In order to study the mechanical properties of Z-pins reinforced laminated composite single-lap adhesively bonded joint under un-directional static tensile load, damage failure analysis of the joint was carried out by means of test and numerical simulation. The failure mode and mechanism of the joint were analyzed by tensile failure experiments. According to the experimental results, the joint exhibits mixed failure, and the ultimate failure is Z-pins pulling out of the adherend. In order to study the failure mechanism of the joint, the finite element method is used to predict the failure strength. The numerical results are in good agreement with the experimental results, and the error is 6.0%, which proves the validity of the numerical model. Through progressive damage failure analysis, it is found that matrix tensile failure of laminate at the edge of Z-pins occurs first, then adhesive layer failure-proceeds at the edge of Z-pins, and finally matrix-fiber shear failure of the laminate takes place. With the increase of load, the matrix-fiber shear failure expands gradually in the X direction, and at the same time, the matrix tensile failure at the hole edge gradually extends in different directions, which is consistent with the experimental results. KEYWORDSZ-pins reinforced composite adhesively bonded single-lap joints; failure mode; uniaxial tensile test; strength prediction; progressive damage

The mechanical properties of Z-pins reinforced composites adhesively bonded single-lap joints (SLJs) under un-directional tension loading are investigated by experimental and numerical methods. Three kinds of joint configurations, including SLJs with three/two rows of Z-pins and "I" array of Z-pins, are investigated by tension test. The failure modes and mechanism of reinforced joints with different Z-pins numbers and alignment are analyzed, and the comparison is performed for the failure strengths of no Z-pins and Z-pins reinforced joints. According to experimental results, failure modes of three kinds of joints are all mixed failure. It turns out that the Z-pins are pulled out ultimately. The strength of joints of more Z-pins at the end of the overlap area is relatively bigger for the joint of the same Z-pins numbers. The strength of joints with Z-pins compared with non Z-pins joints is growing at 16%. Finally, the three-dimensional distribution of interfacial stress in the lap zone of three kinds of Z-pins reinforced joints is simulated, and the numerical results are in good agreement with the experimental results. It is effective that the numerical calculation of stress analysis is verified. KEYWORDS Z-pins reinforced composite single-lap joint (SLJ); failure mode and strength; un-directional tension test; interfacial stress

On the basis of the existing experimental results and considering five kinds of failure modes, failure prediction of adhesively bonded single-lap laminates joints with adherend thickness 3mm, adherend thickness 2mm and defect in the adhesive layer under uniaxial tensile loading is performed by progressive failure analysis method. The numerical analysis of composites adhesive joints is implemented in ANSYS Parametric Design Language (APDL) with commercial finite element codes ANSYS. The error of computaional and experimental failure loads is 3.0%. Evolution of adhesive progressive damage is simulated effectively and the initial position and reason of damage is discovered. Furthermore, a finite element simulation is carried out to analyze the stress distributions in the mid-surface of the adhesive layer and the bonding interface. It is found that stress concentration is all emerged near by 1.25mm on the overlap zone ends, that is the initial point of damage, and it is the main factor that the joint strength is affected by peel/shear stress concentrations at overlap zone ends. The computational results are in good agreement with the experimental values.

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