Failure load prediction of adhesive joints under different stress states over the service temperature range of automobiles

To predict the failure loads of adhesive joints under different stress states over the service temperature range of automobiles,adhesively bonded carbon fiber reinforced plastic( CFRP)/aluminum alloy joints under shear stress state( thickadherend shear joints,TSJ),normal stress state( butt joints,BJ) and combined shear and normal stress states( scarf joints with scarf angle 45°,SJ45°) were manufactured and tested at-40,-20,0,20,40,60 and 80 ℃,respectively. The glass transition temperature Tgof the adhesive and CFRP,failure loads and fracture surfaces were used to analyze the failure mechanism of CFRP/aluminum alloy joints at different temperatures. A response surface,describing the variations of quadratic stress criteria with temperature,was established and introduced into the cohesive zone model( CZM) to carry out a simulation analysis. Results show that the failure of CFRP/aluminum alloy joints was determined collectively by the mechanical performances of adhesive and CFRP. Besides,reducing temperature or increasing the proportion of normal stress of adhesive layer was more likely to cause fibre tear or delamination of CFRP,resulting in a more obvious effect of CFRP. The validity of the prediction method was verified by the test of scarf joints with the scarf angle of 30°( SJ30°) and 60°( SJ60°) at-10 and 50 ℃.

Effect of Laser Processing Pattern on the Mechanical Properties of Aluminum Alloy Adhesive Joints

Adhesive bonding is a promising joining technology for joining lightweight aluminum structures,offering advantages such as the absence of additional heat input,connection damage,and environmental pollution.To further enhance the strength of aluminum adhesive joints,this study investigates the influence of laser surface treatment on their mechanical properties.Specifically,the effect of laser processing patterns and their geometric parameters on aluminum alloy adhesive joints is examined.A fiber laser is used to process crater array and multi-groove pattern on A6061 aluminum surface.The impact of crater overlap ratio and groove distance on various aspects,including aluminum surface morphology,roughness(Sa),adhesive joints shear,tensile strength,and failure modes is discussed.Laser confocal microscope tests,water contact angle tests,lap shear tests,and cross tensile tests are employed to analyze these parameters.The results indicate that as the crater overlap ratio increases,the S_(a) value of the aluminum surface increases.Moreover,the shear strength of adhesive joints initially increases and then decreases,while the tensile strength consistently increases.On the other hand,an increase in groove distance leads to a decrease in S_(a),as well as a reduction in both shear and tensile strength of adhesive joints.For shear loading conditions,mechanical interlocking is identified as one of the bonding mechanisms in aluminum adhesive joints featuring crater array and multi-groove patterns.The formation of interlocking structures is found to be influenced by the aluminum surface pattern and its associated parameters,as revealed through failure surface analysis.Specifically,adhesive and crater or groove interactions contribute to the formation of interlocking structures in specimens with a crater overlap ratio of -60% or groove distances of 120,180,300,and 400μm.Conversely,specimens with overlap ratios of 0%,40%,and 60% exhibit interlocking structures formed by the adhesive and crater edge.

Study on ASTM Shear-loaded Adhesive Lap Joints

Finite element analyses and experiments are conducted to analyze the mechanical behavior of ASTM shear-loaded adhesive lap joints. Adhesive is characterized for the stress-strain relation by comparing the apparent shear-strain relations obtained from finite element analysis and experiments following ASTM D 5656 Standard. With the established stress-strain relation, two failure criteria using equivalent plastic strain and J-integral are adopted to predict the failure loads for joint specimens following ASTM D 5656 and ASTM D 3165 Standard, respectively. Good correlation is found between the finite element results and the experimental results. The strength of ASTM D 3165 specimens with debonding defects is also studied. Calculation results shows that experiment data following the standards provide only relative material constants, such as apparent shear modulus and strengths. Further investigation is required to find out the engineering properties needed for actual joint design. For the specimens with debonding defects, the locations of defects have great effects on their load bearing ability.

Determination of key parameters of Al–Li alloy adhesively bonded joints using cohesive zone model

The key parameters of the adhesive layer of a reinforcing patch are of great significance and affect the ability to suppress crack propagation in an Al–Li alloy patch-reinforced structure.This paper proposes a method to determine the key parameters of the adhesive layer of adhesively bonded joints in the Al–Li alloy patch-reinforced structure.A zero-thickness cohesive zone model(CZM)was selected to simulate the adhesive layer’s fracture process,and an orthogonal simulation was designed to compare against the test results.A three-dimensional progressive damage model of an Al–Li alloy patch-reinforced structure with single-lap adhesively bonded joints was developed.The simulation’s results closely agree with the test results,demonstrating that this method of determining the key parameters is likely accurate.The results also verify the correctness of the cohesive strength and fracture energy,the two key parameters of the cohesive zone model.The model can accurately predict the strength and fracture process of adhesively bonded joints,and can be used in research to suppress crack propagation in Al–Li alloy patch-reinforced structures.

Determination of Water Diffusion Coefficients and Dynamics in Adhesive/Carbon Fiber Reinforced Epoxy Resin Composite Joints

To determinate the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints, energy dispersive X-ray spectroscopy analysis（EDX） is used to establish the content change of oxy- gen in the adhesive in adhesive/carbon fther reinforced epoxy resin composite joints. As water is made up of oxygen and hydrogen, the water diffusion coefficients and dynamics in adhesive/carben fiber reinforced epoxy resin composite joints can be obtained from the change in the content of oxygen in the adhesive during humidity aging, via EDX analy-sis. The authors have calculated the water diffusion coefficients and dynamics in the adhesive/carbon fiber reinforced epoxy resin composite joints with the aid of beth energy dispersive X-ray spectroscopy and elemental analysis. The de- termined results with EDX analysis are almost the same as those determined with elemental analysis and the results al- so show that the durability of the adhesive/carbon fther reinforced epoxy resin composite joints subjected to silane cou- pling agent treatment is better than those subjected to sand paper burnishing treatment and chemical oxidation treat- ment.

Enhancing adhesive bond strength of CFRP/titanium joints through NaOH anodising and resin pre-coating treatments with optimised anodising conditions

Adhesively Bonded Carbon Fibre Reinforced Plastic(CFRP)and titanium alloy have been extensively used as a hybrid structure in modern aircrafts due to their excellent combination of mechanical properties and chemical stabilities.This study utilised NaOH anodising method to create micro-rough titanium surfaces for enhancing adhesive bonding between titanium alloy and CFRP laminates.A special and simple technique named Resin Pre-Coating(RPC)was also employed to improve the surface wetting of anodised titanium and grinded CFRP substrates.The influences of anodising temperature and duration on the surface morphology,wettability and adhesive bond strength were investigated.The single lap shear test results showed that the bond strength of specimens anodised at 20℃for 15 min improved by 135.9%and 95.4%,respectively,in comparison with that of acid pickled and grinded specimens(without RPC treatment).Although increasing the anodising temperature and duration produced rougher titanium surfaces,the adhesively bonded joints were not strong enough due to relatively friable titanium oxide layers.

Damage Failure Analysis of Z-Pins Reinforced Composite Adhesively Bonded Single-Lap Joint

In order to study themechanical 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 bymeans 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.

Effects of assembly errors and bonding defects on the centroid drift of a precision sleeve structure

Adhesive joints are widely used in precision electromechanical products,and their bonding process has significant effects on the performance of an assembled product.This paper presents a numerical study on the bonding assembly of a sleeve structure of a precision inertial device using a finite element method,where the stresses due to curing and relaxation behaviors are considered.The effects of assembly errors and bonding defects on the centroid drift of the sleeve structure were found and analyzed quantitatively.This study can help understand the zero-drift mechanism of the precision inertial device and contribute valuable data for its error compensation.