lecture 20 materials selection - Materials Selection and...

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Dr. M. Medraj Mech. Eng. Dept. - Concordia University Mech321 lecture 20/ 1 Outline • Introduction • Design Requirements •Exampls: - Example 1: Strong and light Tie-Rod - Example 2: Stiff & Light Tension Members - Example 3: Torsionally stressed shaft - Example 4: Light and Strong Beam - Example 5: Light and Stiff Beam Dr. M. Medraj Mech. Eng. Dept. - Concordia University Mech321 lecture 20/ 2 Materials Selection and Design: Introduction For selection, one must establish a link between materials and function, with shape and process playing also an important role ( We will focus on the function part ) Materials Attributes : physical, mechanical, thermal, electrical, economic, environmental. Function Shape Process Dr. M. Medraj Mech. Eng. Dept. - Concordia University Mech321 lecture 20/ 3 Function: support a load, withstand temperature, transmit heat, etc. What does the component do ? Objective: make thing cheaply, light weight, increase safety, etc., or combinations of these. What is to be maximized or minimized ? Constraints: make thing cheaply, light weight, increase safety, etc., or combinations of these. What essential conditions to be met ? Free variables : Which design variables are free ? Design Requirements From which we obtain: - Screening Criteria: go / no-go criteria - Ranking Criteria: an ordering of the materials that “go” Dr. M. Medraj Mech. Eng. Dept. - Concordia University Mech321 lecture 20/ 4 Example 1: Strong and light Tie-Rod • Tie-rod is common mechanical component. • Tie-rod must carry tensile force, F, w/o failure . • L is usually fixed by design. • While strong, need lightweight, or low mass . A = x-area L Tie-rod Objective: Constraints: Free variables : Function: Minimize mass: M = A L ρ ……………………. (1) • L = fixed length
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lecture 20 materials selection - Materials Selection and...

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