The interface crack was analyzed in two recent papers which considered applied tension and shear fields separately. The unrealistic oscillatory singularities and the ensuing material interpenetration were eliminated in these solutions by assuming small frictionless contact zones near the crack tips. The present paper presents a solution for the interface crack under combined normal and shear tractions. Both tensile and compressive normal tractions are considered and numerical results of the extents of the contact zones, shear stress-intensity factors, and interface crack opening profiles are presented.

An experimental and analytical study was conducted to examine the free-edge delamination mode of failure in a (±30/±30/90/90) S Boron/ Epoxy laminate. The initiation and stable growth of the delamination for static tension loading conditions were identified using ultrasonic tech niques. A finite element representation for the test specimen was con structed using conventional elements. The interlaminar stress distribution at the laminate midplane was found to be in agreement with published results. The finite element representation was used to model the initiation and stable growth of the delamination. An applied force versus longitudinal strain curve was obtained from the model based on the data for the longi tudinal strain versus the extent of the delamination. The applied force versus longitudinal strain curve obtained from the model was between the two sets of data obtained from the specimens. The model also predicted the strain level at which the laminate showed a marked decrease in stiff ness. Energy release rates were evaluated by a simple computational scheme that does not require a special singular element or knowledge of the existence of a stress singularity in the solution. The results of these computations are combined with the experimental data and discussed in terms of the initiation and stable crack growth characteristics of the delamination.

Computational models for predicting transient temperature distributions, residual stresses, and residual deflections for girth-butt welds are described. Comparisons of predicted and measured temperatures for a two-pass welded pipe show agreement to within 9 percent and 17 percent of the measured values for passes one and two, respectively, the model for predicting residual stresses and residual deflections is based on a finite-element representation recognizing individual passes, temperature dependent elastic-plastic constitutive behavior, elastic unloading for material in the nonlinear stress-strain range, and changes in geometry due to the deformation of each weld pass. Load incrementation and incremental stress-strain relations are also used. Results for a two-pass girth-butt welded pipe show good correlation between residual stresses and residual deflections obtained from the computational model and data obtained from a welded 304 stainless steel pipe.

This paper presents the results of an impact testing program that was conducted to characterize the energy absorption and failure characteristics of selected composite material systems and to compare the results with aluminum and steel. Composite tube specimens were constructed using graphite/epoxy (Gr/Ep), Kevlar/epoxy (K/Ep), and glass/epoxy (Gl/Ep) prepreg tape and were autoclave cured. Vertical impact and static compression tests were performed on 56 tubes. Tests results for energy absorption varied significantly as a function of lay-up angle and material type. In general, the Gr/Ep tubes had specific energy absorption values that were greater than those for K/Ep and Gl/Ep tubes having the same ply construction. Angle-ply Gr/Ep and K/Ep tubes had specific energy absorption values that were greater than those for 1024 steel tubes. Gr/Ep and Gl/Ep angle-ply tubes exhibited brittle failure modes consisting of fiber splitting and ply delamination, whereas the K/Ep angle-ply tubes collapsed in an accordian buckling mode similar to that obtained for metal tubes.

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