► Detailed overview on safety assessment aspects of railway axles. ► Combines questions of basic and applied research with questions of practical application. ► Proposals for further improvement of ...railway axle safety.
The paper gives an overview on safe life and damage tolerance methods applied to railway axles. It describes failure scenarios due to fatigue crack initiation and propagation. Besides common aspects of design, specific features such as corrosion and impact damage from flying ballast are discussed which may reduce the fatigue strength of axles during service. Potential effects of non-metallic inclusions from the steel manufacturing process are addressed in the context of the very high number of loading cycles railway axles are designed for. With respect to damage tolerance general lines of fracture mechanics residual lifetime analyses are introduced. More specific discussion is provided on aspects such as the threshold value of fatigue crack propagation and reliability aspects of non-destructive inspection.
Stress exists ubiquitously and is critically important for the manufacturing industry. Due to the ultrasensitive mechanoresponse of the emission of 1,1,2,2,‐tetrakis(4‐nitrophenyl)ethane (TPE‐4N), a ...luminogen with aggregation‐induced emission characteristics, the visualization of stress/strain distributions on metal specimens with a pure organic fluorescent material is achieved. Such a fluorescence mapping method enjoys the merits of simple setup, real‐time, full‐field, on‐site, and direct visualization. Surface analysis shows that TPE‐4N can form a nonfluorescent, crystalline uniform film on the metal surface, which cracks into fluorescent amorphous fragments upon mechanical force. Therefore, the invisible information of the stress/strain distribution of the metal specimens are transformed to visible fluorescent signals, which generally matches well but provides more details than software simulation. Remarkably, fatigue crack propagation in stainless steel and aluminum alloy can be observed and predicted clearly, further demonstrating the ultrasensitivity and practicability of TPE‐4N.
A pure organic mechanoresponsive luminogen with ultrasensitivity and aggregation‐induced emission characteristics is used as a coating on metal specimens for the visualization of the stress/strain distribution and fatigue crack propagation. The invisible information of mechanical strain on metal specimens is now visible to the naked eye as a fluorescent signal in real‐time, full‐field and on‐site.
•A series of lightly reinforced concrete beams were tested in three point bending.•Qualitative DIC analyses provided insight into the experimental cracking behaviour.•Crack branching was observed in ...all of the reinforced concrete beams.•The crack branching was found to be related to the beam height and ductility.
Relatively few fracture-oriented experimental studies have been conducted on concrete that is reinforced. An experimental investigation was therefore undertaken to explore the cracking process in lightly reinforced concrete (RC) beams and to observe the details of the localised fracture process zone development. More specifically, the aims were to investigate the relationships between beam height (120mm, 220mm and 320mm), steel reinforcement ratio (0.1–0.5%), ductility and the onset of crack branching. RC beams were tested in three-point bending and experimental surface strains and crack openings were inferred using digital image correlation (DIC). It was found that the presence of the reinforcement prevented premature fracture and led to crack branching where a single crack bifurcated in the region of the compression zone. In the larger beams the branching developed at a lower relative height and a greater reinforcement ratio led to a shallower branching angle. These observations were associated with ductility measures for lightly reinforced concrete beams.
Structural damage identification has received considerable attention during the past decades. Although several reviews have been presented, some new developments have emerged in this area, ...particularly machine learning and artificial intelligence techniques. This article reviews the progress in the area of vibration-based damage identification methods over the past 10 years. These methods are classified in terms of different damage indices and analytical/numerical techniques used with discussions of their advantages and disadvantages. The challenges and future research for vibration-based damage identification are summarised. This review aims to help researchers and practitioners in implementing existing damage detection algorithms effectively and developing more reliable and practical methods for civil engineering structures in the future.
This paper presents the investigations of the tension-softening constitutive relation of concrete and the numerical method for mode I fatigue crack propagation in concrete. Firstly, the static ...loading, fatigue loading, and fatigue–static loading were carried out on 191 notched three-point bending (TPB) beams. With the experimental results, the tension-softening constitutive relation of concrete under fatigue loading was proposed from the view of energy conservation, where the equilibrium relation between the energy dissipated by crack propagation and the external work was established. Secondly, by combining the constitutive relation with the stress intensity factor (SIF)-based crack propagation criterion, the numerical method for mode I fatigue crack propagation in concrete was developed. Finally, the applicability of the numerical method was validated by comparing the numerically derived fatigue life, fatigue crack propagation length, crack mouth opening displacement (CMOD), and SIF with the experimental results. It is concluded that the numerical method proposed in this paper is significantly helpful in evaluating the fatigue performance of concrete structures.
In this study, the effect of nano-SiO2 (up to 25 wt%) on the mechanical properties of an anhydride cured epoxy resin was investigated with particular attention on the fatigue crack propagation ...behaviour (FCP). The Young's modulus showed good agreement to the Halpin-Tsai predictions for contents up to 15 wt%. The addition of silica nanoparticles evokes an increase in fracture toughness (up to 74%). However, the augmentation of the critical stress intensity factor rises with respect to the filler loading, although no linear correlation is found. Additionally, a plateau-like behaviour is observed for the fracture energy release rate at filler contents above 15 wt%. The FCP behaviour is improved in all three regimes of fatigue crack propagation. Particle debonding in combination with subsequent plastic void growth and shear yielding of the matrix are identified as major energy dissipating mechanisms in all three regimes of FCP.
•Rate-dependent quantitative gaps were revealed among the three measurement methods for rock crack propagation.•Equivalent crack-velocity-dependent strain thresholds for the CPG, DIC and VISIBLE ...techniques are in linear fit.•Reasons for the gaps between DIC and CPG were clarified from the viewpoint of fracture process zone.•Three recommendations were proposed for the calibration of crack propagation measurement results.
The rate-dependent measurement gaps among the crack propagation gauge (CPG), digital image correlation (DIC), and Visual methods for measuring dynamic rock crack propagation were determined using a case study. Dynamic notched semi-circular bending (NSCB) tests of a rock material, namely, red sandstone, were conducted using a modified split Hopkinson pressure bar system to form different crack propagating velocities (CPVs). From the viewpoint of the initial crack time, a normal strain threshold of 2% in the DIC was effective in obtaining a match between the CPG and DIC methods at a low CPV. However, the selected 2%–5% normal strains in the DIC were pivotal factors that could compromise the results from the CPG and Visual methods with a low CPV in terms of the peak CPV, whereas 2%–3% normal strains were recommended for cases with a high CPV. In addition, the equivalent crack-velocity-dependent strain thresholds (tiDIC equal to tiCPG and tiDIC equal to tiVisual) for the CPG, Visual, and DIC techniques displayed a linear fit with the CPV. The measurement gap between the DIC and Visual methods was narrower than the measurement gap between the DIC and CPG methods. The critical initial crack time of CPG for red sandstone needed the condition of a CPV of approximately 500 m/s. A potential explanation for these gaps was proposed in terms of the changes in the fracture process zone with CPV, and three suggestions were subsequently recommended based on the experimental results to aid in the interpretation of other experimental results.
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