Experimental And Numericial Investigation On Progressive Failure Response Of Composite Bolted Joint

Composites are widely used in different branches of engineering and structural systemslike those in aerospace and automobile industries, power plants, etc. The composite jointshave become a very important aspect because the structural properties of the compositestructure are determined by its joints.70%of composite structure damage occurs in joint.Failure load and failure mode of composite joints are critical. Bolted joint is commonmechanical fastened joints used for joining the composite parts. So many researchers areinterested in bolted composite joints. In this paper, failure response of composite bolted jointswas carried out by experimants and numerical methods. The following aspects have beenresearched in detail:Firstly, since there were a lot of contact pairs, ABAQUS was used to analyze the contactfinite element of T joint. Contact surface friction coefficient and bolt clamping load were twoaspects which could influence contact properties. Different friction coefficient and boltclamping load were used to simulate the stress distribution of bolt-hole in T joint. At last,different external loads were used to analyze the stress of T joint.Secondly, XFEM was used to predict the failure of bolted single-lap composite joint. Sincethe joint problem was contact finite element which was a three-dimensional problem, andtraditional composite laminate was treat as shell which can not solve the contact problem well.So MATLAB code written by author was used to calculate three-dimensional equivalentmaterial properties of laminate which can simplify the failure simulation of composite joint.To test and verify the advantages of XFEM on failure analysis of composite joint, Firstly,progressive failure simulation result of bolted single-lap composite joint with one bolt wascompared with the experiments result in literature, and the influences of mesh size on crackpropagation path and failure response were investigated. Failure responses of two kinds ofjoints with different laminate designs are studied, too. Secondly, influences of geometricparameters on failure load and bearing strength of joint were investigated. Two geometricparameters include plate width-to-hole diameter ratio (W/D) and the edge-to-hole diameterratio (E/D). At last failure of joint with two bolts was simulated, too. The simulation results oftwo types of joint were compared with each other. Thirdly, experiments were used to investigate the influence of geometric parameters onfailure response of bolted single-lap composite joint. Geometric parameters were the distancefrom the free edge of plate to the diameter of bolt hole (E/D) ratio and the width of thespecimen to the diameter of bolt holes (W/D) ratios. In the experiments, specimens used fortesting material stiffness, strength and failure of bolted single-lap composite joints were madeby VARI process. In order to simulate failure of joint, engineering constants of compositelaminate in joint were tested, and then influence of bolt torque on failure load of joint wereinvestigated, at last effects of geometrical parameters on failure load and failure modes onjoints were studied.Finally, in numerical analysis,3D Hashin failure criteria was chosen for finite elementanalysis of composite joints. Two kinds of progressive failure models developed inABAQUS/Standard and Explicit were used to simulate failure of joints. User subroutinesUSDFLD and VUMAT were used in these two models, respectively. In subroutine USDFLD,stiffness degradation occurred when failure criteria was satisfied. In subroutine VUMAT, oncefailure criteria was satisfied, stiffness degradation occurred, and the stress was calculated bysubroutine. Two finite element models showed an excellent agreement with experimentalresults. Compared with finite element model developed in ABAQUS/Standard, modeldeveloped in ABAQUS/Explicit with subroutine VUMAT was introduced in this paper.Explicit model was found to could improve the convergence speed and reduce thecomputation time. The results of the numerical analysis were presented with a focus onproviding a more detailed insight into the progressive failure process. User subroutine UMATand cohesive method were used to investigate failure of joints under compressive load.In conclusion, the analysis of different bolted composite joints has been carried outsystematically and it will provide useful references to practical engineering problems.