Correct Option: D

Shear strain , τ =	cosα
	sinφ.cos( φ - α )

where, α = 0 = rake angle , φ = shear angle

∴ τ =	1
	sinθcosθ

∴ T = sinφcosφ

	dt	= cos ²φ - sin ²φ
	dφ

or φ = 45°

∴ τmin =	1
	{ sin (π /4).cos(π /4) }

∴ τmin =	1	= 2
	{ sin (1 /√2) × (1 /√2) }