Abstract: Several waste materials are often used in the mixt-design of asphalt concrete materials to manufacture green construction materials and among them recycled asphalt pavement (RAP) is a favorite material that can be utilized as partial replacement of natural stone aggregates. Addition of such waste and recycled materials may have a negative influence on the mechanical properties and strength or performance of asphalt pavements. In particular, resistance of asphaltic overlays made by some amounts of RAP material against cracking and crack propagation can be reduced and it is necessary to investigate possible effects of RAP addition on cracking resistance of asphalt mixtures. Passage of traffic loads from the cracked overlays and asphaltic pavements can activate all basic tensile and shear mode crack deformations (i.e., pure mode I, pure mode II and pure mode III). In addition, due to the visco-elastic nature of bitumen used in the asphalt mixture, the risk of crack propagation and failure at low temperature conditions is higher than the intermediate and high temperatures. Therefore, in this research, the influence of adding RAP material on the fracture toughness of all three basic fracture modes (namely, K_Ic, K_IIc and K_IIIc) is investigated using edge-notched disc bend (ENDB) specimens. Fracture toughness tests are conducted on hot mix asphalt (HMA) mixtures containing 0, 20 and 40 % RAP material (as replacement of natural aggregates) at five low temperatures of 0, -6, -12, -18, -24 oC. Based on the results, all fracture toughness data were decreased by increasing the temperature from -24oC to zero and increasing the RAP content from 0 to 40%. Depending on the test temperature and mixture type (HMA with or without RAP content) the K_Ic and K^IIc values were varied from 0.5 to 1.1 MPa.m^0.5. This range for KIIIc value was in the lower limit of 0.35 MPa.m^0.5 and 0.75 MPa.m^0.5. Some fracture indexes such as fracture toughness ratios (K_IIc/K_Ic, K_IIIc/K_Ic, K_IIc/K_IIIc, and Kopening/Kshearing-eff) and effective fracture toughness were determined and discussed for the investigated HMA mixtures at different temperatures.

DOI: 10.5267/j.esm.2026.3.003
Keywords: Modified and control HMA mixtures, RAP content, Pure modes I, II, III fracture toughness values, Low temperature conditions, ENDB test, Fracture toughness ratios, Effective total fracture toughness

Abstract: In this research a doughnut-shaped specimen (DSS) is utilized for analysis of mixed mode I/II (tensile/compression and in-plane shear) fracture problem. The DSS sample is a ring specimen containing two same line cracks in the inner surface of the ring that can be loaded either by diametral compression forces applied to the outer surface of ring or diametral tension force applied to the inner surface of the DSS sample. By changing the geometrical and loading parameters including crack length ratio, type of applied loading and direction of loading relative to the cracks, the state of crack tip stresses and deformations is altered. It is shown that the DSS sample under both tensile and compressive point force loading can introduce pure mode I, pure mode II and different tensile-shear, and compression-shear deformations. The variations of three fracture parameters namely modes I and II stress intensity factors (KI and KII) are determined for the DSS sample under different geometrical and loading conditions via performing several finite element analyses. It is shown that the type of applied loading (tensile or compression) has a noticeable influence on the magnitudes of crack tip parameters. The crack inclination angle corresponding to pure mode II (pure shear deformation) are also determined for both compressed and tensile DSS specimens. This angle depends on the applied loading type, crack length ratio and inner to outer ring radius ratio.

DOI: 10.5267/j.esm.2026.3.002
Keywords: Doughnut-Shaped Specimen (DSS), Diametral compression point load, Diametral tensile pin loading, Mixed mode I/II, Stress intensity factors, Numerical analyses, Geometry and loading type effects, Pure mode II crack inclination angle

Abstract: This study presents a finite element modeling framework for predicting dry sliding wear in WC–Co by integrating Archard’s wear law with the UMESHMOTION subroutine in Abaqus. Pin-on-disk experiments were conducted to obtain the steady-state friction coefficient, wear coefficient, and surface profile, which were used to calibrate the numerical model. A short sliding distance of 1 mm was simulated and subsequently scaled to represent a 1000 m sliding test, enabling substantial reduction in computational cost. The model accurately reproduced the experimental wear behavior, predicting a maximum wear depth within 8% relative error (0.23 μm simulated vs. 0.25 μm measured), and captured the overall geometry of the wear track. Sensitivity analysis confirmed the linear dependence of wear depth on the wear coefficient and sliding distance, supporting the validity of the scaling strategy. The results demonstrate that combining FEM, UMESHMOTION, and a sliding-distance scaling approach provides an efficient and reliable method for long-distance wear prediction in hard materials. This framework is applicable to tribological component design and can be extended to more complex multi-physics wear mechanisms in future studies.

DOI: 10.5267/j.esm.2026.3.001
Keywords: Dry sliding wear, Finite element method, UMESHMOTION, Tungsten carbide, Pin-on-disk, Archard’s law

Abstract: Unsaturated soils and granular materials play a pivotal role in geotechnical and environmental engineering, with water under tension markedly influencing their mechanical behavior, particularly strength and deformation. To elucidate the impact of matric suction on the macroscopic mechanical response, this study presents a modeling approach for capillary interactions between spherical particles in a partially saturated medium using the Discrete Element Method (DEM). The PFC3D software is employed to calibrate mesoscale interparticle contact parameters to replicate uniaxial compression tests performed on a reference material under saturated conditions. Suction effects are incorporated via an intergranular contact force based on the Hill contact model, which considers matric suction magnitude, particle radius, and interparticle spacing. Numerical results demonstrate that suction can be realistically represented by an adhesion force at particle contacts. The model is further extended to simulate triaxial tests, examining the evolution of cohesion and internal friction angle with increasing suction. Both parameters exhibit an upward trend with suction, reflecting the influence of capillary forces and suction-induced densification. Finally, a mathematical model using logarithmic functions is developed to describe the evolution of mechanical parameters as a function of suction, yielding high coefficients of determination (R² > 0.95) and providing reliable predictive capabilities.

DOI: 10.5267/j.esm.2026.2.004
Keywords: Suction, Discrete element method, Compressive strength, Contact model

Abstract: One of the key principles of rational environmental management is finding ways to recycle by-products. Gypsum-bearing waste such as phosphogypsum (PG) is a large-scale waste. Resolving the problem of its accumulation is a global challenge. Phosphogypsum is a by-product of orthophosphoric acid and phosphate fertilizer production. PG mainly consists of calcium sulfate dihydrate and can be considered as an alternative to natural gypsum rock in gypsum binder production. However, previous studies have shown that the structural and morphological features of PG particles are the cause of the high water demand of phosphogypsum binders (PGB) and the resulting low physical and mechanical properties of consolidated phosphogypsum paste. This study examined the possibility of increasing PGB efficiency by increasing their dispersion, including by grinding. The study found that grinding PGB after calcination generally improves its properties and can be recommended as an effective manufacturing technique for reducing the impact of the structural and morphological properties of phosphogypsum from various sources on the quality of the final product. The compressive strength of PGB after grinding to a specific surface area of ≈480 m²/kg ranged from 3.06 to 5.41 MPa after 2 hours of mixing and from 6.78 to 13.68 MPa in the dry state.

DOI: 10.5267/j.esm.2026.2.003
Keywords: Industrial waste, Phosphogypsum, Phosphogypsum based binder, Grinding, Heat evolution

Abstract: Hybrid laminated composites, integrating High Strength (HS) carbon and glass fibers (E, S) within an epoxy matrix, deliver an optimal compromise between lightweight design, mechanical strength, and cost-effectiveness for applications in industrial, aerospace, automotive, and civil engineering sectors. This study presents a three-dimensional optimization of mechanical performance through a multi-objective genetic algorithm (MOGA) under static loading conditions. The design variables encompass the number of plies (6 to 12), fiber orientation angles (-90°≤ θ ≤90°), and ply materials: HS-Carbon/Epoxy (CF-EP), E-Glass/Epoxy (EG-EP) and S-Glass/Epoxy (SG-EP). A constraint mandating 25% CF-EP placement at the core to maximize stiffness while minimizing stresses. The objectives are to enhance the longitudinal modulus (Ex) and reduce von-Mises stress, while ensuring compliance with the Tsai-Wu failure criterion. An analytical model, implemented in MATLAB, incorporates stiffness matrices, Tsai-Wu failure indices, and von-Mises stress calculations, demonstrating a 30% increase in stiffness and effective mitigation of stress concentrations through centralized CF-EP placement. These findings are corroborated by finite element method (FEM) simulations conducted in ANSYS, which exhibit strong agreement with analytical predictions. This hybrid methodology offers a strong framework for developing high-performance laminated composites, significantly impacting applications requiring structural reliability and efficiency.

DOI: 10.5267/j.esm.2026.2.002
Keywords: Genetic algorithm, Hybrid composites, Optimization, Finite element method (FEM), ANSYS

Abstract: Historic masonry monuments are particularly vulnerable to dynamic loading due to aging materials, limited ductility, and the absence of seismic design considerations. This study presents a numerical assessment of the Perry Memorial Arch, a historic masonry structure located in Bridgeport, Connecticut, under gravity, wind, and seismic loading conditions. A three-dimensional finite element model was developed in ANSYS to evaluate stress distribution, deformation patterns, and dynamic response using static analysis, modal analysis, and nonlinear time-history analysis. The structure was modeled using macro-level material representations for stone masonry, brick masonry, and concrete, with material properties derived from code-based references due to the absence of in-situ testing data. Wind loading was evaluated in accordance with ASCE 7-16, while seismic performance was assessed using location-specific spectral parameters and selected ground-motion records with Peak Ground Accelerations (PGA) ranging from 0.10g to 0.16g. Results indicate that the arch performs satisfactorily under gravity and wind loading, although stress concentrations develop near supports under extreme wind conditions. Seismic analysis shows that the structure remains stable for PGA values up to 0.12g, while higher intensities lead to localized stress amplification, particularly in the in-plane direction. This study provides a screening-level seismic performance assessment of a historic masonry monument in a moderate seismic region and offers insights to support future retrofit planning and preservation strategies for similar heritage structures.

DOI: 10.5267/j.esm.2026.2.001
Keywords: Perry Memorial Arch, Historic masonry structures, Seismic analysis, Dynamic loading, Finite element modeling

Abstract: The article presents a five-year industrial validation of eliminating open gear drives in spiral classifiers by implementing a direct drive with a torque arm, alongside an assessment of cumulative effects on reliability, process efficiency, and operating economics. The relevance of the study is conditioned by the fact that a substantial share of the classifier fleet remains structurally obsolete: open gear trains constitute the root cause of mechanical instability (wear, lubricant leakage, misalignment) while simultaneously degrading the quality of diagnostic signals, thereby impeding the deployment of PdM/AI. The objective is to deliver a comprehensive, instrumentally substantiated evaluation of the long-term reliability and economic feasibility of direct drive under real-world conditions, and to demonstrate how removal of the failure root cause creates a data-ready mechanical platform for predictive maintenance and digital twins. The novelty consists in an industry-scale confirmation (January 2020, June 2025) of a fundamental transition from managing wear consequences to eliminating wear at the kinematic-scheme level: a sealed gearmotor (IP66) in combination with a torque arm and flanged connection obviates the open gear pair, dramatically elevating the vibration signal-to-noise ratio and rendering vibrodata coherent for PdM. It is shown that mechanical stabilization of the drive is in itself a critical precondition for trustworthy condition analytics. The principal findings confirm a multifactor modernization effect: a 33% increase in section throughput and a 19% rise in classification efficiency; 100% drive technical availability with zero unplanned downtime over 43,800 h; a lower confidence bound of MTBF at 14,600 h versus a characteristic service life of ~2,800 h for traditional drives; a persistently low vibration level < 2.0 mm/s (ISO 10816 category A) instead of 4.5–7.8 mm/s (C) for open gears; a 20% OPEX reduction and a 95% decrease in lubricant consumption, with payback in 14–18 months. The article will be of use to concentrator and plant managers, mechanical engineers, and reliability specialists.

DOI: 10.5267/j.esm.2025.12.001
Keywords: Spiral classifier, Direct drive, Torque arm, Reliability, Vibration diagnostics, Predictive maintenance