Load, Stress and Strain

Load, Stress and Strain

• 2.
  Definition of Strengthof Materials?? Strength of Materials also called mechanics of materials, is a subject which deals with behavior of solid objects subjected to stresses and strains. The Strength of Materials is subject, which refers to various methods for calculating the stresses and strains in structural members such as beams, columns and shafts. The methods employed to predict the response of structure under loading.
• 3.
  Definition of load& Its Types  Load is defined as the set of external forces acting on a mechanism or engineering structure which arise from service conditions in which the components work  Common loads in engineering applications are tension and compression. Tension:- Direct pull. Eg: Force present in lifting hoist Compression:- Direct push. Eg:- Force acting on the pillar of a building Sign convention followed: Tensile forces are positive and compressive negative
• 4.
  Types of Load Thereare a number of different ways in which load can be applied to a member. Typical loading types are: 1. Dead/ Static load- Non fluctuating forces generally caused by gravity. 2. Live load- Load due to dynamic effect. Load exerted by a bus on a bridge 3. Impact load or shock load- Due to sudden blows. 4. Fatigue or fluctuating or alternating loads: Magnitude and sign of the forces changing with time.
• 5.
  Definition of Stress Theforce of resistance per unit area, offered by a body against deformation is called stress. The external force acting on the body is called the load or force. The load is applied on the body while the stress is induced in the body. When the resistance offered by material against the deformation and applied are equal then loaded material is said to be in equilibrium condition.
• 6.
  When a materialis subjected to an external force, a resisting force is set up within the component, this internal resistance force per unit area is called stress. If P= 1000N and A= 10 m² Then Stress=??? A P Area Load Stress  
• 7.
  2. STRAIN When abody is subjected to some external force, there is some change of dimension of the body. The ratio of change of dimension of the body to its original dimension is known as strain. Strain is a dimensionless quantity.  Tensile strain- Ratio of increase in length to original length of the body when it is subjected to a pull force  Compressive strain- Ratio of decrease in length to original length of the body when it is subjected to a push force.  Volumetric strain- Ratio of change of volume of the body to the original volume.  Shear strain-Strain due to shear stress.
• 8.
  Types of Stress
• 9.
  TYPES OF DIRECTSTRESS  Normal stress (σ) is the stress which acts in direction perpendicular to the area. Normal stress is further classified into tensile stress 1. Tensile stress is the stress induced in a body, when it is subjected to two equal and opposite pulls (tensile forces) as a result of which there is a tendency in increase in length It acts normal to the area and pulls on the area
• 10.
  1. Tensile Stress P=R σ=P/A Tensilestress =Resisting force/ cross sectional Area = Applied force/ cross sectional area Tensile strain = Decrease in length/ Original length= dL/L
• 11.
  2. Compressive stress P=R σ=-P/A Compressivestress:- Stress induced in a body, when subjected to two equal and opposite pushes as a result of which there is a tendency of decrease in length of the body Compressive stress =Resisting force/ cross sectional Area = Applied force/ cross sectional area Compressive strain = Decrease in length/ Original length= - dL/L
• 12.
  3. Shear stress StressInduced in a body, when subjected to two equal and opposite forces which are acting tangentially across the resisting section as a result of which the body tends to shear off across that section.  Angle φ is called shear strain. As φ is very small,  φ=tanφ=DD1/AD=dl/h  Hence shear strain=dl/h