USING HUGE PENDULUM IMPACT TESTER TO

Materials Science and Technology (MS&T) 2013 October 27-31,2013, Montreal, Quebec, Canada Copyright ©2013 MS&T'13® Measurement and Modeling of High Strain-rate Deformation

USING HUGE PENDULUM IMPACT TESTER TO EVALUATE THE DYNAMIC FRACTURE TOUGHNESS AND CRACK BEHAVIOR OF PIPELINE STEELS Jian F A N G I : Jianwei Z H A N G 、 X i n g H U A N G 〗 , Lei W A N G ^ 1 School of Materials Science and Metallurgy, Northeastern University, Shenyang 110819, China ^Baosteel Research Institute, Baoshan Iron & Steel Co., Ltd., Shanghai 201900, China ^Shenzhen W A N C E Testing Machine C o ” Ltd., Shenzhen 518055, China Keywords: Drop Weight Tear Test, instrumented impact testing, Crack Tip Opening Angle, pipeline steel

Abstract A 40kJ instrumented pendulum machine has been used to perform D W T T test for an A P I X 8 0 pipeline steel to acquire the force-displacement curve, which divides the total D W T T energy into crack initiation and propagation subdivisions. A parameter of crack propagation energy density is proposed to characterize the ductile fracture toughness, independent of thickness, notch shape. Moreover, K e y Curve method is employed to establish the relationship between crack extension and tup displacement, which provides a w a y to investigate the crack behavior and D W T T energy distribution from fracture surface. Then C T O A c , as a measure of material resistance to ductilefracture,could be reliably estimated by the accurate determination of crack propagation energy, exclusive of non-steady state stage and shear lips.

Introduction High strength and toughness pipeline steels are highly involved in the transmission industry of crude oil and natural gas from the North Pole zone to North America and other areas where the petroleum products are prosperously consumed [1]. Towards the service conditions and operation circumstances of these pipelines, heavy responsibility for an adequate fracture control plan should be placed on the structural integrate design. Relative to material performances, prevention of initiation and assurance of arrest should be addressed [2]. Concerning the crack initiation, parameters like J-integral, Crack tip opening displacement ( C T O D ) have been already standardized and well fulfilled, like A S T M El820 [3]. In the mean while, The use of Charpy upper-shelf-energy, i.e. U S E , to predict the crack arrest resistance of full-scale pipeline plate with approximate linear correlation was historically successful for the medium and lower toughness steels, but failed to the emerging high gade pipeline steels, e.g. X80-X100, with U S E more than 200J even at very low temperature [4]. In stead, as a

remarkable technical progress from Charpy, Drop Weight Tear Test, D W T T provides the alternative approach to estimate the material resistance to ductilefracture.Most significantly, the critical Crack Tip Opening Angle, C T O A c over the steady-state stage of crack propagation derived from D W T T has been also ascertained as a measure of crack arrest capacity, conveniently and economically conducted in a mill test. Whereas h o w to recognize such a stable crack extension period is still a technical difficulty. In the present study, K e y Curve method [5] has been employed to correlate the dynamic crack extension to the obtained force-displacement relation from an instrumented D W T T test. The stable crack growth range thereafter has been directly measured on thefracturesurface of the D W T T specimen, helpful to the accurate definition of crack propagation energy as an input for the estimation of C T O A c , exclusive of the non-steady state stage not only existing shortly after the peak loading point, but due to the formation of shear lips as well.

Principles Ductile fracture model by Martinelli —Venzi A s above, the pressed V notch type D W T T specimen has been considered as the best available method for a mill test to evaluate the ductilefracturerecently. According to the ductilefracturemodel proposed by Martinelli and Venzi [6], the correlation between C T O A c and D W T T energy absorbed merely to the crack propagation, Ep, could be described as Eq. (1).

CT0Ar=2twr

A