Mechanical Testing of Materials

Topics: Tensile strength, Materials science, Solid mechanics Pages: 12 (3265 words) Published: September 20, 2012
Experiment 2
A Characterization of Cast Iron, 1045 Annealed and Cold-Rolled Steel, 2024-T4 Aluminum, PMMA, and PP through Tensile, Impact, and Fracture-Toughness Tests. Aibar Nurmukhanov
MSE 308, Section AB3
Date Due: 02/23/2012
Date Received: _________

The experiment observed the mechanical deformation process of different materials by three tests: tensile test, impact test, and fracture-toughness test. The materials evaluated in the tensile test were annealed 1045 steel, cold rolled 1045 steel, 2024-T4 aluminum and cast iron. 2024-T4 aluminum is concluded to be most ductile (25.7 % reduction in area) and cast iron the most brittle (123 MPa). Effects of cold rolling in 1045 steel are apparent, as it has the highest strength among the materials tested (402 MPa yield strength). Impact test measured the impact energy of 1045 steel, 2024 aluminum, polypropylene (PP), and poly(methyl methacrylate) (PMMA). This test also observed the effect of temperature on material ductility. The fracture-toughness test was performed on 2024-T4 aluminum to determine a KIC of 35.3 MPam. From the experiment, it was found that the brittle-ductile transition temperature of PP is between 0 0C and room temperature, whereas the transition temperature of 1045 steel is between 25 0C and 100 0C.

The foundation of Materials Science lies in characterization of a material’s properties. Among those properties the greatest interest lies in the strength of materials, being the most basic requirement for any kind of construction. This lab aims first to describe the strength of 1045 annealed and cold-rolled steel, 2024-T4 aluminum, and cast iron through tensile testing. This includes characterization of yield strengths, modulus of elasticity, ultimate tensile strength, and fracture strength for each material. An emphasis is placed on elastic-plastic deformation in terms of ductility and how temperature and fatigue can affect this transition. Elastic and plastic behavior is described as follows, Elastic behavior: (1)

Plastic behavior: (2)
Where elastic deformation is reversible, related by constant modulus of elasticity, E, and plastic deformation is irreversible, following a power law modeled by the strength coefficient, K, and strain hardening exponent, n. Description of plastic deformation requires application of true stress and true strain,

These account for the area reduction due to elongation of the sample, resulting in higher actual stresses than those used as engineering values. Ductility and hardness are described in terms of plastic deformation, hardness being a material’s resistance to plastic deformation. For a quick grasp of each material’s ability to deform plastically, Rockwell hardness tests are conducted for each sample. Additional insight is provided by observing the fracture surfaces of materials; ductile materials naturally neck, but also break in way that result in rough surfaces, while brittle materials break smoothly with little reduction in area.

To observe how ductility of materials varies with temperature, impact tests are performed on samples of 0oC and 100oC in addition to room temperature (24.5oC). The energy absorbed upon impact follows an integration of Newton’s 2nd Law: E = v00Pdt (6)

where P is the load experienced by the material upon impact, v0 is the impact velocity, and integrating across the impact duration, t. Ductile materials are able to extend the integration limits to generally give a larger area, and thus, more energy absorption. Ductile to brittle transition temperatures are found in almost all materials. At high temperatures, plastic fracture requires less stress and eventually becomes lower than the yield stress, resulting in drastic ductility change. This lab will look for the transition in 1045 steel, 2024-T4 aluminum, polypropylene (PP) and poly(methyl methacrylate) (PMMA), Charpy impact test being used for metals...
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