Paper Topic:

Discuss stress and strain on building materials. Include in your discussion compressive and tensile strengths of materials.

Stress and Strain 1

Several mechanical properties of materials that are important in design are ascertained by applying tension , compression or shear load on the material . Of the three , the most common mechanical stress-strain tests are performed in tension (Callister , 1997 . When performing tensile tests , the load and elongation are measured in relation to the cross-sectional area or original length of the material (before the elongation . These geometric factors are normalized to the respective parameters of engineering stress and engineering strain where l is the instantaneous length of the specimen (Schaffer

, et . al 1999 . For some materials , especially for most metals , subjected to low levels of tensile load , stress and strain are linearly related . The linear relationship is referred to as Hooke 's law . As the stress is increased however , Hooke 's law ceases to be applicable as the linear relationship between stress and strain results to a curve . At this instant plastic deformation occurs , which means that the deformation becomes permanent and nonrecoverable (Callister , 1997 . When stress is increased further , it will reach a maximum before resulting to fracture (the separation of the material into two or more pieces . The maximum stress on the stress-strain curve is referred to as tensile strength and is the maximum stress that can be sustained by a material in tension When this stress is maintained , fracture will result

Compression tests are also done in almost the same manner as the tensile test except of course the force applied is compressive instead of tensile (Callister , 1997 . Compressive stress and strain are computed using the same formula presented above . By convention compressive force is taken to be negative which results to a negative stress . In compression

Stress and Strain 2

since lo will be greater than l , the strain will likewise be negative And just like tensile strength , compressive strength is the maximum compressive stress applied to a material which when sustained results to the material being crushed

Stress and Strain 3

References

Callister , W . Jr (1997 . Materials science and engineering : An introduction . Canada : John Wiley Sons , Inc

Schaffer , J , Saxena , A , Antolovich , S , Sanders , T . Jr Warner , S (1999 . The science and design of engineering materials . New York McGraw-Hill Companies , Inc...

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