514 HOLMES ET AI 三的 fragments surviving to saturation as the strain is increased, both sets of data suggest a rather sharp transition as indicated by the anova analyses where the sizes of the fragments become decidedly 700 smaller as the strain in the SFC specimen is increased. Interestingly, ANOVA analyses of the data from the NOTS- DI SFC specimen shown in Figure 3 indicate that from the three groupings the average size of the fragments lengths surviving to saturation are indistinguishable at the 95% confi- dence level with a p value of 0.48. The sizes of the fragments surviving to saturation appear to remain 0.0150. 0.0250, ami. 350 40.45 constant as saturation is approached. These results suggest that adhesion strength and stress build-up Figure 3 Plots of average sizes of fragments surviving to in the fiber break regions may have a significant saturation from SFC specimens composed of E-glass fibers treated with n-octadecyl triethoxysilane (NOTS_ D1)and Pact on the formation of small fragment lengths bare E-glass fibers embedded in DGEBA/m-PDA (Bare2_9) as saturation is approached ate(PU04E03)matrices. The error bars represent one standard deviation for the multiple fragments formed at a give strain increment. To maintain clarity in the graph, the error bars for the PU04E03 specimen are not The uniform distribution and fiber break locations shown, but are comparable to those for the Bare2_9 speci- from carbon fiber SFC specimens nating between open and solid symbols. For a given data In 2000, the 2nd round robin assessment of the SFFT set,the point where a group becomes distinguishable from was conducted under the auspices of VAMAS the previous group is represented by a change of symbol Approximately 100 AS-4 carbon fiber/DGEBA/ I Color figure can be viewed in the online issue, which is PDA SFC specimens were prepared in five batches availableatwww.interscience.wileycomJ by the michigan State University Composites Labo- ratory. 5 The National Institute of Standards and Technology (NIST)randomized the samples from larity, error bars were omitted for the PU04E03 these batches and distributed them to seven labora specimen, but are comparable to those given for the tories for testing. In Figure 2, the correlation coeffi- Bare2_9 SFC specimen. It should be noted that the cients of the break locations from 12 specimen dispersion data for the pol pecimen is tested in the nist extractable from the fragment evolution data pro- diamond symbols) along with the E-glass data dis- vided in table i cussed above. When the break locations were fitted Analysis of variance(ANOVA)analyses on each to a uniform distribution, 58% of the 12 specimens specimen depicted in Figure 3 were performed by exhibited correlation coefficients at saturation of dividing the fragments into three to five groups. The 0.999 or greater. However, all of the probability plot groupings are indicated in Figure 3 for each speci- correlation coefficients of the carbon fiber SFC speci men by the alternation between open and solid sym- mens were greater than 0.993. To verify the consis- bols as the strain is increased. For the bare 9 tency of these results, the fragment length data at men, the first three groups (upto N 3.5% turation from three additional laboratories were were indistinguishable at the 95% confidence transcribed to yield relative break locations. The with a P value of 0.15. The fourth grouping for the transcribed data are shown in Figure 4 along with Bare2-9 data set, delineated by open squares, was the correlation coefficients obtained from the NIST distinguishable from the third grouping, delineated data. Analyses of these data indicate that 43% of the by solid diamonds, at the same confidence level 42 specimens tested yield correlations greater than with a P value of 0.008. In a similar manner the first 0.999 with all data exhibiting correlations greater three groupings (< 0.2.9% strain) of the polyisocya- than 0.991. It appears that the extensive debonding able with a P val n(PU04E03)were indistinguish- observed in the carbon fiber SFC specimens causes alue of 0.72. However the fourth the fit of the fiber break locations to the uniform grouping was distinguishable from the third at the distribution to be very slightly reduced in these 95% confidence level with a P value of 0.04, whereas specimens. However, greater than 0.99x goodnes the fourth and fifth groupings were indistinguish- of-fit of these data to a uniform distribution able with a p value of 0.10 suggests that the expected distribution of the Although the data from these two specimens indi- ordered fragment lengths at saturation should cate a general downward trend in the size of the conform to(1) Journal of applied Polymer Science DOI 101002/appclarity, error bars were omitted for the PU04E03 specimen, but are comparable to those given for the Bare2_9 SFC specimen. It should be noted that the dispersion data for the polyisocyanurate specimen is extractable from the fragment evolution data pro￾vided in Table I. Analysis of variance (ANOVA) analyses on each specimen depicted in Figure 3 were performed by dividing the fragments into three to five groups. The groupings are indicated in Figure 3 for each speci￾men by the alternation between open and solid sym￾bols as the strain is increased. For the Bare2_9 speci￾men, the first three groups (upto  3.5% strain) were indistinguishable at the 95% confidence level with a P value of 0.15. The fourth grouping for the Bare2_9 data set, delineated by open squares, was distinguishable from the third grouping, delineated by solid diamonds, at the same confidence level with a P value of 0.008. In a similar manner, the first three groupings (< 0.2.9% strain) of the polyisocya￾nurate SFC specimen (PU04E03) were indistinguish￾able with a P value of 0.72. However, the fourth grouping was distinguishable from the third at the 95% confidence level with a P value of 0.04, whereas the fourth and fifth groupings were indistinguish￾able with a P value of 0.10. Although the data from these two specimens indi￾cate a general downward trend in the size of the fragments surviving to saturation as the strain is increased, both sets of data suggest a rather sharp transition as indicated by the ANOVA analyses where the sizes of the fragments become decidedly smaller as the strain in the SFC specimen is increased. Interestingly, ANOVA analyses of the data from the NOTS_D1 SFC specimen shown in Figure 3 indicate that from the three groupings the average size of the fragments lengths surviving to saturation are indistinguishable at the 95% confi￾dence level with a P value of 0.48. The sizes of the fragments surviving to saturation appear to remain constant as saturation is approached. These results suggest that adhesion strength and stress build-up in the fiber break regions may have a significant impact on the formation of small fragment lengths as saturation is approached. The uniform distribution and fiber break locations from carbon fiber SFC specimens In 2000, the 2nd round robin assessment of the SFFT was conducted under the auspices of VAMAS. Approximately 100 AS-4 carbon fiber/DGEBA/m￾PDA SFC specimens were prepared in five batches by the Michigan State University Composites Labo￾ratory.15 The National Institute of Standards and Technology (NIST) randomized the samples from these batches and distributed them to seven labora￾tories for testing. In Figure 2, the correlation coeffi￾cients of the break locations from 12 specimens tested in the NIST laboratory are plotted (open diamond symbols) along with the E-glass data dis￾cussed above. When the break locations were fitted to a uniform distribution, 58% of the 12 specimens exhibited correlation coefficients at saturation of 0.999 or greater. However, all of the probability plot correlation coefficients of the carbon fiber SFC speci￾mens were greater than 0.993. To verify the consis￾tency of these results, the fragment length data at saturation from three additional laboratories were transcribed to yield relative break locations. The transcribed data are shown in Figure 4 along with the correlation coefficients obtained from the NIST data. Analyses of these data indicate that 43% of the 42 specimens tested yield correlations greater than 0.999, with all data exhibiting correlations greater than 0.991. It appears that the extensive debonding observed in the carbon fiber SFC specimens causes the fit of the fiber break locations to the uniform distribution to be very slightly reduced in these specimens. However, greater than 0.99x goodness￾of-fit of these data to a uniform distribution suggests that the expected distribution of the ordered fragment lengths at saturation should conform to (1). Figure 3 Plots of average sizes of fragments surviving to saturation from SFC specimens composed of E-glass fibers treated with n-octadecyl triethoxysilane (NOTS_D1) and bare E-glass fibers embedded in DGEBA/m-PDA (Bare2_9) and polyisocyanurate (PU04E03) matrices. The error bars represent one standard deviation for the multiple fragments formed at a give strain increment. To maintain clarity in the graph, the error bars for the PU04E03 specimen are not shown, but are comparable to those for the Bare2_9 speci￾men. Groupings for ANOVA analysis are formed by alter￾nating between open and solid symbols. For a given data set, the point where a group becomes distinguishable from the previous group is represented by a change of symbol (e.g., circles change to triangles for the PU04E03 specimen). [Color figure can be viewed in the online issue, which is available at www.interscience.wiley.com.] 514 HOLMES ET AL. Journal of Applied Polymer Science DOI 10.1002/app