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whoever could give a detailed explanation? 
Difference between toughness and strength?
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Discussion Overview
The discussion focuses on the difference between toughness and strength in materials, exploring their definitions, relationships, and implications in material science and engineering. Participants delve into the technical aspects of these concepts, including their representation in stress-strain curves.
Discussion Character
- Technical explanation
- Conceptual clarification
- Debate/contested
Main Points Raised
- One participant defines strength as resistance to deformation and describes the stress-strain relationship, emphasizing the yield point and ultimate tensile strength.
- Another participant explains toughness as the resistance to failure or crack propagation, noting its relationship to strength and the energy required for crack propagation.
- A participant illustrates the stress-strain curve, stating that strength corresponds to the height of the curve on the stress axis, while toughness is represented by the area under the curve.
- Some participants suggest that a good structural alloy should possess both high strength and toughness.
Areas of Agreement / Disagreement
Participants present multiple perspectives on the definitions and relationships between toughness and strength, with no consensus reached on a singular explanation. The discussion remains unresolved regarding the nuances of these concepts.
Contextual Notes
Participants reference specific terms and concepts such as the yield point, ultimate tensile strength, stress intensity factor, and J-integral, which may depend on specific definitions and contexts not fully explored in the discussion.
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Astronuc
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Strength refers to resistance to deformation, and also to a large elastic range. In the Elastic region of the stress-strain relationship, the relationship is described by a linear function, such that [itex]\sigma[/itex] = E [itex]\epsilon[/itex], where [itex]\sigma[/itex] is the stress, E is the Elastic modulus, and [itex]\epsilon[/itex] is the strain.
At a point called the yield point, the relationship between stress and strain depart from linear, and the material yields meaning that permanent or inelastic and plastic deformation occur.
Beyond the yield point or yield strength, less stress is required for a given amount of strain (deformation). This proceeds up to the ultimate tensile strength, which is where uniform elongation is measured. At this point, a tensile specimen begins to 'neck', i.e. the change in cross-section becomes non-uniform. Also, beyond the ultimate tensile strength, the strain increases without additional stress. If the load is not immediately removed, the material will strain to failure.
Toughness is the resistance to failure or crack propagation. It is somewhat related to strength. Very strong materials will have low toughness, i.e. low tolerance for flaws or defects, i.e. incipient cracks.
Toughness relates to the amount of energy absorbed in order to propagate a crack. Materials with high toughness require greater energy (by virtue of force or stress) to maintain crack propagation. Toughness is described in terms of a stress intensity factor (K) or J-integral, or the strain energy release rate of nonlinear elastic materials, (J).
See - http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_epfm_J.cfm - for more on J-integral.
At a point called the yield point, the relationship between stress and strain depart from linear, and the material yields meaning that permanent or inelastic and plastic deformation occur.
Beyond the yield point or yield strength, less stress is required for a given amount of strain (deformation). This proceeds up to the ultimate tensile strength, which is where uniform elongation is measured. At this point, a tensile specimen begins to 'neck', i.e. the change in cross-section becomes non-uniform. Also, beyond the ultimate tensile strength, the strain increases without additional stress. If the load is not immediately removed, the material will strain to failure.
Toughness is the resistance to failure or crack propagation. It is somewhat related to strength. Very strong materials will have low toughness, i.e. low tolerance for flaws or defects, i.e. incipient cracks.
Toughness relates to the amount of energy absorbed in order to propagate a crack. Materials with high toughness require greater energy (by virtue of force or stress) to maintain crack propagation. Toughness is described in terms of a stress intensity factor (K) or J-integral, or the strain energy release rate of nonlinear elastic materials, (J).
See - http://www.efunda.com/formulae/solid_mechanics/fracture_mechanics/fm_epfm_J.cfm - for more on J-integral.
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Thank you Astronuc. Much helpful.
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rdt2
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bullet said:whoever could give a detailed explanation?
Picture the stress-strain curve for an elastic-plastic metal. Strength is how high the curve reaches on the stress axis. Toughness is the area under the curve (and so related to energy).
A good structural alloy is both strong and tough.
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