Definitions and Long answer questions Flashcards

1
Q

Define stress

A

A function of applied load and area, units Pa

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2
Q

Define stress concentration factor

A

Dimensionless ratio of actual stress and theoretical calculated nominal stress

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3
Q

Define stress intensity factor

A

Related to conditions in a cracked component under load. Due to singularity, actual stress cannot be estimated. Uses far field stress and crack size. Units Pa.m^1/2

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4
Q

Define strength

A

A materials ability to withstand applied stress

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5
Q

Define fracture toughness (Kic)

A

A components ability to resist extension of a crack or withstand applied stress intensity K

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6
Q

What quantitative relationships does stress intensity factor give?

A

Crack length
Component and flaw geometry
Stress intensity factor
Applied stress

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7
Q

What is the Linear elastic fracture mechanics LEFM approach

A

All materials contain flaws
K,may be calculated fro a particular loading and crack configuration
Failure is predicted if K exceeds Kc
Mode 1 plane strain fracture toughness is an experimentally determined property

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8
Q

Strength vs fracture toughness

A

As strength increases fracture toughness decreases

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9
Q

Name some life limiting factors of materials

A
Material defects
Design
Fabrication methods
Operating conditions 
Fatigue failure from cyclic loading
Stress intensity factor
High strain rate impact
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10
Q

Mode 1 failure is?

A

Opening ( most common on practise)

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11
Q

Mode 2 failure is?

A

Sliding, materials with planes of weakness e.g. Laminates

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12
Q

Mode 3 failure is?

A

Tearing mode. E.g. Torsional loading

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13
Q

Why can’t inglis be used for cracks?

A

Cracks would have no volume so max stress would be infinite

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14
Q

How is thickness related to K?

A

For thin specimens K can’t be predicted as it cannot be determined from plane stress dominated tests

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15
Q

How can a Time vs Flaw Size graph be used?

A

Predict component life span, by using critical crack size cyclic loading to calculate the number of cycles it will take to grow a crack to critical length under normal operating conditions

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16
Q

What problem remains when Inglis can’t be used in a crack?

A

Unknown stress for a singularity problem that depends on far field stress and defect size (STRESS INTENSITY FACTOR)

17
Q

What does the cut off line on a FAD represent?

A

It is used to prevent plastic collapse and its at the Lr max value