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Browsing Materials Research Group by Author "Atrens, A."
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Item Metadata only Analysis of a rock bolt failed in service(Curran Associates, 2002) Gamboa, E.; Atrens, A.; International Corrosion Congress (15th : 2002 : Granada, Spain)This paper describes a fractographic investigation of a rock bolt failed in service in a NSW colliery and relates the failure to service conditions. Optical microscopy revealed that the fracture surface contained a dark thumbnail shaped area 1.9 mm deep. The rest of the fracture surface was quite shiny. There was no necking or other evidence of plasticity. This fracture appearance is consistent with stress corrosion cracking (SCC) followed by fast brittle fracture. There were secondary cracks also indicative of SCC. SEM observation characterized the SCC surface. This failure analysis has indicated that rock bolts can fail in service in a brittle manner with no prior warning at stresses much lower than their ultimate tensile strength. This represents a new failure mode for a critical mine component, that is critical for mine safety. There is no prior experience with this failure mode, and laboratory work is needed to understand the failure mechanisms. With understanding of the failure mechanism, it will be possible to devise counter-measures.Item Metadata only Environmental influence on the stress corrosion cracking of rock bolts(Pergamon-Elsevier Science Ltd, 2003) Gamboa, E.; Atrens, A.In order to understand rock bolt Stress Corrosion Cracking (SCC), a series of experiments have been performed in Linearly Increasing Stress Test (LIST) apparatus. One series of experiments determined the threshold stress of various bolt metallurgies (900 MPa for Steel A, and 800 MPa for Steel B and C). The high values of threshold stress suggest that SCC begins in rock bolts when they are sheared by moving rock strata. Typical crack velocity values have been measured to be 2.5 × 10-8 m s-1, indicating that there is not much benefit for rock bolt steel of higher fracture toughness. Another series of experiments were performed to understand the environmental conditions causing SCC of steel A and galvanised Steel A rock bolt steel. SCC only occurred for environmental conditions for which produce hydrogen on the sample surface, leading to hydrogen embrittlement and SCC. Fracture surfaces of LIST samples failed by SCC were found to display the same fracture regions as fracture surfaces of rock bolts failed in service by SCC: Tearing Topography Surface (TTS), Corrugated Irregular Surface (CIS), quasi Micro Void Coalescence (qMVC) and Fast Fracture Surface (FFS). Water chemistry analysis were carried out on samples collected from various Australian mines in order to compare laboratory electrolyte conditions to those found in underground mines. © 2003 Elsevier Ltd. All rights reserved.Item Metadata only Fractography of SCC features for rock bolts(2003) Gamboa, E.; Atrens, A.; International Conference on Environmental Degradation of Engineering Materials (2nd : 2003 : Bordeaux, France)Item Metadata only Material influence on the stress corrosion cracking of rock bolts(Pergamon-Elsevier Science Ltd, 2005) Gamboa, E.; Atrens, A.Rock bolt stress corrosion cracking (SCC) has been investigated using the linearly increasing stress test (LIST). One series of experiments determined the threshold stress of various bolt metallurgies (900 MPa for 1355AXRC, and 800 MPa for MAC and MA840B steels). The high values of threshold stress suggest that SCC begins in rock bolts when they are sheared by moving rock strata. SCC only occurred for environmental conditions which produce hydrogen on the sample surface, leading to hydrogen embrittlement and SCC. Different threshold potentials were determined for a range of metallurgies. Cold work was shown to increase the resistance of the steel to SCC. Rock bolt rib geometry does not have a direct impact on the SCC resistance properties of the bolt, although the process by which the ribs are produced can introduce tensile stresses into the bolt which lower its resistance to SCC. © 2004 Elsevier Ltd. All rights reserved.Item Metadata only Metallurgical aspects of rock bolt environment fracture(International Conference on Fracture, 2005) Gamboa, E.; Villalba, E.; Atrens, A.; International Conference on Fracture (11th : 2005 : Turin, Italy)The aim of this research was to understand the Stress Corrosion Cracking (SCC) of rock bolts. The laboratory tests have produced fracture surfaces similar to those from service. The experimental study elucidated the environmental condition leading to rock bolt SCC, and was used to determine the threshold stress and the threshold potential. A hydrogen embrittlement mechanism is proposed.Item Metadata only Relationship of laboratory tests of rock bolt SCC to service failures of rock bolts(TMS, 2003) Gamboa, E.; Atrens, A.; International Conference on Hydrogen Effects on Material Behavior and Corrosion Deformation Interactions (2002 : Moran, Wyo.); Moody, N.The stress corrosion cracking of rock bolts has been explored using Linearly Increasing Stress Tests (LIST). In LIST testing, a sample is exposed to the environment of interest and the stress is slowly increased until failure. SEM examination of the fracture surfaces is used to help identify the fracture mechanism. Rock bolt steel subjected to LIST testing in air and distilled water showed ductile failure and a dimple rupture failure surface. In contrast, rock bolt steel subjected to LIST testing in dilute sulphate/chloride solutions showed subcritical crack growth followed by brittle fracture. Analyses of rock bolts, which have failed in service, have indicated similar failures. The LIST test in the sulphate pH 2.1 provides a good foundation for a test to mimic service SCC, to be used to study the influences of rock bolt metallurgy and to explore countermeasures to service SCC. The transgranular nature of the SCC fracture, and the fact that SCC occurs at room temperature in the sulphate pH 2.1 solution point to the likelihood that the SCC mechanism probably involves hydrogen. Current work is (1) exploring the details of the fracture mechanism, (2) carrying out a detailed fractographic comparison between the service failures and the sulphate pH 2.1 fractures, and (3) exploring the issue of environment specificity.Item Metadata only Stress corrosion cracking fracture mechanisms in rock bolts(Kluwer Academic Publ, 2003) Gamboa, E.; Atrens, A.Rock bolts have failed by Stress Corrosion Cracking (SCC). This paper presents a detailed examination of the fracture surfaces in an attempt to understand the SCC fracture mechanism. The SCC fracture surfaces, studied using Scanning Electron Microscopy (SEM), contained the following different surfaces: Tearing Topography Surface (TTS), Corrugated Irregular Surface (CIS) and Micro Void Coalescence (MVC). TTS was characterised by a ridge pattern independent of the pearlite microstructure, but having a spacing only slightly coarser than the pearlite spacing. CIS was characterised as porous irregular corrugated surfaces joined by rough slopes. MVC found in the studied rock bolts was different to that in samples failed in a pure ductile manner. The MVC observed in rock bolts was more flat and regular than the pure MVC, being attributed to hydrogen embrittling the ductile material near the crack tip. The interface between the different fracture surfaces revealed no evidence of a third mechanism involved in the transition between fracture mechanisms. The microstructure had no effect on the diffusion of hydrogen nor on the fracture mechanisms. The following SCC mechanism is consistent with the fracture surfaces. Hydrogen diffused into the material, reaching a critical concentration level. The thus embrittled material allowed a crack to propagate through the brittle region. The crack was arrested once it propagated outside the brittle region. Once the new crack was formed, corrosion reactions started producing hydrogen that diffused into the material once again.Item Metadata only Stress corrosion cracking of rock bolts(Australian Fracture Group, 2004) Gamboa, E.; Villalba, E.; Atrens, A.; Structural Integrity and Fracture International Conference (2004 : Brisbane, Qld.); Atrens, A.The aim of this research was to understand the Stress Corrosion Cracking (SCC) of rock bolts. The laboratory tests produced fracture surfaces similar to those from service. The fracture surface has the following types: TTS (Tearing Topography Surface) at the origin of the SCC, CIS (Corrugated Irregular Surface) and qMVC (quasi Micro Void Coalescence) at the interface with the final fast fracture. The experimental study elucidated the environmental conditions leading to rock bolt SCC, and was used to determine the threshold stress and the threshold potential. A hydrogen embrittlement mechanism is proposed.