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

2. 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

3. 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 ?

4. 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

5. Polyolefin

6. Polyolefin relationship with strain rate

7. Polycarbonate

8. Relationship with Strain Rate

9. Highly glass-filled polymer

10. Background information

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

12. Types of high rate problems

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