In long-term operations, seasonal imbalance in the thermal load may adversely affect the heat transfer performance of the energy piles, potentially resulting in thermal accumulation within the ground ...and eventual system failure. The heat transfer performance of energy pile systems during long-term operation under unbalanced thermal loads must be investigated. Moreover, the design parameters of energy piles are usually constrained by the requirements of foundation structural design, resulting in energy piles being densely arranged. Hence, the influence of pile spacing on the heat exchange performence of energy piles must be comprehensively understood. In this study, two- and three-dimensional energy-pile heat transfer models were established and innovatively coupled based on an engineering project currently under design. Numerical simulations were performed to investigate the heat transfer behavior of energy-pile groups subjected to unbalanced thermal loads and the effect of pile spacing on their heat exchange performance. Furthermore, design recommendations regarding the determination of the proportion of thermal loads to be borne by the energy piles in a hybrid GSHP system were provided. The results indicate that the proposed 2D-3D coupled modeling approach is able to simulate the heat exchange performance of large-scale energy pile groups. Pile spacing considerably affects the long-term thermal performance of energy-pile groups, especially in cases with small pile spacings. The influence of pile spacing on the heat exchange capacity of energy piles can be considered in the design phase by incorporating a group effect coefficient η, which are calculated to be 0.165, 0.470, 0.732, and 1 for pile spacings of 2 m, 4 m, 6 m, and 10 m, respectively.
In order to raise the hardness and strength of the surface layer of mechanical components and induce favorable residual compressive stresses, case‐hardening procedures have become established in the ...heat treatment of steel. In this work, a calculation concept for the fatigue strength of components that have been case‐hardened through carburizing heat treatment is being developed. The residual stress and the load stresses in complex‐shaped, carburized materials are determined using a finite element (FE) model. The fatigue limit of the components is derived using probabilistic methods and taking into account hardness gradients, residual stresses, and non‐metallic inclusions. The model is validated with available axial bending fatigue test data and then used to predict the rotating bending fatigue limit of samples with various geometries and heat‐treatment conditions. This work demonstrates the capability of combining probabilistic and FE‐based modeling to represent complex interactions between variables that affect the fatigue of heat‐treated components, such as steel cleanliness, notch shape, case‐hardening depth, or loading conditions.
Highlights
Combined FE‐based and probabilistic methods can predict fatigue strength accurately.
Interplay of heat‐treatment output, geometry, load, and material is considered.
Crack initiation position gets shifted by increased case‐hardness depth.
Fatigue strength reduction due to defects in steel depends on load concentration.
Monopile foundations are known as the most common foundation solution for offshore wind turbines (OWTs). However, the state of practice for designing monopile foundations in high seismicity areas is ...still limited. In particular, the impact of soil liquefaction on the seismic soil-foundation-OWT interaction is not yet well understood. In this paper, three-dimensional (3D), fully-coupled, nonlinear finite-element analyses performed in the OpenSees numerical platform were used to evaluate the seismic performance of a series of hypothetical 5 MW OWTs on monopile foundations in layered, liquefiable sites. A suite of earthquake recordings with and without strong velocity pulses (i.e., near fault, pulse-like and ordinary motions, respectively) was used to investigate the impact of ground motion characteristics on the seismic response of the OWT system. Also, the influence of soil-structure interaction and earthquake shaking coupled with extreme environmental loading (i.e., wind and wave loads) on the seismic performance of soil-OWT systems was evaluated. The numerical results showed pile movements induced by extreme climate loading led to a bias in permanent settlement accumulation across the foundation area and accumulation of soil deformations in the proximity of the pile. Ground motion velocity pulses increased the cyclic stress demand in soil and, therefore, the potential for the occurrence of soil liquefaction. A subsequent, limited numerical sensitivity study showed that the foundation rotations of the OWT system were influenced by ground motion characteristics such as polarity and velocity pulses, and the presence of the wind and wave loads. The cumulative absolute velocity (CAV) was identified as the optimum ground motion intensity measure for permanent foundation settlement and tilt as well as for peak transient foundation tilt of the OWT system under extreme environmental loadings. The net outcome of these factors determined the magnitude and orientation of the foundation rotations at the end of shaking. This study highlights the importance of considering the effects of extreme loadings and pulse-like motions in the design and performance of OWT systems.
•The impact of soil-structure interaction as well as the coupling of earthquake shaking with extreme environmental loadings (i.e., wind and wave loads) on the seismic performance of soil-OWT systems were evaluated.•The presence of wind and wave loads increased the bias in permanent settlement across the foundation footprint area and the accumulation of soil deformations near the pile.•The presence of velocity pulses in the input ground motion increased the cyclic stress ratio of soil layers, enhancing the potential for soil liquefaction in both loose and dense sand layers.•The cumulative absolute velocity (CAV) was identified as the optimum ground motion intensity measure for permanent foundation settlement and tilt as well as for peak transient foundation tilt of the OWT system under extreme environmental loadings.•The numerical results showed that the magnitude and orientation of foundation rotations were a net outcome of ground motion characteristics (in terms of polarity and velocity pulse) and the presence of the extreme environment loads.
While the directionality and integrity of microscopic fiber arrangement play an important role in governing the mechanical properties and deformation behavior of unidirectional carbon fiber ...reinforced polymer (UD-CFRP) composites, minimizing or eliminating the deformation-induced evolution of fiber arrangement is crucial for maintaining the high performance of the advanced composite materials. In the present work, we elucidate the depth-sensing deformation mechanisms of UD-CFRP under different cutting strategies of conventional single-pass and multi-pass by experiments and corresponding micromechanical finite element simulations. Experimental and simulation results reveal diversiform maps of fiber arrangement evolution in subsurface damage layer under different cutting strategies, as well as their correlations with machined surface quality in terms of surface finish, residual stress and mechanical properties. Subsequently, a novel cutting strategy of reverse multi-pass is proposed to tailor the directionality and integrity of microscopic fiber arrangement in subsurface damage layer, which is accompanied with reduced subsurface damage layer, lowered surface roughness and enhanced hardness and elastic modulus, as compared to the cutting strategy of conventional multi-pass. Current findings provide a theoretical basis for the understanding of formation mechanisms of machined surface of CFRP composites, as well as the rational selection of cutting strategies for improving the machinability of CFRP composites.
Analytical investigations, micromechanical finite element simulations and experiments jointly demonstrate the feasibility of tailoring fiber arrangement accompanied with enhanced mechanical properties of UD-CFRP by rationally selected reverse multi-pass cutting strategy. Display omitted
A three dimensional finite element model (FEM) is introduced in this work in order to simulate the melt pool size during the Selective Laser Melting (SLM) process. The model adopts the Optical ...Penetration Depth (OPD) of laser beam into the powder bed and its dependency on the powder size in definition of the heat source. The model is used to simulate laser melting of a single layer of stainless steel 316L on a thick powder bed. The results of the model for the melt pool depth are validated with the experimental results. The model is then used to predict the effect of different scanning speeds on the melt pool depth, width, and length. The results showed that the melt pool size varies from the beginning of a track to its end and from the first track to the next. The melt pool size, however, reaches a stable condition after a few tracks. This concept was used to simplify the process modeling in which reduces the computational costs.
Display omitted
•The developed Finite Element model is able to predict the melt pool size accurately in the SLM process.•The rate of change in the width of the melt pool by altering the speed is not the same as that of the depth.•The melt pool dimensions reached a steady condition after the third track.•The melt pool depth of each track stayed almost constant after about 2mm from the beginning of the track.
•A novel time integration algorithm is proposed for a dislocation density-based model.•The coupling of microscopic dislocation density and macroscopic plasticity is guaranteed in the model.•The ...proposed method is superior to the existing two-level iteration method.•The influence of shot peening parameters is clarified on grain refinement.
Shot peening has been widely used in processing various components since it can bring in residual compressive stress and effectively refine the grain size of impacted area. To simulate grain refinement induced by shot peening, the dislocation density-based model has recently been introduced, however, the existing time integration algorithm is not stable and usually leads to divergent solutions in iterations. In this paper, a novel time integration algorithm is proposed for the dislocation density-based model. Based upon the algorithm, numerical studies on multi-shot AISI4340 steel are carried out with different coverages, velocities, shot diameters, and peening angles. It is shown that the method converges faster than the two-level iteration method, and the predicted dislocation cell structure sizes after shooting are consistent with experimental results. Besides that, increasing coverage can refine the size of a dislocation cell, which is closely dependent on the shot diameter, impact velocity, and angle. Thus, to achieve the desired grain size or the depth of refinement, it is necessary to take the shot diameter and velocity into account simultaneously.
Many classic hyperelastic models fail to predict the stress responses of soft materials in complex loading conditions with parameters calibrated through one simple test. To address this fundamental ...issue, we propose a new micro–macro transition for the microstructural hyperelasticity modeling, which is further integrated into the full network framework. With a Gaussian chain distribution, this new mapping scheme yields an explicit one-parameter hyperelastic model in terms of principal stretches. This new linear model achieves remarkable success in capturing the stress responses in multi-axial deformation modes for soft materials with an absence of strain stiffening effect, which is beyond the capability of the widely used neo-Hookean model. A new two-parameter hyperelastic model is further developed by combining the new micro–macro transition and non-Gaussian Langevin chain distribution. Compared with other two-parameter hyperelastic models based on Langevin statistics, such as the eight-chain model, affine full network model, and equilibrated microsphere model, our new model exhibits greatly improved predictive ability for complex loading types. The new model is also implemented for finite element analysis, which shows the ability to capture the responses of soft materials with heterogeneous strain distribution. In all cases, the parameters in our models can be determined through the data of uniaxial loading tests, along with the behaviors in other loading modes being well forecast, which is a challenge for various other existing hyperelastic models. This novel micro–macro transition is shown to properly capture the inherent correlations between different deformation modes, which may advance fundamentally modeling hyperelasticity and other constitutive behaviors for soft materials.
While it is well-established that early detection and initiation of treatment of developmental dysplasia of the hip (DDH) is crucial to successful clinical outcomes, research on the mechanics of the ...hip joint during healthy and pathological hip development in infants is limited. Quantification of mechanical behavior in both the healthy and dysplastic developing joints may provide insight into the causes of DDH and facilitate innovation in treatment options. In this study, subject-specific three-dimensional finite element models of two pigs were developed: one healthy pig and one pig with induced dysplasia in the right hindlimb. The objectives of this study were: (1) to characterize mechanical behavior in the acetabular articular cartilage during a normal walking cycle by analyzing six metrics: contact pressure, contact area, strain energy density, von Mises stress, principal stress, and principal strain; and (2) to quantify the effect on joint mechanics of three anatomic abnormalities previously identified as related to DDH: variation in acetabular coverage, morphological changes in the femoral head, and changes in the articular cartilage. All metrics, except the contact area, were elevated in the dysplastic joint. Morphological changes in the femoral head were determined to be the most significant factors in elevating contact pressure in the articular cartilage, while the effects of acetabular coverage and changes in the articular cartilage were less significant. The quantification of the pathomechanics of DDH in this study can help identify key mechanical factors that restore normal hip development and can lead to mechanics-driven treatment options.
Soft impact of GLARE fiber metal laminates Li, Kaikai; Qin, Qinghua; Cui, Tianning ...
International journal of impact engineering,
August 2023, 2023-08-00, Letnik:
178
Journal Article
Recenzirano
•Soft impact of fiber metal laminates (FMLs) by metal foam projectiles was considered.•The global deformation and local denting were active failure modes.•An effective FE model was validated by ...experimental results.•Damage evolution and energy dissipation mechanism were revealed.
Dynamic response of fully clamped GLARE fiber metal laminates (FMLs) subjected to closed-cell aluminum foam projectile impact has been investigated experimentally and numerically. FMLs with various layup angles are made of glass fiber prepreg and aluminum alloy with identical thickness among each type of layers. The active failure modes of FMLs, including the global deformation and local denting with cracks of the metals, fiber fracture, delamination and interlayer debonding are observed in the experiments. It is shown that the damage degree and deflections of FMLs decrease with increase of the thickness. FMLs of the oblique angle layups have similar deformation and failure modes as the orthogonal layups. Finite element (FE) simulations are performed and are in good agreement with the experimental results. Most kinetic energy of the metal foam projectiles is dissipated by the deformations of the metal layers, the deformations and fracture of the composite layers, debonding and foam compression. The impact resistance of FMLs can be enhanced by increasing the interlayer bonding strength.
The effects of stress and plastic strain distributions on the hydrogen embrittlement fracture of the U-bent martensitic steel sheet specimen were investigated. The hydrogen embrittlement testing of ...the U-bent specimen was performed. Fracture morphology mainly consisting of intergranular fracture was found inside the hydrogen charged U-bent specimen, which indicated that the crack initiation took place in the interior, and shear lips were found near both surfaces of the U-bent sheet. The synchrotron X-ray diffraction measurement and the finite element simulation were utilized to analyze the stress and plastic strain distributions in the thickness direction of the U-bent specimen. The elastic strain distributions obtained by the measurement showed a good agreement with the simulation. The crack initiation site of the hydrogen-charged U-bent specimen was considered to be correspondent with the region where the tensile stress was the highest, suggesting that the maximum tensile stress predominantly determine the crack initiation.
PDF