Performance Study Of Composite Mechanically Fastened Joints And Joint Design

Composite materials with properties of high specific strength, high specific stiffness anddesign versatility have been extensively used in aviation structure to reduce the structureweight，which has become one of the important symbols of advanced aircraft. Compositemechanically fastened joint is an important link in composite structure design, and it’s aproblem must be solved when composite materials are used in aircraft main structures. For theproperties of anisotropy and brittleness of composites, composite joints strength is affected bymany factors and failure modes of which are complex. Exploreing methods to improvecomposite joint strength and efficiency has important engineering significance and applicationvalue. In this paper, the main research contents of mechanically fastened joints of compositelaminates consists of the following three parts:The paper’s first part studied the strength and damage modes of composite single pinjoints. First, the basic failure modes of composite bolted were obtained by experiment and theinfluence factors were analyzed. Then, based on composite progressive damage mechanism, atwo-dimention finite model was developed to analyze the effects of geometrical parameters,the clearance and interference-fit and stacking sequence on joint strength and failure modesusing the ABAQUS finite element analysis software. Mechanically fastened joints often leadto a reduction of load capacity of the composite structure because the fibers are interruptedaround the hole. An experimental and numerical study was carried out to investigate thescheme of local reinforcement. The numerical study was performed by the three-dimentionprogressive damage model implemented in the user material subroutine of theABAQUS/explicit program, VUMAT. Delamination was incorporated using a cohesiveelement layer between laminates and reinforcement layer.The second part, related investigations were performed to determine the load distributionand joint strength of multi–pined composite plates. A refined finite element model wasdevelopmented to study the load distribution of multi-pined composite based on the3Dcomposite equivalent engineering elastic constants. The model predicting the load distributionshowed an excellent agreement with experimental results. Moreover, results were comparedwith those calculated using the lay-up FEM. In addition, a study was carried out to analyse theeffects of stacking aequence and number of pins. And the method of load distribution optimization design of multi-pined was studied. Moreover, An experimental study was carriedout to investigate the the effects of number of pins and arrange styles on failure load. Andfinite element model of composite multi-pin joints was established to predict strength basedon3D progressive damage user material subroutine program (VUMAT).In the last part, a new joint of hybrid composite-to-metal bolted joints was designed andmanufactured by vacuum assisted resin infusion (VARI). The results indicate that theconnecting structure is simple to manufacture and it has important engineering applicationvalue. And the hybrid connecting structure was optimized through the parametric study basedon the3D progressive damage finite element model.