Failure Analysis of Adhesively Bonded Structures: From Coupon Level Data to Structural Level Predictions and Verification

This paper presents a predictive methodology and verification through experiment for the analysis and failure of adhesively bonded, hat stiffened structures using coupon level input data. The hats were made of steel and carbon fiber reinforced polymer composite, respectively, and bonded to steel adherends. A critical strain energy release rate criterion was used to predict the failure loads of the structure. To account for significant geometrical changes observed in the structural level test, an adaptive virtual crack closure technique based on an updated local coordinate system at the crack tip was developed to calculate the strain energy release rates. Input data for critical strain energy release rates as a function of mode mixity was obtained by carrying out coupon level mixed mode fracture tests using the Fernlund–Spelt (FS) test fixture. The predicted loads at failure, along with strains at different locations, were compared with those measured from the structural level tests. The predictions were found to agree well with measurements for multiple replicates of adhesively bonded hat-stiffened structures made with steel hat/adhesive/steel and composite hat/adhesive/steel, thus validating the proposed methodology for failure prediction.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42764/1/10704_2005_Article_0646.pd

Modeling of Composite Materials for Energy Absorption

erform laboratory experiments for characterizing basic damage mechanisms and monitoring the damage variables during impact using nondestructive evaluation techniques to determine the model constants and damage parameters. Introduction Automotive structures manufactured from carbonfiber based composites offer the potential for significant advantages in weight, durability, design flexibility, and investment cost. While substantial experience with graphite-fiber laminated composites exists in the aerospace community, little knowledge exists in how carbon-fiber composites respond in automotive type applications during impact-induced "crash" loading conditions (i.e., "crush"). Furthermore, predictive analytical and numerical tools required to accurately evaluate and design carbon-fiber automotive structures for crush do not currently exist. This project aims to understand and quantify the basic deformation and failure mechanisms active in carbon-fiber materials during veh