Papers by Author: Zhi Li

Abstract: The stress distributed in the mid-bondline of the joints made of aluminium alloy and an epoxy adhesive was determined with the ANSYS software. The results from the FEA showed that the values of the peak stresses of the all the stress components (including the longitudinal stress Sx, the peel stress Sy, the shear stress Sxy, the 1st principal stress S1 and the von Mises equivalent stress Seqv) distributed in the mid-bondline are changed a little as the notch distance L was increased while the notch depth d was not great than 0.6mm. But the evidently changes occurred when the notch depth d was great than 0.9 mm for the stress Sx, Sy and S1 distributed in both the mid-bondline and the interface of the lap zone. When taken the stress distributed in the middle part of the lap zone into account, the peak stress at the point in the mid-bondline corresponding to the edge of the notch decreased firstly and then increased again as the notch distance L was increased from 0 mm to 8 mm. The proper geometry of the notch in the specimen was chosen by finite element analysis.

Abstract: The elastic finite element analysis (FEA) and the experimental method of testing the cleavage strength of the joint were used to investigate the effect of the recessing as well as its length on the stress distribution in both the mid-bondline and the adherend near the interface along the bondline of adhesively bonded steel cleavage joint. The results from the FEA simulation showed that the peak values of the stresses distributed in the mid-bondline were nearly the same when the length of the arranged recessing was not greater than 10 mm except that the shear stress Sxy was increased a little when the length of the recessing was increased. For the normal stress Sy near the interface of the joint with a 16 mm length recessing, the peak stress in the adherend is about 49% higher than the one in the adhesive at the left edge of the joint. And it is supported with the results from the experiments that the ultimate load of the steel-to-steel cleavage joint decreased a little when the gap length was less than 10 mm.

Abstract: The 3-D elasto-plastic finite element method (FEM) was used to analyze the thermal stress in the laminated composite (SiC/6061Al) under the condition of a temperature cycling of 200 0C-30 0C- 200 0C-30 0C. The results from the FEM analysis showed that the hysteretic peak value of the von Mises equivalent stress in the substrate 6061Al was increased significantly as the temperature loading cycles processed on but it was nearly the same after the first cycle in the interface layer SiC of the laminated composite. The elastic strain in the substrate 6061Al varied within the range of -0.15% to 0.15% and the maximum plastic deformation was equal to about 0.26 %. The results also showed that the maximum normal stress Sx was increased from 32.8 MPa to 87.9 MPa after ten cycles and the work-hardening of the substrate 6061Al occurred during the stress and strain hysteresis loop.

Abstract: The normal stress distributed in the mid-bondline of the adhesively bonded joint under cleavage loading was investigated using the elastic finite element method (FEM) and the strain gauges method to reveal the real normal stresses distribution in the metal-to-metal joint while the load was increased. The results from the finite element analysis (FEA) showed that there is always a peak stress of the normal stress Sy in the mid-bondline occurred at a point close to the loading pin axis. When the load was increased from 0.5 kN to 3 kN, there was also a point located at about x = 16mm along the length of specimen where there is without any normal stress at all. The result of stress Sy from the FEA is nearly the same as that one obtained from the strain gauges method. It was also found that there was a evidently hardness change in the bonded zone of the adherend made from structural steel or pure copper, which can be used to explain the procedure of the joint and discuss the distribution model of the normal stress Sy in the joint under the cleavage loading.

Abstract: The effect of the preformed deflection angle in the lap zone on the failure mode and the stresses distribution in the single-lap joint made of the epoxy adhesive and the aluminium adherend was investigated using elasto-plastic finite element method (FEM) and the experimental method of the shear strength testing. The failed surfaces were studied with the diagrams of scanning electron microscopy (SEM). The results from the numerical simulation showed that all the peak stresses in adhesively bonded single lap joint were decreased first and increased again as the preformed deflection angle was increased from 00 to 150. The lowest values occurred when the angle was taken as 100 and its strength is 22.1% higher than that of the standard one as the peak stresses were decreased and the stress distributed more evenly. The SEM images also show that the failure mode of the joint was transmitted from the adhesion to the mixed one as the deflection angle increased.

Abstract: In order to understand the effects of the metal components embedded in adhesive fillets on the strength of adhesively bonded single lap joint, the failed surfaces were studied with diagrams of scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectrometer. The stress distribution along the length of the bondline of single lap steel joints was also studied with an elasto-plastic finite element analysis (FEA) model to understand its effect in the view of mechanics. The SEM images and the FT-IR spectra diagrams revealed that the failure in the interface was primarily mixture mode with fillets and they also presented the interface strength being higher and there were more polar links formed in the adhesive fillets with metal components. The result obtained from the numerical modeling is in compliance with it from experiment that the stress distributed in lap zone of the joint is gentler when a couple of steel wires embedded in fillet.