ETC Materials Testing & Quality Assurance 3 — Questions and Answers
Question 1: What does a control chart's Upper Control Limit (UCL) represent in a manufacturing process?
- The maximum allowable engineering specification
- Three standard deviations above the process mean (Correct answer)
- The target dimension on a drawing
- The highest value ever recorded in production
Correct answer: Three standard deviations above the process mean
The UCL is set at three standard deviations (3σ) above the process mean, indicating the upper boundary of normal process variation.
Question 2: A sample of concrete is tested at 28 days and fails to meet the specified compressive strength. Which standard governs acceptance criteria for concrete cylinder tests in the US?
- ASTM C31 / ACI 318 (Correct answer)
- AASHTO T 22 / ASTM E8
- AWS D1.1 / ASME IX
- ASTM E399 / ASTM B117
Correct answer: ASTM C31 / ACI 318
ASTM C31 covers making and curing concrete test cylinders, and ACI 318 specifies the acceptance criteria based on 28-day compressive strength averages.
Question 3: In radiographic testing (RT), what does a higher film density number indicate?
- The film received less radiation exposure
- The film is darker, indicating more radiation exposure (Correct answer)
- A larger defect was detected in the weld
- The source-to-film distance was too short
Correct answer: The film is darker, indicating more radiation exposure
Film density is a logarithmic measure of film blackening; higher density means the film is darker due to greater radiation exposure.
Question 4: What is the significance of a material's fracture toughness (KIC)?
- It measures resistance to surface scratching
- It quantifies a material's ability to resist crack propagation (Correct answer)
- It determines the maximum operating temperature
- It defines the endurance limit under cyclic loads
Correct answer: It quantifies a material's ability to resist crack propagation
Fracture toughness KIC is the critical stress intensity factor at which a pre-existing crack will propagate, used to predict catastrophic failure.
Question 5: When performing a liquid penetrant test (PT), what is the purpose of the developer step?
- To clean the surface before applying penetrant
- To draw entrapped penetrant out of discontinuities for visibility (Correct answer)
- To magnetize the part for better penetrant adhesion
- To harden the penetrant so it can be scraped off
Correct answer: To draw entrapped penetrant out of discontinuities for visibility
The developer acts as a blotter, drawing penetrant back out of surface-breaking discontinuities and spreading it to create a visible indication.
Question 6: A technician is using magnetic particle testing (MT) on a ferromagnetic part. Longitudinal magnetization is best used to detect which type of discontinuity orientation?
- Discontinuities parallel to the longitudinal axis
- Discontinuities transverse (perpendicular) to the longitudinal axis (Correct answer)
- Subsurface voids at any orientation
- Discontinuities at 45° to the surface
Correct answer: Discontinuities transverse (perpendicular) to the longitudinal axis
Magnetic flux lines run along the longitudinal axis; discontinuities perpendicular to the flux lines cause maximum flux leakage and are most detectable.
Question 7: In a six-sigma quality program, what defect rate (in parts per million) corresponds to six-sigma performance?
- 66,807 ppm
- 6,210 ppm
- 3.4 ppm (Correct answer)
- 0.34 ppm
Correct answer: 3.4 ppm
Six-sigma quality corresponds to no more than 3.4 defects per million opportunities (accounting for a 1.5-sigma process shift).
ETC Materials Testing & Quality Assurance 3
What does a control chart's Upper Control Limit (UCL) represent in a manufacturing process?