The crack quasi-static growth and analysis of interlaminar crack resistance of layered composite

Using the model of quasi-static crack growth and test result of the double cantilever beam (DCB) sample of layred carbon/epoxy composite, the general regularities of the interlaminar crack resistance of mode 1 were studied. The main attention was focused on the variability of crack resistance associated, on the one hand, with the continuity of the fracture process, and, on the other hand, with the non-homogeneity of the material structure, which causes local random deviations from the average characteristics of the material.The dissipation energy rate (total crack resistance) and crack resistance function (R-curve) were extracted from test results and their properties analyzed.

Dual cracks propagation behavior in hybrid skin–stiffener joint

There is increasing demand for Carbon Fiber Reinforced Polymers (CFRP) especially in aerospace engineering. Due to their high specific strength-to-weight ratio, these composites offer more characteristics and considerable advantages when compared to metals. Metals, unlike composites, offer plasticity effects to evade high stress concentrations during post-buckling. Under compressive load, composite structures show a wide range of damage mechanisms where a set of damage modes combined together may lead to the structural collapse. The numerical analysis is conducted to investigate the effect of the dual cracks growth for the cracks embedded between plies of the skin and between plies of the stiffener hat. The dual fractured configuration is loaded to study the impact of dual cracks on load carrying capacity of the skin–stiffener joint and mode of fracture initiation and growth. Numerical method of Virtual Crack Close Technique is applied for predicting interlaminar crack initiation and interlaminar crack growth as well as in-plane crack mechanisms to predict the design of crack free joint.

Ultrasonic Interface Wave for Interlaminar Crack Detection in Steel–Titanium Composite Pipe

The bimetal composite pipe has found wide ranging applications in engineering owing to its excellent mechanical and physical performances. However, the interlaminar cracks which are usually invisible and inaccessible may occur in the bimetal composite pipe and are difficult to detect. The ultrasonic interface wave, which propagates along the interface with high displacement amplitudes and low dispersion at high frequencies, provides a promising nondestructive testing (NDT) method for detecting cracks in the bimetal composite pipe. In this study, the interlaminar crack detection method in the steel–titanium composite pipe is investigated analytically and experimentally by using interface wave. The interface wave mode in steel–titanium composite pipe is first identified and presented by theoretical analyses of dispersion curves and wave structures. The selection of suitable excitation frequency range for NDT is discussed as well. Then an experiment is conducted to measure the interface wave velocities, which are in good agreement with the corresponding numerical results. In addition, interlaminar cracks with different locations in steel–titanium composite pipe are effectively detected and located, both in the axial and circumferential directions. Finally, the relationship between the reflection coefficient and the crack depth is experimentally studied to predict the reflection behavior of interface wave with crack. The numerical and experimental results show the interface wave is sensitive to interfacial crack and has great potentials for nondestructive evaluation in the bimetal composite pipe.