Exam_A_Summary_Flashcards_Brainscape
(29 cards)
What is the design stress typically taken as in design codes?
Design stress is taken as σ_d = 2/3σ_y (2/3 of yield stress) to prevent brittle fracture and ensure safety.
Why is relying on plastic deformation as a warning sign of failure risky?
Because brittle fracture can occur below the yield stress without plastic deformation.
What does the Charpy Impact Test evaluate?
Fracture toughness and whether a material operates above the Ductile-Brittle Transition Temperature (DBTT).
What are the design standards for Charpy impact energy in pipelines and nuclear reactors?
Oil & gas: ≥65 J at 40°C. Nuclear: operate at least 50% above DBTT (on upper shelf).
How does radiation affect the Charpy impact curve?
Shifts curve to the right: upper shelf energy decreases, DBTT increases.
What do S-N curves represent in fracture design?
They show the relationship between stress (S) and number of cycles to failure (N), used for fatigue analysis.
What is the role of stress concentration factors in fatigue design?
They shift the S-N curve downward to form the design curve.
What are the common fatigue life prediction methods considering mean stress?
Modified Goodman, Gerber, and Soderberg diagrams.
What is Miner’s Rule used for?
To calculate cumulative fatigue damage: D = Σ(n_i/N_i), failure expected when D ≥ 1.
What is the criterion to avoid fracture in fracture mechanics?
Ensure applied K (stress intensity) never exceeds fracture toughness K_IC.
What does the stress intensity factor K depend on?
Crack length, geometry, and applied stress.
State Paris’ Law for fatigue crack growth.
da/dN = A(ΔK)^m, where A and m are material constants, ΔK is the stress intensity range.
How is Paris’ Law used?
To predict number of cycles for a crack to grow to critical size; used for inspection intervals.
What is meant by anisotropy in fibre-reinforced composites?
Mechanical properties vary with direction due to fibre alignment.
How are fibre-reinforced composites tested?
In the direction aligned with fibres to maximize stiffness, strength, and toughness.
Name three types of fibre-reinforced composites and their typical applications.
Polymer matrix: transport/turbines; Metal matrix: aerospace; Ceramic matrix: high-temp environments.
Give example properties of Titanium MMC.
Tensile strength: 1600 MPa, E: 200 GPa, fatigue resistance: >10,000 cycles at 1300 MPa.
Give example properties of CMCs.
Fracture strength: ~250 MPa, flat stress-cycle curve (damage tolerant).
Derive the rule of mixtures for a unidirectional composite under longitudinal loading.
See notes
What is the rule of mixtures equation for longitudinal modulus?
E_c = E_f * V_f + E_m * V_m.
Derive the rule of mixtures for a unidirectional composite under transverse loading.
See notes
What is the rule of mixtures equation for transverse modulus?
1/E_c = V_f/E_f + V_m/E_m.
What is the impact of high fibre volume fractions under transverse loading?
Reduces transverse properties due to poor matrix flow and fibre contact.
Why is least distance of separation between fibres important?
Below a threshold, matrix can’t flow, leading to voids and weak bonding.
