Inplane shear stress-strain tests

The inplane shear stress-strain tests reported here have been well demonstrated to be a reliable test for matrix-dominated properties in composites 141). For the selected mechanical properties that were monitored, their sensitivity to the thermal history was well demonstrated. In particular, the embrittlement process during the sub-Tg annealing or physical aging has been clearly observed. This decrease in molecular mobility, which gives rise to an increase in relaxation time and hence a decrease in toughness, can be rationalized as a decrease in free volume in an approach towards the equilibrium glassy state. 

Standard Recommended Practice for Inplane Shear Stress-Strain Response of Unidirectional Reinforces Plastics.", ASUl American National Standard ANSI/ASTM D 3518-76, pp. 859 - 864 in 1977 Annual Book of ASTM Standards, American Society for Testing and Materials,... 

Miller, J.D., Harris, W.C. and Zajac, G.W., Surf. Interface Anal., 20,977-983 (1993). Petit, P.H., A simplified method of determining the inplane shear stress-strain response of unidirectional composites. American Society for Testing and Materials. Philadelphia. PA,... 

Two quantities can be measured to describe a material s resistance to crack propagation fracture toughness, IQ, and strain energy release rate, G. Different stress states can be applied, with the most common being the opening mode (Mode I). Materials can also be tested in inplane shear (Mode n) and in torsional shear (Mode III). Testing in these modes typically involves strain rates much lower than those associated with impact teste such as the Charpy and Izod methods. Other methods... 

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