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Strength  Elongation General Information Strength meas Strength  Elongation General Information Strength meas

Strength Elongation General Information Strength meas - PDF document

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Uploaded On 2015-06-07

Strength Elongation General Information Strength meas - PPT Presentation

The chart helps identify materials which can be easily deformed into new shape s during manufacturing Designers like to use metals with significant elongations to failure becaus e they are more forgiving of harsh treatment eg car chassis nails Simpl ID: 82193

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Strength - Elongation General Information Strength measures the resistance of a material to failure, given by the applied stress (or load per unit area) The chart shows yield strength in tension for all materials, except for ceramics for which compressive strength is shown (their tensile strength being much lower) Elongation measures the percentage change in length before fracture Elongation to failure is a measure of ductility Physical Insights Ceramics have very low elongations (1%) because they can not plastically deform Metals have moderate elongation to failure (1-50%) with deformation occurring by plastic flow Thermoplastics have large elongations (䀀100%) because the molecules can stretch out and slide over one another Rubbers have long elastic elongations because the chains can coil/uncoil elastically Thermosets have low elongations (5%) because the molecules are bonded together into a network so that they cannot slide over one another One way to strengthen a metal is to make plastic flow difficult – this reduces the ductility and elongation Strength - Elongation Example Uses Few components are designed to elongate significantly - examples are impact protection like crash barriers. The chart helps identify materials which can be easily deformed into new shapes during manufacturing Designers like to use metals with significant elongations to failure because they are more forgiving of harsh treatment, e.g. car chassis, nails Simple Questions What is the difference between elastic and plastic deformation? Why is lead used on old roofs and roof flashings? Select materials for a car bumper. Select materials for a bungee rope. Select materials for drawing pins. Further Questions Why can’t rubbers be formed into shapes easily, even though they can be subjected to large deformations? Metals and alloys Ceramics Polymers Wood and wood products Composites Select chart: Young's modulus - Density · Young's Modulus - Cost Strength - Density · Strength - Toughness · Strength - Elongation · Strength - Cost · Strength - Max service temperature · Specific stiffness - Specific strength · Electrical resistivity - Cost · Recycle Fraction - Cost · Energy content - Cost