MODERN MECHANICAL ENGINEERING

IMPACT TEST:  -   In  a  impact  test a  specially prepared notched specimen  is fractured  by a  single  blow from a heavy hammer and energy required being a measure of resistance to  impact.  Impact  load is produced  by a  swinging  of an impact weight W (hammer) from a  height h. Release of the weight from the height h swings the weight through the arc of a circle, which strikes the specimen to fracture at the notch (fig..  Kinetic energy of the hammer at the time of impact is mv 2 /2, which is equal to the  relative  potential energy of  the  hammer before  its release. (mgh),where m is the  mass of  the  hammer  and v = 2gh  is its tangential velocity at  i...

 A special case of law of conservation of energy with particular reference to heat and work. • Definition: Heat and work are interconvertible. • When a system undergoes a thermodynamic cycle then the net heat supplied to the system from surroundings is equal to the net work done by the system on its surroundings. First law for a process When a system executes a process the change in stored energy of the system is numerically equal to the net heat interactions minus the net work interactions during the process.  dE =δQ-δW So there exists a property of a closed system such that a change in its value is equal to the difference between heat supplied and the work done during the change of state. The property, E is called energy of the system. The energy resides within the system and it increases or decreases with change of state. Further , δQ = dE + δW . First law for an isolated System The energy of an isolated system is always constant. An isolated system is one in which there is...

  Elasticity :   This is the property of a material to regain its original shape after deformation when the external forces are removed. When the material is in elastic region the strain disappears completely after removal of the load, The stress-strain relationship in elastic region need not be linear and can be non-linear (example rubber). The maximum stress value below which the strain is fully recoverable is called the elastic limit. It is represented by point A in figure. All materials are elastic to some extent but the degree varies, for example, both mild steel and rubber are elastic materials but steel is more elastic than rubber.  Plasticity:  When the stress in the material exceeds the elastic limit, the material enters into plastic phase where the strain can no longer be completely removed. Under plastic conditions materials ideally deform without any increase in stress. A typical stress strain diagram for an elastic-perfectly plastic material is show...

BRINELL  HARDNESS TEST:  - Hardness of  a  material is generally defined as Resistance  to the  permanent  indentation under static and  dynamic load.  When a material is required to  use  under direct static or dynamic loads, only indentation hardness test will be useful to find out resistance to indentation.  In Brinell hardness test, a steel ball of diameter (D) is forced under a load (F) on to  a surface of test specimen. Mean diameter (d) of indentation is measured after the  removal of the load (F).  Title:   Brinell hardness test.   Aim:   To determine the hardness of the given specimen using Brinell hardness test. Specimen and specimen Brinell h...

What is  Rockwell Hardness test and how to perform in the lab? Rockwell test is developed by the Wilson instrument co U.S.A in 1920. This test is an indentation test used for smaller specimens and harder materials.  The test is subject of IS: 1586.In this test indenter is forced into the surface of a  test piece in  two  operations, measuring the permanent  increase  in depth  of  an  indentation from the depth increased from the depth reached under a datum load  due to an additional load.  Measurement of indentation is made after removing the additional load. Indenter  used is the cone having an angle of 120 degrees made of black diamond. LAB WORK - Title   Rockwell Hardness test  ...