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Abstract
Fiber-reinforced plastics (FRPs) are typically difficult to machine due to their highly heterogeneous and anisotropic nature and the presence of two phases (fiber and matrix) with vastly different strengths and stiffnesses. Typical machining damage mechanisms in FRPs include series of brittle fractures (especially for thermosets) due to shearing and cracking of matrix material, fiber pull-outs, burring, fuzzing, fiber-matrix debonding, etc. With the aim of understanding the influence of the pronounced heterogeneity and anisotropy observed in FRPs, “Idealized” Carbon FRP (I-CFRP) plates were prepared using epoxy resin with embedded equispaced tows of carbon fibers. Orthogonal cutting of these I-CFRPs was carried out, and the chip formation characteristics, cutting force signals and strain distributions obtained during machining were analyzed using the Digital Image Correlation (DIC) technique. In addition, the same procedure was repeated on Uni-Directional CFRPs (UD-CFRPs). Chip formation mechanisms in FRPs were found to depend on the depth of cut and fiber orientation with pure epoxy showing a pronounced “size effect.” Experimental results indicate that in-situ full field strain measurements from DIC coupled with force measurements using dynamometry provide an adequate measure of anisotropy and heterogeneity during orthogonal cutting.
NOMENCLATURE
| CFRP | = | Carbon Fiber-Reinforced Plastic |
| I-CFRP | = | Idealized CFRP |
| UD-CFRP | = | Uni-Directional CFRP |
| MD-CFRP | = | Multi-Directional CFRP |
| PCD | = | Poly-Crystalline Diamond |
| VARTM | = | Vacuum-Assisted Resin Transfer Molding |
| DIC | = | Digital Image Correlation |
| SEM | = | Scanning Electron Microscopy |
| α | = | Rake Angle, ° |
| γ | = | Relief Angle, ° |
| θ | = | Fiber orientation, ° |
| t | = | Depth of cut, mm |
| Vc | = | Cutting speed of the tool, mm/min |
| Vf | = | Fiber volume fraction |
| Fc | = | Cutting force, N |
| Ft | = | Thrust Force, N |
| GIc | = | Strain energy release rate in Mode I, N/mm |
| σY | = | Yield Stress, MPa |
| ϵxx | = | Direct strain in x-direction |
| ϵyy | = | Direct strain in y-direction |