# SUMMARY : IMPORTANT CONCEPTS & QUESTIONS (1)

## SUMMARY : REVIEW OF VARIOUS CONCEPTS FROM TOPICS OF MACHINE DESIGN

SUMMARY MADE OF VARIOUS TOPICS OF MACHINE DESIGN FOR REVISION AS WELL AS INTERVIEW POINT OF VIEW.

### T.O.F. SUMMARY

ANS. THEORIES OF FAILURE came in play to find the effect of failure in mechanical components undergoing complex stresses; where exact cause of failure was difficult to find.

Q2. NAME THE FIVE THEORIES OF FAILURE (STATICS).

ANS. 1. MAXIMUM PRINCIPAL STRESS THEORY/MPST (RANKINE THEORY) 2.MAXIMUM PRINCIPAL STRAIN THEORY (MPSNT)/ST. VENANT THEORY 3. MAXIMUM SHEAR STRAIN THEORY(MSST)/ TRESCA AND GUEST THEORY 4.MAX. STRAIN ENERGY THEORY (MSET)/ (HAIGH AND BELTRAMI THEORY) 5. MAXIMUM SHEAR STRAIN ENERGY THEORY/(MSNET)/DISTORTION ENERGY THEORY/VON MISES – HENKY THEORY

Q3. WHAT IS STRESS CONCENTRATION?

ANS. Stress concentration is defined as the “localisation of high stresses in a machine element due to irregularities or abnormalities present in the element and abrupt cross section changes”.

Q4. MENTION CAUSES OF STRESS CONCENTRATION.

ANS. The Causes Of Stress Concentration are ; 1.VARIATION IN MATERIAL PROPERTIES 2. LOAD APPLICATION 3.ABRUPT CHANGES IN SECTION 4. MACHINING AND OTHER SCRATCHES

Q5. WHAT ARE THE WAYS TO REDUCE STRESS CONCENTRATION AS WELL AS ITS EFFECTS?

ANS. The ways to reduce stress concentration are as follows:

1.UNDERCUTTING
3.REDUCTION OF DIAMETER
4.MATERIAL REMOVAL

Q6. WHAT DO YOU MEAN BY FATIGUE FAILURE?

ANS. The materials undergoing fatigue loading used to fail at a particular value of stress. This stress magnitude is usually lower than the ultimate tensile strength of the material. Sometimes, it may be less than the yield strength of the material.

Moreover, as the no of stress cycles increases, the failure inducing stress magnitude decreases.

It usually shows the decreasing resistance OR ability of material to withstand stress(Strength).

This phenomenon of decreased resistance of the material to fluctuating stresses is termed as FATIGUE FAILURE.

Q7. WHAT DO YOU MEAN BY ENDURANCE LIMIT AS WELL AS FATIGUE LIFE?

ANS. ENDURANCE LIMIT defined as the maximum stress amplitude of a completely reversed stress that a standard specimen can sustain for an unlimited no of cycles without fatigue failure.

FATIGUE LIFE defined as the no of stress cycles that the standard specimen can complete during the test before the appearance of first fatigue crack.