Evaluation of Numerical Methods to Model Structural Adhesive Response and Failure in Tension and Shear Loading

Abstract

Improved energy efficiency in transportation systems can be achieved with multi-material lightweight structures; however, joining often requires the use of adhesive bonding and design efforts are challenged by the paucity of data required to represent adhesives in numerical models. The data for three epoxy structural adhesives tested in tension and shear over a range of strain rates (0.001-1000 s-1) is reported. The range of experimentation addresses regular operation and extreme conditions (crash scenarios) for vehicles. The data was implemented with cohesive and solid elements; and the models were assessed on their ability to reproduce adhesive material response. Good agreement was achieved using both approaches. In average the coefficients of determination (r 2) between measured experimental response and simulations were 0.81 for tension and 0.59 for shear, with 2 % difference in the prediction of stress at failure. The cohesive formulation was computationally efficient and reproduced rate effects, but was limited in representing the response of the non-toughened epoxy. The solid element formulation required longer simulation times, but yielded similar accuracy for tension (2 % difference in stress to failure and r 2 values of 0.98, on average). However, the shear response accuracy (r 2 = 0.53) was reduced by coupling between shear and tension strain rate effects. Numerical simulation of structural adhesives requires constitutive models capable of incorporating uncoupled deformation rate effects on strength. The results of this study indicate that a cohesive model can provide adequate representation of an adhesive joint for tensile and shear loading across a range of deformation rates.

Experimental and Numerical Analysis of Epoxy Based Adhesive Failure on Mono- and Bi-Material Single Lap Joints Under Different Displacement Rates

“…The average element quality and aspect ratio were observed as 0.97 and 1.21 respectively. CZM parameters for DP460NS under different strain rates were introduced at Trimino et al's [12] study. Values for critical fracture energy for normal and shear separation were taken from this study.…”

“…However, these parameters are interconnected between and impose bond strength crucially [9,10]. Although some of the studies report different adhesive strengths with high fluctuation [5,[11][12][13]] experiments need to be performed by considering all factors into account to clarify results. From this perspective of view, separate works have been conducted by researchers by taking thickness, overlap length, adherend type, adherend thickness, strain rate, and surface quality into consideration.…”

“…When adhesive thickness set from 0.3 to 1.0, stress in joints tended to reduce. Trimino et al [12] employed epoxy adhesives (include 3M DP460NS) to determine strain rate dependency. They applied quasi-static and impact tests on the adhesive samples.…”

“…They found that there is a good agreement between the experiment and the CZM. Trimino et al [12] utilized DP460NS adhesive to find cohesive zone parameters and reported linear fits for tensile and shear strength of adhesive for different strain rates. They made some assumptions on determining the fracture behavior of adhesive.…”

“…Mechanical properties of Al-7075 T7, SAE 304[27] and the DP 460NS[12] SLJs have been tested by using the Instron 8801 testing system(Fig. 2)for each strain rate.…”