Question

If somebody could assist me with the below questions, I would greatly appreciate it! Thank you!

1. Discuss the trade-off between strength and ductility in design. For example, are there design situations where ductility would be more important than strength?

2. Is there any range of stress that can be applied to a material without appreciably altering some of its material properties? Explain.

**I would really appreciate it if the answer could be typed!

Answer 1

Solution

1.

Ductility is the ability of material to undergo deformation against applied load without leading to fracture. Strength on the other hand is the ability of the material to resist fracture
When a ductile material is acted by force it will deform to adapt to the applied stress, Ie it will absorb more energy than a brittle material.

Limitations of strength based design are
• Cross-sections are capable of resisting a certain value of actions
based on assumed failure criterion
• Actions are obtained often from linear elastic analysis, and are
factored to provide certain factor of safety
• Strength design itself provides no information or control on the level
of deformation produced at that factored load level
• No information about behavior of the member if loads or actions
were to exceed the factored design load

Main reasons why ductility plays an important role more than strength are
1. Formability property
    For complex shaped object, we either go for casting or forming procedure.Forming procedures like stamping drawing, forging etc are cheap and fast. These depends on Formability property of material which is directly linked to the ductility.
There fore all the manufacturing process that requires forming procedures, ductility of material is an important factor rather than strength

2. Safety
   Brittle materials fails rapidly while ductile material takes time to fail. Ie it can absorb energy and the failure will be gradual. This property isthe main reason why all structural components have ductile material embedded into it like steel bars, which gives a time for safely evacuation in case of structural failure.
Each structural failure is indicated by ductile deformation which is actually a safety index of upcoming failure.

4.All seismic design codes around the world recognize the importance of ductility as it plays a vital role in structural performance against earthquakes. Well-detailed steel and reinforced concrete (RC) structures, fulfilling the ductility requirements of codes are expected to undergo large plastic deformations with little decrease in strength.

5.Heat treatment and enhancing material properties
Only ductile materials are heat treated and allows for change in material property by heat treatment methods.

Hence to conclude it is important to recognize, explicitly evaluate and provide Ductility in key locations and members for improved performance for extreme loads

2.

Stresses can be applied to a material without altering some of its material properties. There is range of this applied stress and that range is upto the elastic limit of the material.

Elastic Limit

• The elastic limit is the limit beyond which the material will no longer go back to its original shape when the load is removed
• It is the maximum stress that may be developed such that there is no permanent or residual deformation when the load is entirely removed.
• It is up to point ‘E’ in the graph

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Once the elastic limit is crossed the material starts to yield.

Yielding is the deformation of material with Avery little change in stress value. After yielding the material gets deformed permanently and plastic strains(RESIDUAL STRAINS) are left behind the material upon removal of Stresses. Hence the properties exhibited by a yield material will be different from the parent material. These properties can be hardness, ductility, malleability, resilience. The reasons for this is due to work hardening effects due to yielding and residual strains left behind and related grain orientation changes.

Until the material is deformed upto elastic limit, material will come back to original shape and all strains are elastic meaning that no permanent deformation will be left behind. Stresses upto elastic limit have 100% elastic recovery and the material properties remain same as that of parent material.

The given question is solved

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