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Based on three kinds of composite T-joints with different connection way for tension test outside the plane, it was obtained contrastively that how the ordinary adhesive, Z-pin reinforcement and stitching reinforcement three different fitting influence tensile strength, damage failure process and failure mode of composite T-joints. The test results showed that compared with ordinary adhesive connection mode, tensile strength of the Z-pin reinforcement and stitching reinforcement T-joints increased by 13.6% and 11.4%, respectively; and the largest deformation increased by 19.2% and 15.1%, respectively. After reaching maximum load condition, the ordinary adhesive T-joints had brittle failures, but Z-pin reinforcement and stitching reinforcement T-joints all showed that the ductile damage behavior, corresponding to the load-displacement curve appeared saw-tooth wave platform. Obviously, the Z-pin reinforcement T-joints had the most significant reinforcement effect on tensile properties of composite laminates T-joints.

In this paper, the effect of elevated temperature on the behavior of carbon fiber-reinforced T300/BMP350 unidirectional laminates was studied by loading static tensile on 0°, 90°and ±45° lay-up. The stress-strain relationships of the laminates under different temperatures were obtained. The effect of temperature on the mechanical properties of materials was systematically studied. The damage and failure mechanisms of the material were studied by analyzing the material stress-strain curves and the failure modes. Results show that the T300/BMP350 polyimide matrix composites have a strong resistance to high temperature. For 0° and 90° lay-up, the retentions of tensile strength and modulus are more than 80% and 50%, respectively. High temperature has little effect on the material failure modes. Finally, based on the test results, an empirical formula which relates strength and temperature of the material was fitted.

Experimental and numerical investigations of adhesively stiffened composite panels were performed to discuss the load-carrying capacity of different design at stiffener run-out. The compression experiment revealed that the failure was initiated at the edge of the run-out and propagated across the skin-stiffener interface. A fracture mechanical approach to utilize cohesive finite element was adopted in the numerical analysis of these specimens. It was shown that the finite element analysis using solid element and cohesive element was able to qualitatively predict the crack growth characteristics for each specimen

In order to determine the mechanical properties of the carbon/polyurethane composite laminate with splicing ply, the tensile testing were performed on laminate specimens which has been designed specially. The tensile elastic modulus and tensile strength were obtained from the experimental datum. The breakage happened in place of joint gap. The stiffness of the composite laminate was affected by the oblique splicing ply significantly, but the strength is mainly determined by the continuous layers. The laminate is failure in low load. The numerical analyses using linear elastic and progressive damage model were conducted with the commercial the finite element model (FEM) software ABAQUS. The linear elastic FEM is established to calculate the inter-laminar stress. The progressive model is used to predict the strength on the basis of numerical computation. There are three different criteria used here in the strength prediction. By combining the damage model with classical lamination theory, the behavior of laminates under plane stress loading is predicted. The results show that the experimental tests are in good agreement with the finite element simulation.

The tensile strength of carbon fiber reinforced resin matrix layer splice laminate was studied. Three specimens (M1.M2.M3) were cut from laminates with different joint location and the number of layer splice. Load schemes were performed and typical load-displacement curves of three specimens were recorded. The result shows that the joint location has seriously effect on the tensile strength and modulus of specimens. The tensile strength of M2 is obviously lower than that of M1 and M3. Furthermore finite element ABAQUS6.5 was also used to simulate the course of experimental test. The result shows that shear stress concentration occurs on the joint of model. The shear stress on the model M1 and M2 has the similar trend and concentrates in the middle of the joint area. And on the model of M3 the shear stress has a completely different trend from the M1 and M2 model. On the M2 the shear stress concentration is slightly higher than the other two. It indicates that the tensile strength of M2 is the lowest among the three models. So, the inter-laminar shear stress is the major factor leading tensile failure. The experimental tests are consistent with the finite element analysis.

Delamination is one of the important damage modes in the fiber-reinforced composite laminates. The interlaminar fracture toughness is the key parameter in delamination failure analysis of composites. The stress analysis by a finite element modeling has shown that the shear stress is very large near the ply splicing area. So the delamination failure is mainly dependent on the mode II fracture toughness. A new way of loading in tensile testing is proposed for the measurement of mode II fracture toughness. Specific specimen with splicing plies has been designed and used for the experiment. Testing study on the carbon-fiber-reinforced laminate with ply splicing was performed. Steady crack propagation has been seen by the tensile testing of the specimen. Mode II fracture toughness GIIC of the laminate has been determined by the experiment data analysis. The experiment and numerical analysis shows that the tensile testing for the measurement of mode II interlaminar fracture toughness is feasible.

The Bauschinger effect (BE) of X80 Pipeline Steel was tested through axial tension and compression loading. Forward and reverse axial loading schemes were performed to investigate the influence of deformation history on the mechanical character. The curves of forward and reverse stress-strain were both recorded. The results show that the yield strength decreases as the pre-plastic strain increases. On the basis of the experimental data, an empirical formula was derived regarding the decrement of the yield strength as a function of the pre-plastic strain. Additionally, further investigations on the BE of X80 steel were conducted by bending tests. The bending moment-strain curves were all recorded for both first and reverse loading. It shows that the yield moment also decreases as the pre-plastic strain increases. Based on the theory of elastic-plastic mechanics, the formula of yield moment decrement as the pre-plastic strain increase was obtained. The results show that the experimental tests are in good agreement with the formula prediction.