Question
(a) State four properties of timber. (b) With the aid of a sketch , explain the following defects on timber: (1) knot; (ii)shake (C) Define the following terms as applied to metals: (i) stress; ii) strain; (iii) elastic limit. (d) Draw a stress strain curve for steel.
Solution
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(185 Votos)
Luciano
Mestre · Tutor por 5 anos
Resposta
(a) Four properties of timber:1. **Strength**: Timber has high compressive strength, tensile strength, and shear strength, making it suitable for structural applications.2. **Stiffness**: It has good stiffness, meaning it can resist deformation under load, which is crucial for structural integrity.3. **Workability**: Timber is relatively easy to work with using hand tools and machinery, making it versatile for various construction and manufacturing processes.4. **Sustainability**: Timber is a renewable resource when harvested responsibly, making it an environmentally friendly choice for construction and furniture making.(b) Defects on timber:(1) **Knot**: A knot is a natural defect that occurs where a branch joins the trunk of a tree. It is often stronger than the surrounding wood and is commonly used in structural applications. However, it can also be a weak point if not properly oriented.(ii) **Shake**: Shake is a defect characterized by the separation of the wood fibers along the grain, often due to improper drying or seasoning. This can lead to cracking and splitting, making the timber less stable and potentially weaker.(c) Definitions related to metals:(i) **Stress**: Stress is the force per unit area within materials that arises from externally applied forces, uneven heating, or permanent deformation. It is typically measured in units such as pascals (Pa) or megapascals (MPa).(ii) **Strain**: Strain is the deformation or displacement that occurs in a material in response to an applied stress. It is a measure of how much the material deforms and is typically expressed as a percentage or a fraction.(iii) **Elastic Limit**: The elastic limit is the maximum stress that a material can withstand without undergoing permanent deformation. Beyond this limit, the material will not return to its original shape once the stress is removed, indicating the onset of plastic deformation.(d) Stress-strain curve for steel:To draw a stress-strain curve for steel, follow these steps:1. **Start at the origin (0,0)**: This represents the initial state of the material.2. **Draw the initial linear portion**: This portion of the curve is typically steep and represents the elastic region of the material. The slope of this portion is the Young's modulus of the material.3. **Indicate the elastic limit**: This is the point where the material transitions from elastic to plastic deformation. It is usually marked by a slight deviation from the straight line.4. **Draw the plastic region**: This portion of the curve is usually more gradual and represents the material's ability to undergo plastic deformation. The curve will continue to rise as the material is subjected to higher stresses.5. **Indicate the ultimate tensile strength (UTS)**: This is the maximum stress the material can withstand before failure. It is usually the highest point on the curve.6. **Draw the fracture point**: This is where the material fails and the curve ends.The resulting curve will show the relationship between stress and strain for the material, with the elastic region being linear and the plastic region being more curved.