Characterization of Low-Velocity Impact Damage in Toughened Non-crimp Fabric Laminates
摘要
The damage response of resin-infused composites was investigated using quasi-static indentation (QSI) and instrumented drop-weight impact testing. The test specimens were composed of non-crimp fabrics using +45°, 90°, –45°, and 0° plies. The goals of the testing were to identify damage responses that may differ from prepreg thermoset materials and provide damage characterization data to evaluate current damage prediction analyses and aid improvements to current damage models. The damage was characterized using X-ray computed tomography (CT) and ultrasonic testing (UT). Incremental QSI loading was used on a single specimen to investigate damage growth in nine steps at progressively higher loads. Real-time acoustic emission data were used to determine the unloading points. Unlike typical prepreg thermoset composites, the force–displacement was smooth and showed no obvious indications of damage. The primary damage consisted of large lines of fiber fracture on the plies near the impact surface and delaminations through the thickness. Nine specimens were impacted at nominal impact energies of 25 ft-lbs, 30 ft-lbs, and 35 ft-lbs. The force histories at each energy followed nearly identical paths. Again, no obvious signs of damage were observed in any of the force histories. The general damage response in the dynamic tests was similar to the QSI-loaded specimens. However, repeat specimens impacted with a given impact energy showed variations in the damage. Some characteristics of the damage response were different than those typically observed in thermoset composites made from prepreg materials and will need to be evaluated using current analysis methods.