Papers by Keyword: Brittle Fracture

Abstract: This paper integrates a comprehensive overview of cylindrical shell simulations by means of finite element analysis, focusing on both ductile and brittle fracture behaviors under explosive loading. Special attention is given to high-carbon alloy steels that exhibit pronounced cleavage or quasi-brittle behavior and can produce smaller, higher-velocity fragments under certain conditions. We discuss key numerical approaches for fragmentation modeling and shrapnel kinetic energy calculations, and explore the relevant constitutive equations—particularly the Johnson-Cook law for high strain-rate plasticity and Linear Elastic Fracture Mechanics (LEFM) parameters for cleavage-type fracture. Emphasis is placed on microstructural factors (grain size, carbide distribution) that govern fracture and fragment mass distribution. We incorporate experimental findings on brittle fracture of steels under internal blast, highlighting how microcrack formation, alloy carbides, and high hardness can alter fragmentation and shell initial velocity.

Abstract: This paper gives a thorough investigation on the fracture failure of the blowout preventer (BOP) ram. Through appearance inspection, magnetic powder inspection, physicochemical inspection, metallographic inspection and scanning electron microscope (SEM), the main fracture reason of the BOP ram is that there was some original cracks in the BOP ram before fracture, during the service process the bop ram is subjected to impact load, therefore brittle fracture occurs due to the high brittleness of the gate material (which is caused by large internal structure) and low anti-crack propagation ability. Key words: Blowout preventer (BOP) ram; Fatigue break; Brittle fracture; Failure analysis

Abstract: Material used for screw production was investigated due to its inconvenient properties which caused the screw breaking on threads or in the head during the installation. Chemical composition of analyzed material corresponded with standard STN 17153 according to technological drawing for specific product. The metallographic analysis showed that failure of screws happened due to improper microstructure resulting from unsuitable thermal treatment of material. Fine inclusions based on aluminum nitride (AlN) and chromium carbonitride (Cr(C,N)) were segregated along the ferritic grain boundaries. Coarse aluminum nitride inclusions (AlN) in ferritic matrix affected the character of present fracture surface characterized by cleavage facettes. The fracture was propagated step by step following the planes with the increased concentration of inclusions across the whole cross-section of the screw.

Abstract: The paper deals with the impact toughness and fracture mode of the low-alloy 09G2S steel in the as-delivered state and in the condition after equal-channel angular pressing (ECAP) and annealing at impact bending in the temperature range of 293-203 [K]. The results on impact toughness KCV and fracture mode of Charpy test specimens made of the 09G2S steel in the as-delivered state and in the condition after hardening are presented. There is a decrease in the steel impact toughness in the examined temperature range after annealing at 673 [K], ECAP, and ECAP with annealing compared to the corresponding value for steel in the as-delivered state. For the 09G2S steel treated with various techniques, the temperature-KCV plot drop occurs smoothly, without abrupt changes, in the examined temperature range, in contrast to the behavior of this value with the upper threshold of the fracture appearance transition temperature for the steel in the as-delivered state.

Abstract: The paper presents the results of tests of metallic materials at low temperatures. It is shown that with the decreasing of temperature, the mechanical characteristics of materials change significantly: strength limits, yield strength increase, and relative elongation decrease. It is shown that the temperature of the brittle-viscous transition depends on the lattice parameter of the materials. The higher the lattice parameter is, the lower is the temperature of the brittle-viscous transition. It is shown that the lattice parameter can be used to estimate the temperature of the brittle-viscous transition

Abstract: This article presents the results of a study of martensitic steels. Studied steels: OZH9K14N6MZD, 12X18N10TL, 07X13G28ANFL. The object of the study was the optimization of properties for use in cryogenic technology. The purpose of the study is to increase the strength and service life of products for various purposes. The destruction of steel 12X18N10TL and 07X13G28ANFL was investigated. It has been established that 07X13G28ANFL steel is more preferable for cryogenic use and is recommended by the authors.

Abstract: Based on research of the low temperature fracture property of high grade steel pipe, it shows that X70, X80 steel pipe and X80 tee have high Charpy impact toughness. However, as the wall thickness increases, the shear area of DWTT decreases rapidly, and the thickness effect is significant. The research results show that the original wall thickness impact specimen fracture of steel pipe may not be ductile, for design temperature less than -30°C and wall thickness greater than 40mm. The brittle fracture was caused by structural factors. The Charpy impact energy, which just reflects the toughness of materials, does not show the fracture appearance as it would occur in service, because of the different specimen geometry and high rate of impact. The brittle fracture can occur at low temperature and low stress even with a high Charpy impact energy, the conditions of brittle fracture should be established under combination of the wall thickness, temperature and other factors. In this work, it is clarified that measurement of the fracture toughness under service temperature should be used to control low stress brittle fracture, besides the Charpy impact energy to ensure the material toughness.

Abstract: In order to find out the causes of weld cracks in the main steam pipe welded joint of a power plant, a series of relevant tests are specially formulated, which include room temperature tensile and high temperature tensile test, room temperature impact test, the crack tip metallographic observation, crack fracture scanning electron microscope observation, oxide film thickness measurement, and so on. By analyzing the metallographic photographs of the crack, the crack character is preliminarily determined. In addition, the direction of crack extension is determined by the thickness of oxide film in different parts. The crack failure mechanism has been identified. The results show that the welding heat crack occurs in 1# crack initiation position; and the crack initiation in 2# weld crack (primary crack) position is caused by the root defect of welding seam and lead to a high brittleness, which results in the crack failure by crack propagating in operational process gradually.

Abstract: Computational modelling of the crack growth in brittle and quasi-brittle materials used in mechanical, civil, etc. engineering applies the cohesive zone model with various traction separation laws; determination of micro-mechanical parameters comes then from static tests, microscopic observation and numerical calibration. Although most authors refer to ill-possedness and need of artificial regularization in inverse problems (identification of material parameters), some difficulties originate even in nonlinear formulations of direct and sensitivity problems. This paper demonstrates the possibility of proper analysis of the existence of a weak solution and of the convergence of a corresponding numerical algorithm for such model problem, avoiding non-physical assumptions.

Abstract: Beam welded joints made from fine grain steels show martensitic micro structure, high weld hardness and thus low toughness in the weld seams. At the same time there is a risk for these welds to have crack-like defects that cannot be detected during the production and which grow due to cyclic loading. If such structures are used in areas with low ambient temperatures, it may come to brittle failure of the component. To secure components against such failure, fracture mechanic tests were carried out on electron beam welded SE(B)-samples made from S690QL and S960QL and the J-integral was determined. In order to describe the scattering of the results in the temperature transition region the results were evaluated by means of the Master Curve concept in accordance with ASTM E 1921. Afterwards the reference temperature in the transition range, T₀, was determined and correlated with the T_27J- temperature of Charpy V-notch tests.