Crack Growth Failure Research Articles

Crack-growth inhibition by designing dendritic pattern for soft adhesives

Soft adhesive layers show promise in various engineering applications, including biomedicine, automotive, semiconductor, and aerospace industries. However, cavities trapped at the interface due to poor contact will significantly inhibit their adhesion capacity, leading to rapid crack-growth failure. Significant efforts in these applications within a confined contact area are focused on mitigating the effects and enhancing the debonding work of the interface without changing the materials, such as using bioinspired micropillars. However, soft adhesives with isolated contact elements face limitations due to manufacturing complexity and the collision of micropillars under large deformation. This study proposes a simple and effective method to reduce the hydrostatic pressure around the crack tips by designing a dendritic pattern within the confined area. This approach inhibited interface crack growth well and improved adhesive performance. As a result, the crack failure was delayed, with the stretch ratio enhanced by more than 36 %, while the debonding work increased by 85 % compared with the circular adhesive layer. This study demonstrates that adhesion capacity can be significantly improved while reducing material usage by designing dendritic patterns.

Crack Growth and Fatigue Strength of Deck‐Rib Welded Joints in Orthotropic Steel Decks Integrating Mean Stress Effect

ABSTRACTFatigue tests were conducted to investigate the effects of mean stress, stress range, and deck thickness on crack growth and fatigue failure of the deck‐rib welded joint. According to the experimental results, a fatigue failure criterion and a fatigue evaluation method for deck‐rib welded joints, which consider mean stress effect, was proposed. The results indicated that the stress range remains the dominating factor, but the influence of mean stress cannot be ignored. It was proposed that the crack length reaching approximately 150 mm and the depth reaching around 70% deck thickness can be taken as the fatigue failure criterion, while increase in mean stress would reduce the critical crack length but increase the critical crack depth. Besides, multiple cracks will weaken the fatigue strength. It is recommended to use Walker method and the FAT 71 curve with enhancement factor to evaluate the fatigue strength under symmetrical stress cycle.

Quantifying sandstone crack extension and expansion via deep learning methods

This study investigates the damage evolution of sandstone under loading stresses, which can lead to irreversible plastic deformation and reduced project stability service life. To achieve this objective, we identify and quantify the emergence and expansion process of sandstone cracks using deep learning methods. Specifically, our approach employs a crack segmentation model enhanced by an attention mechanism, achieving a remarkable effective crack detection MIoU of 93.38. Through the application of connectivity domain analysis, skeleton extraction, and orthogonal projection techniques, we extract crucial crack parameters, which are subsequently formulated into equations to determine their actual dimensions. These evolving parameter variations serve as the foundation for predicting the sandstone's entire damage progression, encompassing both microscopic crack growth and eventual catastrophic failure preceding macroscopic manifestation of damage. Validation of our method through uniaxial compression tests on sandstone specimens confirm its efficacy and practical applicability. In conclusion, this study presents a novel framework for quantifying sandstone crack evolution, providing invaluable insights into the intricate mechanisms governing damage fracture progression in rocks.

Criticality of volumetric defect structure on fatigue properties of stainless steel 316L fabricated by laser powder direct energy deposition

As one of the significant metal additive manufacturing (AM) processes, laser powder direct energy deposition (LP-DED) has established its role in specific applications, including component repair, coatings, and multi-material structure. However, one of the limiting factors for the wide adoption of LP-DED is the formation of volumetric defects during the printing process. These defects are one of the crucial causes of poor and scattered mechanical properties, especially fatigue performance, by accelerating fatigue crack initiation, growth, and final failure. Unraveling defect structure-fatigue correlations can help understand how defects are affecting fatigue properties, how critical they are, and, finally, what solutions can be utilized to diminish their harmful effects. In this research study, novel defect features, including size features, shape descriptors, and location features, were proposed and investigated regarding fatigue properties in LP-DED. Accordingly, stainless steel 316L (SS 316L) blocks were fabricated by LP-DED. After cutting out the dog-bone samples by wire electric discharge machining (EDM), X-ray Computed Tomography (XCT) and subsequent fatigue tests were conducted. The defect features and their statistical descriptors were extracted from XCT data. By statistical analysis of the features, valuable insights regarding their correlations with fatigue life were realized.

Compressive residual strength of the pultruded glass-fiber composite after tension-compression fatigue

We experimentally determined the decrease of residual compressive strength of the pultruded glass-fiber laminate after tension-compression cyclic loading. The adapted Arcan rig was used for tension-compression fatigue tests. The cyclic load was applied with the critical stress ratio R=−0.87. The residual compressive strength was determined after applying the predefined number of loading cycles with the stress amplitudes of 242 MPa and 173 MPa. The results indicated that the residual compressive strength was reduced about 20% at 77% of fatigue life under the stress amplitude of 242 MPa and at 83% of fatigue life under the stress amplitude of 173 MPa. The microstructural analysis showed that the crack growth path and failure mode depend on the stress amplitude.

Enhancing Reliability and Safety in Industrial Applications: Assessing the Applicability of Energy b-Value to Composites.

This study investigates the fracture behavior of glass fiber-reinforced plastic (GFRP) under various loading conditions using acoustic emission (AE) testing. Using fracture tests and time series analysis of AE signals, parameters such as b-value, improved b-value (Ib-value), and energy b-value (be-value) were examined to understand crack initiation, growth, and structural failure. The stress-strain curve revealed distinct responses during tensile and step loading, and time series analysis highlighted variations in amplitude, AE energy, and Kaiser and Felicity effects. Under tensile loading, the Ib-value exhibited a linear decrease, while step loading introduced complexities, including the Felicity effect. The be-value, incorporating energy considerations, fluctuated, providing insights into micro-cracks and macro-cracks. Statistical analysis demonstrated a consistent decrease in the be-value, emphasizing its potential for long-term monitoring. This study provides a comprehensive technique for assessing composite material fracture behavior, enhancing understanding for critical applications in hydrogen storage vessels and pressure pipes as well as advancing reliability and safety in industrial sectors.

Conventional shot peening treatment effects on thermal fatigue crack growth and failure mechanisms of a solid solution alloy

This study presents the effects of conventional shot peening as a surface post-treatment method on the fatigue crack growth behavior and failure mechanism of a solid solution alloy used in the flat seal component under thermal fatigue conditions. The study employs a combination of experimental tests and finite element simulations to evaluate the effect of shot peening on thermal fatigue crack growth behavior. The corrected J-integral and Paris model are used to calculate the stress intensity factor and predict the thermal fatigue crack growth behavior, respectively. Additionally, the ZENCRACK method is employed to predict thermal fatigue life. The results indicate that shot peening induces compressive residual stress, leading to a decreased distribution of thermal stress, particularly along the crack propagation path. The simulated fatigue life curve obtained by ZENCRACK demonstrated a good agreement between the simulated and experimental crack growth results. The incorporation of shot peening caused a significant reduction in the rate of thermal fatigue crack growth, and the simulated stress intensity factor analysis revealed an increase during the heating stage. Consequently, the thermal fatigue crack propagated during the heating-up process. SEM evaluation reveals that the shot peening post-treatment impacts both thermal fatigue crack initiation and propagation. Furthermore, the failure mode of shot-peened specimens involves inter- and trans-granular cracking, while non-shot-peened specimens exhibit trans-granular cracking.

Failure analysis of blowholes in welded boiler water walls

Water walls are subjected to thermo-mechanical loading, which potentially leads to fatigue crack initiation and growth from the weld defects. This study comprehensively analyzes the blowout failure (blowholes) occurring in boiler water walls. An experimental-simulation mixed approach has been adopted to establish the effect of weld defects on fatigue crack initiation, crack growth, and ultimate failure by blowhole. The effect of the defect position on the propagation and failure has also been modeled by extended Finite Element Method (XFEM) based on the criteria of energy release rate. A combination of XFEM and Direct Cyclic Analysis (DCA) is used to calculate low-cycle fatigue life. The cracks are shown to have originated from lack-of-fusion defects, causing the membrane to disconnect and reducing heat transfer efficiency, which may lead to localized thermal hotspots and membrane rupture, leaving molten slag residues on the airside of water walls.

Crack growth behavior and failure prediction for a granite under compressive fatigue

Crack growth behavior and failure prediction for a granite under compressive fatigue

Interface failure analysis of coating in gun barrel under thermal-pressure coupling effect

This paper is devoted to research the interface failure mechanism of coating in gun barrel, three interface failure models (interface shear failure, interface bending failure and interface crack growth failure) of coating in gun barrel are built with consideration of thermal-pressure coupling effect, and the failure criterion is given. The critical failure length/thickness ratio of coating segments for different failure models during firing process are calculated based on temperature field simulation result, then by comparison of the calculation results, the main interface failure way of coating in gun barrel is confirmed.

Fatigue Crack Growth Behavior and Failure Mechanism of Nickel-Based Alloy GH4169 under Biaxial Load Based on Fatigue Test of Cruciform Specimen

Due to the complex geometry and various cyclic loads, aeroengine components are often in a multiaxial complex stress state during service. Multiaxial fatigue is a major cause of many air accidents. It is of great significance to study the fatigue failure mechanism of aeronautical materials. This paper carries out biaxial fatigue tests on cruciform specimens and uses the surface replication method to record the initiation and propagation process of crack. Based on these fatigue tests, this paper studies the multiaxial fatigue characteristics of nickel-based alloy GH4169 for aeroengines and analyzes the fatigue crack growth behavior and failure mechanism of nickel-based alloys under a complex multiaxial stress state.

Numerical simulation and experimental investigation of laser joining Ti6Al4V alloy and CFRTP with embedded Ti6Al4V alloy

Laser joining technology shows a great application prospect in the connection of Carbon Fiber Reinforced Thermoplastic Composite (CFRTP) and titanium alloy with the advantages of high production flexibility and strong heat input controllability. In this paper, a laser joining of the Ti6Al4V alloy and the CFRTP with embedded Ti6Al4V alloy is proposed to enhance the mechanical properties of laser joining CFRTP and titanium alloy. The CFRTP with embedded Ti6Al4V alloy is prepared by hot-pressing. Numerical simulations of laser joining the Ti6Al4V alloy and the CFRTP with embedded Ti6Al4V alloy are performed by applying the finite element method. To better understand the process parameters, the joining process under different laser powers and scanning speeds are simulated, and the temperature field and the shape of molten pool are calculated. In addition, the shape of molten pool calculated using the simulation model exhibits good agreement with experimental results to substantiate the established model. The microstructure characteristics and energy dispersive spectroscopy results are analyzed. The failure load, fatigue life, and failure mode for laser joining CFRTP/Ti6Al4V alloy are studied. The results indicate that the tensile failure load of the joint exceeds 10195.6 N, obtained by using the optimal process parameters based on simulation. The tensile fracture occurs in CFRTP base material. Moreover, the specimen ruptures at the overlap region of Ti6Al4V alloy under fatigue cyclic loading and the fatigue failure mode is edge through crack growth failure.

Inspection and maintenance planning for offshore wind structural components: integrating fatigue failure criteria with Bayesian networks and Markov decision processes

Exposed to the cyclic action of wind and waves, offshore wind structures are subject to fatigue deterioration processes throughout their operational life, therefore constituting a structural failure risk. In order to control the risk of adverse events, physics-based deterioration models, which often contain significant uncertainties, can be updated with information collected from inspections, thus enabling decision-makers to dictate more optimal and informed maintenance interventions. The identified decision rules are, however, influenced by the deterioration model and failure criterion specified in the formulation of the pre-posterior decision-making problem. In this paper, fatigue failure criteria are integrated with Bayesian networks and Markov decision processes. The proposed methodology is implemented in the numerical experiments, specified with various crack growth models and failure criteria, for the optimal management of an offshore wind structural detail under fatigue deterioration. Within the experiments, the crack propagation, structural reliability estimates, and the optimal policies derived through heuristics and partially observable Markov decision processes (POMDPs) are thoroughly analysed, demonstrating the capability of failure assessment diagram to model the structural redundancy in offshore wind substructures, as well as the adaptability of POMDP policies.

Fracture of brittle solid with an internal penny-shaped crack: Semi-circular bending test and numerical simulation

Semi-circular bending (SCB) tests are usually performed on samples with a bottom notch to investigate the mechanical properties of certain materials. Few studies have been conducted on the propagation of internal cracks in SCB tests despite the fact that the existence of internal defects is inevitable in most materials. When using the three-dimensional internal laser-engraved crack method, internal cracks are generated without causing any damage to the surfaces of the sample. Here, SCB tests are performed on samples with internal cracks at different depths. The crack growth process, failure mode, and macro- and micro-fractography are analyzed. Numerical simulations are carried out, revealing the distribution of the stress intensity factors around the crack tip and the internal crack growth path. The simulation results are consistent with those of the SCB tests. The results show that: (1) The propagation mode of internal cracks is mixed in the SCB tests; (2) The existence of internal cracks significantly reduces the failure load of the samples; (3) Dynamic fracture occurs in the intact samples of groups A and B1 (depth: 30 mm), while the failure of the samples of groups B2–B5 is due to the internal crack propagation. (4) Based on the J-integral and the maximum tensile stress criterion, the distribution of the stress intensity factors around the crack tip and the fracture path are in agreement with the test results.

Fracture performance of GFRP-RC beams with working cracks in alkaline environment for eight years

The development trend of glass fiber-reinforced polymer-reinforced concrete (GFRP-RC) beams partially or entirely replacing reinforced concrete beams has gained acceptance. However, related research on long-term fracture durability is insufficient. This paper aims to investigate the long-term fracture durability of GFRP-RC beams, 36 GFRP-RC beams under the alkaline corrosion environment and sustained load for eight years were subjected to three-point eccentric loading experiments. The load crack opening distance (P-CMOD) curve and the corresponding fracture energy were obtained. The results show that the bearing capacity and residual fracture energy retention (ER) of GFRP-RC beams with working cracks in the APS (alkaline + pre-cracks + sustained load) group were 18.71% and 26.38% lower, respectively than those in the AS (alkaline + sustained load) group. After analyzing the critical CMOD curves for each service period with failure probabilities of 60% and 85%, a long-term crack growth failure probability model for the service time t and the critical CMOD was proposed, which provide a non-destructive damage assessment method for GFRP-RC beams in actual service.

Property prediction and crack growth behavior in cold sprayed Cu deposits

Low ductility of metallic deposits manufactured by cold spraying (CS) impedes potential mechanical performances in industrial applications. Through appropriate annealing treatment, the amount of both, non-bonded interfaces and work hardening promoted dislocations during CS can be significantly reduced. Consequently, the annealed samples exhibit higher strength and fracture strain than the as-deposited ones. Cu was selected as a reliable material for CS. To correlate Cu deposit strength with primary process parameters and material properties, the Cu powder strength was assessed. Crack characterization of Cu deposits was performed by in-situ microscopic observations during tensile testing. The direct observation of crack initiation, growth and final fracture allows revealing failure mechanisms. The in-situ tests allow distinguishing the effects of reduced initial defect sizes due to annealing and improved ductility in the vicinity of initial defects on possible crack growth and part failure. Considering the necessary compromise between strength, uniform elongation, ductility and microhardness, a post-spraying annealing process is desirable for CSed Cu deposits. The identification of macroscopic and micro-mechanical properties attained under respective process parameters and influences of annealing processes therefore allow identifying solutions for improvements of CSed deposits for load-carrying applications, which is a prerequisite for using CS as additive manufacturing technique.

Research on size effect of fracture toughness of sandstone using the center-cracked circular disc samples

In order to investigate the size effect and reason of rock fracture toughness, the split loading test was carried out in the GCTS rock mechanics testing machine using the center-cracked circular disc (CCCD) samples with diameters of 50 mm, 100 mm, 150 mm and 205 mm, respectively. The lengths of fracture process zone (lFPZ) were determined by the maximum normal stress criterion. The size effect of the lFPZ , fracture toughness test value (KIc), and fracture energy (Gf) were analyzed. The influence of the lFPZ on the size effect of the KIc was revealed. The crack growth paths and failure characteristics of the samples were discussed. The results show that the lFPZ and the KIc increase linearly with the sample size, and there is obvious size effect within the range of the test. The KIc and the lFPZ do not always increase linearly with the size in a larger size range, but gradually stabilize by extrapolation analysis. The lFPZ increases with the size, which means the release of stored energy increases with the size corresponding to the size effect of the Gf, and in turn leads to the size effect of the KIc. It is helpful to deeply understand the cause of the size effect reason of rock fracture toughness.

Coupled explicit-damping simulation of laser shock peening on x12Cr steam turbine blades

Timeous prevention of, and recovery from, downtimes due to in-service failure of crucial power plant components, like turbine blades, portends huge consequences in the form of operational and financial viability concerns. Intensive research and development in manufacturing, re-manufacturing and condition-based maintenance of these components have birthed a novel technique, which deploys high intensity lasers to induce compressive residual stresses to the surface of the blades. This paper presents the application of an alternate computational modelling technique in simulating this surface treatment technique on X12Cr steel, an exotic steam turbine blades material, while also investigating the economic parameters of the induced residual stresses. A numerical model is developed in this work using the commercial finite elements software ABAQUS©. The results show this computational modelling technique as being time efficient. The parametric outcomes of the simulation agreed with experimental results, lending credence to its validity. Induced compressive stresses as high as 700 MPa and depths close to 1 mm from the surface of the blade were obtained. This by indication can prospectively quell crack initiation, growth and unplanned failure of the blade while in service, with the introduced simulation technique offering a solution for timely, non-destructive mechanical integrity enhancement of engineered components.

Role of deposition strategy and fill depth on the tensile and fatigue performance of 300 M repaired through laser directed energy deposition

Laser directed energy deposition repair provides significant advantage over current grind-out repair methods for 300 M steel, with samples containing 40% deposit producing equivalent low cycle fatigue behaviour to unfilled 10% grind-outs, though with reduced tensile strength. High cycle fatigue is associated with crack initiation at defects or locally softened regions due to in-situ tempering. While deposition strategy influences the degree of tempering, both layer and track delay strategies produce equally soft regions leading to similar fatigue limits regardless of fill depth. Layer delay specimens perform better overall due to more uniform tempering, which prevents concentrated crack growth and premature failure.

Influence of fiber orientation, temperature and relative humidity on the long‐term performance of short glass fiber reinforced polyamide 6

AbstractAs a result of processing of short fiber reinforced thermoplastics, the fiber orientation varies throughout a product giving rise to a pronounced anisotropic mechanical response. Different flow conditions in a product result in spatial variation in both short‐ and long‐term mechanical properties. In this study, a modeling approach is presented to evaluate the lifetime of short fiber reinforced polyamide 6, both in plasticity‐ and crack growth controlled regions of failure. In the plasticity‐controlled region, a viscoplastic model based on separation of the load angle (by means of Hill's equivalent stress formulation) and time dependence of the yield stress is used in the form of an associative flow rule. The influence of temperature and relative humidity on the magnitude of the plastic flow rate is described by using an apparent temperature approach combined with a Ree‐Eyring formulation. The depression of the glass transition temperature in the polyamide 6 matrix with increasing amount of absorbed moisture was used to predict the anisotropic deformation kinetics in a humid environment. Similar to the plasticity controlled failure, in slow crack growth controlled failure region the effect of temperature, relative humidity, and load angle on the lifetime under a fatigue load is investigated. The apparent temperature approach could also be successfully applied to predict the slow crack growth failure, while the load angle dependence is shown to scale similar to the plasticity‐controlled failure with the Hill's equivalent stress.