On The Stress Response Of Adhesively Bonded Joint Under The Izod Impact Test

In this paper, by taking the adhesively bonded butt joint as the research object, anelastic-plastic model of adhesively bonded butt joint under Izod impact test was establishedbased on the finite element method(FEM), the effect of impact velocity, the mass of impactblock, mechanical properties of the adhesive, adhesive thickness and the impact point werestudied using the finite element software. The main research results are as follows:1) Numerical analysis of the stress response for adhesively bonded butt joint duringIzod impact test was studied by finite element software ANSYS and itsLS-DYNA(NSTAR). The results obtained show that the stress distribution of upper andlower adhesive tended to be symmetrical, and the stress reached to the peak value on bothsides of the adhesive. As the time went on, the equivalent stress in the middle of bondlineincreased rapidly at first and then rised gently until it reached to the peak stress, finally itdropped sharply until the end of impact time.2) An elastic model was set up based on linear Drucker-Prager yield criterion usingthe finite element software ABAQUS. The influence of impact velocity on the stress andstrain response for adhesively bonded butt joint during Izod impact test was studied. Theresults showed that the element damage ratios, strain rate and equivalent stress (Seqv)increased rapidly with the increasing of impact velocity. The peak stress Seqv at the pointnear the upper surface of the specimen occurred earlier. From the response curve of Seqv itcould be seen that the rising rate and peak value of von Mises equivalent stress Seqv inelement1(near the upper surface of the specimen) when the impact velocity was3.2m/s,so it is suitable for Izod impact test for the adhesively bonded steel butt joint.3) An elastic-plastic model was established using finite element software ANSYS，thestrain rate sensitive of the adhesive was taken into account using Cowper–Symondsconstitutive model. The effect of impact velocity on the stress and strain response foradhesively bonded joint was analyzed using this finite element model. It indicated thatrising rate increased with the rising of impact velocity, the value of equivalent stress wasbigger when the impact velocity was higher during the same impact time. The yield stressof adhesive is approximately equal to yield strength when the impact velocity is3.2m/s,then yield point of equivalent stress rised with the increasing of impact velocity, it meantthat the bigger the impact velocity, the higher the yield strength of adhesive.4) The influence of impact block mass on the stress and strain response was investigated using the elastic-plastic model when the impact velocity is3.2m/s. As theincreasing of impact block mass, the rising rate and peak value of equivalent stressincreased slightly, so did the yield point of adhesive. It can conclude that the mass ofimpact block had a little effect on the stress response under this impact velocity.5) The influence of the mechanical properties of adhesives on the stress and strainresponse was studied when the impact velocity and block mass were v=3.2m/s andm=2.5kg, respectively. The results showed that the equivalent stress of adhesive isproportional to the elasticity modulus during stage of elastic deformation, the bigger theelasticity modulus, the higher the equivalent stress; the rising rate and peak value of SEQVwere related to the Tang modulus and yield strength, respectively. The rising rate and peakvalue of SEQV were increasing with the rising of Tang modulus and the yield strength, itresulted in higher impact toughness for this joint under impact load.6) Effect of adhesive thickness on the stress and strain response was studied on thebasis of previous study. The results showed that the rising rate of equivalent stressdecreased with the increase of adhesive thickness, the value of SEQV is lower as theadhesive thickness is bigger under the same impact time. It demonstrated that increasingthe adhesive thickness appropriately was beneficial to enhance the fracture toughness ofadhesively bonded butt joint during Izod impact test.7) Adopting the elastic-plastic finite element model, we discussed the influence of theimpact point on the stress response of adhesively bonded butt joint during Izod impact test.It concluded that: the biggest peak value of normal stress occurred at the impact point L-2,the biggest peak value of shear stress occurred at the impact point L-1; the farther thedistance between the impact point and adhesive layer, the lower the SEQV of adhesivelybonded butt joint under Izod impact.8) An elastic-plastic failure model for adhesively bonded butt joint under Izod impactwas established. The stress response of butt joint bonded by adhesive-5was analyzedthrough this model. The results showed that:(1) The stress distribution of upper and loweradhesive layer tended to be symmetrical, and the peak value appeared on the both sides ofthe adhesive.(2) In the direction of adhesive thickness, the highest peak value occurred atthe location away from the impact point.(3) In the direction of adhesive height, the peakstress increased firstly and then decreased. The shorter the distance away from the bothsides, the higher the rising rate and peak value of the stress.9) The elastic-plastic failure model was employed to study the stress and strain response of butt joints bonded by three different adhesives during Izod impact test. Thenumerical results showed that: For these butt joints bonded by three types of adhesive, theorder of peak value for normal stress is: adhesive-6＞adhesive-5＞adhesive-7, the orderfor shear stress is: adhesive-6＞adhesive-7＞adhesive-5, and the equivalent stress is:adhesive-6＞adhesive-5＞adhesive-7, the fracture toughness and impact toughness foradhesive-6is highest among these adhesives.