查看更多>>摘要：To clarify the train-track traction behaviour in the low adhesion zone, a three-dimensional (3D) train-track coupling dynamic model was developed, in which the train was modelled as a rigid multi-body system with 8 vehicles. The vehicles are connected through coupler devices, which are simplified as nonlinear springs and dampers. The modified FASTSIM algorithm is utilized to obtain the wheel/rail creep force, which can consider the interfacial conditions. A new anti-slip control algorithm was proposed where the traction power could be adjusted to ensure the maximum utilization of wheel/rail adhesion. This control algorithm is achieved by iterating among the traction power, rotational speed and rotational acceleration of each wheelset. Numerical simulation results showed that the traction force would be reduced to a certain level to achieve maximum admissible force when the anti-slip control algorithm is activated. The rotational speed, traction force, creep force, creepages, and coupler force in contaminated conditions were investigated. The results show that the model can effectively simulate the traction process under the low adhesion state, which provides a certain theoretical reference for railway applications.
查看更多>>摘要：In this study, the residual strength of the post impacted glass/polyester laminates is investigated by the conduction of tension after impact (TAI) loading. The specimens are placed on a rigid plane and subjected to low velocity impact using a drop weight impact tower. Damage areas are detected by using visually inspection and measuring the size of the permanent impression on the surface of specimens. The relationships between the impact energy and degradation of mechanical properties have been stablished for the composites. The residual tensile strength for the impact-damaged laminates is predicted using new model. The correlation between the experimental and new model results is found to be good. Two models proposed by Caprino and Koo have been using to compare the results.
查看更多>>摘要：The life and failure mode of polyoxymethylene (POM) and POM/carbon black (CB) spur gears were assessed under different torque levels. A new experimental approach was performed to obtain the transition torque of polymer based gears by employing the online temperature monitoring and step-loading. The gear life versus contact stress was experimentally investigated and a life prediction model was proposed. Dynamic mechanical thermal analysis (DMTA) assessment was employed to determine the viscoelastic behavior of gear materials. The POM/CB gears exhibited improved load capacity, heat performance and service life. The POM/CB gear material demonstrated higher storage modulus and lower hysteresis heating as compared to pure POM gear material. The addition of CB nanoparticles switched the failure mode from fracture to tooth thinning and tooth tip plastic deformation at lower levels of torque (6, 8 and 10 Nm). At higher torque levels (12 and 14 Nm), the POM/CB gears showed 52% and 65.2% increases in the service life, compared to the pure POM gears, and finally failed under thermal material flowing.
查看更多>>摘要：In this paper, an isotropic damage evolution law of initially intact and pre-damaged ductile metallic strands is assessed using a well-established uncoupled procedure that relies on the static tensile tests of the wires that form the strands and on a numerical algorithm to simulate pre-damaged strand response. The strands construction is 1 x 7 and their diameter values vary from 9.5 mm to 14.3 mm. Pre-damaged strands account for a prescribed number of surface wires cut in both symmetric and asymmetric patterns prior loading, which defines the initial damage level. A detailed discussion is provided regarding the effect of the initial damage pattern (symmetric or asymmetric) on the damage evolution law and damage critical values reached by the strands. Assuming a linear damage evolution for the wires, intact and pre-damaged strands possess increasing multilinear homogenized damage evolution laws. A discussion is provided on the interpretation of the damage index given by the uncoupled fracture energy-based criteria in terms of the strands damage evolution using a damage homogenization approach. Numerical results indicate that the maximum allowable number of surface cut wires is two considering both asymmetric and symmetric distributions. Greater number of cut wires induces that the strand damage state evolves to an unstable condition, evolution that is steeper for the asymmetric distribution case.
查看更多>>摘要：An explosion failure occurred in a buffer tank at an oil transfer station. The explosion fragments flew out, causing 2 deaths and 1 injury. To analyze the root cause of the failure, visual inspection, thickness measurement, mechanical test, chemical composition test, corrosion product analysis, fracture analysis, pressure-bearing capacity check, explosion analysis, and operational condition investigation were conducted. The results showed that the chemical composition and mechanical properties of the buffer tank meet the standard requirements; the metallographic structure of the steel is ferrite, pearlite, and a small amount of Widmanstatite, and the structure has not deteriorated after a long time of service; the buffer tank has local corrosion, and the pressure-bearing capacity still meets the design requirements; operational condition investigation revealed that when the buffer tank burst, the operating personnel were conducting pressure test on the newly-built pipeline outside the station. The pressure test medium used was air. The buffer tank was isolated from the pressure test equipment, and the valve connecting the pressure test pipeline and the buffer tank had internal leakage. Gas entered the buffer tank, causing an overpressure explosion of the tank, and the overpressure wave leads to the collapse of the wall and casualties. Explosion energy analysis showed that the location of casualties was within the range of overpressure wave casualties. In order to avoid such incidents, the use of gaseous media for pressure testing should be avoided.
查看更多>>摘要：In this paper, a new life assessment framework is proposed based on the elastic-viscoplastic modeling and the damage behavior for the structural component under multiaxial non-proportional loading at high temperature. The viscoplastic constitutive model with the ability to capture the non-proportional hardening effect is used to obtain the stress-strain fields, in which a new method based on the rotation of strain axis is proposed to evaluate the notch rotation factor. The damage model, which can comprehensively capture the multiaxial fatigue-oxidation-creep behaviors, is used to assess the failure life. In addition, the proposed framework is evaluated by the life results under proportional and non-proportional fatigue loadings at 650 °C, and the errors are found to be within a factor of 2.
查看更多>>摘要：The paper presents a method of determination for the probability of a scaffold failure at maximum loads which are measured in one week. The research concerns scaffolding which were used on construction sites. The method assumes that the geometries (including imperfections} are deterministic and are compliant with the conditions measured on the construction site. The material properties of the scaffolding components, which cannot be measured, are generated from the normal distribution. Failure is treated as a random event occurring when one component or a group of components fails. The failure event is described by a set of serial diagrams concerning stands, transoms, and additional elements, as well as a mixed diagram concerning a wall anchoring. Probabilities of a failure were determined for 120 scaffolding and their values were obtained in a range from 10~(-9) to almost 10°. A positive or negative evaluation of the scaffolding depends on the level of the acceptable risk of failure. If reliability predictor (parameter similar to reliability index) is equal to 4.7, 41% of the scaffolds used for 12 weeks do not ensure safety of construction workers. If the reliability predictor is equal to 3.5, the percentage of unsafe scaffolds is 17%. The presented results concern frame scaffolds, erected next to elevations and forming planes. It is probable that for frame scaffolds with more complex geometries and modular scaffolds, the results will be different.
查看更多>>摘要：A detailed failure analysis was carried out on a skirt plate used in the reduction shaft of Corex plant at Areal Gas Distribution that failed after seven years of service. The analysis involved composition, hardness, mechanical properties, impact toughness, microstructure and phase analysis in the failed plate, and after solution annealing the plate for different lengths of time. It was found that the plate completely embrittled due to formation of massive Cr_(23)C_6 type carbides and σ-phase (FeCr) for prolonged service at high temperature (- 850 C), observed through microstructure and EDS analysis).The elongation of the steel was reduced to 1-4% and impact energy dropped to 5 Joule due to the embrittlement. The fracture surface showed intergranular brittle failure. After solution annealing treatment, the massive carbides and phases were mostly dissolved resulting in the restoration of the property. Hence it is suggested for solution annealing treatment in the in-service plates to improve their life. In addition, periodic monitoring of the plates through replica test and NDT could help in assessment of health of the plates for preventive measure.
查看更多>>摘要：A reliable predictive method is developed based on the progressive fatigue damage modeling technique to estimate the fatigue life of high-speed composite craft. In this method, at each loading cycle, the occurrence of different failure types would be inspected and based on the failure type, either gradual or sudden degradation rules would be followed to update the material properties. This procedure continues until the final failure of the structure. To implement this method, a MATLAB code is developed based on material degradation rules which integrating with the Abaqus it can be used for complex geometries. This method enables us to predict the fatigue life of composite structures with different layup configurations under arbitrary loading conditions only by knowing the static and fatigue behavior of unidirectional laminates. To even more reduce the number of required tests, the energy-based unified fatigue life model is employed. Owing to the low number of required tests, this method can be very cost-effective in the design stage of composite structures that are intended to endure cyclic loads.
Taiye Waheed AdejumoMustapha Mohammed AlhajiMusa Alhassan
10页
查看更多>>摘要：Sudden failure of road pavement structure from Minna through Kataeregi to Bida in Niger State, Nigeria, occurred in 2020 due to high traffic volume of overloaded trucks. The high traffic volume was necessitated by the collapse of two alternative routes (Tegina-Makera-Mokwa and Lambata-Bida-Mokwa roads) that were previously being used by these heavy trucks. Methodology used to study the causes of this sudden failure includes interaction with the Niger State Ministry of works, visual route survey of the entire road, conduction of trial pits within the worst sections of the road and collection of soil samples for analysis and finally, generation of soil profile within these sections to show the probable causes of the sudden failure. Result of visual route survey revealed that the entire stretch of the road which geologically cut across basement complex from Minna to Kataeregi and Bida basin from Kataeregi to Bida, has failed with potholes, pavement cracks, ruts, large depressions and embankment failures. However, some sections were observed to have collapsed completely. Trial pits conducted within the collapsed sections also showed defects including thick organic soil layer underlying road embankment, clay of high plasticity underlying organic soil layer and shallow water table within the region of the basement complex. A long and high embankment across a wide river channel was observed to have failed due to the failure of the thin metal sheet tubes employed to move the heavy flood water across the embankment. It was then concluded that these defects resulted from poor geotechnical investigation prior to construction and the poor expertise of the firm involved in the construction of the road.
NSTL
Elsevier