AME 4 Q2

Correct Answer: D) The ratio of the design load to the maximum load a structure can support, providing a margin of safety against failure.

• Explanation: The safety coefficient (or factor of safety) is defined as the ratio of the maximum load that a structure or component can support to the design load it is expected to carry. This ratio provides a margin of safety to ensure that the structure can handle unexpected stresses or loads beyond the designed limits, preventing failure and ensuring safety under real-world conditions.

Incorrect Options:

A) The ratio of the maximum load a structure can support to the load it is designed to support, ensuring the structure's performance under normal conditions.

• Explanation: This option is close but slightly incorrect because it describes a similar concept to the safety coefficient but focuses on performance under normal conditions rather than ensuring safety against unexpected loads. The safety coefficient specifically ensures that there is a margin for unexpected or extreme conditions, not just normal conditions.

B) The ratio of the minimum load a structure can support to the load it is designed to support, ensuring the structure’s resilience in extreme conditions.

• Explanation: This option is incorrect because it incorrectly describes the safety coefficient as the ratio of the minimum load a structure can support to the design load. The safety coefficient is concerned with the maximum load the structure can support relative to the design load, not the minimum load.

C) The ratio of the applied load to the ultimate load a material can withstand, ensuring the material’s durability under expected conditions.

• Explanation: This option describes a different concept, which is more related to the strength of materials rather than the safety coefficient. It focuses on the applied load relative to the ultimate load, which is not the same as the factor of safety, which specifically compares the design load to the maximum load.

Correct Answer: C) The internal resistance of a material to forces that twist or slide parallel to the surface, calculated as the force applied parallel to the area divided by that area.

• Explanation: Shear stress is the internal resistance of a material to forces that cause layers within the material to slide or twist parallel to each other. It is calculated by dividing the force applied parallel to the surface by the area over which the force is applied. Shear stress measures how well a material can withstand forces that cause internal sliding or deformation parallel to its surface.

Incorrect Options:

A) The internal resistance of a material to forces that push or compress it together, calculated as the force applied per unit area.

• Explanation: This describes compressive stress, not shear stress. Compressive stress occurs when forces push a material together, causing it to compress. It is calculated as the compressive force divided by the cross-sectional area. Shear stress, in contrast, involves forces that cause sliding parallel to the surface.

B) The internal resistance of a material to forces that pull it apart, calculated as the force applied per unit area.

• Explanation: This describes tensile stress, not shear stress. Tensile stress occurs when forces pull a material apart, causing it to elongate. It is calculated as the tensile force divided by the cross-sectional area. Shear stress, however, involves forces that cause internal sliding or twisting parallel to the surface, not pulling apart.

D) The internal resistance of a material to forces that bend it, calculated as the force applied perpendicular to its length divided by the cross-sectional area.

• Explanation: This describes bending stress, not shear stress. Bending stress occurs when forces cause a material to bend, creating tension on one side and compression on the other. It is related to the bending moment and the geometry of the material. Shear stress specifically refers to forces that cause internal sliding or twisting parallel to the surface, rather than bending.

Correct Answer: C) The ability of a material to permanently deform without breaking when a force is applied.

• Explanation: Plasticity refers to a material’s ability to undergo significant permanent deformation without fracturing when subjected to stress. This means that the material can be reshaped or molded under applied forces and retain the new shape after the force is removed. Plasticity is a key property in materials like metals and polymers that allows them to be formed into various shapes without breaking.

Incorrect Options:

A) The ability of a material to return to its original shape after being deformed by a force.

• Explanation: This describes elasticity, not plasticity. Elasticity is the property of a material to return to its original shape and size after the applied force is removed, provided the material has not been deformed beyond its elastic limit. Plasticity, on the other hand, involves permanent deformation.

B) The ability of a material to withstand an applied load without deformation.

• Explanation: This describes stiffness or rigidity, not plasticity. Stiffness refers to a material's resistance to deformation under load. While plasticity involves deformation, it specifically refers to permanent deformation rather than the ability to resist deformation.

D) The ability of a material to conduct heat and electricity efficiently.

• Explanation: This describes thermal and electrical conductivity, not plasticity. Conductivity relates to how well a material can transfer heat or electrical current, which is a different property unrelated to how a material deforms under stress.

Correct Answers:

A) Material fatigue and environmental conditions

• Explanation: Material fatigue refers to the weakening of a material caused by repeated loading and unloading cycles, which can affect the safety coefficient by reducing the material’s ability to withstand stress. Environmental conditions (such as temperature, humidity, and corrosive elements) can also influence material properties and performance, impacting the safety coefficient. These factors can cause deterioration or changes in the material’s behavior, affecting its load-bearing capacity and, consequently, the safety coefficient.

C) Operational load conditions and manufacturing tolerances

• Explanation: Operational load conditions affect the safety coefficient because the loads a structure or component is subjected to during use can vary. If the actual operational loads are higher than anticipated, the safety coefficient must account for these variations to ensure safety. Manufacturing tolerances refer to the permissible limits of variation in dimensions and properties of a component. Variations in manufacturing can affect how well the component performs under load, influencing the safety coefficient. Components produced outside specified tolerances may not perform as expected, potentially reducing the effective safety margin.

Incorrect Options:

B) Design aesthetics and color of the material

• Explanation: Design aesthetics and color of the material do not influence the safety coefficient. These factors are related to the visual and aesthetic aspects of a component, not its structural performance or safety. The safety coefficient is concerned with the material’s ability to handle stresses and loads, which is not impacted by aesthetics or color.

D) Size of the component and its surface finish

• Explanation: While the size of a component can affect its load-bearing capacity, it is not a direct factor influencing the safety coefficient in the same way as material fatigue or operational conditions. Surface finish can affect friction and wear but does not directly influence the safety coefficient. The safety coefficient is more directly affected by factors that impact the material’s strength and performance under load rather than surface characteristics alone.

Correct Answer: C) The measure of a material's stiffness or resistance to elastic deformation, calculated as the ratio of tensile stress to tensile strain within the elastic limit.

• Explanation: Young's modulus (also known as the modulus of elasticity) quantifies a material's stiffness or resistance to elastic deformation. It is defined as the ratio of tensile stress to tensile strain within the material's elastic limit. This means that Young's modulus measures how much a material will stretch or compress under a given amount of force, provided the deformation is reversible (elastic).

Incorrect Options:

A) The measure of a material's ability to deform under compressive stress, calculated as the force per unit area that causes deformation.

• Explanation: This option describes compressive stress rather than Young’s modulus. While Young’s modulus is related to stress, it specifically measures the ratio of stress to strain, not just the ability to deform. It’s also not limited to compressive stress; it applies to tensile stress as well.

B) The measure of a material's ability to resist shear stress, calculated as the force parallel to the surface divided by the area.

• Explanation: This describes shear modulus (or modulus of rigidity), not Young’s modulus. Shear modulus measures a material’s resistance to shear stress, which involves parallel forces causing layers to slide against each other. Young’s modulus specifically measures resistance to tensile or compressive stress.

D) The measure of a material's ability to return to its original shape after being deformed, calculated as the change in length divided by the original length.

• Explanation: This describes elastic strain rather than Young’s modulus. While the ability to return to the original shape is related to elasticity, Young’s modulus is defined as the ratio of stress to strain, not just the change in length divided by the original length. Elastic strain measures deformation, but Young's modulus measures the material's stiffness in response to that deformation.