Search Results (122)

This study presents a detailed experimental comparison of the rotordynamic and thermal performance of automotive turbochargers supported by two distinct hydrodynamic bearing configurations: fully floating ring bearings (FFRBs) and semi-floating ring bearings (SFRBs). While both designs are widely used in commercial turbochargers, they exhibit significantly different dynamic behaviors due to differences in ring motion and fluid film interaction. A cold air-driven test rig was employed to assess vibration and temperature characteristics across a range of controlled lubricant conditions. The test matrix included oil supply pressures from 2 bar (g) to 4 bar (g) and temperatures between 30 °C and 70 °C. Rotor speeds reached up to 200 krpm (thousands of revolutions per minute), and data were collected using a high-speed data acquisition system, triaxial accelerometers, and infrared (IR) thermal imaging. Rotor vibration was characterized through waterfall and Bode plots, while jump speeds and thermal profiles were analyzed to evaluate the onset and severity of instability. The results demonstrate that the FFRB configuration is highly sensitive to oil supply parameters, exhibiting strong subsynchronous instabilities and hysteresis during acceleration–deceleration cycles. In contrast, the SFRB configuration consistently provided superior vibrational stability and reduced sensitivity to lubricant conditions. Changes in lubricant supply conditions induced a jump speed variation in floating ring bearing (FRB) turbochargers that was approximately 3.47 times larger than that experienced by semi-floating ring bearing (SFRB) turbochargers. Furthermore, IR images and oil outlet temperature data confirm that the FFRB system experiences greater heat generation and thermal gradients, consistent with higher energy dissipation through viscous shear. This study provides a comprehensive assessment of both bearing types under realistic high-speed conditions and highlights the advantages of the SFRB configuration in improving turbocharger reliability, thermal performance, and noise suppression. The findings support the application of SFRBs in high-performance automotive systems where mechanical stability and reduced frictional losses are critical. Full article

Accurate seismic performance assessment of flexure-shear critical reinforced concrete (RC) columns necessitates precise hysteresis modeling that captures their distinct cyclic characteristics—particularly pronounced strength degradation, stiffness deterioration, and pinching effects. However, existing hysteresis models for such circular RC columns fail to comprehensively characterize these coupled cyclic degradation mechanisms under repeated loading. This study develops a novel hysteresis model explicitly incorporating three key mechanisms: (1) directionally asymmetric strength degradation weighted by hysteretic energy, (2) cycle-dependent pinching governed by damage accumulation paths, and (3) amplitude-driven stiffness degradation decoupled from cycle count, calibrated and validated using 14 column tests from the Pacific Earthquake Engineering Research Center (PEER) structural performance database. Key findings reveal that significant strength degradation primarily manifests during initial loading cycles but subsequently stabilizes. Unloading stiffness degradation demonstrates negligible dependency on cycle number. Pinching effects progressively intensify with cyclic advancement. The model provides a physically rigorous framework for simulating seismic deterioration, significantly improving flexure-shear failure prediction accuracy, while parametric analysis confirms its potential adaptability beyond tested scenarios. However, applicability remains confined to specific parameter ranges with reliability decreasing near boundaries due to sparse data. Deliberate database expansion for edge cases is essential for broader generalization. Full article

Polymer blending techniques enable the tailoring of desired properties for diverse applications. This study investigates the effect of PMMA content on the thermomechanical, chemical, mechanical, and fatigue life properties of PC/ABS/PMMA (polycarbonate/acrylonitrile–butadiene–styrene/polymethylmethacrylate) ternary blends. To this end, various characterization analyses, as well as tensile, impact, and fatigue tests, were conducted. The results indicate that the viscoelastic modulus improves with increasing PMMA content in ternary blends. Furthermore, PC/ABS/PMMA blends exhibit an immiscible phase morphology. The elastic modulus, yield strength, and tensile strength increase with higher PMMA content, while the elongation at break and impact strength decrease. Fatigue strength and the fatigue strength exponent were found to vary nonlinearly with PMMA content. Compared to PC/ABS blends, PC/ABS/PMMA blends demonstrated improvements of approximately 12% to 58% and 26% to 117% in hysteresis energy and the dynamic elastic modulus, respectively. Additionally, fatigue life cycles improved by 5% to 11% at low stress amplitudes. This experimental study provides comprehensive insight into the complex interplay among the chemical, thermomechanical, mechanical, and fatigue properties of ternary PC/ABS/PMMA blends, highlighting their potential for applications requiring balanced or tailored structural and material characteristics. Full article

This paper presents a modeling framework for hysteretically nonlinear piezoelectric composite beams using functional differential equations (FDEs). While linear piezoelectric models are well established, they fail to capture the complex nonlinear behaviors that emerge at higher electric field strengths, particularly history-dependent hysteresis effects. This paper develops a cascade model that integrates a high-dimensional linear piezoelectric composite beam representation with a nonlinear Krasnosel’skii–Pokrovskii (KP) hysteresis operator. The resulting system is formulated using a state-space model where the input voltage undergoes a history-dependent transformation. Through modal expansion and discretization of the Preisach plane, we derive a tractable numerical implementation that preserves essential nonlinear phenomena. Numerical investigations demonstrate how system parameters, including the input voltage amplitude, and hysteresis parameters significantly influence the dynamic response, particularly the shape and amplitude of limit cycles. The results reveal that while the model accurately captures memory-dependent nonlinearities, it depends on numerous real and distributed parameters, highlighting the need for efficient reduced-order modeling approaches. This work provides a foundation for understanding and predicting the complex behavior of piezoelectric systems with hysteresis, with potential applications in vibration control, energy harvesting, and precision actuation. Full article

The significant phase transformation hysteresis in TiNi alloys limits their performance. To address this, copper (Cu) was added as an alloying element to reduce hysteresis. This study synthesized three compositions of Ti₅₀Ni_50−xCu_x (x = 0, 5, 7 at.%) shape memory alloys (SMAs) via vacuum arc melting to optimize the Cu content. The alloys were homogenized through hot rolling to maintain stable mechanical and shape memory properties. The hot-rolled Ti₅₀Ni₄₅Cu₅ alloy demonstrated excellent shape memory behavior, achieving 100% thermal recovery after one cycle at 4% and 6% strain and 99.2% recovery after six cycles at 4% strain. It also exhibited outstanding mechanical performance, with a tensile strength of 900 MPa and 40% elongation. Microscopic analysis using scanning electron microscopy (SEM) with energy-dispersive X-ray spectroscopy (EDS), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM) revealed that Cu preferentially segregates at grain boundaries, suppressing the formation of the Ti₂(Ni,Cu) phase. This moderate segregation, combined with hot rolling, promotes the reprecipitation and uniform distribution of phases, reducing the likelihood of premature fracture caused by stress concentration during deformation. The moderate thickness and uniformly distributed martensite, as well as the Type II twins with strong deformation ability, significantly improved the shape memory properties of Ti₅₀Ni₄₅Cu₅. This study provides valuable insights into the microscopic mechanisms influenced by Cu in TiNi alloys and proposes a novel strategy for controlling precipitate phases through adjustments in alloy composition and optimized processing conditions. Full article

Exhaust manifolds accumulate creep and fatigue damage under cyclic thermal loading, leading to localized failure. Understanding a material’s mechanical behavior is crucial for accurate life assessment. This study systematically investigated the low-cycle fatigue (LCF) and creep–fatigue interaction behaviors of medium-silicon molybdenum ductile iron. It was found that QTRSi4Mo exhibited cyclic hardening at room temperature and 400 °C, whereas it exhibited cyclic softening at 600 °C and 700 °C for low-cycle stress–strain responses. During creep–fatigue tests with hold time, variations in the strain amplitude did not alter the hysteresis loop shape or the hardening/softening characteristics of the material. They only induced a slight upward shift in the yield center. Additionally, stress relaxation primarily occurred in the initial phase of the hold period, so the hold duration had little effect on the final stress value. The investigation of creep–fatigue life models highlighted that accurately characterizing the damage induced by stress relaxation during the hold stage is critical for creep damage evaluation. The calculated creep damage results differed greatly from the experimental results of the time fraction model (TF). A combined approach using the strain energy density dissipation model (T-SEDE) and the Ostergren method demonstrated excellent predictive capability for creep–fatigue life. Full article

Silicon-based materials provide a new pathway to break through the energy storage limits of battery systems but their industrialization process is still constrained by inherent diffusion hysteresis and unstable electrode structures. In this work, we propose a novel structural design strategy employing a modified spray freeze drying technique to construct multidimensional carbon nanostructures. The continuous morphological transition from carbon nanowires to carbon nanosheets was facilitated by the inducement of ultralow-temperature phase separation and the effect of polymer self-assembly. The unique wrinkled carbon nanosheet encapsulation effectively mitigated the stress concentration induced by the aggregation of silicon nanoparticles, while the open two-dimensional structure buffered the volume changes of silicon. As expected, the SSC-5M composite retained a reversible capacity of 1279 mAh g⁻¹ after 100 cycles at 0.2 C (1 C = 1700 mAh g⁻¹) and exhibited a capacity retention of 677.1 mAh g⁻¹ after 400 cycles at 1 C, demonstrating excellent cycling stability. This study offers a new strategy for the development of silicon-based energy storage devices. Full article

Steel structures subjected to earthquakes or extreme cyclic loadings may undergo extensive damage and fractures due to ultra-low-cycle fatigue (ULCF). Although assessments of damage initiation and evolution parameters have been carried out for some steels exposed to low-cycle fatigue, so far, these parameters for structural steels exposed to ULCF have neither been sufficiently studied nor quantified. Accordingly, this paper provides the results of finite element analysis (FEA) concerning the ULCF behaviors of S355 and S690 steel specimens. Calibration of the damage parameters is performed in SIMULIA Abaqus 6.11 FEA software using a direct cyclic algorithm and available experimental data. Kliman’s model for the hysteresis energy of cyclic loading is used to analytically verify the damage parameters. In addition, available experimental data were obtained from cyclic axial strain tests on S355 and S690 steel specimens according to the ASTM International standard E606/E606M-21. Finally, the non-linear Chaboche–Lemaitre (C–L) combined isotropic–kinematic hardening model is used for the characterization of the ULCF behavior of S355 steel in a simple cylindrical bar. It is found that the two damage initiation parameters are 5.0 and −0.8, the first damage initiation parameter is dominant when modeling the number of cycles to failure, and the second damage initiation parameter is a material constant. Full article

Discontinuity damage and shear strength weakening under dynamic loading are important causes of engineering rock instability. To study the damage mechanism of rock discontinuities under dynamic loading and the law of shear strength weakening after disturbance, the dominant controlling factors of dynamic loading-induced discontinuity damage were analyzed using the discrete element method. The evolution characteristics and formation mechanism of discontinuity damage were revealed, and the shear strength weakening law of discontinuities under dynamic loading was quantitatively characterized and verified by laboratory tests. The results are as follows: (1) Due to the symmetry of the structural distribution and material properties, a 2D UDEC-Tri model containing a discontinuity specimen was established. The number of failure blocks and the crack development length were calculated using Fish scripting in UDEC. Based on the orthogonal design method, it was found that the dominant controlling factors of dynamic load-induced discontinuity damage are the dynamic load frequency, peak dynamic load, and cycle number. (2) In the rising stress stage, the discontinuity mainly accumulates energy, causing minor damage with slight shear crack development. In the falling stress stage, energy release increases the damage, leading to significant shear and tensile crack growth with a hysteresis effect. The cracks are symmetrically distributed on both sides of the discontinuity. (3) The greater the damage to the discontinuity caused by the dynamic load disturbance, the more obvious the shear strength weakening after the disturbance. By comprehensively considering the symmetry characteristics of the damage distribution and strength weakening law of the discontinuity, and based on mathematical analysis, the model of discontinuity shear strength weakening after dynamic load disturbance was established. The model considers three dominant controlling factors: the dynamic loading frequency, peak dynamic load, and cycle number. The research results reveal the damage mechanism of discontinuities under dynamic loading and obtain the shear strength weakening law, which provides a reference for the stability evaluation of engineering rock masses under dynamic loading. Full article

The integration of recycled powder (RP) as a partial cement replacement in concrete, combined with fiber reinforcement, facilitates the development of high-ductility recycled powder concrete (HDRPC) with enhanced mechanical properties. This approach holds significant potential for effectively recycling construction waste and reducing carbon emissions. To improve the seismic performance of prefabricated joints in industrial prefabricated building production, experimental tests under low-cycle reversed cyclic loading were conducted on four HDRPC prefabricated joints, one HDRPC cast-in-place joint, and one normal prefabricated concrete joint. The study systematically analyzed damage patterns, deformation ductility, stiffness degradation, hysteresis energy dissipation, and other performance characteristics. The results demonstrate that HDRPC effectively mitigates crack width and shear deformation in the joint core area, achieving a 17.8% increase in joint-bearing capacity and a 33.3% improvement in displacement ductility. Moreover, HDRPC improves specimen damage characteristics, enhances joint shear capacity and flexibility, and reduces the demand for hoop reinforcement in the joint core area due to its exceptional shear ductility. Based on the softened tension–compression bar model, a crack-resistance-bearing capacity equation for HDRPC joints was derived, which aligns closely with shear test results when cracks develop in the joint core area. Full article

The work undertaken in this paper is the comparative analysis of the accumulation of plastic strain energy in the as-received and pre-deformed (overloaded) material states, performed on the example of S420M steel. For this reason, the low-cycle fatigue tests on S420M steel specimens were conducted under controlled deformation conditions, and both as-received (undeformed) and pre-deformed specimens were used in the tests. The results of the low-cycle tests were analyzed in terms of dissipated energy. This study found that pre-straining of S420M steel specimens causes a reduction in the energy of the hysteresis loop at all strain amplitude levels. This results in a slight increase in the fatigue life of pre-strained specimens compared to as-received specimens. Based on the analysis, it was also found that despite the different lifetimes obtained at the same strain amplitude levels, the fatigue characteristics in terms of energy of the as-received and pre-strained samples are statistically the same. Experimental verification of the analytical models used to describe hysteresis loops confirmed their suitability for describing fatigue behavior for specimens made of steel in both the as-received and pre-strained state. Full article

In this paper, the low-cycle reciprocating load test was carried out on four-limb concrete-filled steel tubular (CFST) lattice columns with different slenderness ratios and axial compression ratios, and the seismic performance was studied. Two performance indicators, namely damage and hysteretic energy dissipation, were defined as the objective functions, and the axial compression ratio was used as an optimization variable to perform the multi-objective optimization analysis of four-limb CFST lattice columns. Optimization using the max–min problem approach aims to optimize the axial compression ratio to minimize damage and maximize the dissipation of hysteresis energy. The seismic performances before and after optimization were determined using a restoring force model and were evaluated by the finite element method under different axial compression ratios. The results show that, under low-cycle reciprocating loads, the load–displacement hysteresis curve is a bow shape (Members 1 and 2), inverse S-shape (Member 3), and approximate shuttle shape (Member 4). Through multi-objective optimization, the optimized axial compression ratio is 0.25 and the finite element analysis indicates that the optimal seismic performance is at an axial compression ratio of 0.25. Through the optimized design, the maximum horizontal load of lattice columns, the elastic stiffness, the dissipation capacity, and the seismic performance are all improved, under the premise of satisfying the structural safety. Full article

Column frames connected using Tang Dynasty straight tenon joints represent a unique structural system characterized by historical significance and architectural ingenuity. Consequently, an experimental model, resembling the straight tenon joint style of the Tang Dynasty Foguang Temple East Hall, was constructed using two square beams (Fangs) and three columns in this study. Through low-cycle repeated load tests, hysteretic curves, stiffness degradation, energy dissipation capabilities, and certain other indicators were analyzed under four distinct vertical load levels. The results reveal that increasing the vertical load can effectively improve the fullness of the hysteresis curve and the peak restoring force of the column frame. Moreover, a pronounced pinch effect was found in the hysteretic curve of the column frame, indicating that a higher vertical load can strengthen the frame’s restoring force within a specific range of horizontal displacement, thereby maintaining its structural stability. With increasing vertical loads, the maximum restoring force and stiffness of the column frame are elevated, enhancing the structure’s energy dissipation capacity and partially mitigating its stiffness degradation. However, it is noteworthy that as the horizontal load displacement increases, higher vertical loads result in a more rapid decline in the frame’s restoring force, reducing the effectiveness of improving the energy dissipation capabilities of the column frame. Full article

Anaerobic digestate represents a valuable organic by-product, with one of the main challenges being its enhanced utilization. Pelletization offers potential benefits by improving the digestate’s storability, facilitating transport, and significantly expanding its application as a fertilizer or biofuel. Understanding the mechanisms of densification and their impact on the final product quality is essential and served as the inspiration for this research. Its primary focus was stress relaxation and the subsequent elongation of pellets within the compaction chamber (in-die). It investigated the hypothesis that elastic recovery, resulting from internal stress relaxation once the compressive force is removed, has direct implications for pellet quality. The investigations were conducted using a Zwick universal machine. Samples of digestate with varied moisture levels, i.e., 10, 13, 16, 19, and 22%, were loaded with amplitudes of 8, 11, 14, 17, and 20 kN. Ten loading and unloading cycles were employed. Elastic recovery (in-die) (ER_in-die) in the investigated digestate increased with rising MC and compaction pressure but decreased with increasing cycle number. There was little correlation between ER_in-die and pellet strength. Permanent strain energy exerted the greatest influence on pellet quality. Permanent strain energy had the greatest influence on pellet quality. Examining hysteresis loop behavior emerged as a promising area for further research to better understand springback phenomena. Full article

Laser ablation was used to successfully fabricate multiferroic bilayer thin films, composed of BaTiO₃ (BTO) and CoFe₂O₄ (CFO), on highly doped (100) Si substrates. This study investigates the influence of BaTiO₃ layer thickness (50–220 nm) on the films’ structural, magnetic, and dielectric properties. The dense, polycrystalline films exhibited a tetragonal BaTiO₃ phase and a cubic spinel CoFe₂O₄ layer. Structural analysis revealed compression of the CoFe₂O₄ unit cell along the growth direction, while the BaTiO₃ layer showed a tetragonal distortion, more pronounced in thinner BTO layers. These strain effects, attributed to the mechanical interaction between both layers, induced strain-dependent wasp-waisted behavior in the films’ magnetic hysteresis cycles. The strain effects gradually relaxed with increasing BaTiO₃ thickness. Raman spectroscopy and second harmonic generation studies confirmed BTO’s non-centrosymmetric ferroelectric structure at room temperature. The displayed dielectric permittivity dispersion was modeled using the Havriliak–Negami function combined with a conductivity term. This analysis yielded relaxation times, DC conductivities, and activation energies. The observed BTO relaxation time behavior, indicative of small-polaron transport, changed significantly at the BTO ferroelectric Curie temperature (Tc), presenting activation energies E_τ in the 0.1–0.3 eV range for T < Tc and E_τ > 0.3 eV for T > Tc. The BTO thickness-dependent Tc behavior exhibited critical exponents ν ~ 0.82 consistent with the 3D random Ising universality class, suggesting local disorder and inhomogeneities in the films. This was attributed to the composite structure of BTO grains, comprising an inner bulk-like structure, a gradient strained layer, and a disordered surface layer. DC conductivity analysis indicated that CoFe₂O₄ conduction primarily occurred through hopping in octahedral sites. These findings provide crucial insights into the dynamic dielectric behavior of multiferroic bilayer thin films at the nanoscale, enhancing their potential for application in emerging Si electronics-compatible magneto-electric technologies. Full article