Abstract
M.Ing.
In the design and analysis of components and structures, detailed information
on the material behaviour and its properties is required. When a material
is loaded dynamically, such as in metal punching, the material properties
may not be the same as when loaded statically. This is known as the strain
rate sensitivity of a material, which implies that properties such as the yield
strength, tensile strength and ductility may vary with the rate at which the
material is loaded.
South Africa is one of the large stainless steel producing countries. Seventy
percent of the known chromium ore reserves are found in the Bushveld Igneous
Complex in the Northern Province and Mpumalanga. To compete
on the global stainless steel market it is essential that the South African
producers have all the relevant product information directly available.
Considerable research has been performed on mild steel at different strain
rates and temperatures[1]. Work has also been done on some austenitic
stainless steels. Very little, or no work has been done in this regard on ferritic
and martensitic stainless steels and on the proprietary alloy 3CR12[2].
The aim of this thesis is to investigate the strain rate sensitivity of Types
304, 430 and 316 stainless steel, 3CR12 corrosion resistant steel and mild
steel at different temperatures. To achieve this, tensile tests are performed.
at strain rates between 10's -1 to approximately 100s -1 and at temperatures
ranging from -40°C to 140°C. Shear tests are also performed at various strain
rates, to investigate the effect that material behaviour has on a typical metal
working process. The results obtained show that all the materials tested are strain rate sensitive.
The strain rate sensitivity varies as a function of the material tested
and the testing temperature. Constitutive models which take into account
the strain rate sensitivity at room temperature for all the materials are also
presented. These models describe the behaviour of the material fairly accurately.
Three dimensional plots are also presented which depict how the yield
strength, tensile strength and elongation vary as a function of both strain
rate and temperature. These plots clearly show material trends for the strain
rates and temperatures tested.