Ductile unstable failure test has been made on the high strength control-rolled steel over a wide temperature range. The effects of separation, compliance of the loading system and also temperature on the ductile unstable failure features have been investigated in detail by using compact specimens. The test results were mainly analysed with respect to material and applied tearing moduli. The main conclusions are as follows.
(1) Stable-unstable behavior is in good agreement with theoretical prediction except that material tearing modulus at instability is larger than 300.
(2) Even at the low temperature range where separation is notable, the specimen showed high resistance to tearing instability.
(3) Separation which initiated before the maximum load point, did not induce brittle fracture and also tearing instability. On the contrary, it prevents the initiation of brittle fracture by decreasing the plastic constraint.
