1979-02-01

THE EFFECT OF THICKNESS, STRAIN LEVEL & STRAIN RATE ON THE NDT TEMPERATURE OF LOW CARBON STEELS 790827

Two candidate ROPS steels and a common grade of low carbon steel were used to study the effects of thickness, strain rate and strain level on the nil-ductility transition temperature (NDTT). The NDTT was determined by using a modification of ASTM Standard Test Method E208. Comparison tests were made with Charpy V-notch specimens.
No general correlation was found between the thickness modified NDT temperatures and the Charpy energy absorption of specimens of similar thickness. However, a good correlation was observed between the NDT temperature and the 100 percent brittle fracture appearance temperature of the Charpy specimens.
A thickness modified NDTT test provides a reasonable simulation of the critical regions of ROPS structures during a rollover. Brittle fracture of ROPS structures is not desirable above the minimum ambient operating temperature where the vehicle is used. Hence the thickness modified NDTT test may provide additional information for material selection and the specification of recommended operating temperatures.
Low carbon steels are commonly used in the manufacture of Rollover Protective Structures (ROPS). These steels exhibit a dramatic transition from high to low toughness as temperature is lowered. The temperature at which this transition occurs is highly dependent on the strain rate as well as on the material thickness of the particular structure. These factors can be considered in the performance of ROPS for machines exposed to low ambient temperatures.
A simple materials evaluation test that reflects cold temperature suitability is needed for the selection and for specifications of acceptance and manufacturing quality control of ROPS materials.

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