Edexcel GCE Product Design - Performance Characteristics of Materials PDF

Image result for dudley sixth logo Edexcel GCE PRODUCT DESIGN. 2: Performance Characteristics of Materials Textbook pages 25-31 Based on Wood, Plastic and Metals: Strength, toughness, ductility, malleability, etc....

Image result for dudley sixth logo Edexcel GCE PRODUCT DESIGN. 2: Performance Characteristics of Materials Textbook pages 25-31 Based on Wood, Plastic and Metals: Strength, toughness, ductility, malleability, etc. Learning Outcomes Name and identify the different material characteristics based on wood, plastic and metal. Describe the material characteristics, how this can be tested and the reasons this is relevant. Explain the reasons for using each material and why it is best suited based on the characteristics. a) Conductivity Electrical resistivity is a fundamental property of a material that quantifies how strongly that material opposes the flow of electric current. A low resistivity indicates a material that readily allows the flow of electric current. Resistivity is commonly represented by the Greek letter ρ. Examples shown are ring with 4 metals and a test rig to measure thermal and electrical resistance. b) Strength Strength of materials, also called the mechanics of materials, is a subject which deals with the behavior of solid objects subject to stresses and strains. These images show: 1.The different types of stress that can be applied to materials. 2. Steel girders with built in expansion room. 3. Smart stress plastic that shows where forces are being applied. Materials testing for strength Torsion: A simpler definition is ‘twisting’ force. The amount a material/component Compression: can withstand if fixed at both ends. Forces pressing together or the ability to withstand loads applied from both ends acting inward. This can be tested using an Ametek test. Shear: Tension: This is to test the ability of material fixed at both ends to withstand the shear force The ability to withstand applied to it. stretching forces ‘tensile’ pulling on both ends of a piece of material. This is tested using a Universal Testing Machine c) Elasticity ‘Elasticity’ refers to the ability of an object or material to resume its normal shape after being stretched or compressed; stretchiness. Although this is associated with elastic/rubber bands the property of ‘elasticity’ refers to any type of material. Woods, plastics and metals. This is seen clearly in this beautiful steam bent bench showing the elastic nature of walnut. d) Plasticity ‘Plasticity’ refers to the ability and quality of a material being easily shaped or moulded. ‘Plastic’ means the ability of any material to change shape These three images show examples of thermo-plastic polymers, steel and a timber and ceramic composite. e) Malleability ‘Malleability’ is a substance's ability to deform under pressure- known as compressive stress. If malleable, a material may be flattened into thin sheets by hammering or rolling. Malleable materials can be flattened into metal leaf. Many metals with high malleability also have high ductility. Copper is a good example of this as it is very useful for plumbing and is ductile. The polymer splint shown allows the person applying the dressing to mould this to the shape of the limb. f) Ductility Ductility is when a solid material stretches under tensile stress. If ductile, a material may be stretched into a wire. Ductility is a measure of a material's ability to undergo significant plastic deformation before rupture, which may be expressed as percent elongation or percent area reduction from a tensile test. According to Shigley's Mechanical Engineering Design significant denotes about 5.0 percent elongation. g) Hardness ‘Hardness’ is a measure of the resistance to localised plastic deformation induced by either mechanical indentation or abrasion. Some materials (e.g. metals) are harder than others (e.g. plastics, wood). Rockwell. The Rockwell scale is a hardness scale based on indentation hardness of a material. The test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload. h) Toughness ‘Toughness’ is the ability of a material to absorb energy and plastically deform without fracturing. One definition of material toughness is the amount of energy per unit volume that a material can absorb before rupturing. This IZOD impact testing rig is used to produce a large force from a pendulum arm on one focused point. i) Durability ‘Durability’ is the ability of a physical product to remain functional, without requiring excessive maintenance or repair, when faced with the challenges of normal operation over its design lifetime. This is a double edged sword as plastics have proven too durable and there is a worldwide pollution problem which threatens our eco-system. j) Biodegradability ‘Biodegradability’ is the ability of organic substances and materials to be broken down to simpler substances through the action of enzymes from micro-organisms. If this process is complete, the initial organic substances are entirely converted into simple inorganic molecules such as water, carbon dioxide and methane. Rubber is a well known bio-polymer and there are many being developed that use starch, sugar, cellulose and synthetic materials including: Polylactic Acid (PLA)Biopol (PHB), Colagen and Gelatin. Biodegradeable Materials Biodegradeable Materials are capable of being broken down (decomposed) rapidly by the action of micro-organisms. Biodegradable substances include food scraps, cotton, wool, wood, human and animal waste, manufactured products based on natural materials (paper, and vegetable-oil based soaps). It is vital that future products are designed to be recycled, made from bio-degradeable materials and have minimum environmental impact.