In this article, we have analyzed the interaction of arbitrarily oriented cracks under anti-plane deformation in a bi-directional functionally graded material (bi-FGM) using strain gradient elasticity (SGE) theory. The first crack is aligned along the x 1 -axis, and the second crack is aligned along the x 2 -axis, each obtained by rotating the global x y -coordinate system to their respective local systems. The material gradation within the bi-FGM follows an exponential distribution in the x y -plane. Using SGE theory, which incorporates two characteristic lengths of the material, ℓ and ℓ ′ , to account for the effects of volumetric and surface strain gradients, we adopt a robust methodological framework. This involves the application of Fourier transforms and a novel approach of hypersingular integro-differential equations. By solving the resulting system of equations with Chebyshev polynomial expansion techniques and appropriate collocation points, analytical expressions are obtained for stress intensity factor (SIF), strain distributions, stresses, and crack surface displacement (CSD) profiles for both cracks. An illustrative numerical case study is presented to show the influence of the orientation angle on the various fracture parameters. In addition, we explore the impact of intercrack distances, providing a thorough understanding of the interaction between crack geometry and bi-directional material gradation. Moreover, the variation in the CSD profile under linear and quadratic loading conditions is examined to highlight the influence of loading patterns on crack behavior. These findings offer a deeper understanding of the fracture mechanics in bi-FGMs under the influence of strain gradient elasticity.
Background One of the basic motives for carrying-out the analytical study of delamination reported in this paper is the fact that there are many situations in which multilayered beams are used as moving components in various engineering applications. Very often these components move with acceleration. Therefore, forces of inertia have to be considered when analyzing delamination fracture.Objective This paper is focussed on delamination analysis of a multilayered non-linear viscoelastic inhomogeneous beam structure which rotates around a motionless axis. At the same time, a particle is moving non-uniformly along the upper surface of the beam.Methods The forces of inertia in the system "multilayered beam - particle" are considered and used when analyzing the delamination fracture in terms of the strain energy release rate.Results The strain energy release rate is derived. The integral J is used for confirmation of the strain energy release rate.Conclusions Practical applications of the analysis are presented. The beam thickness is determined by applying the analysis developed. Some important parameters related to the safety functioning of the system "multilayered beam - particle" like critical lengths of the beam and the delamantion crack are also obtained.
This study investigates the mechanical properties and fracture behaviour of unfilled acrylonitrile styrene acrylate (ASA) polymer material produced by 3D printing. Tensile tests and explicit dynamic finite element analysis were conducted on dogbone specimens printed in three directions: XY, XZ and ZX (the plane of the largest surface relative to the build platform). A comprehensive material characterization approach is presented, incorporating scanning electron microscopy (SEM) analysis, stress-strain evaluations, and virtual simulations using finite element analysis (FEA). These simulations have the potential to predict multiple fracture zones, ensuring a cautious design approach that accounts for numerous scenarios beyond the scope of physical test data. A comprehensive thermo-mechanical analysis was performed using GENOA GUI software specifically for the XY and ZX printing directions. The results of the virtual simulation showed good agreement with the experimental data and provided information about the fractures, voids and residual stresses caused by interlayer temperature changes during the printing process.
Recent developments in steel alloys metallurgy followed the automotive industry need for enhanced crash safety, fuel economy and customer satisfaction. In this work, a group of innovative steel alloys, belonging to different Advanced High Strength Steels generations, sourced from available studies, were subject to a comparative study to test their toughness in a reference fracture mechanics scenario. A commercial FEM code was used, employing two widespread approaches to fracture mechanics. The results allowed to make considerations about the use of some popular steel alloys in the automotive industry, highlighting the importance of FEM in the mechanical engineering sector.
In order to investigate fragmentation mechanism in thermally tempered glass, crack propagation and crack divergence were observed with high-speed photography using Cranz-Schardin type camera. Tempered glass of 3.5 mm and 10 mm thick and zone-tempered glass of 5 mm were used as specimens. In addition to the conventionally known bifurcation as crack divergence, branching type was also seen. Differences in propagation energy were seen between bifurcation and branching after at once divergence by Caustics method. Bifurcation and branching mechanism were explained using the concept of stress σ CR which was introduced for explanation crack connection phenomenon seen in zone-tempered glass. The new crack generated by two cracks colliding also existed, and its collision angle of the two cracks had a major influence on its formation by stress σ CR . Stress σ CR was not always explained by stress intense factor K 1 because it has characteristics of time dependance and not necessarily plastic deformation.
Glass strength in plate glass was measured using the Quasi-static method to investigate its mechanical properties. New findings concerned with stress relaxation phenomena being generated at once after loading and time dependent fracture were seen even at room temperature. Load reduction phenomenon at room temperature has gone unnoticed for many years, because its value was 2–4.5 N in Caustics method, although measurement error approximately was 5 N in ordinary 4-point bending test method. Fracture in plate glass was inferred to be caused not only by applied stress to glass but also through complex behavior involving several factors. The concept of stress relaxation phenomenon under strain points that do not occur or occur over a lengthy period of several decades at least will be necessary to reconsider. Almina ceramics showed fracture characteristics closer to plate glass than silicon carbide which also called a ceramics.
The rotating shafts in gearboxes operate at various speeds and loads, which can lead to fatigue failure. One of the fundamental causes of damage is vibration due to unbalance, misalignment, or non-uniformity during rotation, which have a detrimental effect on fatigue strength. In this study, the influence of unbalance parameters on the high cycle fatigue behavior of AISI 1045 steel drive shafts was investigated. A completely new fatigue testing equipment is proposed and fully fabricated to examine the factors such as eccentricity due to test mass assignment, operating speed and loading radius affecting fatigue strength of AISI 1045 steel. The results show that the fatigue strength of the unbalanced specimen is lower than that of the pure bending specimen.
This paper uses five materials to compare and analyze the life estimation results of six commonly-used critical plane models for multiaxial fatigue life. It is found that the estimation results of different models differ significantly for the same material. For the different materials, the estimation results of the same model are sometimes lower than the test results and sometimes higher than the test results. Among the six commonly-used critical plane models, the Fatemi-Socie model can provide satisfactory fatigue life prediction results for shear cracking materials. The reliability of life estimation results by different life prediction models depends on whether the fatigue damage parameters in the prediction model are reliable, and also on whether the expression of the prediction model is reasonable. In addition, the prediction results of the model are also related to the cracking form of the material. Based on the verification results, the applicability of each model was evaluated, and it was pointed out that further research is needed on the applicable conditions of commonly-used critical plane models.
In this study, interaction between a main crack and a surrounding layer of cracks is considered. Stress Intensity Factors during these interactions are obtained using Dimensional analysis (DA) based on the J-integral method. Amplification and shielding effects on the resulting stress field are shown. Besides, orientations as well as positions of cracks with respect to the main crack are considered as crucial parameters to quantify these effects. A series of illustrated examples is given and obtained results are compared with those of other researchers.
Gas turbines require proper operation and maintenance, and predicting the creep crack initiation life of turbine blades made of a solidification-controlled Ni-based superalloy is crucial. A unified life assessment method was developed to assess creep crack initiation life at various stress-concentrated regions, using a misorientation parameter which is equivalent to the relative notch opening displacement. This parameter can predict creep crack initiation life using crystal orientation distribution measured by the EBSD method. In this study, the influence of the specimen plate thickness was investigated, and it was confirmed that there is no issues with practical applicability.
The influence of various patch shapes with different composite materials on the behavior of the repaired aluminum (2024-T3) plate with a central circular notch was investigated. Finite element analysis FEA for different scenarios of the repaired plate has been performed to obtain normal stress σ Y and stress concentration factor SCF. Comparison of FEA results was done to investigate the effect of parameters such as the material and shape patch. Also, the comparison between the effects of using a single patch and a double patch on the repaired plate was done. In the analysis, the patch shapes considered with the same volume are rectangular, circular, trapezoidal, triangle, regular hexagonal, rotated regular hexagonal, elliptical, rotated elliptical. Based on the reduction of SCF and σ Y , the comparison of results revealed that the optimum composite patch shape applied on a central circular notch plate, repaired, depends on the repair method, i.e., using a single or double patch. The optimum patch shape is a rotated regular hexagonal shape when using a single patch, but a rectangular shape when using a double patch.
This manuscript presents a moving semipermeable crack based on an electric-magnetic-polarization saturation (EMPS) model in magneto-electro-elastic (MEE) materials using the singular integral equation method. Propagation velocity-dependent a system of singular integral equations has been developed based on the EMPS model. Analytical solutions of developed singular integral equations and other fracture parameters are presented in this manuscript. Electric and magnetic semipermeable crack face boundary conditions have also been implemented at the center of the crack based on closed-form solutions with the help of an iterative method. Electric displacement, magnetic induction at the center of the crack, electric and magnetic zone lengths, and local stress intensity factors have been studied with respect to electric, magnetic, and mechanical loading for different propagation velocities. The final reveal is that electric displacement at crack surfaces has a miner effect with respect to magnetic loading. In contrast, electric displacement increases as electric loading increases and decreases as mechanical loading increases for all propagation velocities. Moreover, Normalized electric zone length and crack tip opening potential (CTOP) have a miner effect with respect to magnetic loading, while significantly affected with respect to electric and mechanical loading.
This study investigates the mechanical behavior of hybrid composites reinforced with natural jute fiber and glass fiber in varying volume fractions, using a constant volume of epoxy resin. Specimens were fabricated using the hand layup method and subjected to tensile testing as per ASTM standards. Different volume fractions and fiber orientations were tested under eccentric tensile loading, with varying single edge notch to width (a/W) ratios. The results revealed that as the jute fiber volume fraction increased, both fracture load and fracture toughness decreased. Additionally, fracture load decreased with increasing (a/W) ratio, while fracture toughness showed an increase. Specimens with 0 degrees/90 degrees fiber orientation exhibited the highest fracture load and toughness. Statistical and fractographic analyses validated the experimental findings, with Taguchi method ranking jute fiber percentage as the most significant factor influencing fracture behavior, followed by the (a/W) ratio. ANOVA results confirmed that jute fiber percentage was the dominant factor. Minimal error was observed in the confirmation experiments during regression analysis. Scanning Electron Microscopy (SEM) of fractured surfaces revealed that the interaction between epoxy, jute, and glass fibers had a significant impact on fracture load and toughness. The findings offer an in-depth understanding of the influence of jute fiber content and (a/W) ratio on the mechanical properties of jute-natural epoxy hybrid composites.
Water hammer is a common hydraulic phenomenon in industrial systems, particularly in aerospace and automotive applications. It occurs when fluid pressure inside a pipeline increases dramatically over a very short period, potentially causing loud banging noises, vibrations, and system damage. This paper first conducts an experimental study on the water hammer effect in a hydraulic pipeline of an aircraft, analyzing the characteristics of water hammer pressure and pipeline strain. A finite element model of the water hammer effect is then established for the experimental system, allowing for numerical simulations using AMEsim. Finally, the finite element model of the pipeline is created in ANSYS, and the strain responses are analyzed using the fluid-structure interaction (FSI) method, with the numerical simulation results from AMEsim as input conditions. The findings show that the numerical simulation results for water hammer pressure are in good agreement with experimental data, with most errors within 2% and a maximum error of 4.88%. The strain simulation results also demonstrate good consistency with the experimental data, with most errors within 4% and a maximum error of 7.56%. Finally, the fatigue damage and fatigue life of the pipeline under the conditions of water hammer fluctuations were analyzed.
Background Given their distinct composition and gradient structure, cracks in functionally graded materials (FGMs) can provide serious difficulties. Predicting failure and improving material design require an understanding of fracture dynamics in FGMs. The manner in which cracks initiates and propagates can be influenced by the constant changes in material properties. Because of variations in material toughness over the gradient, cracks propagate differently than in homogeneous materials.Objective The FGM is loaded in three point bending and four point bending loading conditions, and the obtained crack propagation angles and crack propagation paths are showcased in the present paper.Methods A functionally graded material beam (FGM) is modeled using dummy thermal load condition for obtaining varying material properties in desired direction for finite element analysis. An initial crack/defect is incorporated in the FGM beam at bottom mid location. The FGM beam is considered as simply supported beam and the same boundary conditions are applied to it.Results Detailed comparison of crack propagation paths is made between the three point bending and four point bending loading conditions.Conclusion In case of three point bending loading only mode I condition of failure is occurring, where as in case of four point bending loading all the three modes condition i.e., mode I, II & III of failure is occurring also called as mixed mode failure condition.
A prediction model for a weld hydrogen cracking, so called cold cracking, in high strength steel welds was developed by a coupled thermo-elastic-plastic and hydrogen diffusion analysis in the y-groove weld joint. In the weld cracking tests, the critical preheat temperature to prevent cracking was increased with thicker plate thickness and higher hydrogen concentration in the weld metal. The cracks were initiated at the weld metal in the root region where exhibits significant tensile residual stress by the welding. The y-groove weld joints with different plate thickness were modeled by FEM with the actual weld configuration and material properties in the base metal, heat affected zone (HAZ) and weld metal. Hydrogen was put in the weld metal as an initial condition, then welding simulation was conducted by a coupled thermo-elastic-plastic and hydrogen diffusion analysis. In the hydrogen diffusion analysis, the α -multiplication method, which stress gradient term in the diffusion law was multiplied, was applied to express realistic hydrogen diffusion enhanced by a hydrostatic stress field. Hydrogen accumulation occurred in the root region which showed highest residual stress. The point showing highest hydrogen accumulation was well corresponded to the crack initiation site. It was found that cracking was enhanced with thicker plate and higher initial hydrogen concentration because of higher tensile residual stress and higher hydrogen accumulation in the root region, respectively. Based on the FE analysis and comparison with the experimental results, the local criterion for weld cold cracking was proposed that can be useful to estimate the critical preheating temperature in the y-groove weld tests with different welding conditions.
The bow spring centralizer is a crucial tool for enhancing casing centralization and cementing quality. In order to study the replacement of metal materials by thermoplastic composite materials with bow-spring centralizers, this paper completed the mechanical experiment of thermoplastic composite materials, studied the numerical simulation analysis of the working process of the bow centralizer of thermoplastic composite materials, and explored the influence law of the bow wall thickness, radius, chord length and limiting distance of the bow-spring centralizer on the mechanical properties. The results indicate that thermoplastic composite materials can replace metal materials; increasing the wall thickness of the bow can enhance the reset force and load-bearing capacity; as the bow radius and chord length increase, the reset force initially increases and then decreases, while the tensile and compressive stresses shows little variation; the limiting distance can effectively improve the reset force, but it may lead to an increase in local pressure stress of the bow-spring centralizers,the trends of the restoring force and stress changes are consistent with those expressed by the pseudo-rigid body analytical formula. For a 5.5-inch thermoplastic composite bow spring centralizer, the optimal structural parameters are: a wall thickness of 9 mm, a radius of 325 mm, a chord length of 255 mm, and the best limiting distance is 4 mm.
The aim of this work is to investigate fracture mechanical characteristic of aluminum alloy 6061 by the small punch test in low range of deformation rate. The results of the force-displacement of the puncher curve and scanning electron microscope observation of fracture surface of deformed specimen are used to discuss fracture toughness of the material. The obtained results show that the influence of the displacement rate on the force - displacement of the puncher cannot be clearly seen. The mechanism of fracture properties of aluminum alloy 6061 is quite complicated and there is a large difference between the fracture surface of the top side which contacts with the punch head and the fracture surface of the bottom side. The bottom side shows not only crack in the direction perpendicular to the applied external force but also crack along the direction of the crack ring. The local ductile fracture might dominate to induce the initial crack due to shear stress. Then, the crack spreads via the direction perpendicular to the applied external force as well as along the direction of the crack ring without any dimples. Meanwhile, tensile stress plays an important role in breaking the specimen in half.
BACKGROUND: The feed pipeline made from 30408 stainless steel of a new unit leaked during the air pressure test. OBJECTIVE: The present work aims to examine the specific cause of pipeline cracking, and providing effective approaches to avoid similar failures. METHODS: Macroscopic inspections of the cracked pipe defects were made on site immediately after leakage. Mechanical properties and hardness of specimens machined from the failed pipe were tested. In addition, microscopic analyses including material composition, microstructure observation and crack morphologies of the failed part were performed to get detail information. Composition of the feed raw material was also analyzed to identify whether it had been contaminated by corrosive elements or not. RESULTS: No impurity composition was found in the feed raw material. The element constituents, yield strength, tensile strength and hardness of the cracked pipe fulfill standard requirements. A number of scratches and defects with a size of several microns were found on the inner wall of the leaked pipe, and they were believed to be formed at the perforation step during pipeline processing. Liquation cracks were found at the pipeline butt weld joint, and they laid hidden dangers for the safety and steady operation of the pipeline. CONCLUSION: The overall analysis results indicated the pipeline leakage during air pressure test was caused by cracks initiated around inner wall defects, which sabotaged the bearing capacity of the pipe by wall thickness reduction and stress concentration. Therefore, improving the inner wall surface quality at the perforation step may help to avoid such failure. The metallurgical effect and weld stress caused during the welding process promoted the initiation and propagation of liquation cracks. The tendency of welding hot crack formation could be reduced by taking strict composition control of the welding rod and adopting reasonable welding parameters.
