Mechanical Properties Flashcards
Density
Density is the mass per unit volume of a material, influenced by the arrangement of atoms or molecules. It determines how a material interacts with forces such as gravity and buoyancy. Materials with tightly packed atomic structures generally have higher densities, while those with open, porous structures or lower atomic mass have lower densities.
The atomic mass and packing density affect density.
Metals have high densities due to closely packed atoms in crystal lattices. Polymers or porous materials have lower densities due to voids or loosely arranged chains.
Hardness
Hardness is the resistance of a material to localized plastic deformation, indicating how well it can withstand surface wear and tear. It is critical for applications requiring abrasion resistance and durability.
Hardness is influenced by the strength of atomic bonds. Materials with strong covalent or ionic bonds (e.g., diamond, ceramics) exhibit higher hardness. Metallic bonding provides moderate hardness, while polymers exhibit lower hardness due to weaker van der Waals forces between chains.
Elastic Modulus
Elastic modulus measures a material’s stiffness, reflecting its resistance to elastic deformation under stress. It indicates the ability of a material to return to its original shape after force removal, crucial for understanding material behavior under loads.
Elastic modulus is determined by the strength and arrangement of atomic bonds. Strong, directional bonds (e.g., covalent or ionic) result in high elastic moduli. Ceramics and metals have high elastic moduli due to strong atomic interactions, while polymers have lower moduli due to flexible molecular chains.
Flexural Strength
Flexural strength, or bending strength, is the ability of a material to withstand deformation under load during bending. This property is important for materials subjected to bending forces rather than axial tension or compression.
Flexural strength depends on atomic bonding and microstructure. Materials with strong atomic bonds and minimal internal defects exhibit higher flexural strength. Brittle materials like ceramics have high flexural strength but fail suddenly, while metals and polymers can flex more before failing.
Compressive Strength
Compressive strength is the ability of a material to withstand compressive forces without permanent deformation or failure. This property is critical for materials used in load-bearing applications such as construction and infrastructure.
Resistance to compression arises from the strength and rigidity of atomic bonds. Ceramics and metals typically have high compressive strength due to their atomic structures resisting close packing. Materials with flexible molecular arrangements, like polymers, usually have lower compressive strengths.
Fracture Toughness
Fracture toughness measures a material’s ability to resist crack propagation, crucial in preventing rapid failure from stress-induced cracks. A high fracture toughness indicates greater energy absorption before fracturing.
Fracture toughness depends on atomic bonding and microstructure. Metals with ductile atomic structures can absorb more energy before fracturing, resulting in higher toughness. Ceramics, with strong, directional bonds, have lower toughness as they resist dislocation movement. In polymers, cross-linking can enhance toughness by preventing crack growth.
Brittle Fracture
Brittle fracture occurs when a material breaks suddenly without significant plastic deformation, characterized by rapid crack propagation. This type of fracture is typical in materials like glass, ceramics, or some metals at low temperatures.
Brittle fracture arises from atomic structures lacking energy absorption mechanisms. Strong, directional atomic bonds (common in ceramics) prevent dislocation movement, leading to quick crack propagation. Materials with rigid, highly ordered atomic structures are more prone to brittle fracture, especially under tensile stress or at low temperatures.
