# Lab #1 - 1 INTRODUCTION A FRACTURES Steel and aluminum are...

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1. INTRODUCTION A. FRACTURES Steel and aluminum are considered ductile materials in that they exhibit plastic deformation prior to fracture. Brittle materials, such as rock, glass and concrete, exhibit no plastic deformation prior to fracture and display a fracture strain of less than approximately 5%. Ductile materials absorb a significant amount of energy, unlike brittle materials, which absorb a deplorably minor amount. By performing tensile stress-strain tests, important mechanical properties, such as ductility, can be determined. Mechanical properties, although generalized, are subject to change due to prior deformation, the presence of impurities and heat processes. Modulus of elasticity, on the other hand, only changes due to a change in temperature. [1] B. HISTORICAL BACKGROUND The theory of ductile fracture was developed over the period of seventeen years. The theory includes width effects from tension tests and numerous crack configurations. [2] The theory of brittle fractures was developed in 1961, and discuses the rapid propagation of cracks. [3] The ultimate strength is found using the equation for the critical crack length and obtainable stress-strain curve. Ultimate strength represents the maximum stress a material can withstand while being stretched and pulled before necking. Basically all mechanical properties of a specimen can be determined and/or calculated after performing the necessary tensile tests. [2] C. LABORATORY ON OBSERVATION OF A TENSILE TEST In this laboratory section, six specimens were tested to failure to determine the mechanical properties. Strain was calculated by the computer and provided in a table.

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= ε ∆LL0 Eq. 1 ε = Strain ∆L = Change in Length (elongation) (mm) L0 = Original Length (mm)
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Lab #1 - 1 INTRODUCTION A FRACTURES Steel and aluminum are...

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