Overview of Mechanics of Materials (1): From the Discipline to Load Classification

Mechanics of Materials: The study of the internal effects of external forces on materials,, that is,, a material's resistance to failure,(or strength,: strength)is the subject of this discipline.

l Internal Changes in Materials

  1. Deformation: deformation / is expressed as strain(strain).

 

  2. Resistance to Force: resisting / is expressed as stress(stress).

 

l Types of Deformation

  1. Elasticity(elasticity): When a body deforms under an external force and that force is removed,, it tends to return to its original shape..

      A. EX) Rubber, Springs

      B. A property appearing only in solids with a definite shape

 

   2. Plasticity(plasticity): When a body deforms under an external force and that force is removed,, it does not return to its original state./ Permanent deformation

l Load: An external force acting on a body

   1. Classification of Loads by How They Act

      A. Axial load[=Normal load](Axal load=normal load): A load acting along the material's axis(in the normal)direction

         i. Tensile load(tensile load) : A load acting to pull a material along its axis

         ii. Compressive load(compressive load) : A load acting to compress a material along its axis

 

      B. Shear load(shear load): A load acting perpendicular to the material's axis

 

      C. Bending load(bending load): A load acting when, a material is bent

 

      D. Torsional load(torsional and twisting load): A load acting when, a material is twisted

 

    1. Classification of Loads by Duration of Application

 

        A. Static load:

            i. Its magnitude and direction do not change with time.

            ii. If magnitude and direction do change with time,, the changes are small enough to be neglected.

 

       B. Dynamic load: Its magnitude or direction changes with time..

            i. Repeated load: A load in which forces of different magnitudes act repeatedly and continuously.

            ii. Alternating load: A load whose magnitude and direction change with time, Vibration may produce superposition effects.

            iii. Impact load: A load that applies a large force through a momentary impact.

 

    2 Classification by Load Distribution

 

        A. Concentrated load: The load is concentrated at a particular location.

        B. Distributed load: A load distributed over a certain length or area

        C. Moving load: A load that acts while moving over a body

            i. EX) When a train passes,, the load acting on the railway is an example.