Analysis ASTM 1037

8/12/2019 Analysis ASTM 1037

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Analysis of ASTM D 1037

accelerated-aging test

J. Dobbin McNattCarol L. Link

Abstract

The ASTM D 1037 six-cycle accelera ted -a ging tes t forwood-based panel products was analyzed to determine how

each successive a ging cycle and selected st eps in each cy-cle contribute to panel deterioration. Hardboard, particle-boar d, f lakeboard, wa ferboard, a nd oriented stra ndboar dwere evaluated. The rate of panel deterioration generally

decreased with each successive aging cycle. Four cyclesof accelera ted a ging ha d essential ly the sa me effect onpanel bending strength and sti f fness as the standard sixcycles. Deletion of th e 20-hour freezing st ep from th e a g-ing cycle had practically no effect on the outcome of the

exposure. Deletion of the steaming steps, however, re-sulted in less panel deterioration. Deletion of both freez-ing and st eaming steps produced a bout t he same a mountof panel deterioration as deletion of the steaming stepsalone. In some cases, interpretation of results depended

on whether bending strength and sti f fness calculationswere based on init ial specimen thickness or thickness after

aging. Findings from this study indicate definite oppor-tunities for developing an abbreviat ed alterna tive to thecurrent time-consuming accelerated-aging test. We pro-pose a n a lternat ive exposure, which will be investigatedin a fu ture s tudy .

The current U.S. test for evaluating bond durabil i tyof phenolic-bonded particleboard and other wood-baaedpanels subjected to severe exposures is the six-cycle accel-

era ted-ag ing t est in ASTM D 1037 (3). The Na tiona l B u-

reau of Standards (NBS) developed this test in the 1930sto determine fiberboard sheathing durability (16). Thevarious exposures used were baaed on NBS experiencewith aging of paper ; wet t ing and freezing steps were add-ed because f iberboard sheat hing ma ybe subjected t o thistype of exposure. No attempts were made to determinehow much each exposure step contributed to fiberboarddeterioration.

The most often reported problem with the ASTM D1037 test is that it is much too long to be used as an in-plant quality control check. Each of the six cycles contains

six individual exposure steps. The test normally takes2-1/2 weeks to complete s ince th e cycle can be int errupt ed

only at the freezing step. After accelerated aging, addi-tiona l time is needed t o recondition the specimens before

sti f fness and strength can be measured.The tw o objectives of our stu dy w ere to 1) eva luat e the

progressive deterioration of products with each successive

exposure cycle in the ASTM D 1037 test; and 2) deter-mine how various steps in the ASTM D 1037 six-cycletest contribute to panel deterioration. Results of this studywere used to develop a less time-consuming accelerated-

aging test , which wil l be evaluated in a future study.

Literature review

Two approaches to predicting long-term durability ofexposed wood-based panels are mentioned in the litera-ture (6,13):

1. Ident ify the fac tors that cause degradat ion and de-

termine their individual influence. Then, devise a labo-ra tory test tha t closely approximat es actua l-use condi-tions, compressed in time.

2. Select severe laborat ory exposures tha t ca use

changes in properties that can be correlated reliably withproperty changes under actual-use conditions.

The ASTM D 1037 test clear ly represent s t he second

approach; exposures include soaking in 120F water,steaming at 200F, freezing at 10F, and drying at 210F.These condit ions would not be found in the environment .A temperature of 10F is possible, but the panel wouldprobably not be saturated . Maximum roof sheathing tem-peratures close to 170F have been recorded in the Unit-ed States (14,29).

Some researchers concluded that the 20-hour freezing

portion of the ASTM D 1037 test did not significa ntly a f-

The authors are, respectively, Research Forest Products Tech-nologist and Mathematical Statist ician, USDA Forest Serv. , For-est Prod. Lab., Madison, WI 53705-2398. This paper was receivedfor publication in December 1988.

Forest P roducts Research S ociety 1989.Forest P rod. J . 39(10):51-57.

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feet test results and could be eliminated (4,9,30). The WestCoast Adhesive Manufacturers Association (WCA.MA) (30)developed a shorter six-cycle test that gives essentiallythe sa me resul ts a s th e ASTM D 1037 test for va riousphenolic-bonded particleboard (Fig. 1). Sleet (27) andCh ow an d J an owiak (10) found general agr eement be-tween the WCAMA test and the ASTM D 1037 test. Ina ddition, Chow and J an owiak found no difference in re-sults after four or six cycles of either test. Carre (7), onthe other hand, stated that the effect of freezing dependson whether or not the material is saturated with water .The am ount of moisture adsorbed during soaking or steam-ing depends on the ma keup of the ma teria l. Fiberboards,hardboards, and particleboard wil l not adsorb the sameam ount of moisture for a given soaking condition. A vac-uum-pressure soak, high-temperature soak, or both typesof soak ma y be the only wa y t o assure complete sa tura -tion. Dinwoodie (11) stated that a suitable accelerated-aging test must include a freezing step.

Caster (8) found that 20 cycles of a modified versionof the automatic boil test, ASTM D 3434 (2), gave the samegeneral results as the ASTM D 1037 test, but took only2 to 3 days to complete. Knudson and Rosenberg foundgood correla tion bet ween th e ASTM D 1037 six-cycle testand a test consisting of one cycle of 2-hour boil plus l-hourcold wa ter soa k plus 24-hour ovendry. The lat ter t est ha sbeen adopted by MacMillan Bloedel as part of their wafer-board mill qualit y contr ol. J a tha r (15) suggested a single

cycle of 10-minute boil plus 4-minute ice water soak plusl-hour ovendry a s a simple, low-cost, ra pid in-plant qua l-i ty control test for w aferboard. H e found t his test to be

somewha t more severe tha n th e ASTM D 1037 test. Leh-ma nn (20) outl ined a fast dura bi li ty t est for compositematerials that is based on shear testing of specimens after

hot-water soaking in a small pressure cooker. In an earlierstudy , Lehma nn (19) had reported tha t five cycles of 24-hour ovendry plus 2-hour vacuum plus 22-hour pressuresoak (OD/VPS ) and t he ASTM D 1037 test ga ve essentia llythe same bending strength and stiffness reduction for avariety of phenolic-bonded flakeboarde, but internal bondstrength reduction was greater in the ASTM D 1037 test .However, River et a l. (24) found t ha t t he relat ionship be-

tw een OD/VPS an d t he ASTM D 1037 test w as differentfor different panel types. In most studies where effectsof successive cycles were evaluated (5,10,18,21,23-26,30),

the rate of panel degradation decreased as the numberof cycles increased.

Of the standardized accelerated-aging methods, no sin-gle method is universally recognized as outstanding (4,12,13). The ASTM Standard E 632 (1) outlines a systematicapproach that should be used in developing acceleratedtests to predict service life of building materials.

In summa ry, numerous at tempts have been ma de todevise accelerated-aging tests that are shorter and simplerthan the ASTM D 1037 six-cycle test, which was devel-oped more than 50 years ago. Most short quality-controltests have been developed for specific phenolic-bonded par-ticle panel products a nd include cyclic hot-wat er soakingand ovendrying. The usefulness of a freezing step in cyclicexposure is questionable.

Experimental procedure

Our study was conducted in two phases. Phase 1 de-termined the effects of the number of cycles of the ASTMD 1037 accelerated-aging exposure test on the bendingproperties of selected wood-based panel products. Phase 2

evalua ted how selected st eps in the cycle contributed t o-ward panel deterioration. A third phase, the investiga-tion of an abbreviated version of the current cyclic ex-posure in ASTM D 1037, will be conducted in the future.

Five wood-based panel products were evaluated in the

study hardboard lap siding, isocyanate-bonded particle-board, phenolic-bonded laboratory-made flakeboard, wa-ferboard, and oriented strandboard (OSB). All were nom-inally 1/2 inch thick except for the h a rdboard, w hich wa s3/8 inch t hick .

Ten lengths of l-foot-wide by 16-feet-long lap sidingwere obtained. The other ma terials were obtain ed in 4- by8-foot sheets (five sheets each). The laboratory-made flake-

board panels were manufactured in 4- by 8-foot sheetsas a part of the USDA Forest Service program on struc-tural flakeboard from forest residue (21).

Each panel was cut into ninety 3-inch-wide bendingspecimens. Half the specimens were cut with their lengthparal lel to the panel length and hal f wi th their lengthperpendicular t o the panel length. Except for ha rdboard,all specimens were 14 inches long hardboard specimenswere 11 inches long. All specimens were marked to iden-t ify type of material, panel number, location in the panel,

and direction relative to panel length.

Phase 1

For each material, 20 specimens were randomly se-

lected a nd test ed as controls (5 pa nels 2 pa nel direc-tions 2 replicat es) an d 120 specimens w ere ran domlyselected and tested after 1, 2, 3,4, 5, or 6 cycles of accel-erated a ging (5 panels 2 panel directions 2 replicat es).All specimem w ere first conditioned t o equilibrium mois-ture content a t 75F and 64 percent relat ive humidi ty(RH), weighed, and measured. Control specimens weretested in static bending according to ASTM Standard D1037 (3). The remaining specimens were subjected to 1to 6 cycles of the accelerated-aging exposure specified inASTM D 1037. Twenty specimens of each product were

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removed after 1 cycle, 20 specimens after 2 cycles, andso on th rough 6 cycles. All a ged specimens w ere recon-ditioned at 64 percent RH and again weighed and mea-sured prior to testing in static bending. Residual thick-ness swelling of each aged specimen was determined asa percentage of original thickness.

Phase 2

Each cycle in the ASTM D 1037 accelerated-aging testconsists of the following six steps:

In Phase 2 of our study, specimens were tested after be-ing subjected to four or six cycles of the standard expo-sure (all six steps) and three modified exposures: freezingstep (step 3) deleted, steaming steps (steps 2 and 5) delet-

ed, or freezing and steaming steps (steps 2, 3, and 5) de-leted. In the latter two exposures, the drying steps (steps4 an d 6) of th e accelera ted-a ging cycle were combined fora tota l drying t ime of 21 hours.

Specimens were selected and tested as described forPhase 1 so that 20 specimens of each material were testedafter each of 4 or 6 cycles of the modified aging exposures.

Method of analysis

For each material, analysis of variance (ANOVA),with panels as a blocking factor , was used to determineif the mean properties of thickness swelling (TS), modulus

of rupture (MOR), a nd m odulus of elast icity (MOE) werethe same in these test situations: controls, 1 to 6 complete

aging cycles, or 4 or 6 modified aging cycles. If the ANOVAindicat ed tha t a l l the means w ere not t he same, Tukeysmultiple comparisons were used to determine which meanscould not be considered statistically equal at the 5 per-cent level.

Results and discussion

Properties of control specimens

Avera ge propert ies of the control specimens a re givenin Table 1. For al l th e ma terials , th ere were significantdifferences in bending strength and stiffness between spec-

imens cut parallel or perpendicular to the length of a given

panel. For OSB, this difference was due to alignment of

the strands parallel to the 8-foot direction on the face andperpendicular to the 8-foot direction in the core. For hard-board, flakeboard, and waferboard, the stronger and stifferdirection corresponded to t he forming direction of t he pa n-el during ma nufacture. Some a l ignment of part icles orf ibers is common during ma t layup. The wa ferboard wa swea ker in t he 8-foot direction since th is corresponds t othe cross-panel direction of the mat layup during man-ufacture. The lower stiffness of the particleboard in the8-foot direction cannot be explained since this corresponds

to the ma t-forming direction during ma nufacture.

Calculation of aged specimen properties

As specified in ASTM D 1037, MOE and MOR of agedspecimens were calculated using both initial thicknessand thickness af ter aging. In this paper , we refer to theMOE and MOR that were calculated using the ini t ialthickness a s bending resistan ce and load-carry ing capac-ity, respectively. Lehmann (18) found that MOE and MORvalues based on initia l thickness w ere sometimes greateraf t er aging t ha n before aging. Although a ging decreasesspecimen strength by breaking interpa rt icle bonds anddegrading the wood, increased specimen thickness cansufficiently increase resistance to a bending load to moretha n offset th e effects of loss in interpar ticle bonding. S leet

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(27) suggests that if the effect of TS is removed by calcu-lat ing MOE and MOR using actual t hickness, then com-

parisons reflect only degradation of the wood and the gluebond.

Phase 1. Effect of number of cycles

Resi du al TS. Thickness of ea ch specimen w as mea-sured aga in a f ter th e accelerated-aging exposure an d re-conditioning at 64 percent RH. Residual thickness is thedifference between this value and the initial thickness,expressed as percentage of initial thickness. Figure 2

shows the steady increase in thickness for individual spec-imens of the five materials as the number of accelerated-aging cycles increased. Total residual TS (springback)after six cycles of accelerated aging was least for the par-ticleboar d (13%) and g rea test for th e wa ferboa rd (30%).This is characteristic of the behavior of panels made fromf iner pa rt icles (planer sha vings, saw dust) compar ed tothose made from large flat f lakes (wafer, strands) (22,28).

Bendi ng stif fn ess and strength. Figure 3A showsthe progressive decrease in bending resistance with suc-cessive cycles of accelerat ed a ging, ba sed on init ial s peci-men thickness. Data for parallel and perpendicular orien-tations of specimens in the panels are combined for hard-board, part icleboard, f lakeboard, and waferboard, but are

presented separately for OSB where directional propertieswere intentional ly buil t into the panels . Bending resist-ance decreased s teadi ly , but a t a decreasing ra te, for eachsuccessive cycle of accelerated aging. The character of thisdecrease w as similar for h ar dboard, part icleboard, f lake-board, and waferboard specimens. The change for OSBspecimens cut in the parallel direction was more variable,

on the average, bending resistance of OSB decreased lesstha n tha t of the other materials . For OSB specimens cutin the perpendicular direction, most decrease in bendingresistance occurred in the first aging cycle.

Da ta for MOE in Figure 3B a re based on a ctual spec-imen th ickness. As a r esult, th e avera ge MOE of the con-trol specimens wa s much greater t han tha t of specimenstested after one to six cycles of accelerated aging. Thisis part icularly tr ue for OSB cut in the pa ra l lel direction.Average slope of the load-deformation curves for the OSB-pa ra llel specimens a fter on e agin g cycle (591 lb./in.) wa sactua l ly s light ly greater t ha n th at of the control speci-mens (545 lb./in.). Therefore, ben ding resist a nce show edan increase after one aging cycle (Fig. 3A). However, therewa s a s ignificant drop in MOE based on a ctual specimenthickness as a resul t of an a verage 12 percent residualthickness swelling of OSB specimens after one aging cycle(Fig . 2). Put an other wa y, Figure 3A indicat es tha t th eOSB-paral le l specimens retained al l their abi l i ty to re-

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sist deflection under load a fter one a ging cycle (90% re-

ta ined aft er six cycles). Figure 3B, on the other ha nd, in-dicates a 28 percent degradation of the wood and gluebondin th e OSB -para llel specimens a fter one a ging cycle (50%degradation after six cycles). Other materials also showeda much greater decrease in MOE th an in bending resist-ance.

The changes in bending strength, based on initial ora ctua l th ickness (Fig. 4), were m uch like those found forstiffness. Strength retained after six cycles (4A), expressedas a percenta ge of init ial load-carrying capacity , ra ngedfrom 55 percent for particleboard and waferboard to 70percent for OSB when based on initial thickness. Whenbased on actual thickness (4B), retained MOR ranged from32 percent for waferboard to 50 percent for OSB and flake-

board .

Phase 2. Effect of deleting aging steps

Resid ua l TS. Figure 5 shows residual TS of indi-vidual specimens of the five panel products after four orsix cycles of the four aging exposures described in theMethods section.

TS was virtually the same atler four or six cycles ofaccelerated aging. Swell ing was sl ightly reduced whenthe freezing step was deleted. Reduction is more substan-

tial when the steaming step was deleted. Residual TS withboth freezing and steaming st eps deleted w as essential lythe same as when only steaming was deleted. The effectof deleting the steaming step was most evident with hard-board, where average residual TS was reduced from about18 percent to only 2 percent. The effect wa s least for wa fer-board, where residual TS was reduced from 30 percent for

the complete exposure to 20 percent with the steamingstep deleted.

Bendi ng sti ffn ess and strength . Deleting the freez-ing a nd/or stea ming steps from the six-cycle a ccelerat ed-

aging test had lit t le effect on bending resistance (Fig. 6A).Results w ere the sa me wh ether four or six cycles of a ccel-erated a ging were used. When the freezing a nd stea mingsteps were deleted, bending resistance of hardboard in-creased t he most (about 20%); part icleboar d a nd w a fer-board increased about 14 percent. Flakeboard and OSBshowed no consistent change in bending resistance withdeletion of freezing a nd/or st eamin g st eps.

When actual specimen thicknesses were used to cal-culate MOE, deletion of the steaming step resulted in a

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Four cycles of accelerated aging gave essentiallythe same resul ts as s ix cycles.

2 Delet ing t he 20 hour freezing step from the expo-sure cycle did not significantly affect test resul t s .

3 Deleting t he tw o 3 hour steaming steps did signif-icant ly affect resul t s . H o w e v e r for convenience in con-duct ing the t e s t i t would be advantageous to l imi t t heexposure to s imply a hot-wa ter soak a nd o v e n d r y i n g .

4 B ecau se of residual TS interpretat ion of test re-sults can vary depending on whether calculations of bend-

ing strength and stiffness are based on initial specimenthickness or thickness a f i e r a g i n g .5 The following a lterna tive exposure cycle and pos-

sibly o t h e r s wil l be invest igated in a future s t u d y :

significant increase in MOE for all products, ranging from35 percent for OSB to 85 percent for har dboard (Fig. 6B).Deletion of the freezing step, on the other hand, did notaffect the results. Also, results were almost identical afterfour or six cycles.

The bending strength data, whether calculations werebased on initial specimen thickness (Fig. 7A) or actualthickness (Fig. 7B), indicated trends similar to those seen

for s t i f fness . Strength after aging wi thout the freezingstep was essential ly the same a s tha t a f ter the completeaging cycle. Strength after aging without the freezing stepor steaming steps was essential ly the same as that af ter

aging without the steaming steps. Also, test results wereessentially the same after four or six cycles of acceleratedaging. This agr ees with results of Chow an d J an owiak (10).

Conclusions

An analysis of the ASTM D 1037 accelerated-agingtest for wood-based panel products indicat ed definite op-portuni t ies for shortening total exposure t ime wi thoutsignificantly altering effects of aging on residual TS andbending strength and sti f fness.

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