Bolt Failure Research Articles

Failure Characteristics of Joint Bolts in Shield Tunnels Subjected to Impact Loads from a Derailed Train

Impact loads generated by derailed trains can be extremely high, especially in the case of heavy trains running at high speeds, which usually cause significant safety issues to the rail infrastructures. In shield tunnels, such impact loads may not only cause the damage and deformation of concrete segments, but also lead to the failure of segmental joint bolts. This paper presents a numerical study on the failure behavior of segmental joint bolts in the shield tunnel under impact loading resulting from train derailments. A three-dimensional (3D) numerical model of a shield tunnel based on the finite element (FE) modelling strategy was established, in which the structural behavior of the segmental joint surfaces and the mechanical behavior of the segmental joint bolts were determined. The numerical results show that the occurrence of bolt failure starts at the joints near the impacted segment and develops along the travel direction of train. An extensive parametric study was subsequently performed and the influences of the bolt failure on the dynamic response of the segment were investigated. In particular, the proposed FE model and the analytical results will be used for optimizing the design method of the shield tunnel in preventing the failure of the joint bolts due to the impact load from a derailed HST.

Experimental Analysis of Anchor Bolt in Concrete under the Pull-Out Loading

The design of pull-out strength of anchor bolt in concrete is generally based on standards which are assumed to have a single crack failure and the uniform stress. However, in real phenomenon these assumptions are not reliable and a combination of failure modes between the cone and bond failure is commonly found. This research was conducted to analyze the failure mechanism and the strength of the anchor bolt under static pull-out load. Normal strength of concrete-mortar block and the shallow depth of anchor bolt was used in this research. The failure mode, reaction force, and concrete cone stress will be discussed and compared to the design standards. The experimental results clearly show that a combination failure mode between the cone and bond failure of anchor bolt was found, consequently the depth of the cone failure part reduced and the angle of cone slope narrowed. The cone stress and loading capacity of the experimental result is extremely lower than the design standards, which is around a half. Therefore a certain safety factor is required to guarantee the safety of anchor bolt structures.

A Probabilistic based Systems Approach to Reliability Prediction of Solid Rocket Motors

A probabilistic based systems approach is addressed in this study for the reliability prediction of solid rocket motors (SRM). To achieve this goal, quantitative Failure Modes, Effects and Criticality Analysis (FMECA) approach is employed to determine the reliability of components, which are integrated into the Fault Tree Analysis (FTA) to obtain the system reliability. The quantitative FMECA is implemented by burden and capability approach when they are available. Otherwise, the semi-quantitative FMECA is taken using the failure rate handbook. Among the many failure modes in the SRM, four most important problems are chosen to illustrate the burden and capability approach, which are the rupture, fracture of the case, and leak due to the jointed bolt and O-ring seal failure. Four algorithms are employed to determine the failure probability of these problems, and compared with those by the Monte Carlo Simulation as well as the commercial code NESSUS for verification. Overall, the study offers a comprehensive treatment of the reliability practice for the SRM development, and may be useful across the wide range of propulsion systems in the aerospace community.

Seismic response of precast structures with vertical cladding panels: The SAFECLADDING experimental campaign

The SAFECLADDING Project was aimed at improving the connection systems between cladding panels and precast RC buildings in seismic-prone areas. Three design criteria have been assessed: isostatic, dissipative and integrated. They can be realised using different strategies, which are represented by several test setups within the experimental campaign.The paper describes the results obtained with vertical panels arrangement and the comparison with the bare frame, which is the reference for the current design practice that considers panels like non-structural elements. The mock-up and the test sequence were designed to assess all setups with a single frame structure. The mock-up was a one-storey building, made by two parallel frames with two bays and square columns, inserted into pocket plinths. The building was designed for earthquake actions according to the Eurocode 8. Each setup was assessed using increasing levels of action, either with cyclic or pseudo-dynamic tests. The latter were performed both for serviceability and ultimate limit states. The experimental programme for vertical-panels and the bare-frame arrangement involved ten different setups, resulting in a total of twenty-eight tests.As for the isostatic criterion, the results confirm that considering panels as simple masses without stiffness is far from the real system behaviour, even using apposite devices to uncouple panels and frame displacements. In fact, despite a previous and positive experimental qualification, several devices failed in operative conditions tests.Conversely, the integrated criterion requires to bear high loads, transferred by the frame through connections, which becomes the weak point for this configuration, as demonstrated by different failures of bolts and connections.The reliability of the dissipative criterion has been confirmed by twelve tests completed without any damage. This solution in fact combines lower relative displacements with limited loads within connections, avoiding both the compatibility problems and excessive forces.

A mechanical model for conebolts

This paper presents a mechanical model for cone bolts by analysing the cone anchorage function as a wedge-style mechanical anchor. Analytical and numerical methods were employed. The failure of a cone bolt commences with a series of partial shear failure through the grout around the cone, followed by bolt slipping as the actual bearing angle of the bolt decreases to a small value. The theoretical prediction is in good agreement with experimental data in the literature. The effect of the cone’s geometric face angle was also analysed with respect to the bond strength.

Static and fatigue performance of the bolt-connected structural jointed of deep corrugated steel plate member

Corrugated steel plate culvert bridge has been more commonly used as soil steel bridges because it is the cost-effective alternative for railway-highway crossings. The corrugated steel plate culvert bridge is considered the most suitable for quick rebuilding of bridges compared with the conventional bridges. This study intends to experimentally investigate the static and fatigue performance of the bolted connection of deep corrugated steel plate. Test variables are the thickness of deep corrugated steel plate and the types of bolted connection such as bolted-only, gasket, slot hole, and washer. For static test, the failure is mainly caused by a local buckling of deep corrugated steel plate member and bearing failure of bolts. Type of gasket and slot hole showed the largest stiffness so that they may be recommended for structural safety and redundancy under a static flexural behavior. For fatigue test, the bolted-only specimen exhibited no increase in the strain until failure and the highest fatigue life among the test variables. For structural safety under cyclic loading, bolted-only connection is recommended. According to AASHTO LRFD Bridge Design Specification, fatigue life category can be determined as category D level and the fatigue limit was estimated to be 48.3 MPa. The deep corrugated steel plate members tested in this study can provide a sufficient fatigue performance in compliance with the design specification.

FE simulation and experimental tests of high-strength structural bolts under tension

Experimental tests have been completed for high-strength 8.8 bolts for studying their mechanical performance subjected to tensile loading. As observed from these tests, failure of structural bolts has been identified as in one of two ways: threads stripping and necking of the threaded portion of the bolt shank, which is possibly due to the degree of fit between internal and external threads. Following the experimental work, a numerical approach has been developed for demonstration of the tensile performance with proper consideration of tolerance class between bolts and nuts. The degree of fit between internal and external threads has been identified as a critical factor affecting failure mechanisms of high-strength structural bolts in tension, which is caused by the machining process. In addition, different constitutive material laws have been taken into account in the numerical simulation, demonstrating the entire failure mechanism for structural bolts with different tolerance classes in their threads. It is also observed that the bolt capacities are closely associated with their failure mechanisms.

Failure modes of bolt and nut assemblies under tensile loading

Thread failure of bolt and nut assemblies subjected to tension is generally undesired because it is a less ductile failure mode than fracture of the threaded shank of the bolt (denoted bolt fracture). Another issue is that incipient failure of the threads due to over-tightening is difficult to detect during installation. Thus, it is appropriate to investigate the causes of thread failure. A parameter that seems to govern the failure mode of bolt and nut assemblies, despite receiving limited attention in the literature, is the length Lt of the threaded bolt shank located within the grip. This is particularly relevant for partially threaded bolts, where Lt may be short. In the current study, direct tension tests were performed on M16 bolt and nut assemblies with different lengths Lt. The tests showed that Lt≤9mm resulted in thread failure, whereas Lt≥17mm resulted in bolt fracture. For the intermediate range of Lt, both failure modes were observed in replicate tests. Validated finite element simulations were conducted to gain insights into the mechanisms of failure. When Lt was short, necking of the bolt occurred close to the nut so that the overlap between the threads of the bolt and the nut was reduced, which further induced thread failure. This paper suggests several practical approaches for reducing the probability of thread failure.

Fracture Failure of Bolts Assembled in Tuning-Wheel of a Marine Diesel Engine

The bolts assembled on a tuning-wheel of a marine diesel engine were found fractured and loose in service of only 70 days. The damage and fractography features of the bolts were investigated to identify the failure sequence and the failure causes or modes. The crack origins were from the diameter surface of the bolts, and reverse bending and rotating bending fatigue fractures were the dominant failure modes. Various manufacturing defects, such as tight radii of transition fillet between the shanks and the threaded sections of bolts, poor surface roughness, and machined threads rather than cold-rolled threads, were found on the fractured bolts, which created a high stress concentration. A few bolts were loose in the first place during service, the overall stress state of the bolts changed to lead to a non-uniform distribution of load on the bolts. Some bolts had to sustain a great load, which was sufficient to cause fatigue crack initiation at the defective regions of bolts in such a short time period. Unsuitable installation procedures allowed for the possibility of low preload on the bolts leading to bolt loosening when subjected to vibrational loads during service. Additionally, bolt loosening could occur due to severe loading conditions. The bolts on the wheel failed in succession due to poor bolt manufacture and installation.

A Study on the Failure of the Final Reduction Gear Pad Bolt in the Tactical Vehicle

A Study on the Failure of the Final Reduction Gear Pad Bolt in the Tactical Vehicle

Theoretical analysis of a new segmented anchoring style in weakly cemented soft surrounding rock

According to the tensile failure of rock bolt in weakly cemented soft rock, this paper presents a new segmented anchoring style in order to weaken the cumulative effect of anchoring force associated with the large deformation. Firstly, a segmented mechanical model was established in which free and anchoring section of rock bolt were respectively arranged in different deformation zones. Then, stress and displacement in elastic non-anchoring zone, elastic anchoring zone, elastic sticking zone, softening sticking zone and broken zone were derived respectively based on neural theory and tri-linear strain softening constitutive model of soft rock. Results show that the anchoring effect can be characterized by a supporting parameter β. With its increase, the peak value of tangential stress gradually moves to the roadway wall, and the radial stress significantly increases, which means the decrease of equivalent plastic zone and improvement of confining effect provided by anchorage body. When β increases to 0.72, the equivalent plastic zone disappears, and stresses tend to be the elastic solutions. In addition, the anchoring effect on the displacement of surrounding rock can be quantified by a normalization factor δ.

Failure and Fracture Analysis of Bolt Assembled on the Fan Used in the Internal Combustion Engine

Three connecting bolts fractured, which were assembled on the fan used in the internal combustion engine. Detailed fractographic study and metallurgical analysis were focused on the fractured bolts. Fractographic and metallurgical studies indicate that the fracture surface and the microstructure of three bolts exhibit similar features. The fatigue fracture is the main failure mechanism of the bolts. Appearance of the micro-cracks in the thread tip of the fractured bolts makes the stress at the thread regions increase intensively so that the fatigue cracks initiated from the thread regions. Due to the presence of dynamic load, the bolts were never properly tightened during installation which should be responsible for the formation of the cracks.

Load Transfer Behavior of Fully Grouted Cable Bolts Reinforced in Weak Rocks Under Tensile Loading Conditions

To enable a better understanding of the load transfer performance of fully grouted cable bolts, a new laboratory short encapsulation pull test (LSEPT) unit has been designed and constructed. With this unit, both peak and residual capacity can be assessed over a relatively large pull-out displacement range of 100 mm. Various cable bolt failure modes, including relative slippage along the cable/grout and grout/rock interface, can be studied. Both a modified and a plain strand cable bolt confined in a material having a low strength of 8 MPa were tested. Within this testing process, the impact of the design of the bearing plate was considered that was found to alter the failure mode of the modified cable bolt. Other factors are considered, including the influence of borehole diameter, cable surface geometry, and sample strength on the axial performance of cable bolts.

Behavior of Fiber Glass Bolts, Rock Bolts and Cable Bolts in Shear

This paper experimentally compares the shear behavior of fiber glass (FG) bolt, rock bolt (steel rebar bolt) and cable bolt for the bolt contribution to bolted concrete surface shear strength, and bolt failure mode. Two double shear apparatuses of different size were used for the study. The tensile strength, the shear strength and the deformation modulus of bolt control the shear behavior of a sheared bolted joint. Since the strength and deformation modulus of FG bolt, rock bolt and cable bolt obtained from uniaxial tensile tests are different, their shear behavior in reinforcing joints is accordingly different. Test results showed that the shear stiffness of FG bolted joints decreased gradually from the beginning to end, while the shear stiffness of joints reinforced by rock bolt and cable bolt decreased bi-linearly, which is clearly consistent with their tensile deformation modulus. The bolted joint shear stiffness was highly influenced by bolt pretension in the high stiffness stage for both rock bolt and cable bolt, but not in the low stiffness stage. The rock bolt contribution to joint shear strength standardised by the bolt tensile strength was the largest, followed by cable bolts, then FG bolts. Both the rock bolts and cable bolts tended to fail in tension, while FG bolts in shear due to their low shear strength and constant deformation modulus.

Management of traumatic tarsal luxations with transarticular external fixation in cats.

To report our experience with the use of contoured mini circular transarticular external skeletal fixators for the management of traumatic tarsal luxations in 15 cats. Fifteen cats with traumatic tarsal joint luxation treated by using mini circular transarticular external fixators with available clinical records and complete clinical and radiographic follow-up of at least 30 weeks duration were included in the study. Data collected were the signalment, history, type of injury, concomitant injury, frame configuration, stabilization technique, duration of the surgery, time to first use of the operated limb, fixator removal time, complications, final outcome and follow-up. The surgical procedure chosen was based on the type of luxation; partial tarsal arthrodesis was performed in 10 cases, tarso-crural stabilization in four cases, and pantarsal arthrodesis in three cases. Five cats started to use the operated limb immediately after recovering from anaesthesia. In the other 10 cats, time to first use ranged from one to four days (mean 2 days). In one case, early pin loosening due to half pin fixation bolt failure was observed as a postoperative complication. Fixator removal time ranged from 24 to 60 days (mean 45 days). Functional outcome was excellent in 15 cats and good in two. This is a preliminary report about the treatment of tarsal luxations with a mini circular transarticular external fixation system in which early postoperative and long-term results seem to be favourable.

Investigations into the corrosive environments contributing to premature failure of Australian coal mine rock bolts

University of New South Wales (UNSW Australia) had been involved in the study of premature failure of rock bolts in Australia coal mines from the initial identification of the problem in 1999. Rock bolt steel changes over the last decade appear to have not reduced the incidence of failures. A broadened UNSW research project funded by the Australian Research Council (ARC) and Industry has targeted finding the environmental causes through extensive field and laboratory experiments. This paper describes the field studies conducted in underground coal mines, in particular attempts to measure the contribution to corrosion from groundwater, mineralogy and microbial activity. Various underground survey techniques were used to determine the extent of broken bolts, with the presence of both stress corrosion cracking (SCC) and localized deep pitting making no single technique suitable on their own. Groundwater found dripping from bolts across various coalfields in Australia were found to be not aggressive and known groundwater corrosivity classification systems did not correlate to where broken bolts were found. In-hole coupon bolts placed in roof strata containing claystone bands confirmed the clay as being a major contributor to corrosion. Microbes capable of contributing to steel corrosion were found to be present in groundwater, and culturing of the microbes taken from in-situ coupon bolts proved that the bacteria was present on the bolt surface. An ‘in-hole bolt corrosion coupon’ development by the project may have multiple benefits of (1) helping quantify newly developed corrosivity classification systems, (2) providing an in-situ ground support corrosion monitoring tool, and (3) for testing possible corrosion protection solutions.

Sensitivity Analysis of Mission Critical Shear Bolts of Combat Aircraft High-Speed Flexible Coupling

The combat aircraft utilizes high-speed flexible coupling (HSFC) to transmit the power from the aircraft engine gear box to accessory gearbox and to accommodate misalignment arises in the drive line. The HSFC input drive end has three shear bolts with predetermined shear torque set value. The mission-critical shear bolt failure to act above maximum set value will damage the down-line components by excess torque transmission. The premature action of shear bolts below minimum set value will deprive the power to single-engine aircraft transmission which may even lead to loss of aircraft. To realize consistency performance of shear bolts, sensitivity analysis is carried out considering influencing parameters like shear section size, hardness and preload variation. Based on the analysis, grouping of bolts was enabled for consistent performance in shear torques. The experimental validations are carried out to correlate between theoretical prediction and model behavior.

Fracture Failure of Zinc-Plated Hub Bolts by Hydrogen Embrittlement

In this work, the failure behavior of a batch of zinc-plated hub bolts with high strength was detected and analyzed to determine the failure mechanism. The fracture failure occurred at the head-to-shank transition. The initial region of the crack was at the external edge of the bolts. Brittle fractures containing intergranular and transgranular features were observed using a scanning electron microscope. Yawning grain boundaries as well as micropores on the grain surfaces were observed at many areas of the fracture surfaces. According to the analysis results, hydrogen embrittlement is considered as the probable mechanism of the failed specimens. Poor baking treatment may be the reason leading to the incomplete removal of hydrogen.

Estimation of maximum axial force of anchor bolts in consideration of random bolt failures

This paper proposes a method for structural reliability analysis of anchor bolts used in the support skirt of a reactor vessel. The method is based on the conservative assumption that a few anchor bolts within the skirt's inner-wall may fail in a random nature. Under the assumption, the maximum axial forces in the intact bolts are estimated. To reflect the uncertainty, random numbers are generated to simulate the possible failed bolts among a total of 60 bolts, which are circumferentially arranged along the inner side of the wall. Then the outcome of failed bolts together with their locations for every 60 bolts is defined as an experiment of a sample. The locations of failed bolt can significantly affect the stress analysis and its random outcomes require an efficient calculation scheme. In this paper we propose a rapid calculation algorithm, thus the direction of bending moment that causes the worst scenario in the stress analysis of bolts for each experiment can be rapidly found. Taking into consideration of design loads, the finite element method is further employed to calculate the maximum axial bolt force of each experiment. After statistical analysis of maximum axial forces from all experiments, the average maximum axial-force interval that the remaining bolts can withstand under a given random condition is estimated with a 95% confidence level. This interval can be used in conjunction with various results of structural integrity assessment to ensure the structural safety and reliability of a nuclear power plant component.

622 軸直角方向負荷下のねじ締結体のすべり・ゆるみ挙動

The thread joint has been frequently used for the efficient productivity and maintainability as a machine element. However, many troubles such as loosening of bolted joints or fatigue failure of bolt were often experienced. Many attentions must be paid on the improvement of the strength and the reliability of the thread joints. It is generally said that the fastening axial force rapidly decreases by the rotation loosening of nuts if the relative slippage on the interfaces between nuts and fastened body goes beyond a certain critical limit. This critical relative slippage (Scr) that prescribes the upper limit for preventing the loosening behavior has been estimated according to the theoretically obtained equation considering the bending deformation of bolt and the geometrical constraint condition. In this paper, we present the investigated results of the deformation behavior of bolt-nut joint under transverse loading condition. The bending moment of bolt is measured by the quasi-static loading test. The reaction force moment by nut used in the equation for estimating the Scr is evaluated by the comparison of experimental and analytical results from estimated equation. The new equation for estimating the reaction force moment which agrees with measured value is examined and proposed.