Search Results (144)

Carbon fiber-reinforced plastics (CFRPs) offer excellent in-plane mechanical performance, but their relatively low interlaminar fracture toughness makes them vulnerable to delamination, particularly around intralaminar discontinuities such as resin-rich regions or fiber gaps. This study investigates the effectiveness of polyamide (PA) mesh inserts in improving interlaminar toughness and suppressing delamination in CFRP laminates with such features. Two PA mesh configurations were evaluated: a fully embedded continuous layer and a 20 mm cut mesh strip placed between continuous and discontinuous plies near critical regions. Fracture toughness tests showed that PA mesh insertion improved interlaminar toughness approximately 2.4-fold compared to neat CFRP, primarily due to a mechanical interlocking mechanism that disrupts crack propagation and enhances energy dissipation. Uniaxial tensile tests with digital image correlation revealed that while initial matrix cracking occurred at similar stress levels, the stress at which complete delamination occurred was approximately 60% higher in specimens with a 20 mm mesh and up to 92% higher in specimens with fully embedded mesh. The fully embedded mesh provided consistent delamination resistance across the laminate, while the 20 mm insert localized strain redistribution and preserved global mechanical performance. These findings demonstrate that PA mesh is an effective interleaving material for enhancing damage tolerance in CFRP laminates with internal discontinuities. Full article

This review presents a comprehensive synthesis of recent advances in the tensile performance of adhesively bonded joints, focusing on applied aspects and modeling developments rather than providing a full theoretical analysis. Although many studies have addressed individual joint types or modeling techniques, an integrated review that compares joint configurations, modeling strategies, and performance optimization methods under tensile loading remains lacking. This work addresses that gap by examining the mechanical behavior of key joint types, namely, single-lap, single-strap, and double-strap joints, and highlighting their differences in stress distribution, failure mechanisms, and structural efficiency. Modeling and simulation approaches, including cohesive zone modeling, extended finite element methods, and virtual crack closure techniques, are assessed for their predictive accuracy and applicability to various joint geometries. This review also covers material and geometric enhancements, such as adherend tapering, fillets, notching, bi-adhesives, functionally graded bondlines, and nano-enhanced adhesives. These strategies are evaluated in terms of their ability to reduce stress concentrations and improve damage tolerance. Failure modes, adhesive and adherend defects, and delamination risks are also discussed. Finally, comparative insights into different joint configurations illustrate how geometry and adhesive selection influence strength, energy absorption, and weight efficiency. This review provides design-oriented guidance for optimizing bonded joints in aerospace, automotive, and structural engineering applications. Full article

Microbially induced calcium carbonate precipitation (MICP) has emerged as a research focus in concrete crack remediation due to its environmental compatibility and efficient mineralization capacity. The hypersaline conditions of seawater (average 35 g/L NaCl) and alkaline environments (pH 12) within concrete cracks pose significant challenges to the survival of mineralization-capable microorganisms. To enhance microbial tolerance under these extreme conditions, this study employed a laboratory adaptive evolution strategy to successfully develop a Sporosarcina pasteurii strain demonstrating tolerance to 35 g/L NaCl and pH 12. Comparative analysis of growth characteristics (OD₆₀₀), pH variation, urease activity, and specific urease activity revealed that the evolved strain maintained growth kinetics under harsh conditions comparable to the parental strain under normal conditions. Subsequent evaluations demonstrated the evolved strain’s superior salt–alkali tolerance through enhanced enzymatic activity, precipitation yield, particle size distribution, crystal morphology, and microstructure characterization under various saline–alkaline conditions. Whole-genome sequencing identified five non-synonymous mutated genes associated with ribosomal stability, transmembrane transport, and osmoprotectant synthesis. Transcriptomic profiling revealed 1082 deferentially expressed genes (543 upregulated, 539 downregulated), predominantly involved in ribosomal biogenesis, porphyrin metabolism, oxidative phosphorylation, tricarboxylic acid (TCA) cycle, and amino acid metabolism. In concrete remediation experiments, the evolved strain achieved superior performance with 89.3% compressive strength recovery and 48% reduction in water absorption rate. This study elucidates the molecular mechanisms underlying S. pasteurii’s salt–alkali tolerance and validates its potential application in the remediation of marine engineering. Full article

This study aimed to investigate the cracking characteristics of various sweet potato germplasm resources, explore their genetic associations, and identify crack-resistant varieties. Using 40 sweet potato varieties as experimental materials, we systematically analyzed their cracking traits and assessed 24 parameters. The results indicated that genotypic differences significantly influenced sweet potato cracking (p = 1.11 × 10⁻¹⁶). Correlation analyses revealed that skin thickness (r = −0.81, p < 0.01), skin hardness (r = −0.50, p < 0.01), and starch content (r = −0.51, p < 0.01) were highly significantly negatively correlated with cracking incidence. Microscopic observations of the cell structure revealed that the development quality of the cork cambium and vascular cambium during the secondary growth stage plays a crucial role in maintaining the structural stability of the tuber skin, whereas the internal expansion force during the rapid growth phase is a direct factor that induces cracking. A multiple regression prediction model (R² = 0.85) was established based on ten core indices. Furthermore, a comprehensive evaluation system for sweet potato cracking resistance was developed by integrating principal component analysis and the entropy-weighted TOPSIS model (kappa = 0.752, p = 5 × 10⁻⁶), identifying seven extremely crack-resistant and nine crack-resistant varieties. This study is the first to construct a multidimensional evaluation system for cracking traits in sweet potato, offering a reference for breeding crack-resistant varieties and developing cultivation, prevention, and management strategies. Full article

Hybrid additive manufacturing (AM) provides a unique way of fabricating complex geometries with onboard machining capabilities, combining both additive and traditional subtractive techniques and resulting in reduced material waste and efficient high-tolerance components. In this work, a hybrid AM technology was used to create 316L stainless steel (316L SS) components using laser-wire-directed energy deposition (LW-DED) coupled with a CNC machining center on a single platform. Fully reversed fatigue tests were completed to investigate the as-manufactured life span of the additively manufactured structures for three different deposition rates of 6.33 g/min, 7.12 g/min, and 7.91 g/min. High-cycle fatigue test results showed that the fatigue performance of the tested specimens is not dependent on the deposition rates for the investigated parameters, with specimens with a 7.12 g/min deposition rate showing comparatively superior behavior to that of the other deposition rates at higher stress amplitudes. Fractography analysis was used to investigate the fractured surfaces, showing that the crack initiation sites were predominantly near the edges and not affected by the volumetric defects generated during manufacturing. X-ray-computed tomography (X-ray CT) analysis quantified the effect of the as-manufactured porosity on fatigue behavior, showing that the amount of porosity for the build rates used was insufficient to have a substantial impact on the fatigue behavior, even as it increased with the deposition rate. Full article

This study investigates the role of Al alloying in tailoring the oxidation resistance of AlTiCrZrNbTa refractory high-entropy alloy (RHEA) coatings on Zry-4 substrates under high-temperature steam environments. Coatings with varying Al contents (0–25 at.%) were deposited via magnetron sputtering and subjected to oxidation tests at 1000–1100 °C. The results demonstrate that Al content critically governs oxidation kinetics and coating integrity. The optimal performance was achieved at 10 at.% Al, above which a dense, continuous composite oxide layer (Al₂O₃, TiO₂, Cr₂O₃) formed, effectively suppressing oxygen penetration and maintaining strong interfacial adhesion. Indentation tests confirmed enhanced mechanical integrity in Al-10 coatings, with minimal cracking post-oxidation. Excessive Al alloying (≥17 at.%) led to accelerated coating oxidation. This work establishes a critical Al threshold for balancing oxidation and interfacial bonding, providing a design strategy for developing accident-tolerant fuel cladding coatings. Full article

This study develops a computational framework for evaluating the residual strength of tungsten-copper functionally graded materials following crack-arrest hole drilling. The proposed methodology features two pivotal innovations: First, a phase-field isoparametric gradient elements is established through representing the gradient effect within the finite element stiffness matrices, incorporating both Amor and Miehe elastic energy decomposition schemes to address tension-compression asymmetry in crack evolution. Second, a multi-fidelity neural network strategy is integrated with the gradient phase-field element to mitigate characteristic length dependency in residual strength predictions. Comparative analyses demonstrate that the gradient finite element achieves smoother field transitions at element interfaces compared to conventional homogeneous elements, as quantified in both stress and damage fields. The Miehe decomposition scheme outperforms the Amor model in capturing complex crack trajectories. Validation against the average strain energy criterion indicates the present approach enhances residual strength prediction accuracy by 39.07% to 44.05%, establishing a robust numerical tool for damage tolerance assessment in graded materials. Full article

While the effect of ageing has been thoroughly analysed, to improve the cycle life of lithium-ion batteries, its impact on safety in case of a mechanical loading is still a new field of research. It has to be found out how mechanical properties, such as the tolerable failure force or deformation, change over the operational lifetime of a battery. To answer this question, mechanical abuse tests were carried out with pouch cells used in recent electric vehicles in a fresh state and after usage over 160.000 km. These tests were complemented with a detailed component level analysis, in order to identify mechanisms that lead to changed cell behaviour. For the analysed aged cells, a significantly different mechanical response was observed in comparison with the respective fresh samples. The tolerable force was severely reduced (up to −27%), accompanied by a notable reduction in the allowable deformation level (up to −15%) prior to failure, making the aged cells clearly more safety critical. Based on the subsequent component tests, the predominant mechanism for this different behaviour was concluded to be particle cracking in the cathode active material. The found results are partly in contrast with the (few) other already published works. It is, however, unclear if this difference is rooted in different cell chemistries or types, or another battery state resulting from varying ageing procedures. This underlies the importance of further investigations in this research field to close the apparent gap of knowledge. Full article

Cylindrical shells are widely used in pipelines, pressure vessels, and aircraft fuselages due to their efficient internal pressure distribution. However, axial cracks caused by fatigue, environmental effects, or mechanical loading compromise structural integrity, requiring effective reinforcement. This study presents a finite element modeling approach integrating p-refinement techniques for the efficient analysis of axially cracked pipes reinforced with composite patches. The proposed method unifies equivalent single-layer and layer-wise theories into a single finite element type, improving computational efficiency and eliminating the need for multiple element types in transition elements. Benchmark studies show that the proposed model accurately predicts mechanical behavior, with maximum displacement and stress intensity factors (SIFs) deviating by less than 5% from reference solutions. Fracture analysis using the virtual crack closure technique confirms the accuracy of the SIF calculations. In patched cracked pipes, the proposed model achieves a 67% reduction in degrees of freedom compared to conventional p-refinement layer-wise models, while maintaining computational accuracy. Additionally, boron–epoxy composite patches reduce SIFs by up to 40%, demonstrating effective crack reinforcement. These findings support computationally efficient damage-tolerant design strategies for pressurized cylindrical structures in aerospace, marine, and mechanical engineering. Full article

Melon fruit cracking reduces yield, increases transportation costs, and shortens shelf life, which makes the development of cracking-resistant varieties crucial for the industry’s advancement. This study investigated the pathways and genes related to melon fruit cracking through cell morphology observation, endogenous hormone analyses, and transcriptome analysis of two contrasting advanced inbred lines, the extremely crack-resistant line R2 and the crack-susceptible line R6. R2 has small, tightly packed epidermal cells with a thick cuticle, while R6 has larger, more loosely arranged epidermal cells and a significantly thinner cuticle. Hormonal analysis revealed significant differences in abscisic acid, cytokinin, gibberellin, auxin, and salicylic acid contents between R2 and R6 at various fruit developmental stages. The abscisic acid and salicylic acid content in R2 were 1.9–5.2 times and 1.5–3.6 times higher than those in R6, respectively, whereas the gibberellin content in R6 was 1.5–2.3 times higher than that in R2. Pericarp transcriptome analysis identified 4281, 6242, and 6879 differentially expressed genes (DEGs) at 20, 30, and 40 days after anthesis, respectively. Among these, 47 DEGs related to phenylpropanoid biosynthesis (ko00940) and 79 DEGs involved in plant hormone signal transduction (ko04075) were differentially expressed at two or more stages. WGCNA analysis identified six core hub genes that potentially play a role in regulating melon fruit cracking. These findings lay a foundation for further studies on the functional roles of crack-resistant genes and the breeding of crack-tolerant varieties. Full article

Residual stress (RS) in laser powder bed fusion (LPBF) additive manufactured structures can significantly affect mechanical performance, potentially leading to premature failure. The complex distribution of residual stresses, combined with the limitations of full-field measurement techniques, presents a substantial challenge in conducting damage tolerance analyses of aircraft structures. To address these challenges, this study developed a comprehensive simulation framework to analyze the 3D distribution of residual stresses and fatigue crack growth in LPBF parts. The 3D residual stress profiles of as-built samples in 15° and 75° build directions were computed and compared to experimental data. The fatigue crack propagation behavior of the 75° sample, considering 3D residual stress, was predicted, and the effects of residual stress redistribution under cyclic loading were discussed. It shows that the anisotropy of residual stress, influenced by the build direction, can lead to mixed-mode fracture and subsequent crack deflection. Tensile residual stress in the near-surface region and compressive stress in the inner region can cause an inverted elliptical crack front and accelerate fatigue crack growth. Full article

In the damage tolerance analysis of aircraft panels, it was necessary to frequently apply complex boundaries and loads to simulate crack propagation. It was difficult to simulate crack propagation with the conventional finite element method. In this paper, a convenient method for crack propagation simulation in thin-walled structures was proposed. This method combined the extended finite element method (XFEM) and level-set method (LSM). Crack insertion, analysis, result extraction and automatic propagation were realized through the secondary development script in the ABAQUS platform. A specimen with a single center crack was simulated to study the crack propagation behavior under tensile and bending conditions. Also, multiple-crack propagation was simulated. The present work shows that the developed method can not only take the complex loading and boundary conditions into account, but also can give good predictions on the crack analysis. This method provided a convenient and effective secondary development of ABAQUS to solve complex crack problems. Full article

This study investigates the impact of low-temperature stress-relieving treatment on the fatigue life of AlSi10Mg components produced by Laser Powder Bed Fusion (L-PBF). The research focuses on a bicycle crank arm, comparing its performance in as-built and heat-treated conditions. The heat treatment involved stress-relieving at 250 °C for 2 h, followed by water quenching. The study found that the as-built condition exhibited a supersaturated Si cellular-dendritic microstructure, while the heat-treated condition showed coarsening of β-Mg₂Si phases and Si precipitates. This morphological change led to a decrease in hardness and an increase in ductility. Fatigue tests demonstrated that the heat-treated crank arms achieved the target of 100,000 cycles without failure, unlike the as-built samples, which failed prematurely. The fractography analysis identified surface porosity as the primary crack initiation site. The findings suggest that low-temperature stress-relieving treatment can enhance the fatigue performance of L-PBF AlSi10Mg components by reducing residual stresses and improving defect tolerance. Full article

Strain tolerance is a crucial factor affecting the thermal life of coatings, and a higher strain tolerance can effectively alleviate the thermal stresses on coatings during thermal shock. To improve the strain tolerance, the coating structure was optimized by introducing an intermediate transition layer in this study. The intermediate transition layer material was prepared using a 1:1 volume ratio mixture of 6–8 wt. % Yttria-stabilized zirconia (YSZ) and NiCrAlY powders in the experiments. The coating structure consisted of an Al₂O₃-GdAlO₃ (AGAP) anti-erosion layer, a YSZ layer, an intermediate transition layer, and a bonding layer from top to bottom. After thermal shock experiments at 1500 °C, the coatings with the addition of the intermediate transition layer exhibited different failure modes, with the crack location shifting from between the YSZ and the bonding layer to within the intermediate transition layer, compared to the coatings without the intermediate transition layer. Finite element simulation analysis showed that the intermediate transition layer effectively increased the strain tolerance of the coating and significantly reduced the thermal stress. Furthermore, incorporating an embedded micron agglomerated particle-based (EMAP) thermal barrier coating structure into the intermediate transition layer effectively alleviated thermal stresses and enhanced the coating’s thermal insulation performance. Full article

In this article, we discuss an unusual pattern in long-crack behavior at low stress intensity factor ranges ΔK (below ΔK_th), characterized by an initial dip, followed by a plateau, and then an acceleration in fatigue crack growth (FCG) rate. This unanticipated FCG behavior was first observed experimentally in the IMI 834 alloy and reported by Marci in 1996. Such an anomaly is only reported from experimental observation but cannot be understood or explained using the plasticity, roughness, or oxide-induced crack closure assumptions. It also has not been fully explained through either metallurgical analysis or failure mode investigation. The established application of fracture mechanics to the FCG rate (da/dN) assumes that the FCG rate decreases with decreasing ΔK towards the threshold of ΔKth with (da/dN) $\le$ 10⁻⁷ mm/cycle. Yet, some materials exhibit a lack of ΔK threshold dependence for long cracks when tested using constant-K_max or constant-R-ratio testing. An understanding of this anomaly and the related physics poses a scientific challenge. It is also relevant to predict the safe service life of structures subjected to high-frequency and low-amplitude vibrating loads. Here, we provide our interpretation and discuss the significant implications of this phenomenon in the context of damage-tolerant design. Full article