen grin orienttion There ws definite difference in the strengths of specimens with tngentil s compred to rdil grin orienttion in Dougls-fir, ok, nd mple specimens. The effect ws quite different etween Dougls-fir nd the two hrdwoods. Rdilly oriented Dougls-fir specimens were stronger thn tngentilly oriented specimens in 11of 12 comprisons. Conversely, tngentilly oriented ok nd mple specimens were stronger thn their rdilly oriented counterprts in ll 12 comprisons. The grin orienttion effect ws errtic in pine. Rdilly oriented, single-notched solid wood pine specimens were stronger thn their tngentilly oriented counterprts, s explined previously with Dougls-fir; however, grin orienttion intercted with specimen size nd form in doule-notched specimens. This is indicted in Figure 3 y the crossover of three of the four pirs of lines representing the rdil nd tngentil grin orienttions. The lrge ry volumes in ok nd mple (8) cn e expected to increse the resistnce to shering in the tngentil plne nd decrese it in the rdil plne. Pine nd Dougls-fir hve only 7 nd 8 percent trnsverse ry volumes, respectively. Furthermore, the wek erlywood zone in pine nd Dougls-fir offers pth of lest resistnce to sher in the tngentil plne. Ok lso hs wek erlywood nd, ut the high ry volume in ok pprently more thn compenstes for this wekness. Hilrnd s dt (3) for solid southern pine nd overcup ok gree with our findings, ut Stnger nd Blom- TABLE 2. - Results of ANOVA for effects of experimentl fctors nd their interctions on strength of lock-sher specimens (Anlyses I nd II). Proility (p) Source of vrition All species Southern pine Dougls-fir White ok Hrd mple Species 0 Type 0 Species Type Tool Species Tool Type Tool Species Type Tool Size Species Size Type Size Species Type Size Tool Size Species Tool Size Type Tool Size Species Type Tool Size Grin Species Grin Type Grin Species Type Grin Tool Grin Species Tool Grin Type Tool Grin Species Type Tool Grin Size Grin Species izex Grin Type Size Grin Species Type Size Grin Tool Size Grin Species Tool Size Grin Type Tool Size Grin Species Type Tool Size Grin p is the proility tht the null hypothesis is true. The null hypothesis sttes tht there is no rel difference in strength due to the level of fctor; the differences oserved re due to the rndom vrition. The smller p is, the more one would dout the null hypothesis nd the more one would suspect tht rel differences re cused y the different levels of the fctor. p < 0.05, the level selected for rejection of the null hypothesis, is shown in itlics. FOREST PRODUCTS JOURNAL Vol. 39. No. 1 47

6 TABLE 3. - Averge wood filure of onded lock-sher specimens for different comintions of fctors. Averge wood filure Specimen size/ Southern pine Dougls-fir White ok Hrd mple sher tool Tngentil Rdil Tngentil Rdil Tngentil Rdil Tngentil Rdil /no offset /offset /no offset /offset Tngentil grin orienttion. Rdil grin orienttion. Test methods compred in reltive strength rtio, TABLE 4. - Comprision of pprent sher strengths otined y different test methods. Sher plne grin Reltive strength rtio Numertor Denomintor orienttion Southern pine Dougls-fir White ok Hrd mple B A Tngentil Rdil Averge 1.36 C A Tngentil 1.80 Rdil 1.68 Averge 1.74 C B Tngentil Rdil 1.17 Averge Test methods: A - ASTM D 143 (stndrd method for wood sher strength); B - ASTM D 905 (stndrd method for dhesive sher strength); C - Modified ASTM D 905 (method for reduced-size specimen). The rtio of the strength from the method in the numertor to the strength from the method in the denomintor. quist (9) reported higher sher strengths in the tngentil plne for oth solid nd onded rdit pine (Pinus resulting from test method nd grin orienttion nd their interction (Anlysis III). rdit) specimens. Unfortuntely, the Wood Hndook Proility (13) does not seprte tngentil nd rdil grin sher strength vlues for solid wood. Species Test method Grin orienttion c interction TABLE 5. - Significnce of the differences in the pprent sher strength Test grin Solid nd onded specimen forms Southern pine < Dougls-fir < The strength differences etween solid nd onded White ok < specimens with otherwise like chrcteristics were some- White ok d < < Hrd mple < < times quite lrge. For exmple, solid, doule-notched, full-size, tngentil-grin pine specimens tested in the See Tle 2, footnote (). sher tool with offset were 48 percent stronger thn their onded counterprts (1,665 psi compred with 1,127 psi d Outlying dtpoint removed. (Tle 1). However, in 11 of 24 comprisons of pine, Dougls-fir, nd ok, the onded specimens were strong- See Tle 4, footnote (). c With respect to plne of sher tool. grin orienttion nd three test methods. The three er. Only solid mple specimens were stronger in every methods re: test method A - solid wood, single-notched, comprison; this ws most likely n rtifct of the mr- full-size specimen, 1/8-inch offset sher tool (stndrd ginl to very low wood filures chieved in the onded ASTM D 143); test method B - onded-wood, doule- mple specimens. notched, full-size specimen, no-offset sher tool (stn- Millett nd Gillespie (6) reported difference in drd ASTM D 905); nd test method C - onded-wood, strength ofonly out 1 percent etween solid nd ond- doule-notched, reduced-size specimen, no-offset sher ed reduced-size mple specimens tested in the sher tool tool (11) (modified ASTM D 905). without offset (3,950 psi compred with 3,990 psi). In Tle 4 compres the pprent sher strengths o like comprison, we found the solid specimens to e tined y these test methods. The stndrd ASTM D 905 out 10 percent stronger thn the onded specimens. test (method B) resulted in higher strength vlues thn However, we otined n verge of only 57 percent the stndrd D 143 test (method A) in ll four species wood filure in rdilly oriented specimens nd 4 per- (Tle 4). The modified D 905 test (method C) resulted cent in tngentilly oriented specimens (Tle 3), where- in higher strengths thn either the stndrd D 143 or s Millett nd Gillespie otined n verge wood fil- D 905 test methods, with the exception of tngentilly ure of 69 percent. The lrger 10 percent difference we oriented Dougls-fir specimens. The difference etween oserved is gin most likely n rtifct of the low wood methods ws sometimes greter in the cse of tngen filure. tilly oriented specimens (e.g., methods C nd A, pine) Comprison of ASTM D 143, nd sometimes greter in the cse of rdilly oriented ASTM D 905, nd modified ASTM D 905 specimens (e.g., methods C nd B, Dougls-fir). This ws In light of the interctions detected etween the fc- not unexpected considering the interctions etween tors, we conducted third nlysis (Anlysis III) to ex- fctors. plore the effects of nd test for interctions etween The significnce of the effects of test method nd 48 JANUARY 1989

7 grin orienttion when these fctors were pooled is summrized in Tle 5. Test method ws highly significnt (p < 0.001) fctor in ll species. Grin orienttion ws significnt (p < 0.05) fctor for ll species except pine. The test-method y grin-orienttion interction ws highly significnt (p < 0.001) in Dougls-fir, less significnt (p < 0.1) in pine, nd not t ll significnt (p > 0.1) in ok nd mple. The interction in ok ecme mrginlly significnt when one outlying dt point ws removed from the nlysis. To void the effects of the test method y grinorienttion interctions, dditionl nlyses were crried out y individul species nd grin orienttion to test for the significnce of the test method (Anlysis IV), nd y species nd test method to test for the significnce of grin orienttion (Anlysis IV). In the sence of interctions, test method hd highly significnt (p < ) effect on sher strength (Tle 6). In ll ut rdilly oriented Dougls-fir nd rdilly oriented ok, the test methods rnked in order from the highest to the lowest strength s follows: test C, test B, nd test A. When similr nlysis (Anlysis IV) ws crried out y species nd test method, the rdilly oriented specimens were significntly (p < 0.05) stronger in test method B for pine, nd test methods A nd C for Doug- TABLE 6. - Significnce of the differences in pprent sher strengths resulting from different test methods (Anlysis IV). Grin Method-to-method Species orienttion Proility (p) comprison c Southern pine Rdil < C > B > A Southern pine Tngentil < C > B > A Dougls-fir Rdil < B = C > A Dougls-fir Tngentil < C > B > A White ok Rdil C B A White ok d Rdil < C > B > A White ok Tngentil < C > B > A Hrd mple Rdil < C > B > A Hrd mple Tngentil < C > B > A See Tle 4, footnote (). See Tle 2, footnote (). c C > B mens tht the result otined y tet method C ws significntly greter thn the result otined y test method B. Methods underscored y the sme line did not produce significntly different results. Thus, C B A mens C = B nd B = A, ut C A. d Outlying dtpoint removed. TABLE 7. - Significnce of the differences in pprent sher strengths cused y grin orienttion in the sher plne (Anlysis IV). Comprision of Species Test method Proility (p) grin orienttion c Southern pine A R = T B R > T C R = T Dougls-fir A R > T B R = T C R > T White ok A T > R B T > R C T = R C d T > R Hrd mple A T > R B T > R C T = R See Tle 4, footnote (). See Tle 2, footnote (). c R = Rdil, T = Tngentil. d Outlying dtpoint removed. ls-fir (Tle 7). The effect of grin orienttion ws more consistent in ok nd mple (Tle 7). Tngentilly oriented ok nd mple specimens were stronger thn or equl to rdilly oriented specimens. The grin orienttion difference pprently would hve een more pronounced in ok nd mple specimens if we hd otined etter dhesive onds on tngentil surfces (Tle 3). Conclusions The lock-sher test cnnot e presumed to mesure the true sher strength of solid wood or dhesively onded joints. In our study, species, specimen size, specimen type, grin orienttion, nd sher tool ll significntly ffected the pprent strength of lock-sher specimens. There were mny interctions etween these fctors. Species ws the dominnt fctor s should e expected, ut more importntly, it intercted with every other fctor involved in this study. For individul species, sher tool, or more specificlly, the presence or sence of n offset in the sher plne ws the most consistent nd powerful fctor. It ccounted for the gretest differences in the pprent sher strength mesured y the lock-sher method. The tool with no offset produced strengths tht were essentilly equl to, ut most often higher thn, those otined with similr tool with 1/8-inch offset. The lrgest increses in pprent sher strength cused y no offset were in the rnge of 50 to 60 percent. Specimen size ws strong nd consistent fctor in tests using the sher tool without offset. With the offset, size ws n inconsistent ut sometimes strong fctor. The reduced-size specimen usully produced higher strength thn the full-size specimen for specimens otherwise like in shpe, grin orienttion, nd sher tool. The lrgest strength increses with reducedsize specimens were mostly in the rnge of 20 to 40 percent, ut one ws s high s 60 percent. Specimen shpe lso hd strong nd consistent effect on strength. The doule-notched shpe consistently produced strengths equl to or greter thn the single-notched shpe for tests otherwise like in specimen size, specimen grin orienttion, nd sher tool. Specimen shpe hd less of n effect on strength when the offset sher tool ws used. Specimen form sometimes hd strong effect on strength, ut this effect ws inconsistent. In tests with the doule-notched shpe (the only shpe tested for the specimen-form effect), form ws consistent nd significnt fctor only in mple. This my hve een due to the low wood filure (poor ond qulity) in the onded mple specimens. Grin orienttion ws lso strong ut inconsistent fctor. If the test method ws fixed, tngentil-grin ok nd mple specimens were significntly stronger thn rdil-grin specimens of these species. Conversely, for pine nd Dougls-fir, rdil-grin specimens were significntly stronger thn tngentil-grin specimens. The mximum differences for specimens with otherwise like chrcteristics nd sher tool rnged from low of 15 percent in Dougls-fir, to high of 61 percent in ok. If the grin orienttion ws fixed, the modified FOREST PRODUCTS JOURNAL Vol. 39, No. 1 49

8 ASTM D 905 test method (reduced-size specimen) resulted in significntly higher pprent sher strengths thn the stndrd ASTM D 905 test method, which in turn produced significntly higher strengths thn the stndrd ASTM D 143 test method. Recommendtions If comprison etween the strengths of solid wood nd onded specimens is desired or required, the solid wood specimens should e cut from the sme lot of wood, cut in the sme grin orienttion, nd doule-notched. The solid wood specimens should lso e tested in the sme ASTM D 905 no-offset sher tool used for the onded specimens. The specimen size my e either full or reduced, with the understnding tht higher strengths will e otined with the reduced-size specimens thn with the full-size specimens. The grin orienttion in the sher plne should e controlled in oth solid-wood nd onded specimens. The investigtor should lso e wre tht the method producing the higher strengths nd the size of the difference etween the two methods results re species dependent. Literture cited 1. Americn Society for Testing nd Mterils Stndrd test methods for strength properties of dhesive onds in sher y compression onding. ASTM D (1986), Vol Phildelphi, P Stndrd methods of testing smll cler specimens of timer. ASTM D , Vol Phildelphi, P. 3. Hilrnd, H.C Comprison of lock sher methods for determining shering strength of solid wood. Res. Note FPL-030, USDA Forest Serv., Forest Prod. L., Mdison, Wis. 4. Hunt, G.M The preprtion of specifictions for propeller glue. Unpu. Prog. Rept., Project L USDA Forest Serv., Forest Prod. L., Mdison. Wis. 5. McLeod, A.M., L.A. Yolton, W.A. Snorn, nd R.S. Phillips A comprison of shering strengths of glued joints t vrious grin directions s determined y four methods of test. Forest Prod. L. Rept (first issued 1945, reviewed nd reffirmed 1962). USDA Forest Serv., Forest Prod. L., Mdison, Wis. 6. Millett, M.A. nd R.H. Gillespie Precision of the rte-process method for predicting ondline durility. Rept. prepred y Forest Prod. L. for Dept. of Housing nd Urn Develop. Rept. ville from Ntionl Tech. Informtion Serv. Rept. No. PB Norris, C.B Comprison of stndrd lock-sher test with the pnel-sher test. Forest Prod. J. 7(9): Pnshin, A.J., C. DeZeeuw, nd H. P. Brown Textook of Wood Technology. McGrw-Hill Book Co., N.Y. 9. Stnger, A.G., nd R.F. Blomquist A comprison of lock sher, cross-lp tension, nd glueline clevge methods of testing glued joints. Forest Prod. J. 15(12): Sttisticl Anlysis System SAS Institute, Inc., Rleigh, N.C. 11. Strickler, M.D Adhesive durility: Specimen designs for ccelerted test. Forest Prod. J. 18(9): Trux, T.R. nd C.A. Hrrison Comprison of types of glue sher specimens. Unpu. Rept., Project L USDA Forest Serv., Forest Prod. L., Mdison, Wis. 13. USDA Forest Service, Forest Products Lortory Wood Hndook: Wood s n Engineering Mteril. USDA Agri. Hnd. 72 (rev.). Mdison, Wis. 14. Yvorsky, J.M. nd J.H. Cunninghm Strin distriution in mple glue lock sher specimen s indicted y rittle lcquer. Forest Prod. J. 5(2): , nd N.G. Hundley Survey of fctors ffecting strength tests of glue joints. Forest Prod. J. 5(10): JANUARY 1989