STP675

    Fatigue Fracture Micromechanisms in Engineering Plastics

    Published: Jan 1979


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    Abstract

    This paper deals with an examination of fatigue micromechanisms present in polymers of various chemistry and microstructure. At low stress-intensity (ΔΚ) levels in several amorphous homopolymers, poly (methymethacrylate) (PMMA), polycarbonate (PC), poly (vinyl chloride) (PVC), polystyrene (PS), and polysulfone (PSF), each with viscosity-average molecular weight (M¯v) in the range 1 × 105 < Mv < 4 × 105, the macroscopic and microscopic appearances of the fracture surface were observed. Observations were also made in both rubber-modified amorphous polymers such as an acrylonitrile-butadiene-styrene (ABS) copolymer and a rubber-toughened PS-poly (phenylene oxide) blend, and the crystalline polyacetal (PA). Regardless of the degree of surface roughness, the crack front in all these materials advanced discontinuously in increments equal to the bandwidth after remaining stationary for as many as 105 fatigue cycles (in PA). In single-phase amorphous polymers, the discontinuous growth process was identified with the failure of a single craze ahead of the crack tip. At high ΔΚ levels the fracture surfaces of most polymers were striated, with one striation representing the increment of crack advance during one load excursion. It is concluded that large errors can be made in estimating the overall fatigue life of engineering plastics if the significance of the microscopic bands observed at low ΔΚ and the striations observed at high ΔΚ as fatigue fracture markings is misinterpreted.

    Keywords:

    fatigue crack propagation, polymers, discontinuous crack growth, fatigue fracture mechanisms


    Author Information:

    Hertzberg, RW
    New Jersey Zinc professor of metallurgy and professor of chemistry, Materials Research Center, Lehigh University, Bethlehem, Pa.

    Skibo, MD
    Sandia Laboratory, Livermore, Calif.

    Manson, JA
    New Jersey Zinc professor of metallurgy and professor of chemistry, Materials Research Center, Lehigh University, Bethlehem, Pa.


    Paper ID: STP35903S

    Committee/Subcommittee: E08.05

    DOI: 10.1520/STP35903S


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