Problem

If the specific surface energy for soda–lime glass is 0.30 J/m2, then, using data in Table...

If the specific surface energy for soda–lime glass is 0.30 J/m2, then, using data in Table 7.1, compute the critical stress required for the propagation of a surface crack of length 0.05 mm.

Table 7.1 Room-Temperature Elastic and Shear Moduli and Poisson’s Ratio for Various Materials

	Modulus of Elasticity		Shear Modulus
Material	GPa	106 psi	GPa	106 psi	Poisson’s Ratio
Metal Alloys
Tungsten	407	59	160	23.2	0.28
Steel	207	30	83	12.0	0.30
Nickel	207	30	76	11.0	0.31
Titanium	107	15.5	45	6.5	0.34
Copper	110	16	46	6.7	0.34
Brass	97	14	37	5.4	0.34
Aluminum	69	10	25	3.6	0.33
Magnesium	45	6.5	17	2.5	0.35
Ceramic Materials
Aluminum oxide (Al2O3)	393	57	—	—	0.22
Silicon carbide (SiC)	345	50	—	—	0.17
Silicon nitride (Si3N4)	304	44	—	—	0.30
Spinel (MgAl2O4)	260	38	—	—	—
Magnesium oxide (MgO)	225	33	—	—	0.18
Zirconia (ZrO2)a	205	30	—	—	0.31
Mullite (3Al2O3-2SiO2)	145	21	—	—	0.24
Glass–ceramic (Pyroceram)	120	17	—	—	0.25
Fused silica (SiO2)	73	11	—	—	0.17
Soda–lime glass	69	10	—	—	0.23
Polymersb
Phenol-formaldehyde	2.76–4.83	0.40–0.70	—	—	—
Poly(vinyl chloride) (PVC)	2.41–4.14	0.35–0.60	—	—	0.38
Poly(ethylene terephthalate) (PET)	2.76–4.14	0.40–0.60	—	—	0.33
Polystyrene (PS)	2.28–3.28	0.33–0.48	—	—	0.33
Poly(methyl methacrylate) (PMMA)	2.24–3.24	0.33–0.47	—	—	0.37–0.44
Polycarbonate (PC)	2.38	0.35	—	—	0.36
Nylon 6,6	1.59–3.79	0.23–0.55	—	—	0.39
Polypropylene (PP)	1.14–1.55	0.17–0.23	—	—	0.40
Polyethylene—high density (HDPE)	1.08	0.16	—	—	0.46
Polytetrafluoroethylene (PTFE)	0.40–0.55	0.058–0.080	—	—	0.46
Polyethylene—low density (LDPE)	0.17–0.28	0.025–0.041	—	—	0.33–0.40