研究目的
Investigating the fracture behavior of carbon fiber reinforced polymer composites under different loading rates and fiber orientations using optical methods to understand crack initiation and growth mechanisms.
研究成果
The research demonstrates that fiber orientation and loading rate significantly affect the fracture behavior of CFRP composites. Under dynamic loading, crack speeds vary with fiber orientation, and stress intensity factors drop after initiation. Under quasi-static loading, fiber bridging enhances post-initiation load-bearing capacity, leading to higher energy release rates during crack growth. The r-DGS method is effective for full-field measurement of deformations and extraction of fracture parameters in opaque composites, providing insights into mixed-mode fracture and loading rate effects.
研究不足
The study is limited to unidirectional CFRP laminates with specific fiber orientations and loading conditions. The optical method requires reflective specimen surfaces, and measurements are constrained by the sensitivity and resolution of the imaging equipment. Quasi-static tests for α=60° were not conducted due to equipment limitations. The analysis assumes certain crack-tip field models, which may not fully capture all complexities of composite fracture.
1：Experimental Design and Method Selection:
The study used reflection-mode Digital Gradient Sensing (r-DGS) combined with ultrahigh-speed photography for full-field measurement of crack-tip deformations. Specimens were subjected to dynamic impact loading using a modified Hopkinson pressure bar and quasi-static three-point bending tests.
2：Sample Selection and Data Sources:
Single-edge notched unidirectional T800s/3900-2 CFRP laminates with fiber orientations of 0°, 15°, 30°, 45°, and 60° relative to the crack direction were used. Specimens were cut to dimensions of 152 mm × 76 mm ×
3：8 mm for dynamic tests and 152 mm × 56 mm × 8 mm for static tests. List of Experimental Equipment and Materials:
Equipment included a Kirana-05M ultrahigh-speed digital camera, Nikon D100 digital SLR camera, Nikon 70-300 mm lens, beam splitter, speckle target plate, Cordin-659 high energy flash lamps, LED lamps, Instron 4465 universal testing machine, modified Hopkinson pressure bar, gas-gun with steel striker, and aluminum film for reflective coating. Materials were T800s/3900-2 CFRP laminates from Toray Composite Materials America, Inc.
4：Experimental Procedures and Operational Workflow:
For dynamic tests, specimens were impacted using the Hopkinson bar setup, with speckle images recorded at 500,000 fps. For static tests, specimens were loaded in displacement-control mode at
5：007 mm/s, with images recorded at 5 fps. Image correlation was performed using ARAMIS? software to extract displacements and surface slopes. Data Analysis Methods:
Stress intensity factors and energy release rates were extracted from surface slope data using elasto-static and elasto-dynamic crack-tip field equations for orthotropic materials. Crack speeds and other fracture parameters were calculated from the optical measurements.
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