Practical Considerations In Determining Material Properties Susan I. Hill Structures and Materials Evaluation Laboratory University of Dayton Research Institute (937) 229-4704 hillsi@udri.udayton.edu www.udri.udayton.edu Future of Modeling in Composites Molding Processes Workshop June 9-10, 2004

Defining Needs Depends on application and model Impact can be compressive event but material failure is tensile event Localized delaminations, cracking, interfacial bonding in composites Necessary test data are defined by selected model Tensile, compression, and shear data Energy absorption Temperature effect Strain rate effect Failure

Types of tests required May need to go beyond the typical tensile strength, modulus, failure strength data, e.g. Uniaxial compression Confined compression (bulk modulus) Cyclic tension Stress relaxation Resonant Beam ?

Impact-related models Material models exist for structural polymers Lacking for composites FE codes may not incorporate correct material models Current models have poor handling of viscoelastic effects, plastic flow, strain rate effects, and fracture Use of quasi-static data will underestimate material response at higher impact rates

Polyolefin

Polyolefin relationship with strain rate

Polycarbonate

Relationship with Strain Rate

Highly glass-filled polymer

Background information

Defining Needs Strain rate defines test method Quasi-static -- Screw-type test machines 0.0001 to 0.1/s Intermediate (“High”) -- Servo-hydraulic test machines 0.1 to 200-700/s Bar Impact -- Split Hopkinson Bar 200 to 10,000/s

Types of high rate problems

Comparison of tensile specimens used for quasi-static and dynamic tests ASTM D638 Type I ASTM D638 Type V Dimensions in mm.