The document discusses various material failure mechanisms including necking, fatigue, yield point, roughness, bulking, wear, and tear. It defines necking as plastic flow that decreases the cross-sectional area when a material is loaded to its yield point. Fatigue is defined as weakening caused by repeated loads that can cause damage at stress levels below ultimate tensile strength. Yield point marks the transition from elastic to plastic behavior.

1. - By Paarth Gupta

2.  WHEN A MATERIAL IS BEING LOADED TO ITS YIELD POINT, THE
SPECIMEN BEGINS TO "NECK“ (i.e THE CROSS SECTIONAL AREA
OF THE MATERIAL START DECREASING) DUE TO PLASTIC FLOW.
THEREFORE NECKING CAN BE DEFINED AS THE MODE OF DUCTILE
FLOW OF MATERIAL IN TENSION.
 NECKING USUALLY OCCURS WHERE THE SURFACE
IMPERFECTIONS ARE PREDOMINANT.
 NECKING BEGINS AT THE TENSILE POINT, OR ULTIMATE STRESS
POINT.

5.  FATIGUE IS THE WEAKENING OF A MATERIAL CAUSED BY
REPEATEDLY APPLIED LOADS. IT IS THE PROGRESSIVE AND
LOCALIZED STRUCTURAL DAMAGE THAT OCCURS WHEN A
MATERIAL IS SUBJECTED TO CYCLIC LOADING. THE NOMINAL
MAXIMUM STRESS VALUES THAT CAUSE SUCH DAMAGE MAY
BE MUCH LESS THAN THE STRENGTH OF THE MATERIAL
TYPICALLY QUOTED AS THE ULTIMATE TENSILE STRENGTH
LIMIT, OR THE YIELD STRENGTH LIMIT.
 FATIGUE OCCURS WHEN A MATERIAL IS SUBJECTED TO
REPEATED LOADING AND UNLOADING.

7.  DUCTILE METALS DO NOT HAVE A WELL DEFINED YIELD
POINT. THE YIELD STRENGTH IS TYPICALLY DEFINED BY THE
"0.2% OFFSET STRAIN". THE YIELD STRENGTH AT 0.2% OFFSET
IS DETERMINED BY FINDING THE INTERSECTION OF THE
STRESS-STRAIN CURVE WITH A LINE PARALLEL TO THE
INITIAL SLOPE OF THE CURVE AND WHICH INTERCEPTS THE
ABSCISSA AT 0.2%.
 ON A STRESS STRAIN CURVE THE ONSET OF PLASTIC
DEFORMATION IS DIFFICULT TO MEASURE ACCURATELY.

8. 0.2 OFFSET

10.  YIELD POINT REFERS TO AN INDICATION OF MAXIMUM
STRESS THAT CAN BE DEVELOPED IN A MATERIAL WITHOUT
CAUSING PLASTIC DEFORMATION.
 THE YIELD POINT, ALTERNATIVELY CALLED THE ELASTIC LIMIT,
MARKS THE END OF ELASTIC BEHAVIOUR AND THE
BEGINNING OF PLASTIC BEHAVIOUR. WHEN STRESSES LESS
THAN THE YIELD POINT ARE REMOVED, THE MATERIAL
RETURNS TO ITS ORIGINAL SHAPE.

12.  THE ROUGHNESS OF AN SURFACE IS A SURFACE DEVIATION. DEPENDING
ON WHICH OF THE FOUR ROUGHNESS CLASSES A SURFACE BELONGS TO, IT
HAS GROOVES, SCORE MARKS, BUMPS AND SCALE OR IRREGULARITIES IN
THE STRUCTURAL COMPOSITION OR LATTICE STRUCTURE.
ROUGHNESS CAN BE CAUSED BY:
 GROOVES RESULTING FROM THE TOOL'S BLADE, FEED MOTION AND Z-AXIS
AND Y-AXIS FEED
 IRREGULARITIES IN THE LATTICE STRUCTURE

14.  BULKING IS A PHENOMENON THAT OCCURS IN DRY SAND
VOLUME AFTER ABSORPTION OF MOISTURE. THE SAND
VOLUME INCREASES DUE TO THE WATER BUBBLES FORMED
DUE TO WATER PUSHING THE AIR VOIDS PRESENT BETWEEN
THE SOIL GRAINS. THIS WILL RESULT IN 25 % INCREASE IN
VOLUME DEPENDING UPON THE SIZE OF SAND.

16.  A FAILURE IS A BREAKDOWN OF AN OBJECT [SUCH AS METAL,
CONCRETE OR PLASTIC) DUE TO VARIOUS FACTORS THAT AFFECT
THE STRENGTH, STABILITY AND CHEMICAL COMPOSITION OF THE
OBJECT'S STRUCTURE.
 MATERIAL FAILURE IS THE LOSS OF LOAD CARRYING CAPACITY
OF A MATERIAL UNIT. THIS DEFINITION INTRODUCES TO THE
FACT THAT MATERIAL FAILURE CAN BE EXAMINED IN DIFFERENT
SCALES, FROM MICROSCOPIC, TO MACROSCOPIC.

17. FATIGUE FAILURE OF CRANKSHAFTS

18. WEAR IS THE PROGRESSIVE LOSS OF MATERIALS FROM
CONTACTING SURFACES RELATIVE IN MOTION.
ALONG WITH FATIGUE AND CORROSION, WEAR HAS BEEN
KNOWN AS ONE OF THE THREE MAJOR FACTORS LIMITING THE
LIFE AND PERFORMANCE OF AN ENGINEERING COMPONENT AND
AN ENGINEERING SYSTEM, WHETHER THE SYSTEM IS AS BIG AS A
HEAVY MACHINE, OR AS SMALL AS A TINY ELECTRONIC DEVICE.
ALL WEAR PROCESS INVOLVE ONE OR A COMBINATION OF WEAR
MECHANISMS
INCLUDING ABRASION, ADHESION, FATIGUE AND OXIDATION

19. STEEL SURFACE WORN BY ABRASION

20.  TEAR IS DAMAGE THAT NATURALLY AND INEVITABLY
OCCURS AS A RESULT OF NORMAL WEAR OR AGING. IT IS
USED IN A LEGAL CONTEXT FOR SUCH AREAS AS WARRANTY
CONTRACTS FROM MANUFACTURERS, WHICH USUALLY
STIPULATE THAT DAMAGE FROM WEAR AND TEAR WILL NOT
BE COVERED.
 TEAR IS A FORM OF DEPRECIATION WHICH IS ASSUMED TO
OCCUR EVEN WHEN AN ITEM IS USED COMPETENTLY AND
WITH CARE AND PROPER MAINTENANCE.

21.  FOR EXAMPLE, REPEATED IMPACTS MAY CAUSE STRESS TO
A HAMMER'S HEAD. THIS STRESS IS IMPOSSIBLE TO PREVENT
IN THE NORMAL USE OF THE TOOL FOR ITS DESIGNED TASK,
AND ANY ATTEMPT TO AVERT IT IMPEDES ITS
FUNCTIONALITY. AT THE SAME TIME, IT IS EXPECTED THAT THE
NORMAL USE OF A HAMMER WILL NOT BREAK IT
BEYOND REPAIR DURING A REASONABLE LIFE CYCLE.

22. WEAR AND TEAR ON EQUIPMENT AT SEA