Papers by Author: Xiao Ling Zheng

Abstract: Both normal and joggle double lap joints were numerical analyzed to get the stress distribution in mid-bondline and in adherends near the interface using the finite element method (FEM). The results from the numerical simulation show that nearly all the peak values of the stress components as well as the von Mises equivalent stress distributed in both mid-bondline and adherend near the interface of the adhesively bonded joggle double lap joint are significantly decreased to the normal one. It was pointed out that the load bearing capacity of the joggle double lap joint may be higher than that of the double lap joint for its decrease of peak stress, much evenly stress distribution in the middle part of the overlap zone so that more load can be subjected by the joggle double lap joint.

Abstract: The effect of the adhesive thickness on the impact toughness of the adhesively bonded steel joint under impact loading is studied using the experimental method. The results obtained show that the impact toughness increases when the adhesive thickness increased then it decrease as the adhesive thickness increase. When the curing time is set as a constant, the higher the curing temperature is, the lower the impact toughness of the joint. The optimum thickness of the adhesive layer for the specimen of impact toughness test cured at 60 C for 1 h is 0.6 mm and it is 0.4 mm to 0.6 mm for the specimen cured 1 h at temperature of 90 C or higher than it. It is recommended using the notched specimen to decrease the testing deviation.

Abstract: The influence of the fillet with different elastic modulus on the stress distributed in weld-bonded aluminum alloy single lap joint was investigated using elasto-plastic finite element method. The results show that the peak values of the stress along the mid-bondline at the points near the fillet edge were increased as the elastic modulus of the fillet increased. But at points near the both ends of the adherend in over lap zone as well as in the region of the nugget the peak stresses were decreased except longitudinal stress Sx. The peak value of Seqv decreased first, and then it increased again as the elastic modulus in fillet increased. The load-bearing capacity of the whole weld-bonded joints may be improved for the fillet with Adhesive B (825 MPa) for the relative high stress region in nugget was wider and the stress distribution in overlap zone was more uniform.

Abstract: The effect of recessing on the stresses distributed along the mid-bondline in both standard single lap joints and co-axial ones were analyzed using elasto-plastic finite element method (FEM). The results obtained show that the values of the peak stresses of all the stresses distributed in the mid-bondline were changed greatly as the preformed angle in over lap zone was about 10 0 when the high elastic modulus adhesive is used. The effect of the elastic modulus level on the stress distribution (especially the peak stresses) is small in the middle part of the lap zone. When taken the stress distributed in the middle part of the lap zone into account, there is nearly no significant difference between the peel stress distributed in the standard joint and co-axial single lap joint when the adhesives with lower elastic modulus was used. It is recommended that a co-axial joint is suitable for the recessing joint made by aluminum alloy and a higher elastic modulus adhesive.

Abstract: The influence of fillets with different geometry shape on the stress distribution in aluminum alloy weld-bonded single lap joint was investigated using elasto-plastic finite element method (FEM). The results show that it is advantageous of reducing stress concentration in adhesive layer near the ends of the lap zone in single lap weld-bonded aluminum joints and part of the stress transferring from adhesive layer to the nugget when the joints with a couple of right triangle fillets over other shapes. The load-bearing capacity of the whole weld-bonded joints may be improved. The full-triangular fillet is recommended that it be more advantageous of decreasing the stress peak value and making the stress distribution in overlap zone more uniform.

Abstract: The effect of the adhesive thickness and elastic modulus on the stress distribution in the mid-bondline of the adhesively-bonded steel/steel joint under impact loading is analyzed using 3-D finite element method (FEM). The results show that the stress distributed in bondline near the interface was significantly affected by the adhesive thickness and the elastic modulus. When the thickness increased from 1 mm to 2 mm, the values of all the stress components increased evidently along the upper edge of the adhesive but decreased significantly along the lower edge near the loading face. When the elastic modulus of the adhesive was increased, all the stresses increased along either the upper or the lower edge. It is clear that the suitable thickness and the elastic modulus of the adhesive are very important when the adhesively bonded joints subjected to the impacting load.

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.