Thermomechanical Loading Research Articles

Stress–Strain Response of AISI H13 Steel Subjected to Cyclic Thermomechanical Loading

Stress–Strain Response of AISI H13 Steel Subjected to Cyclic Thermomechanical Loading

Effect of ultrasonic vibration on fatigue life of Inconel 718 machined by high-speed milling: Physics-enhanced machine learning approach

Ultrasonic assisted high-speed machining (UAHSM) can be served as a thermomechanical surface sever plastic deformation (SSPD), because of the high-frequency impact load exerting to the sample together with thermomechanical loads due to shearing and plowing. Despite existing of few works which studied the impact of ultrasonic vibration on fatigue life assessment of difficult-to-cut material by experimental approach, they couldn’t provide an in-depth analysis to identify the underlying mechanisms of fatigue due time-consuming and costly fatigue life tests. Hence, elucidating the role of ultrasonic vibration in UAHSM on variation of fatigue life needs further studies. In order to do so, in the present work, a hybrid predictive approach based using ANFIS-based machine learning model and micromechanical Navaro-Rios (NR) fatigue crack propagation model has been introduced to directly correlates the UAHSM’s parameters to fatigue life. Here the former correlates feed rate, cutting velocity and vibration amplitude as process inputs, to surface integrity aspects (SIA) viz residual stress, roughness and grain size as output. Then, the modeled SIA are correlated to fatigue life using the former. The introduced hybrid model was then verified through series of UAHSM by examining the fatigue lives of milled Inconel 718 using four-point bending fatigue tests. Upon confirmation of the developed model, a comprehensive study was carried out to find how the process factors impact variation of SIA and subsequently fatigue. It was found from the results of developed models and confirmatory experiments that the role of ultrasonic vibration on improved fatigue life is mainly due to inducing compressive residual stress and more refined microstructure than the roughness.

Critical current degradation of commercial REBCO coated conductors under thermomechanical loads

Abstract The process to obtain a superconducting joint between Coated Conductors (CCs) involves the simultaneous application of temperature and transverse compressive pressure to promote the joining of the two adjacent REBCO layers. We performed experiments to simulate this procedure by subjecting samples from commercial CCs to different combinations of pressure, and temperature. The objective was to understand the effects of the thermomechanical cycles on the critical current (Ic) and, therefore, determine the upper limit for the achievable current in a superconducting joint between CCs. We observed a reduction of the Ic across the investigated parameter range that is accelerated at higher temperatures and pressures. For instance, the average reduction of Ic measured at 77 K in self-field varied from 45% to 90% when increasing the pressure for samples heated at 820 °C, as compared to samples heated at the same temperature without applied pressure. As a complement to electrical transport measurements, we carried out TEM and EDX investigations to study the relation between the degradation of Ic and alterations in the microstructure of REBCO. These analyses indicate that the concurrent application of temperature and pressure accelerates the decomposition of the REBCO phase. The EDX data suggests that the decomposition products could correspond with a peritectic reaction of the REBCO occurring at lower temperatures, accelerated by the presence of an external pressure. This early decomposition occurs in localized areas of the REBCO layer, constricting the available cross-section for current flow and thereby diminishing the critical current.

Design optimization of continuous fiber composites with thermo-mechanical coupling and load uncertainties

This paper introduces a theoretical framework for the design optimization of continuous fiber composites reinforced with continuous fiber trajectories subject to thermo-mechanical coupling and load uncertainties. Different uniform temperature variations are applied in the structure to investigate the influence of ambient temperature change on the structural performance. To consider the external load uncertainties, a robust design optimization model is proposed where the loads are modeled as hybrid variables, namely magnitudes as random variables and directions as interval variables, with the robust objective determined through a hybrid orthogonal polynomial expansion method. Furthermore, we use a level-set function to represent the structural boundary, with its evolution driven by shape derivatives calculated based on uncertainty analysis. The continuous fiber paths are subsequently determined by the level-set isoline extracted from the structural boundary, which in turn influences the structural mechanical performance due to the material anisotropy of composites. The continuity of continuous fiber and the equal space between adjacent trajectories largely ensure the additive manufacturability of the composites. Three numerical examples are presented to demonstrate the effectiveness of the developed framework. The results show that the ambient temperature variations and load uncertainties largely impact the optimized topology and fiber infill patterns of composites, thus are important to be considered in the design stage. Moreover, the optimized structure can have a 5-fold stiffness per unit mass compared with the initial design thus largely increasing the material efficiency in carrying external uncertain loads.

Effect of different agents on preload force of dental implants with bio high-performance poly-ether-ether-ketone abutments

PurposeThis study evaluated the influence of different agents such as blood, artificial saliva, and normal saline on preload force of dental implants with bio-high-performance poly-ether-ether-ketone (Bio-HPP) abutments to determine its effect on screw loosening. MethodsForty (N = 40) Grade 5 titanium dental implant analog (GM Implant Analog; Neodent, Straumann) with Bio-HPP poly ether-ether ketone (PEEK) abutment and titanium screw was used in the study. The samples were embedded in acrylic split mold. In the control Group C, no agent was added. In the other three groups, blood (B), normal saline (N) and saliva (S) was added in the access cavity of the samples. A sequential torque of 15 Ncm, 20 Ncm, 25 Ncm, 30 Ncm up to 35 Ncm was applied with a digital torque meter (Eclatorq, model: SD-05bn, range:2.5–50 Ncm, torque accuracy: ± 2%cw). Samples were subjected to thermomechanical cyclic loading at 5–550 Celsius for 1000 cycles (Chewing simulator, CS 4.4) to simulate six months of clinical service. Preload was measured as reverse torque value (RTV). Raw data in the form of mean ± standard deviation was documented and subjected to statistical analysis. A one-way ANOVA was performed to contrast the groups. Tukey HSD test was used to determine the multiple comparison assessment (P < 0. 05). ResultsA mean reverse torque value of 35 Ncm ±0.00 was observed in both control and in groups exposed to normal saline (P >.05). Measurements of 33.4 Ncm ±2.51 and 34.8 Ncm ±0.40 were found when exposed to blood and artificial saliva in order (P < .05). When compared with control, exposure to blood showed significant variation in preload (P = .03). ConclusionA significant reduction in reverse torque force was observed when titanium implants and Bio-HPP abutments were exposed to blood, suggesting a potential risk of screw loosening (P < .05). In contrast, minimal decrease and no significant change in preload were noted with exposure to saliva and normal saline (P > .05).

Effect of temperature and adhesive defect on repaired structure using composite patch

In structural engineering, composite patch repairs are widely used to address cracked structures. However, their behavior under thermo-mechanical loading remains complex and less understood. This study examines the repair of a center-cracked plate subjected to both mechanical and thermo-mechanical environments, using finite element analysis in ANSYS. The repair effectiveness is evaluated using the Stress Intensity Factor (SIF) at the crack tip. Findings reveal that increased temperature substantially elevates SIF values. Boron/epoxy patches are most effective under mechanical loading, yielding the lowest SIF, while graphite/epoxy patches excel under thermo-mechanical loading due to their lower Coefficient of Thermal Expansion (CTE). Patch thickness influences SIF differently based on loading conditions; thicker patches decrease SIF under mechanical loading but increase it under thermo-mechanical loading. Furthermore, adhesive defects, particularly at the crack tip, markedly increase the risk of adhesive failure, especially under thermo-mechanical conditions. This research underscores the significant impact of temperature variations on the efficiency of structural repairs, contributing to a deeper understanding of composite patch repair performance in cracked structures.

Numerical characterizations of the thermomechanical response of power modules with ceramic substrates and lead-free bonds

PurposeThe present paper aims to study the influence of the substrate system on the thermomechanical response of various lead-free die attach materials used in power electronics using nonlinear finite element simulations.Design/methodology/approachParticularly, three ceramic substrate systems, including direct copper bonded (DCB) and aluminum nitride (AlN) – as well as silicon nitride (Si3N4) –based insulated metal substrate (IMS) configurations are examined in this study. Additionally, three die attach systems, namely, silver-tin transient liquid phase (TLP), sintered silver (Ag) and sintered copper (Cu) are included in the analysis. ANSYS software is employed to build the finite element models of the power modules and to conduct the nonlinear thermomechanical investigations.FindingsThe simulation results revealed that the IMS, Si3N4 and DCB-based power modules end up with significantly lower interconnect inelastic strains and inelastic strain energies suggesting better fatigue life performance. Additionally, the bonding layer stresses and expected failure mechanism are not influenced by the substrate configuration rather than the bond material. For instance, the silver-tin TLP joints develop high stresses and hence brittle failures are expected. Nonetheless, the sintered Ag and sintered Cu have significantly lower stresses which could lead to fatigue-induced failures.Originality/valuePower electronics use various ceramic-based substrate systems because of their improved thermal conductivity, electrical insulation and heat resistance properties. The proper selection of the substrate structure could highly enhance the thermal fatigue of the power modules. Markedly, the findings of this research are useful for designing highly reliable and effective power modules continuously subjected to thermomechanical loadings.

Fracture studies on cruciform bend specimens of pressure vessel steel subjected to thermo-mechanical loading

The safety of a nuclear power plant during incidents, such as a Loss of Coolant Accident (LOCA), heavily relies on conducting a comprehensive structural integrity assessment of both the Reactor Pressure Vessel (RPV) and its components, specifically to withstand Pressurized Thermal Shock (PTS). PTS is characterized by a combination of steep temperature gradient, resulting from the injected emergency coolant during a LOCA, and internal pressure within the RPV. Majority of the reported fracture assessment studies on RPV steel, whether experimental or numerical investigations, have predominantly focused on standard uniaxial specimens at iso-thermal loading conditions. To better simulate the thermal shock scenario in RPVs, the present work aims to assess the impact of a biaxial stress field on both fracture parameters (crack mouth opening displacement and J-integral) and plastic collapse load. This assessment is conducted through experimental and numerical investigations, both with and without prior transient thermal load. Fracture experiments are performed on cruciform bend specimens, featuring two different biaxiality ratios (1:1 and 2:1). Moreover, numerical studies on cruciform specimens are conducted using finite element analysis to validate and corroborate the observations derived from the fracture experiments.

3D bi-directional auxetic square metastructure with programmable thermal expansion and Poisson's ratio

Multifunctional integration research on metastructures has become the current development trend and hotspot, especially satellite platforms and hypersonic aircraft in the aerospace field. A 3D bi-directional auxetic square metastructure (BASM) with the programmable coefficient of thermal expansion (CTE) and Poisson's ratio (PR) is designed through the combination of re-entrant hexagonal structures and bi-material triangles. Specimens in the form of the 1*2 array are designed and fabricated through 3D printing. The correctness of the results of finite element analysis (FEA) of the BASM is verified by uniaxial compression experiments. Additionally, FEA is adopted to investigate the effective mechanical properties of the BASM with the form of the 2*3 array, and deformation mechanisms are further explored. Results indicate that the CTE, PR, and stiffness of the BASM depend on material combinations and geometric parameters. Under thermal and mechanical loads, the BASM achieves bi-directional regulation of the CTE and PR, encompassing both axial and circumferential deformations. Notably, the deformation mechanisms and critical conditions of the BASM are explored under the thermo-mechanical load. A novel strategy for programming the PR of the BASM is proposed in addition to changing the geometric parameters and the material combinations.

A novel design optimization framework to sustain remanufacturability

The ever-increasing global carbon emissions have urged the need for environmentally conscious/sustainable product design, for which the design for remanufacturing (DfRem) is one potential approach. DfRem targets at designing products that have multiple life cycles, thus significantly reducing raw material usage, energy consumption, and carbon emissions. In this paper, we develop a three-stage framework that consists of (1) systematic design space exploration and a multi-objective optimization formulation to minimize the likelihood of failure causes (such as fatigue and wear) and environmental footprint, (2) topology optimization to further reduce material usage without significantly affecting the load-carrying capability of the product, and (3) post-topology optimization design verification to ensure the proposed design satisfies all design constraints. The environmental impact can be assessed at varying comprehensiveness levels (e.g., design and manufacturing phase, use phase) and in terms of carbon or GHG emission, energy use, and waste generation. Because the novel design framework predominantly adjusted the geometry, we focused on mass-based change and energy savings due to sustained remanufacturability. The multi-objective optimization formulation in the first step results in a Pareto optimal set of possible design solutions that the designer can use for the second step. We demonstrate the utility of this framework through a case study of an engine cylinder head subjected to thermo-mechanical loads, where we find that about 5% of the product mass can be conserved with only about a 3% increase in surface area that has a fatigue life less than 10,000 cycles.

Thermo-Mechanical Coupling Load Transfer Method of Energy Pile Based on Hyperbolic Tangent Model

By employing the hyperbolic tangent model of load transfer (LT), this paper establishes the thermo-mechanical (TM) coupling load transfer analysis approach for an energy pile (EP). By incorporating the control condition of the unbalance force at the null point, the method for determining the null point considering the temperature effect is enhanced. The viability of the presented method is validated through the measured outcomes from model experiments of energy piles. A parametric investigation is conducted to explore the impact of the soil shear strength parameters, upper load, temperature variation, head stiffness, and radial expansion on the axial force, strain, and displacement of the energy pile under thermo-mechanical coupling. The results suggest that the locations of the null point and the maximum axial force are dependent on the constraint boundary conditions of the pile side and the two ends. When the stiffness of the pile top increases, axial stress and displacement increase, while strain decreases. An increase in the drained friction angle leads to an increase in axial stress under thermal-load coupling, but strain and displacement decline. The radial expansion has a negligible influence on the thermo-mechanical interaction between the pile and the soil.

Martensitic transformation induced by cooling NiTi wire under various tensile stresses: Martensite variant microstructures, textures, recoverable strains and plastic strains

Whenever the forward and/or reverse B2 cubic to B19’ monoclinic martensitic transformation in NiTi shape memory alloy wire proceeds under external stress above certain threshold, it generates incremental plastic strains which accumulate during thermomechanical cyclic loading and lead to functional fatigue preventing many promising engineering applications from realization. In this work, unique thermomechanical loading experiments were performed on NiTi shape memory wire with the aim to reveal the mechanism by which the forward martensitic transformation upon cooling under external stress generates plastic strain. Recoverable transformation strains and plastic strains generated by the forward transformation on cooling under various tensile stresses were evaluated, martensite variant microstructures in grains were reconstructed by nanoscale orientation mapping in TEM, martensite textures after cooling at room temperature were evaluated by in-situ synchrotron x-ray diffraction and permanent dislocation defects in martensite were analyzed by TEM. Based on the obtained experimental evidence, it is proposed that the forward martensitic transformation on cooling under stress proceeds via habit plane interfaces between austenite and second order laminate of (001) compound twins in martensite. Depending on the magnitude of the applied stress, the induced martensite reorients, partially detwins and deforms plastically via [100](001) dislocation slip in martensite in extent permitted by the requirement for compatible deformation of grains in nanocrystalline NiTi wire via a single deformation system. During the forward MT upon cooling under highest stresses 600 MPa, the martensite deforms via kwinking deformation enabling generation of large plastic strains 8 %.

Comparative Analysis of Active Bonded Piezoelectric Repair Systems for Damaged Structures under Mechanical and Thermo-Mechanical Loads

Active repair systems employing piezoelectric (PZT) patches have emerged as promising solutions for mitigating crack propagation and enhancing structural integrity in various engineering applications. However, the existing literature predominantly focuses on the application of PZT patches for repairing structures under mechanical loading. In this study, a finite element analysis (FEA) is employed to investigate the repair of a centre-cracked aluminium plate under both mechanical and thermo-mechanical loading conditions. This study explores the influence of key parameters, including temperature, PZT patch thickness, type of PZT material, adhesive material, and adhesive thickness, on the structural integrity and crack propagation behaviour. The results reveal significant differences in stress distribution and crack propagation tendencies under varying loading conditions and parameter settings. These findings emphasize the necessity of considering thermo-mechanical loading conditions and parameter variations when designing effective active repair systems. In conclusion, this study provides valuable insights into optimizing PZT patch-based repair strategies for improved structural integrity and crack mitigation in aerospace and other engineering applications under diverse loading scenarios.

Influence of cervical margin relocation on marginal integrity of resin composite restoration after thermo mechanical loading.

Influence of cervical margin relocation on marginal integrity of resin composite restoration after thermo mechanical loading.

Temperature-dependent mechanical properties and crystal plasticity parameters for additively manufactured Haynes-214 alloy: Experiments and numerical modeling

Our experimental mechanical testing data demonstrated that the additively manufactured (AM) laser powder bed fusion (L-PBF) Haynes-214 alloy exhibits non-linear mechanical properties as the temperature rises from ambient to 870 °C. To gain a deeper insight into the microstructure–property linkages under thermomechanical loading, it is essential to use crystal plasticity (CP) simulations. This approach can reduce the need to conduct expensive high-temperature experimental mechanical testing and account for crystallographic texture and grain morphology effects, which are known to be important in many AM processed materials. However, calibrating a CP model is time-consuming because individual simulations are computationally expensive and hundreds (or more) of iterations over parameter sets may be required. To address this issue, we have designed a machine learning - differential evolution (ML-DE) CP framework that can accurately interpolate the tensile properties of AM L-PBF Haynes-214 alloy across a wide temperature range from ambient to 870 °C, with minimal reliance on experimental data. The framework uses electron backscatter diffraction (EBSD) measurements to generate statistically equivalent microstructural volume elements to serve as inputs to the CP modeling framework. Stress–strain curves were generated from 1000 CP simulations, which serve as the training data set for the three ML regression algorithms explored: linear, extra-trees, and multi-layer perceptron. These three regression models were independently evaluated to compare their efficiency and identify the most suitable algorithm for the given problem. Results revealed that the extra-trees ML regressor outperforms the other models in both qualitative and quantitative aspects with an R2 of 0.98. Subsequently, the differential evolution optimization approach is employed to calibrate the ML-based CP material parameters with experimental results obtained at various temperatures. Finally, temperature-dependent CP material parameters are formulated. The effectiveness and efficiency of the designed framework are validated through comparison with experimental results, demonstrating a high degree of agreement. These calibrated parametric constitutive equations enable further use of the CP model to study the deformation behavior of this alloy under a wide range of thermo-mechanical loading and service conditions.

Deformation and microregion fracture mechanisms in type 316L welded joint under isothermal and thermo-mechanical fatigue loadings

Isothermal (IF) and thermo-mechanical fatigue (TMF) tests were conducted on 316L welded joints to investigate the effects of phase angle (in-phase (IP), clockwise-diamond (CD), and out-of-phase (OP)) and mechanical strain amplitude (±0.4 %, ±0.5 %, ±0.6 %) on deformation and microregion fracture mechanisms. Results reveal that increasing strain amplitude induces a higher softening rate, reduced fatigue life, and more pronounced dynamic strain aging (DSA). Nevertheless, there is a complicated discrepancy in the cyclic deformation between various phase angles. At high strain amplitudes, local embrittlement along the austenite/δ-ferrite interface induces cracking in the weld metal (WM) under both IF and TMF loadings, with TMF life increasing with phase angle. At a lower strain amplitude of 0.4 %, however, fracture location migration and different TMF life were observed. Microstructural analysis reveals that during TMF a lower strain amplitude of 0.4 %, the microstructure in both base metal (BM) and WM evolves from simple planar structures to low-energy substructures, characterized by an increase in kernel average misorientation, geometrically necessary dislocations, and low-angle grain boundaries, together with a reduction in high-angle grain boundaries and twin boundaries. In the WM, increasing phase angle tends to reduce dislocation density and reproduces planar dislocation structures due to enhanced DSA, thereby lowering cellular structure maturity. Conversely, in the BM, dislocation proliferation and interaction intensify, enhancing cellular structure maturity and de-twinning effect, which reduces BM fracture resistance and causes fracture migration from the WM to the BM. Moreover, active DSA under CD loading improves deformation resistance in both microregions, prolonging fatigue life and contributing to the observed different TMF life.

Effect of random variation in input parameter on cracked orthotropic plate using extended isogeometric analysis (XIGA) under thermomechanical loading

Abstract This research introduces the Stochastic Extended Isogeometric Analysis (XIGA) method to investigate fracture behavior of isotropic and orthotropic materials under mechanical, thermal, and thermomechanical loads. Employing knot spans from Isogeometric Analysis (IGA) for domain discretization, the study utilizes identical basis functions for geometry construction and solution discretization. Utilizing Extended Finite Element Method (XFEM) enrichment functions, accurate crack face displacement discontinuity and tip singularity within the stress field are characterized. Additionally, employing a second-order perturbation technique within XIGA framework, the research derives mean and coefficient of variance values for mixed-mode Stress Intensity Factors (SIF). Stochastic variations in material elastic properties, crack length, and crack angle are considered in this computation. Credibility and robustness of the study are confirmed through comparative analyses against available literatures and Monte Carlo Simulations (MCS). The observed exceptional agreement validates the precision and reliability of the proposed stochastic XIGA method for fracture analysis in orthotropic material systems under thermomechanical loading conditions.

Thermal protection technologies for solid propellant rocket engines

The article examines the thermal insulation characteristics of materials used in solid-fuel rocket engines manufactured in the United States, France, Italy, Japan, and other developed nations. The internal surfaces of combustion chambers in these rocket engines are subject to significant stress under thermo-mechanical loading conditions, necessitating specialized protection. The authors identify four categories of reinforced elastomeric materials that most effectively meet stringent requirements. Due to their adaptability, these materials may serve as versatile heat insulators and may be employed in a variety of high-temperature and corrosive surroundings.

Multiscale modelling of CFRP composites exposed to thermo-mechanical loading from fire

Carbon fibre reinforced polymers (CFRP) are prone to structural damage during extreme events such as fire. Typically, modelling the effect of fire on CFRP structures is carried out through mesoscale analysis to predict overall structural performance. In this study, Finite Element (FE) modelling has been conducted to investigate the effects of fire on CFRP specimens at both meso- and micro-scales. The mesoscale analysis informs the microscale analysis to examine the effects of fire on each constituent of the material. A comparison of thermal analysis at the meso- and micro-scales reveals less than a 6% difference in the predicted nodal temperature. For the first time, fire-induced progressive failure analysis has been conducted on the fibres, matrix, and fibre/matrix interface of representative plies within the composite laminates. Fibre breakage, matrix cracking, and interface debonding were accurately captured using representative volume element (RVE) models under thermo-mechanical loading, showing qualitatively excellent agreement with experimental data.

Spectroscopic Study of Strain, Oxidation, and Formation of Few-Layer Graphene at Steel Surfaces Tribologically Tested against MoS2 Films.

MoS2 not only has unique optoelectronic properties realizing photonic and semiconductor applications but also serves as a promising solid lubricant in tribological three-body contacts due to its advantageous friction and wear behavior. Its functionality is defined by elementary processes including strain, oxidation processes, and material mixing. However, these mechanisms were not elucidated for MoS2 having transferred from the MoS2 film synthesized at the main body to a steel counter body during tribological ball-on-disk tests. Using spatially and spectrally high-resolved Raman spectroscopy, we study the compressive and tensile strain within the MoS2 transfer material and analyze the oxidation of molybdenum, sulfur, and iron. In addition, we elaborate on the impact of transition metals modifying the MoS2 films on the strain distribution and oxidation processes. Decreasing intensities of the MoS2 Raman lines are accompanied with enhanced intensities of sulphur and molybdenum oxide Raman signatures which are particularly agglomerated at the edges of the tribological track. The formation of tribochemical oxides, including Mo4O11 in the Magnéli-phase, depends weakly on the type of modifying element, and an oxidation of a modification element itself is not detected. We also identified a tribologically induced formation of disordered few-layer graphene at counter-body surface areas which experienced weak thermo-mechanical tribological load. Our results characterize structural and chemical features of the MoS2 transfer material, thus predicting material failure at the microscopic level.