Determination method of stress concentration relief factors for failure prediction of composite multi-bolt joints

Abstract

Stress concentration relief factor, which reflects the linear relationship between the stress concentration factors of composite joint and those of elastic isotropic joint, was proposed by Hart-Smith for the failure prediction of composite multi-bolt joints. It is deemed to be determined by experiments from either unloaded- or loaded-hole laminates and is suitable for investigations of bypass and bearing stress concentration factors. To examine this viewpoint, in this paper, the stress concentration relief factor is determined by tensile tests of open-, filled- and loaded-hole laminates failing in tensile mode, respectively. It can be found that the loaded-hole has obviously high-stress concentration level, while the filled-hole has slightly higher stress concentration than that of open-hole. Detailed 3D-FE analyses are performed to disclose the stress concentration mechanisms of three hole-laminates. Various stress concentration relief factors are combined to calculate bearing and bypass stress concentration factors, which provide the failure envelope for the strength prediction of composite joints. Moreover, both conventional and modified failure envelopes are discussed. Experimental results of two-, three- and four-bolt joints are provided to investigate the suitability of different failure envelopes. It follows that the stress concentration relief factor for bearing stress concentration factor needs to be determined by a loaded-hole laminate, while that for bypass stress concentration factor can be determined by each of open-, filled- and loaded-hole laminates.

Failure maps to assess bearing performances of glass composite laminates

“…In this concern, reliable and effective assessment methods are required in order to minimize the weights of the joined structure as well as the product and in service life costs. In the literature, very accurate models to predict performances and failure modalities of bolted composite structures are mainly based on the implementation of finite elements numerical models . Such models, although they may predict the mechanical behavior of the structure, require a well‐structured parameterization of the model as well as long calculation times.…”

Coupled continuum damage mechanics and failure envelope method for failure prediction of composite multi-bolt joints

“…Moreover, failure results predicted by bearing-to-bypass stress ratio at the critical hole c 0 are also compared with the results predicted by constant bearing-to-bypass stress ratio u 0 . The experiments of these two kinds of joints can be found in Zhao et al 8 The stiffness values in equation ( 38) are given as…”

“…7 Moreover, multi-bolt joints can easily fail in catastrophic net-tension failure mode, since this cannot be avoided by simple design of geometry and laminate layup of joints, and instead requires a complex optimization based on a failure-prediction method. 8 These disadvantages negatively affect the performance of the multi-bolt joints and may be potential sources of safety hazards in applications involving composite structures. Therefore, it is important to find an efficient numerical approach to investigate the failure characteristic of composite multi-bolt joints.…”

An analytical stress model for composite multi-pinned plates considering the combination effects of pin load and bypass load in different positions

“…Attar 15 used both of analytical and numerical methods to study the effects of geometrical parameters, including edge-to-diameter and width-to-diameter ratio, on stress distribution. Zhao et al 16 studied the stress distribution of open hole, filled hole and pin loaded laminates under tensile load using finite element methods. The results were finally employed in concentration relief factor analysis and modified failure envelopes for strength evaluation.…”