Loads are forces. There are different

sources of forces. Weight, wind and

thermal are some examples. These

act differently. There are gradually,

suddenly applied and impact loads.

All these have different affects.

1. What are various types of forces?

Two types of forces: Constant magnitude and variable magnitude.

Examples of Constant magnitude forces: Weight force acting vertically downwards

Examples of variable magnitude forces

(i) Pressure force

(ii) Wind force

(iii) Inertia force

(iv) Centrifugal force

(v)Thermal force

(vi) Seismic force

(vii) Frictional force, Snow load

2.  Gradually applied load

When a load  applies in installments i.e. load of 100 N applies. First a load of 5 N, then 10 N, 15 N 20 N —————–100 N  applies. Mostly used in tests performed on materials to determine their strengths.

3 Suddenly applied load

When the total force applies in one installment i.e. force of 100 N  applies in one go. It causes 2 times the stress as compared to when the same load applies gradually. For example, when a person sits on a chair.

4.  impact load

Impact load is moving load. The moving body striking another body creates impact load. It causes many times stress when if the same load  applies gradually. Example: force applied in an accident is an impact load, hammering is another example of impact load.

(i) Beating with a stick

(ii) kicking a football

(iii) striking a ball in cricket

(iv) firing a bullet on a person

(v) jumping

It finds the toughness (strain energy up to the point of fracture) of a material. In actual practice most of the loads are a combination of suddenly and impact loads.

5.What is resilience? What is its symbol? What are its units?

Strain energy per unit volume is resilience. Its symbol is ‘u’. Its units are J/mm3.

Total Strain Energy =U

Total strain energy U = Gradually applied Load x Extension/2

    = P δL / 2

    =σ A (P L/AE)/2

     = σ  (P/A) AL/2E = σ σ AL / 2E

      = (σ2/ 2E) x Volume

    u =U / V = σ2/ 2E

        = σ2/2E

Resilience is an elastic property. It applies only within elastic limits.

https://www.mesubjects.net/wp-admin/post.php?post=6210&action=edit          Mech Properties-1

https://www.mesubjects.net/wp-admin/post.php?post=6178&action=edit           Q.A. Gears

https://www.mesubjects.net/wp-admin/post.php?post=6160&action=edit            Q.A. Riveted Joints

https://www.mesubjects.net/wp-admin/post.php?post=6151&action=edit            Q.A. Machine Design-1

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