Thermal Mechanical Loading Research Articles

Numerical modelling of energy piles in saturated sand subjected to thermo-mechanical loads

This study investigates the impact that different magnitudes and combinations of thermal and axial mechanical loads have on the mechanical behaviour of energy piles in saturated sand. The work is based on the results of a series of thermo-hydro-mechanical finite element analyses, which are compared with centrifuge data, and parametric numerical runs. The analyses prove that an increase in heating loads induces a significant amount of stress and displacement in energy piles, with a remarkable mobilisation of their shaft and end-bearing capacity. Temperature variations up to ΔT= 50 °C induce axial stress up to σth=716kPa and pile heave up to dyth=−14.09mm. These temperature variations mobilise an average side shear resistance and an end-bearing load normalised with respect to those mobilised at failure up to qs,ave/qs,ULT,ave=−14.11% and Qb/Qb,ULT=27.35%, respectively. The magnitude of these phenomena depends on the significance of the applied temperature variation, the significance of the applied mechanical load to the foundation head prior to thermal loading with respect to the pile axial capacity and the soil response to additional loading/unloading processes. These aspects serve a major role in the evolution of the foundation constraint, which governs the mechanical performance of energy piles when subjected to thermo-mechanical loads.

A numerical analysis of the shakedown of parts during cyclic thermal mechanical loading

A method for determining the lower bound of shakedown limit at a cyclic thermal and mechanical load is developed on the basis of Melan’s theorem. A computational diagram is proposed and the method is practically implemented for the contact problem in which an unworn rolling stock wheel rolls along a new rail in a curved track section. The numerical analysis makes it possible to define the effect of a creeping rolling stock wheel on the conditions of shakedown with provision for thermal and mechanical loads on the rail-head running surface.

Simulation of μ-Bump and TSV in 3-D Integration

The reduction of package and chip size by the need of cost reduction on one hand and the need of high voltage metallization on chip for power applications on the other hand the thermal electrical-mechanical management concerning the reliability becomes more and more critical. Breakdown failures due to mechanical stress, moisture uptake, migration effects caused by current crowding, temperature gradients due to Joule heating and stress gradients and intermetallic phase growth have an increasing importance. With the help of simulations the weakest links as well as locations with high thermal electrical and mechanical loads can be determined. This will be shown for selected examples.

Creep and Damage Analysis of Reactor Pressure Vessel Considering Core Meltdown Scenario

The Fukushima accident shows that In-Vessel Retention (IVR) of molten core debris has not been appropriately assessed, and a certain pressure (up to 8.0MPa) still exists inside the reactor pressure vessel (RPV). Generally, the pressure is supposed to successfully be released, and the externally cooled lower head wall mainly experiences the temperature difference which may be more than 1000°C. Therefore, in order to make the IVR succeed, it is necessary to investigate the creep behaviour and damage distribution of the RPV under complex thermal-mechanical loadings. Accordingly, considering the unlikely core melt down scenario for a light water reactor (LWR) a possible failure mode of the reactor pressure vessel (RPV) and its failure time has to be predicted for a determination of the loadings on the containment. Due to the thickness of RPV, the high temperature gradient results in various failure modes, i.e., plastic failure and creep failure. In disclosing the failure mechanism, the finite element model has been developed simulating the thermal processes and the visco-plastic behaviours of vessel wall. An advanced model for creep damage has been established to analyze the fracture time and fracture position of a vessel with an internally heated melt pool. Before the above, the stress and strain distributions along the wall thickness are investigated by ABAQUS software. Finally, the result shows that the calculated stress outside the RPV is lower than the yield stress of the material through most thickness. It is concluded that the RPV can maintain its integrity under IVR with given time, even if there exists the internal pressure of 8MPa.

Evaluation of marginal gap at the composite/enamel interface in Class II composite resin restoration by SEM after thermal and mechanical load cycling (An in vitro comparative study)

This study compared in vitro the marginal adaptation of three different, low shrink, direct posterior composites Filtek™ P60 (packable composite), Filtek™ P90 (Silorane-based composite) and Sonic fill™ (nanohybrid composite) at three different composite/enamel interface regions (occlusal, proximal and gingival regions) of a standardized Class II MO cavity after thermal changes and mechanical load cycling by scanning electron microscopy. Materials and methods:Thirty six sound human maxillary first premolars of approximately comparable sizes were divided into three main groups of (12 teeth) in each according to the type of restorative material that was used: group (A) the teeth were restored with Filtek™ P60 and single bond™ Universal adhesive using horizontal incremental technique, group (B)the teeth were restored with Filtek™ P90 and P90 system adhesive using horizontal incremental technique and group (C) the teeth were restored with Sonic fill™ composite and single bond™ Universal adhesive using bulk technique.After specimens were stored in distilled water at 37°C for 7 days, all specimens were subjected to thermocycling at (5° to 55 °C), then submitted to mechanical load cycling (intermittent axial force of 49N and a total of 50.000 cycles). The specimens were observed under scanning electron microscope at (2000 X) to measure marginal gap width (the distance between the dental wall and the restoration) at occlusal, proximal and gingival regions in micrometer using Tescan software, version 3.5. Data were analyzed statistically by one way ANOVA test and least significant difference tests. Results:The results showed that the silorane-based posterior composite (Filtek™ P90) showed significantly the least marginal gap width at the occlusal, proximal and gingival regions after the application of thermal changes and mechanical load cycling in comparison to the two methacrylate-based posterior composite Filtek™ P60 (packable) and the Sonic fill™ (nano-hybrid). Sonic fill™ bulk fill composite that relied on the vibration concept to lower the viscosity of high filler loaded composite material showed significantly lesser marginal gaps width at occlusal, proximal and gingival composite/enamel interface regions in comparison with Filtek™ P60 (packable composite) using horizontal incremental technique. The silorane-based composite (Filtek™ P90) showed non-significant difference in marginal gaps width at the three different regions. While, both methacrylate based Filtek™ P60 and Sonic fill™ composite showed significantly lesser marginal gap width at the occlusal region in comparison with gingival regions. Conclusion: None of the low-shrinkage composite restorative materials tested in this study totally prevented micro-

Material Criteria for Parts Exposed to Liquid Medium Loading

The paper is focused on the study of the material changes which can occur on the basis of mechanical and thermal loading in relation to the functional surfaces of the construction parts. The structural or the mechanical changes can be influenced by ambient environment and in this case, it is the influence of liquid media. The water, hot metal as well as molten glass can be the representatives of the mentioned liquid medium. In relation to the influence of the liquid medium, there is the danger of superposed wears while one of these wears is considered as dominant. Furthermore, occurrence of the corrosion process leads to the increases of the given dominant wear. In relation to the analysis and evaluation of the wear, the simulated tests under the critical conditions are necessary for the correct and precise prediction of the degradation processes. Experimental measurements can be used for the prediction of the material behaviour under the critical operation conditions. In the given work, the attention was paid to the selected materials which were exposed to the mechanical as well as mechanical-thermal loading. The important parameters were achieved with help of the testing device which was modified in a special way. Moreover, the structure changes were observed for the different time intervals or periods. On the basis of the susceptibility to the loading, the conclusions as well as recommendations were summarized for the selected materials.

Multi-Field Coupling Modeling and Analysis for Cylinder Liner of Slow Speed Two Stroke Marine Diesel Engine

To predict accurately the stress and deformation of combustion chamber components of large slow speed two stroke marine diesel engines, based on AVL Fire and ANSYS Workbench software, multi-field coupling modeling and analysis technology was employed to carry out the strength analysis for combustion chamber components of crosshead type marine diesel engine. The boundary conditions, i.e., the temperature field distribution, the mean temperature and the mean heat transfer coefficient are obtained firstly. Then the strength analysis for cylinder liner of crosshead type marine diesel engine under the thermal loads, mechanical loads and thermal mechanical coupled loads was conducted. The results show that the strength meets the design requirement and the stress concentration and the deformation of the cylinder liner were mainly dependent on the thermal load.

Prediction of machining induced microstructure in Ti–6Al–4V alloy using 3-D FE-based simulations: Effects of tool micro-geometry, coating and cutting conditions

Machining process affects surface integrity of Ti–6Al–4V titanium alloyed end-products. During thermal-mechanical loading and subsequent processing that take place in machining, grain size is altered at the subsurface through dynamic recrystallization and subsequent recovery. This can cause softening or hardening of the machined surfaces affecting surface integrity depending on the resultant grain sizes and phase fractions. Prediction of machining induced surface integrity specifically microstructure and grain size can be achieved by using Finite Element-based process simulations and calculated temperature, strain, stress and strain rate fields. This study presents experimental and numerical investigations in machining induced subsurface microstructure, microhardness and grain size in Ti–6Al–4V titanium alloy. Machining surfaces are investigated by measuring subsurface microhardness and grain size and phase fractions in each cutting conditions through scanning electron microscopy and image processing. 3-D FE machining simulations are conducted at the same cutting conditions and tool geometry to predict dynamic recrystallization (DRx) and resultant grain size by utilizing the Johnson–Mehl–Avrami–Kolmogorov model for Ti–6Al–4V alloy. The study also presents investigations and discussions about the effects of machining conditions (tool geometry, coating, and cutting conditions) on the microhardness and grain size in machining Ti–6Al–4V. Numerical modeling results are compared with experimental results and distinct effects of tool edge radius, coating, and cutting conditions on machining induced subsurface microstructure specifically on the changes in grain size due to dynamic recrystallization and recovery have been reported.

Recent Development on Fracture Analysis of Solder Joints

Solder joints failure due to thermal loads and mechanical loads is a significant reliability concern in electronic devices. From literatures, little attention is paid to the development of methods on predicting fracture behavior of solder joint under mixed-mode loading. In reality, the solder joints are exposed to drop impact, vibration loading, bending, and twisting of PCBs. Study on this matter will lead to prediction of fracture load, prevalent fracture mode, exact joint interconnect size and life of joints under brittle and fatigue failure. This paper presents a review of recent fracture analysis on solder joints.

Synchrotron X-Ray Diffraction Measurements Mapping Internal Strains of Thermal Barrier Coatings During Thermal Gradient Mechanical Fatigue Loading

An understanding of the high temperature mechanics experienced in thermal barrier coatings (TBC) during cycling conditions would be highly beneficial to extending the lifespan of the coatings. This study will present results obtained using synchrotron X-rays to measure depth resolved strains in the various layers of TBCs under thermal mechanical loading and a superposed thermal gradient. Tubular specimens, coated with yttria stabilized zirconia (YSZ) and an aluminum containing nickel alloy as a bond coat both through electron beam-physical vapor deposition (EB-PVD), were subjected to external heating and controlled internal cooling generating a thermal gradient across the specimen's wall. Temperatures at the external surface were in excess of 1000 °C. Throughout high temperature testing, 2D high-resolution XRD strain measurements are taken at various locations through the entire depth of the coating layers. Across the YSZ, a strain gradient was observed showing higher compressive strain at the interface to the bond coat than toward the surface. This behavior can be attributed to the specific microstructure of the EB-PVD-coating, which reveals higher porosity at the outer surface than at the interface to the bond coat, resulting in a lower in plane modulus near the surface. This location at the interface displays the most significant variation due to applied load at room temperature with this effect diminishing at elevated uniform temperatures. During thermal cycling with a thermal gradient and mechanical loading, the bond coat strain moves from a highly tensile state at room temperature to an initially compressive state at high temperature before relaxing to zero during the high temperature hold. The results of these experiments give insight into previously unseen material behavior at high temperature, which can be used to develop an increased understanding of various failure modes and their causes.

A Direct Method on the Evaluation of Cyclic Steady State of Structures With Creep Effect

This paper describes a new extension of the linear matching method (LMM) for the direct evaluation of cyclic behavior with creep effects of structures subjected to a general load condition in the steady cyclic state, with the new implementation of the cyclic hardening model and time hardening creep constitutive model. A benchmark example of a Bree cylinder and a more complicated three-dimensional (3D) plate with a center hole subjected to cyclic thermal load and constant mechanical load are analyzed to verify the applicability of the new LMM to deal with the creep fatigue damage. For both examples, the stabilized cyclic responses for different loading conditions and dwell time periods are obtained and validated. The effects of creep behavior on the cyclic responses are investigated. The new LMM procedure provides a general purpose technique, which is able to generate both the closed and nonclosed hysteresis loops depending upon the applied load condition, providing details of creep strain and plastic strain range for creep and fatigue damage assessments with creep fatigue interaction.

Thermal-Structural Analysis of Ni-Based Alloy Panel with Active Cooling Thermal Protection System

In hypersonic environments, the development of aircraft engine presents the mitigation of the extreme thermal environment inside the combustion chamber. This paper establishes the capabilities for combustor panel design. By given the key loading and boundary conditions of the panel structure, the thermal structural analysis determines temperatures and stresses and the optimization improves panel’s robustness subject to thermal mechanical loads. A parametric sweep analysis is carried and the results give the optimal value of the panel face thickness.

Design and research of torque tube used in HTS motor

In order to improve the overall performance of high temperature superconducting (HTS) motor, a radial connection torque tube with high strength and low thermal leakage has been designed. Firstly, fiberglass epoxy composite is chosen as construction material. The structural size of the torque tube is obtained by means of load analysis and theoretical calculation. Secondly, thermal leakage of the torque tube is calculated with both theoretical method and 3D finite-element analysis (FEA). According to the result of the thermal analysis and mechanical loads, the structural stresses of the torque tube are also obtained by FEA method. Lastly, a low temperature test platform is developed to verify the strength and the thermal leakage of the torque tube. The results show that the maximal shear stress of the torque tube is 24.3 MPa and thermal leakage of torque tube is 10.5 W, which satisfy the design requirements of the HTS motor. The torque tube also works in good condition at full-power and full-torque testing of the motor. The design method is also applicable for other similar design of torque tube in other applications.

Strain response of thermal barrier coatings captured under extreme engine environments through synchrotron X-ray diffraction.

The mechanical behaviour of thermal barrier coatings in operation holds the key to understanding durability of jet engine turbine blades. Here we report the results from experiments that monitor strains in the layers of a coating subjected to thermal gradients and mechanical loads representing extreme engine environments. Hollow cylindrical specimens, with electron beam physical vapour deposited coatings, were tested with internal cooling and external heating under various controlled conditions. High-energy synchrotron X-ray measurements captured the in situ strain response through the depth of each layer, revealing the link between these conditions and the evolution of local strains. Results of this study demonstrate that variations in these conditions create corresponding trends in depth-resolved strains with the largest effects displayed at or near the interface with the bond coat. With larger temperature drops across the coating, significant strain gradients are seen, which can contribute to failure modes occurring within the layer adjacent to the interface.

Investigation on Interlaminar Shear Stresses in Laminated Composite Plates under Thermal and Mechanical Loading

In this study the combined effect of thermal environment and mechanical loadings on the interlaminar shear stresses of both moderately thin and thick composite laminated plates are numerically analyzed. The finite element modeling of laminated composite plates and analysis of interlaminar stresses are performed using the commercially available software package MSC NASTRAN/PATRAN. The validity of the present finite element analysis is demonstrated by comparing the interlaminar stresses developed due to mechanical loadings derived using the present FEM with those of available literature. Various parametric studies are also performed to investigate the effect of thermal environment on interlaminar stresses generated in asymmetric cross-ply composite laminated plates of different length to thickness ratios (L/H) and boundary conditions with identical mechanical loadings. It is observed that the elevated thermal environment under identical mechanical loading lead to higher interlaminar shear stresses varying with length to depth ratio and boundary conditions in asymmetric cross-ply laminated composite plates.

Self-adhesive resin cements: a clinical review.

To review the performance of self-adhesive luting agents to determine their clinical evidence. In March 2013, we conducted a literature search by means of PubMed and manually searched German and English medical journals using general search terms (e.g., "self-adhesive resin cements"), detailed search terms (e.g., clinical study "self-adhesive resin cement"), and brand name search terms (clinical study AND "brand name of the cement"). The resulting lists of articles were manually searched for clinical studies. Because of the low number of relevant articles, we decided to broaden our search by including in vitro studies based on a thermal cycling and mechanical loading (TCML) design. The search using the six general search terms yielded a list with over 100 studies with only 13 in vivo studies and 6 in vitro studies based on a TCML design. The other studies either did not comply with the requirements or were not in vitro studies based on a TCML design. Two more in vivo studies could be added after the brand name search. Altogether, 15 in vivo studies and 6 in vitro studies were included in our analysis. Because of the low number of studies available, the clinical evidence of self-adhesive luting agents cannot be assessed in a sufficient manner.

Cyclic Thermo-Mechanical Analysis of Energy Piles in Sand

Geothermal energy piles in sand subjected to cyclic thermal loading with fifty thermal cycles and constant mechanical axial load are analyzed numerically in the present work using the nonlinear transient finite element analysis method. The resulting soil–structure interaction is investigated through these analyses. The stress–strain response of sand is simulated herein using the Mohr–Coulomb constitutive model. Mechanical behavior of energy piles is simulated using the concrete damage plasticity model. Analyses are carried out for floating and end bearing piles in both loose and dense sands subjected to different constant axial load magnitudes at the pile head. Parametric sensitivity studies are performed for different amounts of temperature variation on the pile. It is observed from the results that the mechanical load governs the response of the piles when the piles are subjected to higher mechanical loads close to the limit load value on the pile. However, at low to moderate axial load magnitudes, thermal expansion of the pile causes uplift of the piles. Due to pile uplift, negative shear forces are generated at the pile–soil interface near pile head. The radial strains induced in the pile due to thermo-mechanical loading are observed to be higher than that induced due to only mechanical loading. The axial stress in the piles also increases when pile is subjected to heating.

Study on the Response of Composite Material Cylinder with Metal Liner under Thermal Mechanical Impact

As to the composite cylinder with metal liner under the high temperature and high pressure, thermal mechanical coupling mechanism and response are studied. On the basis of equations for coupling thermal and mechanical impact load and the non-linear thermoelastic finite element equations, the 3-D analysis model of the composite cylinder is established by using the finite element method. The direct coupling analysis is conducted and the variation regularity of the dynamic stress field is obtained. The results show that the thermal mechanical impact loads can cause large transient stress, which influences the strength of the metal liner obviously.

Thermal Stress Analysis of Fiber Wrapped High-Pressure Hydrogen Vessel

In order to reveal the influence of thermal on the stress distribution of fiber wrapped high-pressure hydrogen vessel, the strain and stress of the vessel in pure mechanical loads are studied firstly. Then thermal loads are taken into account, and the thermal stress distribution is given out. The results show that, the stress of the vessel liner changes little when the loads differ from pure mechanical loads to thermal mechanical coupling loads. While in the fiber-wrapped layer, stresses change significantly, and are non-monotonic. In addition, the deformation of the vessel decreases under thermal mechanical coupling loads.

Dislocation evolution during tensile deformation in ferritic–martensitic steels revealed by high-energy X-rays

Deformation processes in Grade 91 (Fe–9%Cr–1%Mo–V,Nb) and Grade 92 (Fe–9%Cr–0.5%Mo–2%W–V,Nb) ferritic–martensitic steels were investigated at temperatures between 20 and 650°C using high-energy synchrotron X-ray diffraction with in situ thermal–mechanical loading. The change of the dislocation density with strain was quantified by X-ray diffraction line profile analysis complemented by transmission electron microscopy measurements. The relationship between dislocation density and strain during uniform deformation was described by a dislocation model, and two critical materials parameters, namely dislocation mean free path and dynamic recovery coefficient, were determined as a function of temperature. Effects of alloy chemistry, thermal–mechanical treatment and temperature on the tensile deformation process in Grade 91 and Grade 92 steels can be well understood by the dislocation evolution behavior.