Characterization of Fatigue Crack Propagation in Short Fiber Reinforced Thermoplastics—A Unified Approach

The paper presents a study conducted to examme the applicability of a unified approach of fatigue crack propagation (FCP) to include a short fiber composite (SFC), which is subjected to tensile cyclic stressing, undergoing generalized plasticity. The proposed approach expressed in the form of da/dN = C( ΔG) ^m /( G _c - G _max ) has recently been shown capable of characterizing a wide range of materials including mild steel, aluminium alloys, PMMA and PVC with a master FCP diagram. For plasticially loaded cracked members, the above formulation is generalized to be as da/dN = C(Δ J) ^m /( J _c - J _max ) and the difference between the J-integral range, Δ J, and the con ventional cyclic J-integral, Δ J _cycl , are elucidated The unified formulation is also shown to be derivable from the thermodynamic theory of irreversible processes, had the cracked surface area been taken as an internal state variable. The measured FCP rates for SFC together with two other polymeric materials, PMMA and PVC, are analyzed using the unified formulation and its validity for producing a master diagram is verified when all FCP data are successfully placed in one single line yielding a satisfactory coefficient of correlation of 0.987.