An alternative shear lag model for composites with discrete interfaces

Discrete interfaces between different phases are common in natural and engineering materials. A new shear lag model is proposed in this paper to investigate the effects of such interfaces, in contrast to existing shear lag models that only consider a fully bonded interface. The equilibrium equations of discretely bonded platelets in a staggered composite are established, with which the tensile stress and deformation in platelets, interfacial shear stress and effective Young's modulus of the composite are theoretically predicted. It is found that the discrete interface leads to not only a higher average stress level in the platelet but also a smaller effective Young's modulus than those in the composite with a fully bonded interface. The former indicates a higher stress transfer efficiency, while the latter results in a larger strain energy under a given externally applied stress, which should be beneficial for improving the load-bearing capacity and toughness, respectively, of the composite. Such enhancing effects become more significant with decreases in the total interface length, partition number of the interface and spacing between bonding segments. Furthermore, an optimal architecture to achieve a higher stress transfer efficiency and a larger strain energy is found, in which the two neighboring platelets in the representative unit cell are discretely bonded with each other in the middle part instead of at two ends. The present research sheds new light on the influencing mechanisms of discrete interfaces on the mechanical performance of composites, which should be of guiding value for the optimal design of composite interfaces.