Question

Discuss the meaning/importance in 2-3 sentences per term (directly copying verbatim answers from thesaurus will carry NO points)

(1) Beach or clamshell marks; (2) Chevron pattern; (3) Creep; (4) Endurance limit; (5) Factor of safety; (6) Fatigue life; (7) Fatigue strength; (8) Fracture mechanics; (9) Fracture toughness; (10) Griffith law; (11) Notch sensitivity; (12) S-N curve; (13) Shot peening; (14) Toughness; (15) Weibull distribution; (16) Weibull modulus.

make sure to type it not hand written.

Answer 1

1. Beach or clamshell marks: Beach marks aremacroscopic progression marks on fatigue fracture or stress-corrosion cracking surface that indicate successive positions ofthe advancing crack front. They take the form of crescent-shapedmacroscopic marks on fatigue fractures representing positions ofthe crack propagation, radiating outward from one or more origins.

2. Chevron Pattern: It is a common fracturefeature produced by separate crack fronts propagating at differentlevels in the materials. A radiating pattern of surface markings orridges, fans away from the origin of the crack. This pattern isvisible with naked eyes.

3. Creep: creep is phenomenological term, whichis responsible for plastic deformation. In some sense creep andsuper plasticity are releated phenomena: in a creep we think ofdamage accumulation leading to failure of sample. Creep ispermanent deformation (plastic deformation) of a material underconstant load (or constant stress) as a function of time. (Usuallyat ‘high temperatures’ ? lead creeps at RT).

4. Endurance limit: whenever a cyclic load isapplied on the material. If the material shows no evidence offracture then this property of the material is called EnduranceLimit. While if the material shows any evidence of fracture duringthe loading this property is called Fatigue limit.

5. Factor of safety: It is used toprovide a design a margin over the theoretical design capacity toallow for uncertainty in the design process .Factor of safety isrecommended by the conditions over which the designer has nocontrol , that is to account for the uncertainties in the designprocess.

6. Fatigue Life: It is the no of cycles ofloading that member sustains before failure. Fatigue Life for samemember varies for stresses of different magnitude and nature andeven for different failures.

7. Fatigue Strength: It is the value of stressamplitude for which failure occurs after a particular no of Ncycles. Fatigue strength varies with the no of cycles required forfailure. It is affected by environmental factors such as corrosion.It is important to the design of parts with high deflection cycles,as yield strength is to the designer who must obtain requisitecontact forces.

8. Fracture mechanics: it is a relatively newsection of materials study under mechanical loading conditions.Using fracture mechanics concept it possible to determine whether acrack of given length in a material with known toughness isdangerous at a given stress level. This mechanics section can alsoprovides guide lines for selection of materials and design againstfracture failures.

9. Fracture Toughness: Is an indication of theamount of stress required to propagate a pre-existing flaw. It is avery important material property since the occurrence of flaws isnot completely avoidable in the processing fabrication, or serviceof a material.

12. S-N Curve: it is a plot of the magnitude ofan alternating stress versus the number of cycles to failure for agiven material. Typically both the stress and number of cycles aredisplayed on logarithmic scales. Given a load time history and a SNCurve , one can use miner’s rue to determine the accumulated damageor fatigue life of a mechanical Part