Strength prediction of composite π joint under bending load and study of geometric and material variations effects

Abstract

This article concentrates on the design of composite π joint, which is an effective connector for integrated composite structures in aerospace structures. A brief review of research on out-of-plane joints is first presented to current practice towards the design of such π joints. Progressive damage models are established to trace failure analysis from damage onset to ultimate collapse of joints, which highlight the failure mechanism and internal mechanical behaviours. Four kinds of failure criteria are used firstly, and after comparing the numerical prediction results with the experimental results, one failure criterion is chosen for the simulation of this joint. Influences of structural and geometric parameters such as structural configuration, overlaminate material, ply angle, fillet radius and upstanding/horizontal leg length of overlaminate on flexural resistance ability are studied to provide ‘optimal’ design schemes. Moment–displacement graphs from the mechanical experiments are presented and physical failure phenomena of the joint under bending load are depicted. The good agreement between the predictions and experimental results gives evidence of the efficiency of numerical analysis.

Experimental and numerical investigation of composite bolted π-joint subjected to bending load

“…Based on a parametric finite element model with embedded cracks validated with test data, an alternative scheme of geometry design for greater reliability was obtained. Yue et al [10] studied in depth the mechanical behavior and failure mechanism of a π-joint under bending load by progressive damage models.…”

Modified maximum stress failure criterion for composite π joints

“…Therefore, the modified maximum stress failure criteria assumes that when the maximum fibermatrix shear stress exceeds the shear strength, the fiber-matrix failure occurs and an inter fiber crack appears on the plane that the maximum fiber-matrix shear stress acts on. The fiber-matrix shear crack angle inclined to coordinate system O123 is given by equation (12).…”

“…Typically the damage initiates in the filler or at the interface between the filler and the overlaminate, then propagates through the filler, causing significant change of stress distribution and load transfer and inducing new damage in the horizontal laminate which leads to collapse of the joints. [3][4][5][6][7][8][9] Finite element (FE) study [10][11][12] on composite p joint strength under tensile and bending loads shows that the material in and around the filler withstands high stress levels, and the stress components in the transverse isotropic plane of the unidirectional fiber reinforced composite, 22 , 33 and 23 , are very large relative to their low strength limits while the stress components in the fiber direction are relatively small. It indicates that the failure analysis in the filler region is important in the strength analysis of composite p joints and the contribution of transverse stress-induced damage should be well considered during the failure prediction.…”

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

“…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] .…”