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Fracture characterization of hybrid composite laminates in modes I and II
No full textIn this work, the Mode I and Mode II interlaminar fracture toughness of a hybrid laminate composite consisting of carbon fiber-reinforced layers and glass fiber-reinforced layers was characterized. Unidirectional laminates were used for the tests, and the stacking sequence was chosen with the aim of achieving pure fracture modes in the tests. Mechanical characterization was carried out using three-point bending tests with different spans, taking into account the effects of indentation, shear, and support rotation. Mode I and Mode II interlaminar fracture tests were performed using the ADCB (Asymmetric Double Cantilever Beam) and AENF (Asymmetric End Notched Flexure) tests, respectively, also considering the effects of shear, local deformation, and rotations due to bending. The data were obtained using a recently published analytical model that allows the resistance curve to be found for each load-displacement data obtained from the testing machine
Ballast Impact Damage Characterization. Determination of Acceptance/Rejection Criteria for Railway Components Made of CFRP.
No full textIn recent years, the railway sector has been developing high-responsibility lighter components (such as the running gear frame), made from composites (mainly CFRP) to meet the new challenges of the sector. However, these components may be more sensitive to damage from impacts compared to conventional metallic ones. In high-speed train operations, elements located on the lower parts of the train are exposed to impacts with ballast stones that are lifted as the train passes (v > 200 km/h), leading to damage (sometimes internal and not visible) that can limit the use of these materials. During the development of CFRP components by Talgo, the damage caused by these types of low-velocity impacts has been analyzed and evaluated. These impacts can cause damage that requires more or less complex technologies (such as ultrasound) for evaluation, which are difficult to implement in maintenance operations. From the studies conducted on CFRP materials (compliant with the EN-45545 standard for fire, smoke, and toxicity), it has been found that acceptable approaches can be used, with easily implementable measures in routine inspections, to estimate the damage caused by ballast stone impacts. In these analyses, it was observed that: a) It is possible to estimate the impact energy level through the depth of the surface damage, b) it is possible to estimate the size of the internal damaged area based on the energy level, and c) it is possible to determine the residual strength based on the size of the internal damaged area. These results allow us to establish both acceptance requirements and criteria for the repair and rejection of material
Polymerization kinetics of a recyclable thermoplastic as a matrix for structural composites
No full textIn this contribution we have performed the kinetic analysis of the curing process and of its thermal decomposition. Due to the presence of a peroxide initiator, polymerization is a complex process involving an induction period for a fast cross-linking reaction. From the kinetic analysis, we have been able to characterize the induction time and the degradation kinetics. Finally, from the analysis of the volatiles we have determine that the main volatile generated during decomposition is the monomer
Long-term performance of injection-molded isotactic polypropylene containing weld lines in unfilled and glass fiber-reinforced grades
No full textThe study of weld lines in polymers is far from settled, especially in predicting how materials perform over long periods under stress. While previous research has explored the behavior of isotactic polypropylene (iPP) in both its unfilled and glass fiber-reinforced forms, the focus has been largely on short-term behavior. However, this study shifts the lens to long-term performance under complex conditions, specifically looking at creep and fatigue. We take a novel approach by considering iPP with 30% glass fiber reinforcement, using tensile samples that induce weld line formation. Creep behavior is measured across a broad range of strain rates and temperatures, aiming to understand the underlying mechanisms that govern material failure. These short-term tests are then linked to more comprehensive long-term evaluations, including cyclic loading and creep-to-rupture tests. Crack growth is assessed using CT specimens, enabling us to capture failure modes that are otherwise difficult to quantify. The study goes further by proposing a new way to model deformation. Instead of relying on traditional methods, we turn to the Eyring equation for a more accurate prediction of failure times under cyclic stress, especially as materials transition to brittle fracture at higher temperatures. These predictions match experimental results, demonstrating the potential of linear elastic fracture mechanics (LEFM) in assessing long-term material performance. Ultimately, this research challenges conventional models and provides a pathway for more accurate long-term predictions, a crucial step for industries relying on polymer materials in demanding environments
Development and integration of printed strain gauge-based sensors for structural health monitoring in composite material repairs of wind turbine blades
No full textStructural health monitoring is essential to ensure safety and extend the service life of critical components in renewable energy systems, such as repaired wind turbine blades. This study presents the development of strain gauges printed using advanced functional printing techniques, optimized for integration into composite materials and tailored to the mechanical characteristics of repaired areas to assess the effectiveness and durability of structural repairs. The integration of these sensors would enable real-time monitoring of key parameters, such as microstrains, during the operation of the blade after repair. The experimental work included the printing of strain gauges, evaluation of different substrates, and cyclic loading tests under controlled conditions to assess the accuracy and sensitivity of the printed gauges. Additionally, composite material coupons were characterized under tensile and compressive loads to analyse the impact of gauge integration on the mechanical properties of the composite. Preliminary results demonstrate the feasibility of this approach, although full validation is required, including aging studies, testing in real operational environments, and exposure to extreme temperature variations prior to industrial implementation
A Novel Sin Model SMEx with Application on COVID-19 and Precipitation Data
No full textThe present study proposes a new and flexible trigonometric extension of the moment exponential distribution, termed the Sine Moment Exponential (SMEx) distribution, developed using the sine-G family of distributions. This model offers an attractive alternative to well-known lifetime distributions by providing enhanced flexibility for analyzing lifetime datasets that exhibit leptokurtic or platykurtic behavior. Several statistical properties of the SMEx distribution are derived, including its moments, quantile function, mean residual life, and order statistics. To assess its performance, five different estimation approaches are applied, including Anderson-Darling estimation, maximum likelihood estimation, Cramervon Mises estimation, ordinary least squares estimation, and weighted least squares estimation. A detailed Monte Carlo simulation study is utilized to illustrate the estimation behavior of these considered estimation procedures. In the end, two datasets associated with COVID-19 and precipitation are utilized to illustrate the applicability and flexibility of the proposed distribution. It is found that the proposed distribution efficiently analyzed these datasets as compared to competitive distributions.OPEN ACCESS Received: 06/10/2025 Accepted: 28/10/2025 Published: 23/01/202
Multi-Objective Optimization and Performance Evaluation of Manifold-Based Cooling Systems for Battery Thermal Management Using RSM and NSGA-II
No full textEfficient thermal management is critical to the safety, performance, and longevity of lithium-ion battery (LIB) energy storage systems. In this study, a novel manifold cold plate featuring an overflow channel with a triangular ridge at the bottom is proposed for a liquid-cooled Battery Thermal Management System (BTMS). A comprehensive multi-objective optimization framework is developed by integrating Response Surface Methodology (RSM), the Non-dominated Sorting Genetic Algorithm II (NSGA-II), and the Linear Programming Technique forMultidimensional Analysis of Preference (LINMAP) decision-making method to minimize the maximum temperature difference (Tcell) and pressure drop (P) across the cooling plate.Thedesign variables include the manifold channel width ratio (λ), the height ratio (φ), the inlet velocity (u), and the triangular ridge angle (θ). Second-order polynomial regression models are constructed and validated using Analysis ofVariance (ANOVA), yielding high coefficients of determination (R2 = 0.9926 forTcell and 0.9600 forP), confirming strong predictive accuracy. Sensitivity analysis reveals that the inlet velocity and channel angle are the primary factors influencing system performance. The LINMAP-based decision-making approach identifies an optimal configuration with λ = 1.031, φ = 1.47, u = 1.671 m/s, and θ = 29.8°, achieving a Tcell of 12.61°C and a P of 6742.99 Pa, with validation errors below 3%. Transient simulations at 0.5 and 1C discharge rates show that the LINMAP-optimized design reduces the maximumcell temperature by 13.12°C and 11.77°C, respectively, compared to the natural convection baseline, and by 1.42°C and 0.76°C compared to the prototype design, while maintaining comparable hydraulic resistance. This work offers valuable guidance for designing and optimizing liquid-cooled batter
Multi-scale thermal modelling and variable scan parameter optimization framework for homogeneous and predictable PBF-LB aerospace components
No full textInvestigation on Dynamical Mechanics of Rock-Backfill Composite Samples under SHPB Test
No full textIn blast-induced caving mining with backfilling, understanding the interaction mechanisms and deformation evolution between rock and cemented tailing backfill (CTB) under coupled conditions is essential for ensuring stability. This study conducted dynamic uniaxial impact tests using the Split Hopkinson Pressure Bar (SHPB) system on rock-CTB composite specimens to investigate their mechanical response at high strain rates. Stress–strain relationships were recorded across a range of strain rates, and corresponding failure mechanisms were analyzed. A coupled SHPB model was also developed using GDEM software to simulate internal stress wave propagation and crack evolution within the composite specimens. Experimental results revealed that the dynamic compressive strength initially increases, then decreases, and eventually stabilizes as the average strain rate (ASR) increases from 27.45 s−1to 68.73 s−1. At strain rates below 60 s−1, the stress–strain curves exhibit a “stress drop” pattern, whereas above 60 s−1, a “stress rebound” behavior is observed. Energy absorption increases with ASR up to 55 s−1, then decreases, followed by a secondary increase. Numerical simulations validated the experimental findings, revealing the formation of both transverse and longitudinal cracks within the CTB. Greater deformation was observed near the transmission bar interface compared to the rock interface. These results offer valuable insights into the dynamic failure behavior of backfilled systems and inform improved backfill design in blast-induced mining operations.OPEN ACCESS Received: 05/08/2025 Accepted: 05/09/2025 Published: 03/02/202
