An NDE test method can detect through cracks of lengths greater than 2-mm. A given component consists of a strip of width 30 mm and thickness 4-mm and is subjected to an alternating load in service of 20±10kN. The material has a fracture toughness ICK= 30 MPam. Laboratory experiments suggest that under these conditions fatigue cracks grow exponentially according to the equation a = a0 exp(λt), where t is the length of time in service in seconds, a0 is the original crack half-length at t = 0 and λ = 10−8 s−1. Determine the minimum inspection frequency of NDE testing (that is, after how many seconds of service) if brittle failure during the intervening period is to be avoided