Materials testing (Destructive)

Question 1

What is destructive testing?

Answer 1

Testing that intentionally loads a specimen to permanent damage or failure to measure properties like strength, toughness, and ductility.

Question 2

Give three reasons to use destructive tests in manufacturing.

Answer 2

To verify material properties against spec, to compare processes/heat treatments, and to investigate failures (root cause).

Question 3

Name four common destructive tests.

Answer 3

Tensile, compression, bend/flexural, and impact (Charpy/Izod).

Question 4

Is hardness testing destructive?

Answer 4

Usually minimally destructive—leaves a permanent indentation; considered acceptable for most components and test coupons.

Question 5

What is the tensile test used to find?

Answer 5

Yield strength/proof stress, ultimate tensile strength (UTS), Young’s modulus, % elongation, and % reduction of area.

Question 6

Define yield strength (simple).

Answer 6

Stress where permanent (plastic) deformation starts—beyond this, the specimen won’t spring back fully.

Question 7

Define ultimate tensile strength (UTS).

Answer 7

Maximum stress reached during a tensile test before necking and fracture.

Question 8

What is gauge length in a tensile test?

Answer 8

The original measured length of the specimen section used to calculate strain (% elongation).

Question 9

Two common tensile specimen shapes.

Answer 9

Dog‑bone flat specimens and round bar specimens with threaded ends or shoulders.

Question 10

Compression test—what does it measure?

Answer 10

Material behaviour under crushing: compressive strength, stiffness in compression, and buckling for slender samples.

Question 11

Why are brittle materials often tested in compression?

Answer 11

They are much stronger in compression than in tension and give more useful data without premature cracking.

Question 12

Bend/flexural test—what is measured?

Answer 12

Flexural strength/modulus; often 3‑point or 4‑point bending for plastics, wood, and ceramics.

Question 13

Difference between 3‑point and 4‑point bend tests.

Answer 13

3‑point loads at the centre (higher shear near the middle); 4‑point applies two loads, giving a constant moment region.

Question 14

Impact testing—name two methods.

Answer 14

Charpy and Izod pendulum impact tests using notched specimens.

Question 15

What does Charpy/Izod impact energy indicate?

Answer 15

Toughness/ability to absorb energy before fracturing, important for assessing brittle vs ductile behaviour.

Question 16

Why are impact specimens notched?

Answer 16

To concentrate stress and create a controlled crack starter so results are comparable.

Question 17

Hardness tests—name three types.

Answer 17

Vickers (HV), Rockwell (HR), and Brinell (HB).

Question 18

Hardness tests—what do they indicate?

Answer 18

Resistance to indentation (linked to wear resistance and approximate strength for some alloys).

Question 19

Shear test—what is measured?

Answer 19

Shear strength—the stress required to cause sliding failure along a plane (e.g., rivets, adhesives).

Question 20

Torsion test—what is measured?

Answer 20

Behaviour under twisting: shear modulus, torsional strength, and angle of twist to failure.

Question 21

Fatigue test—destructive or non‑destructive?

Answer 21

Destructive: the specimen is cycled until crack initiation and eventual failure to determine life at a given stress.

Question 22

Low‑cycle vs high‑cycle fatigue (simple).

Answer 22

Low‑cycle: high strain, few cycles to failure; High‑cycle: lower stress, many cycles (often >10^5).

Question 23

Creep rupture test—what is it?

Answer 23

Holds a specimen under constant load at elevated temperature until it fractures; records time to rupture.

Question 24

Fracture toughness test (simple).

Answer 24

Measures resistance to crack growth (e.g., K_IC) using a pre‑cracked specimen to assess flaw tolerance.

Question 25

Wear/abrasion test—what is measured?

Answer 25

Material loss under rubbing or abrasive contact (mass loss or volume loss per distance).

Question 26

What is proof load testing?

Answer 26

Loading a component to a specified level (below yield) to prove it meets strength requirements without permanent set.

Question 27

Give two common tensile test outputs recorded on a graph.

Answer 27

Stress–strain curve shape and key points such as yield, UTS, and fracture strain.

Question 28

Sample preparation—why is it important?

Answer 28

Specimen geometry, surface finish, and alignment affect results; standards ensure repeatability and fair comparisons.

Question 29

Two standard safety precautions during destructive tests.

Answer 29

Use guards/eye protection against flying fragments and keep clear of moving crossheads/pendulums.

Question 30

Post‑test inspection—what should you record?

Answer 30

Fracture location/type (brittle/ductile), dimensions after test, and any visible defects like necking or shear lips.

Question 31

Ductile vs brittle fracture—visual difference (simple).

Answer 31

Ductile shows necking and fibrous surfaces; brittle shows flat, granular or cleavage surfaces with little deformation.

Question 32

What is reduction of area?

Answer 32

% decrease in cross‑section at the fracture in a tensile test—indicator of ductility.

Question 33

Why test at different temperatures?

Answer 33

Properties like toughness can change—some metals become brittle at low temperatures (ductile–brittle transition).

Question 34

What is a stress–strain curve used for in class projects?

Answer 34

To pick materials that meet strength and ductility needs; estimate stiffness from the initial slope.

Question 35

Bend test for welds—what does it check?

Answer 35

Soundness and ductility of the weld and heat‑affected zone (cracks/opening indicate defects).

Question 36

Compression test on polymers—what failure might you see?

Answer 36

Barrelling (bulging) or buckling for slender specimens.

Question 37

Impact test classroom tip.

Answer 37

Always stand clear of the pendulum arc and secure the specimen firmly; check notch orientation is correct.

Question 38

Hardness test classroom tip.

Answer 38

Avoid testing near edges or previous indents; measure on a flat, clean surface for reliable readings.

Question 39

Link to TIMWOOD: how can destructive testing reduce waste overall?

Answer 39

By validating processes up‑front, it prevents large‑scale production Defects and rework later.

Question 40

Simple calc: A 12 mm diameter steel rod breaks at 9.4 kN in tension. Approx UTS?

Answer 40

Area = π(0.012²)/4 ≈ 1.13e−4 m²; UTS ≈ 9400 / 1.13e−4 ≈ 83 MPa (illustrative school‑level calc).

Question 41

Simple calc: Brinell hardness uses a 10 mm ball and leaves a 3.6 mm indent—what increases HB reading?

Answer 41

A smaller indent (under same load) increases HB—harder material = higher number.

Question 42

Simple calc: In Charpy, Specimen A absorbs 40 J, Specimen B 5 J. Which is tougher?

Answer 42

Specimen A (40 J) is tougher—absorbs more energy before fracture.

Question 43

Which test best compares heat treatments: annealed vs quenched steel?

Answer 43

Hardness and tensile tests—quenched/tempered steel shows higher hardness/strength but may lower ductility.

Question 44

When is proof load preferred over full destructive testing?

Answer 44

When you must verify strength on actual parts without destroying them (e.g., lifting eyes).