E45 - Lab 1 - Mechnanical Properties Intro

E45 - Lab 1 - Mechnanical Properties Intro - Engineering 45...

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E E n n g g i i n n e e e e r r i i n n g g 4 4 5 5 P P r r o o p p e e r r t t i i e e s s o o f f M M a a t t e e r r i i a a l l s s L L a a b b o o r r a a t t o o r r y y © Copyright 2001 Professor Ronald Gronsky the Arthur C. and Phyllis G. Oppenheimer Chair in Advanced Materials Analysis University of California Berkeley, California 94720-1760
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E 45 2 Lab 1 Introduction to Mechanical Properties Objectives To understand the basic properties of strength and toughness of materials To measure the hardness (resistance to surface penetration) of different materials To understand the basic concepts of mechanical stress and strain To measure the effects of stress concentration on deformation behavior Overview This experiment offers practical experience with two hardness testing methods, and an understanding of the slight differences that do not allow the direct comparison of results from the two different techniques. It also illustrates the "stress concentrating" effect of holes (or other irregularities) in a material that can locally raise the average stress applied to the material. Understanding these elementary mechanical properties of materials and their relationship to the application of appropriate materials as components in engineering structures is the most important concept to be learned from this experiment. Equipment A) Hardness Tests 1. Rock well™ Hardness Tester 2. Brinell™ Hardness Tester 3. Brinell™ Microscope with Light Source 4. Test specimens a. mild steel b. stainless steel c. aluminum d. brass e. copper (various thicknesses) B) Stress Concentration Measurements 1. Rubber test sheet with support frame 2. Weight pan with weights 3. Twelve-inch scale graduated in 50 ths and 100 ths 4. Magnifying glass 5. Photoelastic stress analysis equipment 6. Transparent elastomeric specimens
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E 45 3 Background The usefulness of metallic materials in engineering structures primarily depends upon two mechanical properties: high strength and enough ductility to allow the relaxation of stress concentrations through plastic deformation without fracture. In specific cases, though, properties such as dimensional stability, abrasion resistance, corrosion resistance, high impact strength, electrical or thermal conductivity, or other factors can assume primary importance. At ordinary temperatures, metals, alloys, and many other materials will deform when loaded, and for small loads the amount of induced deformation is proportional to the magnitude of the applied load. This strain is elastic in nature, i.e., the material will return to its original shape when the load is removed. But at high loads, permanent changes may occur in the material. With increasing load, a point is reached beyond which irreversible deformation, called plastic deformation, occurs. Most metallic materials are ductile at room temperature. That is, they can be deformed plastically prior to fracture. Brittle materials
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E45 - Lab 1 - Mechnanical Properties Intro - Engineering 45...

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