Three-dimensional progressive damage models for cohesively bonded composite π joint

Abstract

Integrated composite structures can significantly reduce the assembling cost and improve the performance of the aircraft. All-composite π joint, which is a connector of integrated composite structures, has good ability to reduce the weight and assembly cost while retaining good load-carrying capability. To disclose the mechanics behavior of the out-of-plane, complex all-composite joint, the progressive damage methods are investigated for its good ability to trace the damage onset, damage propagation, up to collapse of composite structures. A progressive damage model is established using a new modified maximum stress failure criterion and a material degradation model developed from Chang’s model. The material degradation model takes account of the matrix crack direction, which is predicted by the modified maximum stress-failure criterion. Meanwhile, five other progressive damage models are established and applied to static tensile analysis to study the mechanics behavior of the joint. To evaluate the prediction of the six progressive damage models in joint initial failure, damage propagation, joint strength and stiffness, the numerical results of the six progressive damage models are compared with the experiment results. The effects of failure criteria and material degradation model on the prediction results are discussed in detail. By the comparison, it can be concluded that the progressive damage model consisting of the modified maximum failure criteria and its corresponding material degradation model is considered as the best one for the analysis of the all-composite π joints, because its initial failure prediction, failure process and ultimate failure prediction agree well with the experiment result.

An average failure index method for the tensile strength prediction of composite adhesive-bonded π joints

“…From Fig.2, it follows that the vertical external load passes through the upstanding legs of the U and L laminates and is almost entirely delivered over to the fi llers. Thus the fi llers are the force junction and crucial part in composite π joints since the stretch forceinduced stresses are significantly large with reference to the weak transverse or interlaminar strength of UDCB composite materials, which is accordant with the empirical knowledge [6,9,12] .…”

“…Zhao et al have provided insight into the mechanical behavior of π joints made of unidirectional or woven carbon/ bismaleimide composites with the progressive damage method (PDM), which combines continuum damage mechanics with FEA [9,10] . Suitable progressive damage models based on the modified maximum stress failure criterion for composite π joints have been developed [11,12] . Based on the progressive damage analysis, the researchers have revealed the internal load distribution and failure mechanism of composite π joints under tensile and fl exural loads [12,13] .…”

“…Suitable progressive damage models based on the modified maximum stress failure criterion for composite π joints have been developed [11,12] . Based on the progressive damage analysis, the researchers have revealed the internal load distribution and failure mechanism of composite π joints under tensile and fl exural loads [12,13] . Moreover, Zhao et al have established a FEM using cohesive elements to predict the failure of π joints based on a cohesive zone model (CZM) method, which combines strength-based analysis to predict the damage onset with fracture-mechanics-based analysis to forecast the propagation of delamination [14] .…”

3D Gradual Material Degradation Model for Progressive Damage Analyses of Unidirectional Composite Materials

“…The modified maximum criterion proposed by Zhao et al [37,44] is adopted here to predict the onset of fiber crack and interfiber crack.…”

Model of CEL for 3D Elements in PDMs of Unidirectional Composite Structures

“…However, thus far, there are not proper methods to calculate the 3D CELs while accounting for the various crack directions. In previous work, a modified maximum stress criterion, which could predict the initiation of the fiber failure and inter-fiber failure of unidirectional composite materials, was proposed and combined with a sudden degradation model to investigate the failure of composite π joints ; Zhao, Qin, Chen et al (2014)]. In later work, a 3D gradual degradation model was developed to account for the nonlinear behavior and some damage characters such as the inter-fiber crack orientation, crack closure, etc.…”