Search Results (52)

This study reveals the Vierendeel mechanism of hybrid high-strength steel composite cellular beams (HHS-CCBs) through experimental investigation and finite element analysis (FEA). The forces acting on the openings of composite cellular beams (CCBs) are further analyzed. A calculation method is developed to evaluate the load-carrying capacity of HHS-CCBs under the combined action of bending moment and shear force, which takes into account the shear contributions of the concrete slab and beam flange at circular openings. The accuracy of the proposed formula and the influence of key parameters on load-carrying capacity are thoroughly examined through FEA. The results indicate that within the range of D = 0.6h_s − 0.7h_s and L = 0.7h_s − 1.0h_s (D and L represent the hole diameter and edge distance, respectively; h_s is the height of the steel beam), stress concentration at the beam-end welds could be avoided, the formation of Vierendeel mechanism at the beam-end opening could be ensured, and excessive reduction in load-carrying capacity could be prevented. Furthermore, the high-strength steel (HSS) flange strength and location had a minimal effect on the failure mode of HHS-CCBs. As the flange strength increased, full plasticity was not achieved in the cross-section, and the load-carrying capacity increased nonlinearly. Asymmetric specimens with HSS in the lower flange only and symmetric specimens with HSS in both the upper and lower flanges exhibited comparable load-carrying capacities. The load-carrying capacity calculation formula is applicable to HHS-CCBs with different section types, provided that circular holes are present in the beam web and Vierendeel mechanism damage occurs. However, the flange width–thickness ratio must not significantly exceed the specified limit. Full article

The stress concentration, which appears in loaded structural elements with voids, holes or undercuts, is the main source of premature fatigue failure. So, an increase in fatigue life can be achieved by reducing stress concentrations around the notches. Different techniques can be used to reduce the stress concentration. One of them is the application of additional stress relief undercuts or holes, while a second one relies on the application of overlays glued in the vicinity of notches. The proposed study is focused on the optimisation of notched specimens using a multi-stage optimisation process, including the use of artificial neural networks (ANNs). On this basis, the comparison of the effectiveness of various modern finite element optimisation tools is made. Here, special attention is paid to samples with elliptical holes and the application of the ANN technique in determining the optimal solution for the configuration of stress relief holes. The proposed study is illustrated by the example of a steel specimen with an elliptical opening. Specimens without stress relief holes and with an optimal configuration of stress relief holes are subjected to fatigue tests to confirm the effectiveness of the proposed approach. The performed study revealed that the cutting of additional circular stress relief holes reduces the stress concentration around the elliptical opening by about 12% and leads to an increase in fatigue life by about 79% for the applied material. Moreover, the comparison of the possibilities of the reduction in SCF by the application of stress relief holes, composite overlays and the simultaneous application of composite overlays and stress relief holes for the investigated notched samples is performed. Following the numerical results, it is observed that the use of composite overlays additionally decreases the stress concentration factor in relation to specimens with stress relief holes by an additional 6%. Full article

Many existing reinforced concrete (RC) frames with brick infill walls are vulnerable to earthquake damage, particularly when the walls contain window openings that reduce the lateral resistance. This study aims to examine the seismic performance of RC frames strengthened with U-shaped precast concrete (PC) wall panels. In the proposed method, the window-containing brick infill walls within the RC frames are replaced with factory-fabricated U-shaped PC wall panels, thereby converting the infill into a strong and rigid structural element while preserving the openings. The panels are anchored to the RC frame using post-installed anchors inserted through predrilled holes, allowing for rapid and secure installation with minimal on-site work. To validate the method, five full-scale, one-bay, one-story RC frames were constructed and tested under reversed cyclic lateral loading. Three frames were strengthened with U-shaped PC wall panels of varying thicknesses and large openings. Displacement-controlled cycles following ACI 374.1-05 (R7.0) were applied, with three cycles at each drift ratio stage, and no axial load was applied to the columns. Compared with the reference specimen with a U-shaped brick wall, the strengthened frames exhibited up to 3.29 times higher lateral strength, 4.39 times higher initial stiffness, and 4.33 times greater energy dissipation capacity. These findings demonstrate that the proposed strengthening technique significantly enhances seismic resistance while maintaining the architectural openings, offering a practical and efficient solution for upgrading low-rise RC buildings. Full article

This study investigates the influence of drilling-induced delamination damage on the compressive mechanical behavior of open-hole carbon fiber-reinforced composite laminates and explores the failure mechanisms under dual-defect coupling effects. Specimens with circular delamination defects of varying sizes were fabricated by embedding polytetrafluoroethylene (PTFE) films during the layup process. Ultrasonic C-scan and digital image correlation (DIC) techniques were used to monitor delamination propagation and deformation behavior. A cohesive zone-based numerical model was developed and validated against experimental results to reveal the three-stage failure process in single-defect cases. The validated model was then used to analyze the coupling effects of dual defects (same side and opposite side). The results show that dual delamination defects significantly reduce the compressive load-bearing capacity of open-hole composite laminates. Specifically, same-side defects exhibit a failure mode similar to single-defect structures, while opposite-side defects display a unique failure behavior characterized by dual-crack propagation, further reducing the compressive load-bearing capacity. Full article

The effects of opening size and braiding angle on the tensile behavior of 3D five-way braided composites were systematically studied, and the mechanical properties, failure modes, and fracture characteristics of the composites were comprehensively analyzed. Initially, a static tensile test was conducted. The results demonstrated that both the tensile strength and tensile modulus of the three-dimensional (3D) braided composites decreased as the braiding angle increased. The sensitivity of the tensile modulus to the aperture size increased significantly as the aperture increased. For specimens with varying braiding angles, smaller apertures were more effective in withstanding higher stress concentrations around the opening, with minimal impact on the tensile strength. In comparison to the laminate composites, the 3D braided composites, regardless of braiding angle, retained higher tensile strength after hole formation at the same aperture size. The fracture of the samples was observed and captured using an optical microscope. It was observed that the failure mode of the 3D braided composites progressively transitioned from fiber fractures to interface debonding with an increase in the braiding angle. After hole formation, stress concentration at the aperture edge caused crack propagation along the braiding direction. Larger apertures resulted in more severe cracks, ultimately leading to specimen failure. Full article

To investigate the mechanical behavior of precast columns with openings in the beam–column joint core area under axial loads, a systematic study was conducted to examine the effects of the opening parameters on the axial mechanical performance of precast columns. Two sets of six precast concrete column specimens, with opening ratios of 14% and 22%, respectively, were designed and subjected to axial compression tests. The failure patterns, opening ratios in the core area, and other relevant parameters of the specimens were thoroughly analyzed. Additionally, a finite element model incorporating material non-linearities was developed using ABAQUS (2022) software, and parametric numerical simulations were conducted to further explore the structural response. The results indicated that the variations in the opening ratio had no significant effect on the cracking load of the specimens. However, as the opening ratio increased, the peak load of the compressed columns increased by 8.6%, and the ductility factor increased by 12.9%. The study also reveals that opening ratios below 30%, the casing thickness, and the bolt preload have minimal impact on the bearing capacity of precast columns. These findings provide theoretical support for optimizing hole sizes in dry bolted connections for precast concrete structures. Full article

Acid fracturing is a crucial method for reservoir reconstruction in carbonate reservoirs, and the propagation pattern of acid-etched fractures plays a key role in determining the scope of reservoir enhancement and post-fracturing productivity. However, large-scale physical simulations directly using acid solutions in fracturing experiments are limited, and the fracture propagation patterns under acid fracturing remain unclear. To address this gap, in this study, we collected carbonate rock samples from the Majiagou Formation in the Daniudi area, preparing large-scale fracturing specimens with side lengths of 30 cm. The propagation of acid fracturing fractures was investigated using self-developed true-triaxial acid fracturing equipment. Based on post-fracturing fracture morphology and pressure curves, the effects of fracturing fluid type, injection rate, injection mode, and natural fractures (NFs) on acid fracturing fracture propagation were analyzed. The experimental results showed that the acid solution effectively weakens the mechanical properties of the open-hole section, creating multiple mechanical weak points and promoting the initiation of fractures. Pre-fracturing treatment with low-viscosity acid can significantly enhance fracture complexity near the wellbore and expand the near-well stimulation zone. Lowering the injection rate increases the acid solution’s filtration loss into natural fractures, weakening the cementation strength of these fractures and encouraging the formation of complex fracture networks. Furthermore, employing a multi-stage alternating injection of high-viscosity and low-viscosity acids can reduce fracture temperature and acid filtration loss while also enhancing differential etching through viscous fingering. This approach improves the conductivity and conductivity retention of the acid-etched fractures. The results of this study can provide a reference for the acid fracturing stimulation of fractured carbonate reservoirs. Full article

The purpose of this article is to inform the reader about the results of an experimental investigation into the appropriate manifold geometry for an air-cooled inverter, which is manufactured from an AlSi10Mg powder material using SLM technology. The best approach is to optimize the part geometry for SLM technology so that the placement of support structures required for model fabrication is eliminated as much as possible. A suitable solution was selected based on the design of the most appropriate cross-sectional shape of the openings with the smallest dimensional accuracy deviation and shape deformation. In the experiment, three test specimens were designed; each of them contained eight holes of different shapes, particularly square, rhombic, and circular, with a given range of sizes. The results of the experimental study can help designers select the optimal design of vents and cavities for the chosen AM technology, e.g., for conformal cooling systems. Full article

Simulating composite material structures requires complex constitutive models, which normally require fine meshes to obtain an accurate prediction of their behavior. Pam-Crash software has been used for several years in the automotive industry and has been proved to be an efficient tool for simulating metallic structures, returning good correlations in a fast computational time. However, constitutive models for composite materials in Pam-Crash present some difficulties: some materials are not able to be suitably modeled and the predictive results depend on the mesh refinement. This work proposes a solution for predicting the progressive damage of composite materials in Pam-Crash, which scales the energy dissipated by the damage mechanisms and checks the viability of modeling the material behavior, taking into account the recommended size of finite elements in the automotive industry. The proposed solution is applied for the simulation of Open Hole specimens to evaluate the ultimate strength consistency. After this, it is applied for the simulation of Compact Tension specimens to check the consistency of crack propagation behavior. By considering the target size of the finite elements in the material card definition, the predictions demonstrate great improvement in the equivalence in results between different mesh refinements. Finally, the solution is applied to simulate impact tests on large structures. Good correlations with experimental data are obtained in fast computational times, making this methodology a candidate for application in composite-related automotive simulations. Full article

The scaling of the strength of composite parts with part size is referred to as the size effect. In the presence of notches, stress concentration affects a portion of material that increases with the notch size. Furthermore, in woven composites, the notch and tow size can be comparable, thus demanding a mesoscale approach to properly capture the stress intensification. In this paper, a probabilistic mesoscale method to model the size effect in notched woven composites is presented. First, the stress distribution is estimated with a finite element model, calibrated on experimental Digital Image Correlation data. The FE model simulates the mesoscale heterogeneity of the woven reinforced material and replicates the local stress intensification at the tow level. Then, a three-parameter Weibull-based statistical model is introduced to model the probability of failure from the calculated stress distribution and the volume of the part. An equivalent stress is used to capture the relevant fiber and matrix failure modes and the maximum value within the specimen volume is the random variable of the model. The method is applied to open-hole tension tests of a woven twill carbon fiber–epoxy composite. Two specimen widths and three width-to-diameter ratios, from 3 to 12, are considered. Specimen width produced an observable size effect, whereas the variation of hole size in the range considered did not. The statistical model is found to accurately describe the experimental observations, efficiently replicating an inverse size effect, regardless of hole size, while wider specimens lead to a lower probability of failure. Full article

In rock engineering, the dynamic loads caused by mechanical action and rock blasting have an extremely significant influence on the stableness of surrounding rock masses. To examine the impact of dynamic load on the mechanical properties and fracturing characteristics of hard rocks as well as the failure responses of underground openings, a number of prismatic samples with holes of different numbers and configurations were prepared for dynamic tests employing an SHPB loading device. The experimental results demonstrate that the order of dynamic compressive strength of each group of samples under the impact nitrogen pressure of 0.45 MPa is: G3 > G2 > G5 > G4 > G7 > G6, and the dynamic deformation process of the samples is parted into three phases: linear elastic deformation, plastic deformation and post-peak deformation. A total of three categories of cracks, i.e., spalling cracks, shear cracks and tensile cracks, occur in the specimens. The failure mode of the samples having one or two holes arranged in a vertical direction is controlled by shear cracks, whilst that of the rest groups of pre-holed specimens belongs to tensile-shear failure. The existence of the fabricated holes in the samples significantly weakens the mechanical properties and affects the fracture evolution characteristics, which rely on the quantity and layout of the cavities in the specimens. The interesting results are also discussed and explained, and could supply some insight in the mechanisms of tunnel surrounding rock failure and rock dynamic hazards such as rock burst. Full article

The primary focus of this paper is to investigate the application of ANSYS Workbench 19.2 software’s advanced feature, known as Separating Morphing and Adaptive Remeshing Technology (SMART), in simulating the growth of cracks within structures that incorporate holes. Holes are strategically utilized as crack arrestors in engineering structures to prevent catastrophic failures. This technique redistributes stress concentrations and alters crack propagation paths, enhancing structural integrity and preventing crack propagation. This paper explores the concept of using holes as crack arrestors, highlighting their significance in increasing structural resilience and mitigating the risks associated with crack propagation. The crack growth path is estimated by applying the maximum circumferential stress criterion, while the calculation of the associated stress intensity factors is performed by applying the interaction integral technique. To analyze the impact of holes on the crack growth path and evaluate their effectiveness as crack arrestors, additional specimens with identical external dimensions but without any internal holes were tested. This comparison was conducted to provide a basis for assessing the role of holes in altering crack propagation behavior and their potential as effective crack arrestors. The results of this study demonstrated that the presence of a hole had a significant influence on the crack growth behavior. The crack was observed to be attracted towards the hole, leading to a deviation in its trajectory either towards the hole or deflecting around it. Conversely, in the absence of a hole, the crack propagated without any alteration in its path. To validate these findings, the computed crack growth paths and associated stress intensity factors were compared with experimental and numerical data available in the open literature. The remarkable consistency between the computational study results for crack growth path, stress intensity factors, and von Mises stress distribution, and the corresponding experimental and numerical data, is a testament to the accuracy and reliability of the computational simulations. Full article

The failure of composite laminates under cyclic fatigue loads is complex, as multiple failure mechanisms are in play at different scales and interact with each other. Predicting the remaining fatigue life as well as the residual capacities of a composite laminate or component is crucial, particularly for safety-critical applications. A progressive fatigue model is proposed to describe the catastrophic failure of open-hole laminates under tensile cyclic fatigue. To represent both intra-laminar and inter-laminar damage, a combination of a continuum damage mechanics model (CDM) and a discrete cohesive zone model (CZM) is implemented in the finite element (FE) software Abaqus. The CDM combines fibre- and matrix-dominated S-N curves with the Palmgren–Miner accumulation rule and Hashin’s residual strength to form a fatigue failure criterion differentiating between fibre failure (FF) and matrix failure (MF). The CZM implemented in this work is the CF20 model proposed by NASA. Fatigue cycling is simulated using an external cycle-jump scheme, where the stiffness degradation is conducted between the FE simulations outside of the implicit solver [90/0] s. Glass fibre reinforced polymer (GFRP) open-hole specimens were tested in tensile cyclic fatigue at a load ratio of 0.1. The experiments were reproduced numerically and the results compared. After calibration of a set of parameters based on one load level, the model was able to reproduce the experimental S-N curve very well, predicting a slope of −0.10, while the experimental value was −0.11. The failure sequence of the laminate was also successfully reproduced. The growth of the split from the hole, and its interaction with inter-laminar delamination, was successfully captured. The proposed approach was able to describe the fatigue failure of an open-hole laminate with a minimal set of material inputs using a simplified fatigue damage model while avoiding convergence issues. Full article

In this paper, the damage initiation/propagation mechanisms and failure modes of open-hole carbon fiber-reinforced thermoplastic composites and thermosetting composites with tension, compression, and bearing loads are investigated, respectively, by experiments and finite element simulations. The experimental evaluations are performed on the specimens using the Combined Loading Compression (CLC) test method, the tensile test method, and the single-shear test method. The differences in macroscopic damage initiation, evolution mode, and damage characteristics between thermoplastic composite materials and thermosetting composite material open-hole structures are obtained and analyzed under compressive load. Based on scanning electron microscope SEM images, a comparative analysis is conducted on the micro-failure modes of fibers, matrices, and fiber/matrix interfaces in the open-hole structures of thermoplastic and thermosetting composites under compressive load. The differences between thermoplastic and thermosetting composites were analyzed from the micro-failure mechanism. Finally, based on continuum damage mechanics (CDM), a damage model is also developed for predicting the initiation and propagation of damage in thermoplastic composites. The model, which can capture fiber breakage and matrix crack, as well as the nonlinear response, is used to conduct virtual compression tests, tensile test, and single-shear test, respectively. Numerical simulation results are compared with the extracted experimental results. The displacement-load curve and failure modes match the experimental result, which indicates that the finite element model has good reliability. Full article

Thermoplastic composite structures possess superior properties compared with thermosetting composites, including recyclability and high damage tolerance. However, the poor adhesion properties of thermoplastic composites make their joining process challenging. In this research, three bonding techniques, namely adhesive, mechanical joining, and hybrid bonding, are investigated using lap shear specimens to evaluate their mechanical properties and failure modes. The stress distributions at the joints of the three bonding techniques are analyzed by numerical simulation. The findings demonstrate that hybrid bonding enhances the strength of composite joints, albeit at the expense of some stiffness due to the presence of an open hole. This method is particularly suitable for applications that necessitate robust connections requiring high strength. Full article