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 are macroscopic progression marks on fatigue fracture or stress- corrosion cracking surface that indicate successive positions of the advancing crack front. They take the form of crescent-shaped macroscopic marks on fatigue fractures representing positions of the crack propagation, radiating outward from one or more origins.

2. Chevron Pattern: It is a common fracture feature produced by separate crack fronts propagating at different levels in the materials. A radiating pattern of surface markings or ridges, fans away from the origin of the crack. This pattern is visible with naked eyes.

3. Creep: creep is phenomenological term, which is responsible for plastic deformation. In some sense creep and super plasticity are releated phenomena: in a creep we think of damage accumulation leading to failure of sample. Creep is permanent deformation (plastic deformation) of a material under constant load (or constant stress) as a function of time. (Usually at ‘high temperatures’ ? lead creeps at RT).

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

5. Factor of safety: It is used to provide a design a margin over the theoretical design capacity to allow for uncertainty in the design process .Factor of safety is recommended by the conditions over which the designer has no control , that is to account for the uncertainties in the design process.

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

7. Fatigue Strength: It is the value of stress amplitude for which failure occurs after a particular no of N cycles. Fatigue strength varies with the no of cycles required for failure. 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 requisite contact forces.

8. Fracture mechanics: it is a relatively new section of materials study under mechanical loading conditions. Using fracture mechanics concept it possible to determine whether a crack of given length in a material with known toughness is dangerous at a given stress level. This mechanics section can also provides guide lines for selection of materials and design against fracture failures.

9. Fracture Toughness: Is an indication of the amount of stress required to propagate a pre-existing flaw. It is a very important material property since the occurrence of flaws is not completely avoidable in the processing fabrication, or service of a material.

12. S-N Curve: it is a plot of the magnitude of an alternating stress versus the number of cycles to failure for a given material. Typically both the stress and number of cycles are displayed on logarithmic scales. Given a load time history and a SN Curve , one can use miner’s rue to determine the accumulated damage or fatigue life of a mechanical Part