Z -M. Huang/Composites Science and Technology 64(2004)529-548 Test results(x-strain) Test results (y-strain) Theory (y-strain, without hermal residual stresses) A Theory (x-strain, without Theory (y-strain, with thermal residual stresses Theory (x-strain, with thermal 0 梦0 residual stresses Fig. 14. Measured and predicted ayy vS. Eyy and oyy vS. Exx curves for [+45@]s laminate under biaxial stresses(oyyoxx=1/-1) Material type E-Glass/MY750 reason is the same as the above mentioned If the resin This is because the lamina strengths in these directions compressive strength used is higher, the predicted max- were used to determine the constituent strengths. The imum shear strength will occur at a larger applied com- resin tensile strength was also retrieved from the lamina pressive transverse stress. longitudinal tensile strength, resulting in a higher pre- dicted transverse tensile strength for the lamina. It is Problem 2 (UD T300/BSL914C lamina subjected to seen that the predicted failure envelope on the fourth combined oxr and xy loads). This is the only composite quadrant is approximately a rectangle, whereas the made of T300/BSL914C material system amongst the 14 measured data could be better represented by a mono exercise problems. Correlation between the theory and tonically increased curve as the longitudinal tensile the experiments for this lamina is grossly satisfactory, as stress component decreased from its maximum to zero shown in Fig. 2. The figure clearly indicates that the However, compared with those for problem 2, not experimental deviation for composite strengths can be enough measured data for this problem have been quite large. For the present lamina when the long- available. More experiments are required, especially to tudinal load was small, the difference in the measured determine the data points of the failure envelope on the failure strengths can be as large as 80% of a relative other three quadrants error. Thus, sufficient experimental data should be obtained when they are used to verify theoretical pre- Problem 4 l(900/+300/90)E-glass/LY556/HT907/ dictions DY063 laminate subjected to combined orr and o loads]. Relatively large discrepancy exists between the Problem 3 (UD E-glass/MY750/HY917/DY063 lamina theory and the experiments for this problem, as indi subjected to combined yy and orr loads). Results of this cated in Fig. 4. This is one of the few exercise problems problem are shown in Fig. 3. It may be noted that for which the bridging model predictions did not corre- according to the organizers [4] the problem 3 was actu- late reasonably with the measured data. The dis- ly not an exact UD lamina, but an angle plied lami- crepancy became the largest when the combination of 5°,i.e.[±5° Is. Thus, the the applied biaxial loads, o. andσ near predicted curve(for the laminate) plotted in Fig. 3 is linear line as shown in the slightly different from the corresponding figure shown in Oxx=1.50yy+34.4(MPa). The laminate Ref [1]. Similarly to Problem l, the correlation in the response could not be accurately es longitudinal (x-directional) tension and compression procedure of Ref. [1]. see the discussions given for and the transverse (y-directional)compression is good. problem 10 for more detail. Furthermore, the resinreason is the same as the above mentioned. If the resin compressive strength used is higher, the predicted max￾imum shear strength will occur at a larger applied com￾pressive transverse stress. Problem 2 (UD T300/BSL914C lamina subjected to combined
xx and
xy loads). This is the onlycomposite made of T300/BSL914C material system amongst the 14 exercise problems. Correlation between the theoryand the experiments for this lamina is grosslysatisfactory, as shown in Fig. 2. The figure clearlyindicates that the experimental deviation for composite strengths can be quite large. For the present lamina when the long￾itudinal load was small, the difference in the measured failure strengths can be as large as 80% of a relative error. Thus, sufficient experimental data should be obtained when theyare used to verifytheoretical pre￾dictions. Problem 3 (UD E-glass/MY750/HY917/DY063 lamina subjected to combined
yy and
xx loads). Results of this problem are shown in Fig. 3. It maybe noted that according to the organizers [4] the problem 3 was actu￾allynot an exact UD lamina, but an angle plied lami￾nate with a plyangle of 5
, i.e. [5
]s. Thus, the predicted curve (for the laminate) plotted in Fig. 3 is slightlydifferent from the corresponding figure shown in Ref. [1]. Similarlyto Problem 1, the correlation in the longitudinal (x-directional) tension and compression and the transverse (y-directional) compression is good. This is because the lamina strengths in these directions were used to determine the constituent strengths. The resin tensile strength was also retrieved from the lamina longitudinal tensile strength, resulting in a higher pre￾dicted transverse tensile strength for the lamina. It is seen that the predicted failure envelope on the fourth quadrant is approximatelya rectangle, whereas the measured data could be better represented bya mono￾tonicallyincreased curve as the longitudinal tensile stress component decreased from its maximum to zero. However, compared with those for problem 2, not enough measured data for this problem have been available. More experiments are required, especiallyto determine the data points of the failure envelope on the other three quadrants. Problem 4 [(90
/30
/90
) E-glass/LY556/HT907/ DY063 laminate subjected to combined
yy and
xx loads]. Relativelylarge discrepancyexists between the theoryand the experiments for this problem, as indi￾cated in Fig. 4. This is one of the few exercise problems for which the bridging model predictions did not corre￾late reasonablywith the measured data. The dis￾crepancybecame the largest when the combination of the applied biaxial loads,
yy and
xx, was near to the linear line as shown in the figure, i.e. when
xx=1.5
yy+34.4 (MPa). The resulting laminate response could not be accuratelyestimated using the procedure of Ref. [1], see the discussions given for problem 10 for more detail. Furthermore, the resin Fig. 14. Measured and predicted
yy vs. "yy and
yy vs. "xx curves for [45
]s laminate under biaxial stresses
yy=
xx ¼ 1=  1
. Material type: E-Glass/MY750. Z.-M. Huang / Composites Science and Technology 64 (2004) 529–548 537