Notched tensile test stress-strain behavior

Stress-strain behavior was examined at room temperature, according to ASTM test D638-68, with a crosshead speed of 0.085 mm/sec. Young s modulus (3), ultimate tensile strength (TS), and ultimate elongation to break (e ) were determined. Notched Izod impact tests were made following ASTM test D256-73 usually 4 to 5 specimens were tested. 

Notched monotonic tensile specimens can be a useful approach to begin to understand the effect of structural notches on the behavior of UHMWPE total joint replacement components. Therefore, we developed a testing methodology to characterize the stress strain and fracture behavior of a notched tensile specimen. Additionally, the stress-strain behavior of notched tensile specimens can be used to challenge the Hybrid Constitutive Model for UHMWPE (see Chapter 35) with a multiaxial stress state. Accurate prediction of the behavior of a notched specimen by a simulation utihzing the Hybrid Model would be one vahdation of its accuracy in describing the mechanical behavior of UHMWPEs. 

The novel video-based method used for the evaluation of axial stress-strain behavior of notched cylindrical specimens is a valuable tool. Experimentally, this method is simple to implement and has the advantage of providing strain behavior up to failure using a noncontacting extensom-etry approach. The notched tensile test is also an attractive experimental method with which to check the validity of the development of constitutive models of UHMWPE (see Chapter 35). The methodology has the advantage of creating a multiaxial stress state without contact, and the specimen can be modeled as axisymmetric in finite element analyses. 

Prior to the advent of fracture mechanics as a scientific discipline, impact testing techniques were estabhshed to ascertain the fracture characteristics of materials at high loading rates. It was realized that the results of laboratory tensile tests (at low loading rates) could not be extrapolated to predict fracture behavior. For example, under some circumstances, normally ductile metals fracture abruptly and with very little plastic deformation imder high loading rates. Impact test conditions were chosen to represent those most severe relative to the potential for fracture —namely, (1) deformation at a relatively low temperature, (2) a high strain rate (i.e., rate of deformation), and (3) a triaxial stress state (which may be introduced by the presence of a notch). 

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