Advanced Material Selection in Composites Assignment

Assignment Task

Question

1. A car bumper must absorb a given amount of energy before fracture.

a) Create a fracture toughness–modulus (K1C vs. E) bubble chart (Level 2) to find appropriate materials for car bumper that have a fracture toughness K1C greater than 50 MPa.m1/2, unit price is no more than $3/kg and a toughness G = K2 1C/E greater than 10 kJ/m2.

b) List the top 3 materials ranked by G.

2. A snap-on bottle top must carry on a considerably large amount of deflection without fracture.

a) Create a fracture toughness–modulus (K1C vs. E) bubble chart (Level 2) to identify appropriate polymers for such a snap-on bottle top that have a fracture toughness K1C greater than 1 MPa.m1/2 and a material index K1C/E greater than 3×10-3 m1/2. Make a list of material(s) ranked by K1C/E.

b) If the critical deflection, δ, is defined as 3% of the bottle diameter, D, calculate the maximum crack length, a, which can be allowed on the surface of the bottle top for the candidate(s) identified in (a).

3. A scaffolding made of low carbon steel (wrought, AISI 1020, normalized) weighs 100 kg. It is to be substituted for mass saving purposes. The candidate materials in stock are

• Magnesium alloy: AZ91D, cast;
• Titanium alpha-beta alloy: Ti-6Al-4V, annealed
• High-density wood: Oak (Quercus spp.), Longitudinal

'If the steel scaffolding has a solid square cross-section, how much mass can be saved if it is replaced by these three materials with the same shape

(a) at the constant bending stiffness; 

(b) at the constant bending moment If the steel scaffolding has already been shaped with the best structural efficiency, how much mass can be saved if it is replaced by these three materials with their best structural efficiency

(c) at the constant bending stiffness

(d) at the constant bending moment

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