A Composite Is Made Of Glass Fibers 10 In Volume Fraction And Polymer Matrix 90 In Volume Fraction Illustrated Bel 1 (71.82 KiB) Viewed 35 times
A composite is made of glass fibers (10% in volume fraction) and polymer matrix (90% in volume fraction) illustrated below. The glass fibers are circular in cross-section, with the Young's modulus of Er = 80 GPa and fracture toughness of 15 MPam. At room temperature (i.e. 300 K), the polymer matrix exhibits a time-dependent Young's modulus given by Em = 30/(10 + 5 * 10-6.t) GPa, where t is the time in units of seconds. The glass transition temperature of the polymer matrix is Tg = 260 K. Glass Fibers Volume Fraction: 10% E;=80 GPa Contain surface flaws Polymer Matrix Volume Fraction: 90% E =30/(10+5 +10-6. t) GPa Glass transition temperature: 260 K Composite Tensile Loading Force = ? Total cross section area: 40 mm + u- It is known that the glass fibers contain random thumb-nail surface flaws with the depth of 1 um, and these flaws may grow due to stress corrosion cracking (SCC) when the stress intensity factor exceeds the threshold value of Ken=1.3 MPaym. Answer the following questions in next two pages:
(a) To make sure SCC does NOT take place during the designed service time of 1 week under room temperature, what is the maximum tensile loading force the composite can withstand? It is provided that the composite's total cross section area is 40 mm². (17 points)
(b) Now at a higher surrounding temperature of 310 K, and using the same tensile force obtained above in (a), what would be the new SCC-free service time? (8 points)
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