Search Results (188)

Repeated impact loading can induce progressive fatigue delamination in composite laminates, in which both damage accumulation and strain-rate sensitivity of the interlaminar interface play important roles. In this work, an adopted rate-dependent fatigue cohesive formulation is extended to a three-dimensional framework for simulating interlaminar delamination in composite laminates subjected to repeated impact. The constitutive formulation incorporates separation-rate-dependent critical tractions and fracture toughness together with cumulative fatigue damage, enabling a unified description of dynamic rate effects and progressive interface degradation. A time-incremental algorithm is developed and implemented in ABAQUS 2020/Explicit through a user-defined cohesive element subroutine (VUEL). The cohesive formulation is further coupled with the Hashin intralaminar failure criterion to represent the interaction between interlaminar delamination and intralaminar damage. Numerical simulations are conducted for composite laminates with three structural configurations—conventional, drop-off, and wrapped drop-off—to systematically examine the influence of rate dependence on fatigue delamination under repeated impact. The results show that the developed framework captures the progressive evolution of delamination and impact response under repeated impact and indicate that the sensitivity to rate-dependent interlayer properties depends on both laminate configuration and impact velocity. The present study provides a feasible computational framework for the comparative simulation and assessment of fatigue delamination under repeated impact and offers numerical insight into the role of structural configuration and interfacial rate dependence in composite laminates. Full article

This paper presents a hybrid 1D–3D computational framework for the dynamic analysis of lattice metamaterials for impact protection. Periodic and stochastic lattices are generated automatically; slender members are modeled with beams, and selected regions are locally enriched with 3D solids, with an interface strategy ensuring kinematic compatibility. A PA12 octagonal lattice (30 × 30 × 25 mm) is compressed in Abaqus/Explicit at a high strain rate. Two hybrid configurations, differing by the placement of a 3D unit cell, are compared to a beam-only reference. Global responses (modulus, densification strain, absorbed energy) are consistent across models, while the hybrid scheme recovers local stress concentrations and failure. Full article

In many densely populated towns and semi-urban areas, masonry buildings often stand close to busy roads, exposing them to blasts from improvised explosives or other localized sources. Such structures are rarely designed to resist sudden explosive forces, making severe damage or even progressive collapse likely. Even moderate-intensity blasts can weaken walls, endanger occupants, and cause significant property loss. Unlike reinforced concrete, masonry is highly susceptible to explosive impact. Therefore, understanding how these buildings behave under blast loads and developing affordable protection methods is crucial. Low-rise unreinforced masonry (URM) structures, usually up to about 13 m in height (roughly 2–4 stories), common in villages, semi-urban regions, and conflict-prone zones, are particularly at risk. In many areas, these poorly constructed buildings lack proper engineering design and are therefore highly vulnerable to blast damage. Non-load-bearing internal dividers and perimeter enclosures are especially prone to lateral displacement, which can initiate instability and, in severe cases, lead to overall structural failure. This research focuses on reducing catastrophic damage in URM walls when exposed to close-proximity blast forces using concrete-based protective coatings, both with and without embedded steel-welded wire mesh. The study references a previously tested laterally supported clay brick wall built with cement–sand mortar as the baseline model, with its behavior validated against experimental findings from existing literature. Two blast cases were considered corresponding to scaled stand-off distances of 2.19 m/kg^1/3 and 1.83 m/kg^1/3, representing moderate flexural-shear cracking and full structural failure, respectively. To replicate the observed behavior, a comprehensive 3D numerical simulation was developed using the ABAQUS/Explicit 2020 solver. The model’s predictions were benchmarked and verified through comparison with reported test data. While both blast intensities were used to confirm computational accuracy, the effectiveness of UHPC and UHPFRC protective coatings with and without embedded wire mesh was specifically evaluated under the more severe collapse scenario (Z = 1.83 m/kg^1/3). Results indicated that at a scaled distance of 1.83 m/kg^1/3, the uncoated URM wall could not withstand the blast because of poor tensile and bending capacity. In contrast, the UHPC- and UHPFRC-coatings provided improved confinement and better stress distribution. When welded wire mesh was embedded, crack control improved further, the interface bond strengthened, and a larger portion of blast energy was absorbed and dissipated. Full article

In the aviation industry the so-called ballistic impact of small accidental or human-made sources on aircraft elements during their service life encompasses several scenarios of practical interest. The experimental assessment of ballistic impact requires dedicated infrastructures (such as the light-gas gun system utilized in this study) and exhibits intrinsic difficulties, mainly concerning the proper acceleration of a projectile and the accurate measurement by a high-speed camera of its (inlet and outlet) velocity. As a first objective, this study aimed at characterizing the dynamic response of fiber metal laminates, manufactured ad hoc by the authors with two different stacking sequences currently not available in commerce. The layups included aluminum 2024 T3 and aramid fiber-reinforced prepregs, leading through specific treatments to excellent specific properties. The collision of the laminate with a 25 g, 9 mm radius steel sphere, traveling at speeds ranging from 90 to 145 m/s, caused a variety of scenarios: partial or complete penetration, with the projectile passing through and continuing its trajectory, remaining stuck in the sample (embedment) or even being bounced back (ricochet). The experimental information led to the estimation, for each typology of sample, of a conventional ballistic limit according to the Lambert-Jonas approximation, as a second objective, these data were utilized to validate an accurate heterogeneous model of the samples developed in the ABAQUS^® platform, discretized by finite elements in explicit dynamics and including geometric nonlinearity and contact. We describe plasticity and damage of the metal layers by the Johnson–Cook phenomenological model, progressive failure in the fiber-reinforced plies through a 2D Hashin criterion with damage evolution, and interlaminar debonding at multiple cohesive interfaces governed by the Benzeggagh–Kenane criterion. The outlet speed of the bullet measured during the experiments was retrieved correctly by this model, and a satisfactory agreement of the finite element predictions was found with the deformation patterns and the damage mechanisms identified by post mortem visual inspection. Finally, several discussion points are raised, concerning the robustness of the numerical analyses, the reliability of the constitutive modeling and the identification of the governing parameters. Full article

Man-made hazards pose serious threats to the safety and preservation of heritage structures. With armed conflict becoming increasingly prominent, it is urgent to enhance our understanding of how these structures respond under extreme conditions to drive conservation strategies. The Citadel of Aleppo in Syria, placed on the List of World Heritage in Danger in 2013 due to the civil war, tragically exemplifies the vulnerability of cultural heritage in times of conflict. In such a framework, this study focuses on the Minaret of the Ayyubid Great Mosque of the Citadel of Aleppo as a representative masonry tower to investigate the effects of man-made threats. Based on a 3D finite element model built in the Abaqus/Explicit environment, blast scenarios associated with aviation bombs and human-borne improvised explosive devices (IEDs) were simulated. The Conventional Weapons Effects (CONWEP) model was used to assess the structural response to blast pressures, also as a function of charge size, standoff distance, and modelling parameters (mesh size, strain rate). This study’s outcomes provide insights into the potential damage caused by aviation bombs and IED attacks, advancing the understanding of the vulnerability of tower-like masonry structures to such hazards while also informing future conservation strategies. Full article

This study develops a novel Locally Rib-Reinforced Rotational Hexagonal Honeycomb (LRRH) model. The objective is to systematically enhance the model’s mechanical performance and energy absorption efficiency through geometric morphology construction. The structure combines triangular and hexagonal units through a rotational arrangement, forming a rotating rigid structure (RRH), upon which re-entrant parallelogram units are embedded. A Finite Element simulation was developed in Abaqus/Explicit. Its reliability was validated by comparing the numerical predictions against the outcomes of quasi-static compression experiments. The axial impact response and energy absorption attributes of the configuration were thoroughly evaluated by adjusting the hexagonal cell angles and applying a symmetric design approach. The experimental outcomes indicate that the SEA of the RRH-Type I-180°-180° model surpasses that of the RRH-Type I-105°-105° by 43.68%, and the SEA of the LRRH-Type I-105°-105° achieved a significant 97.88% increase compared to the LRRH-Type I-180°-180° variant. Meanwhile, the SEA of the RRH-Type I-180°-180° honeycomb increased by 121.2% and 11.79% compared with the LRRH-Type I-180°-180° and LRRH-Type I-105°-105° structures. Parametric analysis results indicate that wall thickness and impact velocity are critical factors influencing energy absorption performance. The enhancement of structural thickness considerably strengthens its flexural resistance and pressure tolerance. Full article

Ultrasonic Impact Treatment (UIT), a prevalent surface-strengthening technology for welded structures, combines mechanical shock and ultrasonic vibration to induce plastic deformation and beneficial residual compressive stress at weld toes, effectively enhancing welded joint fatigue performance. This study adopts a full-process numerical simulation approach, integrating the finite element software ABAQUS and FE-SAFE fatigue-life prediction platform to investigate QSTE700TM high-strength automotive steel butt joints. Considering welding-induced initial residual stress, ABAQUS simulates the welding and subsequent UIT processes; explicit dynamic analysis reveals residual stress evolution, with pre- and post-UIT stress-distribution comparisons. The post-UIT residual stress field is input into a static tensile model to obtain load-stress distributions, which are then imported into FE-SAFE with S-N curves for fatigue-life prediction. Simulation results align well with experimental data: UIT improves the fatigue limit of welded specimens by 31.3% and unwelded ones by 42.9%. Additionally, optical and scanning electron microscopes observe fatigue fracture morphologies to further clarify UIT’s fatigue-enhancement mechanism. Full article

This study presents a hybrid experimental–numerical methodology for the preliminary design and optimization of a CFRP crash box intended for high-performance automotive applications. An initial experimental campaign was conducted on frustum-shaped crash boxes manufactured by Pagani Automobili S.p.A., comparing constant and variable thickness configurations through drop tower impact tests to evaluate energy absorption, crushing stability, and failure mechanisms. A lightweight finite element model was developed in Abaqus/Explicit using shell elements and Hashin-based damage criteria, achieving calibration errors below 10% for most parameters and under 15% for peak forces. Geometric enhancements, including continuous flanges, removal of the top surface, and an internal cruciform reinforcement, significantly improved energy absorption (up to 110%) but introduced trade-offs in stroke efficiency and mean force levels. To mitigate these effects, a genetic algorithm was employed to optimize laminate layup by varying ply orientations, resulting in improved stroke efficiency and reduced peak and average forces while maintaining crushing stability. The proposed approach demonstrates that integrating experimental validation with efficient numerical modeling and optimization accelerates the development of lightweight, high-performance crash absorbers, offering a robust framework for motorsport and automotive applications that balances safety, efficiency, and manufacturability. Full article

To address the issues of displacement and insufficient positional stability observed in the clinical use of the PROPEL Mini stent, this study investigates the influence of different biodegradable materials on the mechanical properties of the stent under the constraint of a fixed monofilament braided closed-loop geometry. Finite element analyses are conducted using Abaqus/Explicit to quantitatively evaluate the nonlinear mapping between nominal diameter, axial length, and radial pressure throughout a loading–unloading cycle. The results reveal that while axial behavior is consistent during compression, material-specific plasticity causes irreversible geometric sets in Mg alloy and PLGA models, whereas the PCL stent achieves total elastic recovery to its initial dimensions. During unloading, the Mg alloy stent recovers to a nominal diameter of 28 mm with a reduced axial length of approximately 22 mm, whereas the PLGA stent exhibits a much smaller recovery diameter of 14 mm with an axial length of approximately 23 mm. These post-release configurations directly determine the functional expansion range of the biodegradable stents after implantation. During unloading, the Mg alloy stent provides the highest radial pressure (peak 6.8 kPa) with a functional recovery range up to 26.5 mm, ensuring superior scaffolding stability. In contrast, while PCL achieves the widest recovery (52 mm), its radial pressure is clinically negligible (the maximum value is still less than 165 Pa), and the PLGA model exhibits both insufficient support and a restricted functional recovery limit (13 mm). By using high-strength materials such as Mg alloys, the radial anchoring force of the stent can be effectively enhanced without changing the existing structure, providing a scientific basis for solving clinical displacement problems. Full article

Tetra-missing rib honeycombs (TMRHs), characterized by monoclinic geometry, exhibit high elastic stiffness but suffer from poor deformation stability and reduced axial load-bearing capacity, which limit their applicability in energy-absorbing and load-sensitive engineering structures. To address these inherent drawbacks, this study proposes two symmetry-enhanced tetra-missing rib honeycomb configurations through overall axisymmetric design and subunit-level symmetric optimization. A finite element model was established in Abaqus/Explicit and validated against quasi-static compression experiments, demonstrating good agreement in deformation modes and mechanical responses. Systematic numerical investigations were then conducted to compare the mechanical properties and deformation behaviors of three honeycomb layouts, including the conventional TMRH and the proposed symmetric designs. Furthermore, the effects of impact velocity on mechanical performance were examined to evaluate the dynamic response characteristics of the structures. Finally, the influence of subunit angle parameters on the stiffness, energy absorption, and deformation stability of the tetra-missing rib honeycombs was comprehensively analyzed. The results provide insight into the role of symmetry and geometric parameters in improving the mechanical performance of TMRH-based structures and offer guidance for the design of high-performance auxetic honeycombs. Full article

In this study, a three-dimensional nonlinear finite element (FE) model was developed using Abaqus/Explicit to simulate the effects of internal blasts. The numerical model was validated against two previously published numerical and experimental works, demonstrating strong agreement in deformation results. A parametric study was carried out to evaluate the influence of several key factors on the deformation of the receiver tunnel subjected to an explosion in the adjacent donor tunnel. The investigation considered critical variables such as lining material, tunnel inner diameter, cross-sectional shape, spacing between tunnels, and TNT charge weight. The results clearly indicate that expanded polystyrene (EPS) foam, across various densities, demonstrates superior capacity for absorbing blast waves compared to polyurethane and aluminum foams. Furthermore, it was found that lower-density EPS foam provides enhanced mitigation of deformation in tunnel linings. The findings also revealed that damage to the tunnel walls is more strongly correlated with the tunnel shape where the circular tunnel exhibited the best performance. It showed the lowest deformation and delayed peak response. In addition, tunnel deformation increases markedly with higher TNT charge weights. A blast of 1814 kg produced approximately five times the deformation compared to a 454 kg charge. Moreover, it is seen that increasing the spacing between donor and receiver tunnels from 1.5 D to 2.5 D led to a 38.7% reduction in maximum deformation. Full article

The present paper concerns a new formulation of the optimal design problem of I-shaped multistep steel beam elements, based on the study of the plastic strain spread occurring in the relevant elements, with the aim of determining the length involved by the plastic deformation related to assigned load conditions and different constrained beam schemes. Material behavior is assumed as elastic–perfectly plastic, and the hypothesis of plane cross-sections is accepted. The functions defining the plastic strain spread are analytically obtained in the framework of Euler–Bernoulli beam theory. The proposed optimal design problem is a minimum volume one and the new constraint imposed on the length of the plasticized portion ensures that the minimum volume beam element also represents a maximum plastic dissipation one. Furthermore, the solution to the optimal design problem guarantees that the obtained multistep beam element ensures protection against brittle failure of the beam end sections, provides optimal cross-sections of the different portions belonging to Class 1 and ensures a suitable minimum value of the elastic flexural stiffness to respect the constraint on the deflection. Explicit reference is made to the so-called Reduced Beam Section (RBS), which characterizes the described multistep beam elements. Actually, the proposed formulation represents an innovative approach to obtaining an optimal beam element that really satisfies all the resistance, stiffness and ductility behavioral requirements. Some numerical applications conclude the paper, and their results are confirmed by appropriate FEM analyses in ABAQUS environment. Full article

During the hammer riveting of aircraft composite wing trailing edges, issues such as unclear damage mechanisms resulting from the continuous impact loading of composite materials, difficulty ensuring connection strength, and issues with damage control remain unresolved. This study investigates the dynamic impact load transfer mechanism during hammer riveting, establishes a model which maps the correlation between impact loads and rivet plastic flow, and develops a composite material VUMAT subroutine (a user-defined material subroutine in Abaqus/Explicit) based on the 3D Hashin failure criterion. A progressive damage simulation model for composite materials subjected to multiple hammer riveting operations is constructed. Based on mechanical analysis, a double-sided countersunk rivet with a support structure is proposed to suppress damage during composite hammer riveting. Simulation and experimental analysis demonstrate that, compared to conventional rivets, the new rivet effectively reduces contact stress (by up to 32.29%). Damage zones are concentrated at the straight hole and at the junction between the straight and countersunk holes. Furthermore, damage modes are simplified to matrix compression and tensile stress, with their respective proportions decreasing by 16.7% and 25.9%. Full article

A Machine Learning (ML)-based surrogate modeling framework is presented for mapping structure–property relationships in architected Ti6Al4V cylindrical TPMS metamaterials subjected to quasi-static compression. A Python–nTop pipeline automatically generated 3456 cylindrical shell lattices (Gyroid, Diamond, Split-P), and ABAQUS/Explicit simulations with a Johnson–Cook failure model for Ti6Al4V quantified their mechanical response. From 3024 valid designs, key mechanical properties targets including elastic modulus (E), yield stress (Y), ultimate strength (U), plateau stress (PL), and energy absorption (EA) were extracted alongside geometric descriptors such as surface area (SA), surface-area-to-volume ratio (SA/VR), and relative density (RD). A multi-output surrogate model (feedforward neural network) trained on the simulated set accurately predicts these properties directly from seven design parameters (thickness; unit cell counts in X, Y, and Z directions; unit cell orientation; height; diameter), enabling rapid property estimation across large design spaces. Topology-dependent trends indicate that Split-P exhibits the highest strength, energy absorption, and total SA, and shows the largest variation in SA/VR; Gyroid exhibits the lowest SA with a moderate SA/VR; and Diamond is the most compliant lattice and maintains a higher SA/VR than Gyroid despite lower SA. RD increases with both SA and SA/VR across all topologies. The framework provides a reusable computational tool for architectured lattices, enabling quick prescreening of implant designs without repeated finite-element analyses. Full article

The present research investigates the optimization of the punching process in cold forming manufacturing, focusing on enhancing tool life, reducing damage, and improving product quality. Punching, a shearing process widely used in sheet metal forming, requires careful management of process parameters to prevent tool damage, especially to the punch and die. The research explores various design modifications to the punching tool, including conical, pointed, and stepped shafts, aimed at reducing punching force and minimizing wear, fatigue, and crack formation. Using numerical simulations (ABAQUS/Explicit), the study evaluates the impact of shear angle, punch geometry, and other key parameters on the maximum punching force and stress distribution. The results show that adjusting the punch shaft shape and optimizing the shear angle can significantly decrease stress concentrations, extend tool lifespan, and improve process efficiency. This work provides valuable insights for improving punching tool designs and ensuring longer, more efficient service lives in industrial applications. Full article