Bolt Failure Research Articles

Failure analysis of frequent fracture accident of torsional shear type high strength bolts for steel structure of a thermoelectric 2×350MW unit project in Northwest China

In this paper, the frequent breakage of high-strength torsional shear bolts used in steel structure of a 2×350MW thermoelectric unit in northwest China is taken as an example. By means of macro and micro fracture analysis, physical and chemical inspection, the causes of frequent breakage of high-strength bolts are analyzed and the improvement measures are put forward. The results show that the failure of the 20MnTiB steel high-strength bolt after assembly is hydrogen embrittlement fracture, and the main cause of the failure is the presence of zinc layer on the bolt surface and a large number of zinc microholes on the shallow surface.

Investigation on guided wave characteristics of prestressed bolts based on mechanics of incremental deformations theory

The magnitude of prestress can reflect the degree of anchor bolt failure, but currently there are relatively limited theoretical research methods for the wave characteristics of prestressed bolts. For this reason, this paper establishes a viscoelastic bolt model with prestress based on the Mechanics of Incremental Deformations theory and the Kelvin-Voight viscoelastic theory, and proposes a recursive Legendre polynomial series method (RLPSM) to solve the longitudinal guided wave propagation characteristics in free bolts with prestress. The dispersion and attenuation curves of longitudinal guided waves in free bolts with various prestresses are given, and the influences of prestress on dispersion curves are analyzed. Meanwhile, the ultrasonic guided wave detection system of free bolts with prestress is established for laboratory research, and compared with the theoretical results.

Investigating and modelling of highly stressed firearms parts

Recently, there have been too many Pulemyot Kalashnikova Modernizirovannyi (PKM) machine gun bolts that have failed during the firing process. Due to the increased temperature, higher propellant gas pressure, and thermal accumulation, the bolt body is exposed to sever circumstances for ablating, corroding, and erosion. In this paper, the reasons of failure of PKM bolts during firing were evaluated first based on metallurgical experiments. Then, analysing the failure is done by create an accurate finite element model of the bolt body, calculating the cyclic fatigue life and safety factor, determining the causes of failure and be verified showing that failure locations are exactly as shown in the photographic record. the original bolt dimensions were measured using laser scanning, and a CAD model of the bolt was created. Photographic records, visual inspection, chemical analysis, SEM, and hardness measurements, all these metallurgical experiments have been done. The stress distributions and fatigue behavior of the failed bolt are both determined using the Finite Element Method (FEM). This study suggests that fatigue played a role in bolt failure. Furthermore, SEM examinations reveal that the materials contain dimple fractures. The bolt’s fatigue life was decreased by these dimpled fractures.

Investigation of Parameters Affecting Rotational Behavior of Cold-Formed Steel Connection

This study aims to understand the behavior of connection, which holds an important key to efficient designs of the cold-formed steel structure. The focus is on examining parameters that affect the rotational stiffness and behavior of the cold-formed steel connection made of single-lipped channel sections with a bolt and gusset plate system. The numerical study has been conducted using component-based finite element analysis, with the studied parameters including bolt diameters, number of bolts in the group, size of the bolt group, thickness of the cold-formed steel cross-section, and thickness of the connecting plate. The effect of the variables is evaluated and explained by comparison. The result of the study reveals that the rotational behavior of the connection depends on the details of the assembly. For the given base connection, the parameters that give the greatest effect on the rotation stiffness and the moment capacity are the number of bolts and the bolt diameters, whereas the parameter that provides the least effect is the bolt spacing. On the other hand, the bolt group size is the most influential parameter for the member connection. For both types of connections, the thickness of the cold-formed steel section and the thickness of the gusset plate have shown limited effect on stiffness and strength. Using different variables in assembling the connection can also lead to different failure types, either bolt failure or excessive bolt hole deformation, which leads to plate failure. Doi: 10.28991/CEJ-2023-09-11-08 Full Text: PDF

Experimental study on behavior of top-and-seat-angle with double web-angle (TSDW) connections under fire conditions

Steel beam-to-column connections are more prone to fracture due to tension in the heating and cooling phase of a fire, imposing an important issue on progressive collapse of steel structures in fire. Experiments are conducted in this study on four top-and-seat-angle with double web-angle (TSDW) connections under room-temperature, heating, heating-cooling and after-fire conditions. The effect of temperature histories and loading states on the failure modes and displacement curves of connections is investigated. A numerical model of full-scale TSDW connections is established and validated, and parametric studies are carried out to study the effect of scale ratios, material properties, angle thickness and stiffeners. The experimental results show that the connection may fail due to tearing of bolt holes or shear failure of bolts in the seat angle. The critical temperature of connections is 710 °C for a load ratio of 0.5, and its residual capacity reduces by 23 % after experiencing a maximum temperature of 980 °C. Loading during fire has a significant effect (60 %) on the residual capacity of connections after fire. It is found from numerical simulation that the scale ratio affects failure modes, critical temperatures, residual capacities and failure displacements of connections, and further work is still needed to quantify structural fire similarity. The yield strength and fracture strain are important factors affecting the behavior of steel connections at both ambient and elevated temperatures. Increasing the angle thickness and applying stiffeners can effectively improve the load-bearing capacity of TSDW connections at room temperature. There is an optimal angle thickness (e.g., 8 mm) for improving residual capacity of connections, and the selection of stiffeners should consider its matching with angles. It is recommended to exclude stiffeners for thick angles (e.g., 12 mm) to avoid adverse effect on the fire resistance and post-fire residual capacity of TSDW connections.

Factors Governing the Failure of Subsea Critical Connector Bolts

Impressed current cathodic protection (ICCP) systems are commonly used to shield offshore drilling rigs, pipelines, and subsea equipment in the oil and gas industry. In underwater service conditions, water temperature, salinity and velocity play a major role in the longevity of subsea applications. Interactions between the preceding factors can induce catastrophic failure to critical systems while the underlying cause is unclear. This paper proposes an approach for elucidating the corrosion process accompanying underwater applications. The service conditions of underwater application are simulated in a multidisciplinary system that records various parameters such as water temperature, reference-electrode potential, and electric current at five-minute intervals during the 21 d of the experiment. This novel, experimental, and inexpensive ICCP system was developed on an “Arduino” microcontroller and applied to an actual ASTM A193 B7 bolt tightened on an ASTM A105 flange at different torque levels. Experimental results indicate a direct relationship between the water day-night temperature profile and the cathodic protection performance. Specifically, the ICCP performance declines with increasing temperature. When the ICCP system was activated, gas bubbles are generated on the metal surface. Presumably these bubbles could induce hydrogen embrittlement cracks which were observed in scanning electron microscope images of the bolt cross-sections.

Multiaxial Fatigue Analysis of Connecting Bolt at High-Speed Train Axle Box under Structural Subharmonic Resonance.

Based on the dynamic characteristics of the axle box front cover of high-speed trains in the subharmonic resonance state, the nonlinear single-degree-of-freedom (SDOF) model was proved to be reasonable, and reasons for the ineffectiveness of the common prevention methods for preventing bolt failure were analyzed firstly. Then, dynamic stress of the bolt was simulated by innovatively adopting the linear method based on frequency response analysis. The stress simulation method was verified to be practical under the subharmonic resonance state by analyzing and comparing the experimental and numerical results of the bolted front cover. It was proved that the linear method was accurate enough to simulate the dynamic stress of bolts, which is of great engineering significance. In addition to the transverse resonance stress of bolts caused by drastic vertical vibration of the front cover, the tensile resonance stress at the root of the first engaged thread was too large to be neglected on account of the first-order bending modes of bolts. Next, equivalent stress amplitude of the multiaxial stresses was obtained by means of the octahedral shear stress criterion. Finally, fatigue life of bolts was predicted in terms of S-N curve suitable for bolt fatigue life analysis. It argued that the bolts were prone to multiaxial fatigue failure when the front cover was in subharmonic resonance for more than 26.8 h, and the fatigue life of bolts could be greatly improved when the wheel polygonization was eliminated by shortening the wheel reprofiling interval.

Numerical Investigation of a Sustainable Composite Connection

AbstractDuring the last decade there is an increasing awareness towards sustainable construction solutions. The reason of this shift is that the construction sector contributes to approximately 40 % of the global output of CO2 emissions, thus making it essential to act in lowering this high amount. A key aspect in the successful implementation of sustainable construction solutions is the use of construction materials that can be 100% recycled, such as steel, and that come from renewable sources, such as timber. Therefore, the interest in using steel‐timber composite (STC) elements and connections has grown since they can provide a robust alternative construction technique to traditional ones. The aim of this paper is to investigate the structural performance of a bolted STC shear connection using finite element analysis. The connection under study consists of two dahurian larch glulam elements that are bolted to the flanges of an H‐profile steel element by means of four M6 bolts for each timber component. The numerical model has been validated using the results of an experimental study where a pull‐out test of the same connection is performed [1]. Overall, the numerical results have shown good accuracy. The bolt failure has occurred when 47.5 kN of force had been applied. This amount of load is about 12% less than the failure load found in the experiment. The slip of the numerical model has been found equal to 5.4 mm whereas the slip measured in the experiment has been measured equal to 7.5 mm. In addition, the failure mode that has developed in the numerical model is governed by the formation of two hinges on the bolts which coincides to the experimental one. To sum up, the numerical model has managed to capture to a great extent the structural performance of the composite connection as presented in the experimental findings.

Push-out behavior of GFRP bolts shear connectors in FRP-concrete hybrid beam

GFRP bolt has emerged as a promising shear connector in FRP-concrete hybrid beams due to flexible arrangement and ease of installation. Shear connectors are critical to maintaining the composite action and are key to the design of hybrid beams. 30 push-out tests were conducted to investigate failure mode, ultimate strength, and shear load-slip (P-S) relationship of GFRP bolts. Test parameters included bolt types, layout of bolts, longitudinal row spacing of bolts (Sl), bolt diameter (d), and bolt embedment depth (he). Results revealed that specimens with GFRP bolts exhibited bolt shank shear failure, pry-out failure of bolts, and splitting failure of concrete. In contrast, specimens with stainless-steel bolts suffered bearing failure of bolt holes in the FRP flange. Typical P-S curves of GFRP bolt specimens consisted of micro-slipping and significant-slipping phases, showing non-linear response, while P-S curves of stainless-steel bolts exhibited a linear response till failure. The effect of layout of bolts was found negligible if the longitudinal row spacing and horizontal spacing was not less than 6d and 4d, respectively. Specimens with a larger d and he demonstrated greater shear capacity. Based on the test results, prediction equations associated with failure modes were introduced to predict the capacity of GFRP bolt, which yielded results in accordance with experiments. Additionally, a refined description of P-S relationship was proposed by curving fitting, and the results correlated well with the experiments.

Application of copula-based Bayesian network method to water leakage risk analysis in cross river tunnel of Wuhan Rail Transit Line 3

Water leakage typically infiltrates through bolt holes and segment joints, posing a threat to the stability of tunnel structures. In this paper, we develop a copula-based Bayesian network (CBN) method for dependency modeling of complex systems to conduct risk analysis and management of water leakage in operational tunnels. Thirteen potential factors are used to construct the water leakage risk system, and the permeate water volume is selected as the observation index of water leakage risk. An application to a realistic cross-river tunnel of Wuhan Rail Transit Line 3 is implemented to verify the effectiveness of the developed model. Through correlation analysis, the bolt failure rate and seal breakage and aging rate are diagnosed as critical factors with the greatest impact on the water leakage risk. Forward and backward reasoning enables the model to be dynamically updated to provide decision support for water leakage risk management. This research contributes to the following: (a) expressing the dependence of the factors affecting water leakage; (b) solving the problem of modeling uncertainty and information fusion; and (c) updating the model to realize the safety control of tunnel water leakage.

Machine learning-based identification of segment joint failure in underground tunnels.

Shield tunnels that reside deep within soft soil are subject to longitudinal differential settlement and structural deformation during long-term operation. Longitudinal deformation can be classified into two modes: bending and dislocation deformation. The failure of bolts and engineering treatment techniques differ between these two modes. Therefore, it is imperative to accurately identify the tunnel's longitudinal deformation mode to determine the validity of the segment joint and implement appropriate engineering treatment. Traditional methods for detecting dislocation or opening suffer from high labour costs. To address this issue, this study presents an innovative identification method using a back-propagation neural network (BPNN) to detect segment joint failure in underground tunnels. First, this study collects the tunnel settlement curves of various subways located in the East China soft soil area, and it calculates tunnel settlement-dislocation and settlement-opening datasets using the equivalent axial stiffness model. A corresponding BPNN regression model is subsequently established, and the new settlement curve is the input to this regression model to predict the dislocation and opening, thereby determining the validity of the segment joint. The efficiency of this method is demonstrated through its successful application to the Hangzhou Metro Tunnel. This article is part of the theme issue 'Artificial intelligence in failure analysis of transportation infrastructure and materials'.

Study of the Tensile and Bonding Properties between Cement-Based Grout Materials and High-Strength Bolts

This study investigated the tensile and bonding properties between cement-based grouting materials (CBGM) and high-strength bolts. The associated failure mechanism, load-slip curve, ultimate pull-out load and bond stress were also studied. The effects of anchorage length and square steel tube restraint on the bonding properties were explored on the basis of 24 specimens used in central pull-out testing, and a bond stress–slip constitutive relationship model between high-strength bolts and CBGM was proposed. The results indicate that with the increase in the anchorage length of high-strength bolts, the failure modes of specimens can be divided into three types: the fracture failure of high-strength bolt that occurred when the anchorage lengths ranged from 18 d to 31 d, the specimens that experienced splitting failure with the constraint of square steel tube when the anchorage length was less than 15 d and the high-strength bolt that experienced pull-out failure without the constraint of square steel tubes. When the high-strength bolt experiences tensile failure, the ultimate pull-out load remains constant and the bond stress decreases as the anchorage length of high-strength bolts increases. Due to the lateral constrained effect of the square steel tube, the CBGM embodies a three-dimensional stress state, which can delay the generation and development of internal cracks and enhance the bond strength. A calculation formula was proposed to determine the bond strength between high-strength bolt and CBGM, and a constitutive model of the bond stress–slip constitutive relationship was modeled.

Mechanical testing of intelligent fastening

Loosening of threaded fasteners can lead to a decrease in preload, cause fatigue failure of bolts and seriously reduce the reliability of mechanical structures. Timely detection of such a weakening is an effective method of early prevention of a man-made disaster or economic losses. A promising direction in the field of monitoring the condition of complex structures during their operation is associated with the creation of intelligent materials or smart systems based on the use of sensor elements. The paper considers the main technical problems of operation of an intelligent fastener – a bolted connection with an integrated fiber Bragg grating (VBR). Calculations and strength tests of intelligent fasteners are given, problems arising during the operation of such systems and ways to solve them are described

Investigation of the compression-bending capacity evaluation of non-bolted segmental joints

This study aims to thoroughly investigate the compression-bending capacity of non-bolted segmental joints (without bolt connection or connect bolt failure) and provide a basis for its compression-bending safety evaluation. First, a theoretical model regarding the compression-bending capacity of non-bolted segmental joints was proposed and verified by full-scale failure tests. Second, a comparison between bolted and non-bolted segmental joints on compression-bending capacity was conducted. Third, the influence of the segment thickness and length of the core pressure zone on the compression-bending capacity of non-bolted joints were analyzed based on the proposed theoretical model and joint parameters from six segmental joints with different segment thicknesses, and the basic characteristic compression-bending capacity curves of non-bolted joints were obtained. Finally, for the convenience of engineering applications, a simplified method for calculating the compression-bending capacity of non-bolted segmental joints was proposed. The results showed that the relative errors between the theoretical model and full-scale tests under positive and negative bending were 3.4% and 6.1%, respectively, indicating that the theoretical model had high calculation accuracy. The influence of the bolt on the compression-bending capacity of a segmental joint increased with increasing segment thickness and decreasing axial force. With the same eccentricity, the compression-bending capacity of the non-bolted segmental joint generally increased with the segment thickness. The compression-bending capacity decreased with increasing length of the core pressure zone under positive bending, while under negative bending the reverse is true. The characteristic compression-bending capacity curve of the non-bolted joint passed through the origin and had three characteristic points. There was a basic compression-bending capacity curve that was independent of the joint parameters for non-bolted joints with different segment thicknesses. The proposed simplified method for calculating the compression-bending capacity of non-bolted joints is highly accurate and easy to use.

Investigation into durability degradation and fracture of cable bolts through laboratorial tests and hydrogeochemical modelling in underground conditions

Premature failures of cable bolts caused by durability degradation in underground reinforcement systems have been more and more often observed. To identify various factors affecting the corrosion process, the corrosion processes were examined through laboratorial testing programs as well as hydrogeochemical modelling. Experiments were carried out in simulated underground conditions in “corrosion cells” containing stressed cable bolt specimens as well as groundwater, clay, coal or a combination of the materials. Water chemistry and corrosion pattern analysis of specimens in different testing conditions were conducted. Hydrogeochemical models were established and the formation of corrosion products, the change of ion concentration and factors related to corrosion rates were studied. The results showed the corrosion degree of specimens could be classified into three categories. The dissolved oxygen was the main factor affecting the general corrosion and stress level, pH and electrical conductivity were secondary factors. Erosive ions were main factors affecting localised corrosion which was mainly observed to form at high stress areas. A ‘staple’ like crack initiated at localised corrosion were observed which was identified as a potential site for stress corrosion cracking. The modelling results showed sulphide iron generated in presence of microorganisms which would also accelerate stress corrosion of specimens. The obtained results and proposed methodologies would establish quantifiable data to compare variable mine conditions and help understand the corrosion mechanisms in underground conditions.

Hysteretic Behaviour of Composite Reduced Web Section (RWS) Connections for Seismic Applications

ABSTRACT Whilst there has been research about reduced web section beams; RWS, their seismic behaviour when they are overlaid by slabs is not well understood. This study addresses this by assessing a high-definition finite element representation of non-seismically detailed RWS connections with slabs. The composite action is investigated, focusing on effects of the size and location of the web openings. These connections can reach a 4% interstorey drift, thus comprising special moment frames in accordance with AISC 341. Moreover, beam, column, and joint tearing were avoided entirely, and at the most, brittle failure of bolts in the end plate was observed.

Theoretical analysis on flexural strengthening of RC beams using GFRP composites in terms of strength to the weight ratio: A way forward

Aramid, Glass or Carbon Fibre Reinforced Polymer (GFRP/CFRP) are three types of composites that are commonly used in the civil, mechanical and automobile sectors worldwide. GFRP composites are often used for structural member strengthening, repairs, and rehabilitation. In comparison to CFRP and Aramid FRP composites, GFRP is easily available, inexpensive, good strength to the weight ratio, and has several additional benefits. The strength-to-weight ratio of GFRP composites and steel plates for flexural strengthening of RC beams is investigated in this work. Theoretical analysis for the RC beam strengthened with GFRP composites and steel plates were performed using the established equation based on Indian standards and the ACI code. The self-weight of the beam and the superimposed dead load owing to the block/brick work were taken into account in the design calculations. The beam's load carrying capability is inadequate due to the excessive load, thus it must be strengthened with different materials: GFRP Chopped Strand Mat (CSM) composites or steel plates. The evaluations were conducted under the assumptions that the loss of moment carrying capacity due to concrete deformation caused by bolt holes and failure due to GFRP composite delamination would be disregarded. Strength to weight ratio of GFRP composites and steel plate requirements have been computed and compared for the known dimensions, unit weight and tensile strength of the strengthening materials, and load carrying capability of the strengthened RC beam. Comparative study proves that the flexural strengthening of RC beams using GFRP composites, the strength to weight ratio is much higher than when the identical beams are strengthened with steel plate.

A failure analysis of the cylinder and connection bolts in a buoyancy regulator of an underwater glider

The buoyancy regulator is key device used in underwater gliders for adjusting their buoyancy. This paper studies the failures of the cylinder and the connection bolts during the working processing of the buoyancy by using a finite element method. The effect of the ovality on the sealing and the scratching failures of the cylinder is analyzed. Note that the poor machining accuracy should produce the cylinder sealing and the scratching failures. Some suggestions for improving the ideal cylinder design are introduced. Additionally, the specific reasons of the failures of the connecting bolts for the buoyancy regulator are also investigated. Note that the overload causes the failures of the connection bolts. The loading capacity can be increased by making the connecting flange stiffer or by utilizing the larger bolts. The optimization design methods for the piston and the piston rod are provided according to the simulation results. This paper can provide a failure analysis and structural optimization method for the buoyancy regulators.

Multi-axial fatigue behavior of high-strength structural bolts

In this study, the fatigue failure of high-strength bolts (galvanized and regular) was experimentally and analytically explored under different tension-to-shear cyclic loading ratios. The observed cracking mechanisms were found to be a function of the bolt types and loading conditions. Though the cracks in the galvanized bolts followed the helical shape of the threads, the cracks for the regular bolts were parallel to the shear plan. The predicted fatigue lives under the combined tension and shear loads using the analytical approach matched the experimental results. Utilizing Eurocode SN curves for independent tension and shear demands overestimated the fatigue life of bolts under multi-axial stresses. The resulting SN curves obtained from this study can aid engineers in designing connections where bolts are subjected to multi-axial fatigue load.

Fatigue life analysis of high-strength bolts based on machine learning method and SHapley Additive exPlanations (SHAP) approach

Fatigue failure of high-strength bolts is one of the causes of collapse of steel structures. In this paper, six different machine learning models were used to analyze and predict the fatigue life of high-strength bolts, and the relationship between fatigue life of the bolts and the influencing factors was analyzed by SHAP method. During this process, a data set of fatigue life of high-strength bolts was presented, and 30 percent of the data was randomly selected as the test set. Geometric dimensions and stress states of bolts were as input features, and fatigue life was output label. After training the model, the errors of bolt fatigue life prediction of six machine learning models were compared. Finally, the most adverse factors affecting the fatigue life of the bolts are analyzed. It was found that XGBoost has the best performance on prediction of fatigue life of high-strength bolts, R2 reaches 0.881 and 0.788 in training set and test set, respectively. At the same time, the prediction result of the model is also better than that of the traditional fracture mechanics method. In addition, according to the analysis of SHAP value, the stress amplitude (SA) applied on the bolt has the greatest impact on the fatigue life. Larger SA value will accelerate the expansion of fatigue crack, thus increasing the degree of fatigue damage of the bolt. At the same time, the combination of MAXS (maximum stress applied on high-strength bolts) and SA is the most unfavorable factor to affect the fatigue life of the bolt. Increasing both factors can greatly reduce the fatigue life of the bolt. Finally, the current mainstream steel structure design codes have sufficient safety reserves, and M39 bolt has the best fatigue performance.