Elastocaloric cooling is a promising alternative to vapor-compression systems, offering high efficiency and reduced environmental impact. Despite significant advances in elastocaloric technology in recent years, limited attention has been given to the mechanical systems required to drive elastocaloric materials. Here we show a cam-disc-based elastocaloric drive system with integrated direct work recovery, synchronized by four phase-shifted elastocaloric elements. The system introduces a constant-torque driving approach that maintains nearly constant input power during operation. Experimental results demonstrate a nearly constant camshaft torque of 14.4 Nm and a mechanical-level work-recovery efficiency of about 70% at an actuation force of 40 kN. Numerical simulations further show that integrating force amplification mechanisms can reduce the required camshaft torque and increase work-recovery efficiency to up to 88%. These results demonstrate that efficient drive systems can be realized for elastocaloric devices, paving the way toward their practical deployment.

To achieve early mobilization of patients with unstable pelvic fractures, the osteosynthesis methods used must withstand the loads in the pelvis during everyday movements. There is currently no predictive tool to assess how suitable these methods are for this purpose. The development of such a tool requires an understanding of the effects of joint and muscle loads on the structural behavior of the pelvis during movement. To further this cause, the stress-strain state of the pelvis during a sit-to-stand transfer of a healthy adult male was analyzed. Muscle and joint reaction forces during the motion were predicted using a rigid-body musculoskeletal model. These loads were then utilized in the first-ever dynamic structural analysis of the pelvis during a sit-to-stand transfer using the finite element method. Several similarities in stress distributions during sit-to-stand transfer, gait, and standing were identified by comparing the finite element analysis results with literature. The common areas of increased stress between the three motions are the acetabular notch, the superior edge of the obturator foramen, the attachments of the gluteus maximus on the ilium, and the lesser sciatic notch. The results also provide important insights into global behavior of the pelvic ring and indicate the locations of concentrated stress during sit-to-stand transfer.

The behavior of shape memory alloys exhibits significant asymmetry under tension, compression, and torsion, posing challenges for accurate modeling in engineering applications. This study introduces a novel approach to improve constitutive models by incorporating an asymmetric function that enables independent parameter definitions for tension, compression, and torsion. This innovation allows material parameters to be determined directly from stress-strain data, enhancing model flexibility and practicality. The proposed method is implemented in the widely used Auricchio-Petrini model, extending its capabilities to capture asymmetry in transformation start stress, hysteresis width, transformation plateau length, and hardening slope, all while maintaining thermomechanical consistency. In the proposed material model, the elastic modulus is differentiated for austenite, multi-variant martensite, and single-variant martensite, with the latter exhibiting an introduced asymmetry. The model also incorporates improved temperature dependency. Validation through comparisons with experimental data demonstrate the model's effectiveness in predicting SMA behavior under diverse proportional and non-proportional loading conditions, including superelasticity and shape memory effects.

In recent years, devices based on the elastocaloric effect (eCE) have emerged as one of the most promising alternatives to vaporcompression cooling and heating systems. After a brief overview of elastocaloric materials and elastocaloric devices developed to date, this paper reviews our recent activities in the development of tube-based elastocaloric regenerators loaded in compression. These include the evaluation of novel elastocaloric thermodynamic cycles, the characterization of the elastocaloric and fatigue behavior of Ni–Ti tubes, the thermo-hydraulic evaluation of a tube-based geometry to be applied as an elastocaloric regenerator, the buckling analysis of Ni–Ti tube in compression, and finally the development, numerical modeling, and testing of a tube-based elastocaloric regenerator in both cooling and heat-pumping modes. The developed regenerator shows a durable operation with more than 300,000 cycles, a maximum temperature span of more than 31 K at zero thermal load, and a heating power of more than 60 W at a temperature span of 10 K using only 13.7 g of elastocaloric material. In addition, further improvements of the tube-based elastocaloric regenerators related to a lower thermal mass of the regenerator’s housing are shown and discussed.

A number of engineering components, such as gears, shafts, and bearings, are frequently subjected to high and very localized, static and dynamic stresses and strains. In order to increase the load-carrying capacity and durability of such components, various types of treatments may be applied, primarily including heat treatments. In particular, surface heat treatments are used to selectively enhance the load-bearing capacity of the most heavily stressed regions of the component. As a consequence, the resulting material exhibits a surface layer that is considerably harder and stronger than the material at the core. Such materials, possessing gradually varying material properties, are known as functionally graded materials (FGMs) and with them, the aim is to improve the structural integrity of components in an optimal, targeted manner. In this study, a finite element analysis of the stress-strain response of unnotched and notched specimens made from homogeneous and functionally graded low-alloy steel 42CrMo4 subjected to static loading was performed. Results of the mechanical response of specimens with homogeneous and functionally graded material properties are presented in this study, highlighting significant differences.

The behavior of shape memory alloys (SMAs) varies significantly when subjected to tension, compression, or torsion, greatly influencing their applications in engineering. Despite considerable advancements in this field, accurate modeling of the behavior of SMAs under various loading conditions remains an ongoing challenge. In this study, we propose a flexible approach to improving the response of constitutive models in tension, compression, and torsion by varying the material parameters of the constitutive model with a novel asymmetric function. The function ensures independent definition of parameter values in tension, compression, and torsion. We implement the proposed approach in the Auricchio-Petrini model, which is widely used in engineering studies due to its robustness but originally provides very limited asymmetry. The proposed modification of the original model ensures asymmetry in the transformation start stress, hysteresis width, length of the transformation plateau and hardening slope. The model also distinguishes between the elastic modulus of austenite, multi-variant martensite and single-variant martensite, the latter being also asymmetric in tension and compression. Additionally, we provide an improved temperature dependence and simple relationships to obtain input parameters from well-established experimental tests. The proposed model is validated by finite element simulations and compared with various experimental data. The results demonstrate the effectiveness of the proposed model in predicting the behavior of SMAs under a range of proportional and non-proportional loading conditions, including both superelasticity and shape memory effect.

This study examines the potential application of elastocaloric refrigeration (eC) technology for the subcooling of CO2 in transcritical single-stage refrigeration cycles. Elastocaloric refrigeration, a solid-state refrigeration technology, possesses significant untapped potential due to its environmentally friendly characteristics, primarily its lack of harmful operational fluids. However, its direct stand-alone application has been limited due to the relatively small temperature spans produced by current proof-of-concept elastocaloric devices. Efforts of the scientific community have focused on extending the temperature difference that eC systems can provide, while this work offers an alternative to that challenge, offering an application solution for the current state of technology. The study proposes for the first-time a unique integration of eC technology and CO2 cooling systems, aiming to capitalise on the respective weaknesses of these technologies and transform them into strengths. In the proposed solution, an eC device operates as an external agent to subcool CO2, with the objective of enhancing the energy performance of the refrigeration system. This concept is motivated by the recent advancements in CO2 cooling systems and the growing recognition of subcooling as a promising method to boost the performance of such systems. The hybrid system's performance was evaluated across various ambient temperatures, ranging from 20 degrees C to 35 degrees C, and at an evaporating level of -15 degrees C. It is evaluated by means of a calculation model based on the data obtained experimentally from an elastocaloric regenerator and an experimental CO2 plant. The system's energy efficiency was analysed in comparison to a non-subcooled CO2 cycle, and a third cycle comprising both eC subcooling and an expander for energy recovery from the expansion process. The results demonstrated a considerable increase in the coefficient of performance (COP) with the use of eC subcooling: increments of 2.7 % at 20 degrees C, 4.5 % at 25 degrees C, 9.6 % at 30 degrees C and 13.1 % at 35 degrees C, where more significant increments were observed at higher ambient temperatures. The eC Subcooler with expander reaches increments of 7.5 %, 11.1 %, 18.1 % and 22.2 % respectively. Additionally, the eC subcooler allowed a reduction in the optimum gas-cooler pressure by up to 5 bar at the highest environment temperature. Despite these promising results, the study underscores the necessity for further optimisation and improvement of elastocaloric devices. Additionally, it emphasizes the importance of energy recovery strategies from the expansion process in transcritical CO2 cooling system.

In recent years, elastocaloric cooling has been shown to be one of the most promising future alternatives to vapor compression cooling and heating systems. Many elastocaloric materials (eCM) have large latent heat and large adiabatic temperature changes associated with a martensitic phase transformation. Our group recently built a new active elastocaloric regenerator, resembling a shell-and-tube heat exchanger type made of Ni-Ti tubes loaded in compression. The regenerator showed durable operation and record performance with a maximum temperature span of more than 31 K and maximum heating/cooling power of more than 60 W, equivalent to 4,400 W per kg of the elastocaloric material using only 13.7 g of eCM. It can operate in both cooling and heat-pumping modes. Here, we will present the research behind the development of our elastocaloric regenerator that ranges from material science, thermodynamics, heat transfer, mechanics and design engineering.

In an attempt to increase resource efficiency and reduce carbon emissions, the development of lightweight designs in structural applications is essential. In addition, the lightweight structures often follow complex topologically optimized designs which are more suitable for the application of additive, in contrast to conventional manufacturing techniques. Within the additive manufacturing (AM) process, constituents may be combined to design and produce durable and lightweight materials with predefined mechanical, electrical, and thermal properties, while also accounting for their sustainability and recyclability. Regretfully, due to the lack of research in material behavior, the AM technology implementation in engineering applications is still limited in comparison to traditional manufacturing methods. While the potential of additively manufactured continuous fiber composites has already been recognized in the scientific community, constitutive modeling and damage resistance are seldom reported. Since fiber-reinforced composite structures are rarely designed as unidirectional (UD), this study is focused on numerical analysis of failure for multi-directionally reinforced composite laminates loaded in a uniaxial direction. Specimens are modeled and evaluated using a progressive damage model, proposing guidelines for safer design and application.

Although caloric refrigeration systems, such as magnetic and elastocaloric ones have shown promising potential in the last decade, their application in stand-alone applications remains scarce. Namely, they can provide high COP values and sufficient cooling power but only at a low temperature span between the heat source and the heat sink. However, the performance of the caloric refrigeration systems drops significantly at higher temperature spans (above 30 K), which are usually required in most common refrigeration applications. This work introduces a new concept or future application that matches perfectly with the current state of development of caloric refrigeration technologies, which is their hybridization with vapour compression systems (VCS) through subcooling. In subcooling applications, the required temperature span is low, therefore, the caloric systems can be used to boost the operation of vapour compression refrigeration systems toward higher efficiencies. Based on experimentally obtained data of different prototypes (magnetic refrigeration system, elastocaloric refrigeration system and CO2 transcritical refrigeration plant) the energy results and optimum operating conditions of the hybrid caloric-VCS systems will be presented.

Due to the versatility of its implementation, additive manufacturing has become the enabling technology in the research and development of innovative engineering components. However, many experimental studies have shown inconsistent results and have highlighted multiple defects in the materials’ structure thus bringing the adoption of the additive manufacturing method in practical engineering applications into question, yet limited work has been carried out in the material modelling of such cases. In order to account for the effects of the accumulated defects, a micromechanical analysis based on the representative volume element has been considered, and phase-field modelling has been adopted to model the effects of inter-fiber cracking. The 3D models of representative volume elements were developed in the Abaqus environment based on the fiber dimensions and content acquired using machine learning algorithms, while fulfilling both geometric and material periodicity. Furthermore, the periodic boundary conditions were assumed for each of the representative volume elements in transversal and in-plane shear test cases,. The analysis was conducted by adopting an open-source UMAT subroutine, where the phase-field balance equation was related to the readily available heat transfer equation from Abaqus, avoiding the necessity for a dedicated user-defined element thus enabling the adoption of the standard elements and features available in the Abaqus CAE environment. The model was tested on three representative volume element sizes and the interface properties were calibrated according to the experimentally acquired results for continuous carbon-fiber-reinforced composites subjected to transverse tensile and shear loads. This investigation confirmed the consistency between the experimental results and the numerical solutions acquired using a phase-field fracture approach for the transverse tensile and shear behavior of additively manufactured continuous-fiber-reinforced composites, while showing dependence on the representative volume element type for distinctive load cases.

Despite struggling to achieve the requirements necessary in many industrial applications, the additive manufacturing approach excels in complex designs often encountered in wearable technologies, prosthetics, implants, airfoils, and reverse engineering, where top-down machining can get quite expensive. Since fiber-reinforced composites are rarely used as unidirectional in engineering applications, analyzing the behavior of multilayered additively manufactured composites is critical, yet seldom found in the literature. Therefore, a progressive damage model based on Puck-Schurmann failure criteria has been proposed in this study. The continuous carbon fiber reinforced lamina properties have been acquired based on the available data in the literature and performed uniaxial experiments. The adopted properties were integrated within the damage model subroutine and used in finite element analysis software, while model parameters were calibrated using the response surface algorithms in the design of experiments according to the behavior of a distinctive multi-directionally reinforced test case and validated experimentally.

The development of additive manufacturing technologies has been followed by an increase in material variety, especially by the introduction of numerous types of reinforcements to enhance the mechanical performance of basic polymers. Since the microstructure of these novel composites may vary in types, sizes, shapes, and ratios of reinforcements, it is necessary to optimize these parameters before conducting experimental validation. Hence, a microscale analysis based on representative volume element modeled according to the statistically significant constituent's data acquired from the microscopic analysis is proposed. Moreover, to account for the weak fiber/matrix bounding in comparison with the ideal bond assumption, cohesive behavior can be prescribed at these interfaces. According to the type of reinforcement, three variations of RVE-s have been modeled in the Abaqus CAE environment utilizing periodic boundary conditions, and each was tested for longitudinal, transverse, and shear loading cases. The validation has been conducted on two unidirectional [0] and [90], as well as one multidirectional [45/−45]4s carbon fiber reinforced composite specimens. The experimental tests have been performed quasistatically and monitored using a digital image correlation system. Experimental and numerical results have been systematically compared with the published data, proposing a guideline for the protocol applicability and the necessity for further improvements.

SummaryIn recent years, elastocaloric cooling has shown great potential as an alternative to vapor compression refrigeration. However, there is still no existing elastocaloric device that offers fatigue-resistant operation and yet high cooling/heat-pumping performance. Here, we introduce a new concept of an elastocaloric regenerator based on compression-loaded Ni-Ti tubes, referred to as a shell-and-tube-like elastocaloric regenerator. Our regenerator concept, which can operate in both cooling and heat-pumping modes, enables durable operation and record performance with a maximum temperature span of 31.3 K and heating/cooling powers of more than 60 W, equivalent to 4,400 W/kg of the elastocaloric material. In terms of overall (specific) performance, these results surpass all previously developed caloric (magnetocaloric, electrocaloric and elastocaloric) devices and demonstrate the enormous potential of compression-loaded elastocaloric regenerators to be used in elastocaloric devices for a wide range of cooling and heat pumping applications.

Subcooling methods for transcritical CO2 plants are being studied in order to improve the behaviour of these systems in hot climates, where basic configurations are not competitive enough. To achieve important improvements in the transcritical CO2 performance, it is necessary to perform the subcooling with a refrigeration cycle working with a Coefficient of Performance higher than that of the CO2 system without subcooling. Magnetic refrigeration devices can achieve high Coefficient of Performance values when the temperature difference between the hot sink and cold source is small, and therefore they meet the requirements to be applied as a CO2 subcooling method. This work presents the coupling of two refrigeration technologies: vapour compression and magnetocaloric refrigeration, which has not yet been presented in the literature. The magnetic refrigeration system is, based on the experimental results of the existing prototype, analysed semi-empirically and further evaluated, as a subcooling method for a transcritical CO2 cycle in a wide range of ambient conditions. Gas-cooler pressure, subcooling degree and operating parameters of the magnetic refrigerator were optimized for each condition to obtain the maximum Coefficient of Performance. We show that subcooling with the existing prototype of magnetic refrigeration system can enhance the overall Coefficient of Performance of transcritical CO2 cycle by up to 9%.

In recent years, elastocaloric cooling has shown great potential as an alternative to vapor-compression refrigeration. However, there is still no existing elastocaloric device that offers fatigue-resistant operation and yet high cooling/heat-pumping performance. Here, we introduce a new design of an elastocaloric regenerator based on compression-loaded Ni-Ti tubes, referred to as a shell-and-tube-like elastocaloric regenerator. Our regenerator design, which can operate in both cooling and heat-pumping modes, enables durable operation and record performance with a maximum temperature span of 31.3 K in heat-pumping mode or maximum heating/cooling powers of more than 60 W, equivalent to 4,400 W/kg of the elastocaloric material (at temperature span of 10 K). In terms of both maximum performance metrics, these results surpass all previously developed caloric (magnetocaloric, electrocaloric, and elastocaloric) devices and demonstrate the enormous potential of compression-loaded elastocaloric regenerators to be used in elastocaloric devices for a wide range of cooling and heat-pumping applications.

Elastocaloric cooling is emerging as one of the most promising alternatives to vapor-compression cooling technology. It is based on the elastocaloric effect (eCE) of shape memory alloys (SMAs), which occurs due to a stress-induced martensitic transformation (superelasticity). In recent years, several elastocaloric proof-of-concept devices have been developed and the best of them have already achieved commercially relevant cooling characteristics. However, the proposed devices are not yet ready for commercialization, mostly due to their short fatigue life, which is a consequence of the tensile loading. The fatigue life can be significantly improved if the material is instead subjected to compressive loading, but mechanical instabilities (buckling) and the poor heat transfer of bulky geometries (favorable for compression) are the major challenges to overcome when designing compressed elastocaloric elements. Here, we show for the first time that thin-walled Ni-Ti tubes, which allow for the rapid heat transfer, can withstand more than 10(6) compressive loading cycles without any degradation of the eCE while maintaining high efficiency (coefficient of performance) and adiabatic temperature changes as high as 27 K. This is the largest, directly measured, durable eCE for any elastocaloric material in the high-cycle fatigue regime to date, and so opens up new avenues in the development of durable and efficient elastocaloric devices. (c) 2020 The Author(s). Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license. (http://creativecommons.org/licenses/by-nc-nd/4.0/)

The elastocaloric cooling, utilizing latent heat associated with martensitic transformation in shape-memory alloys, is being considered in the recent years as one of the most promising alternatives to vapour compression cooling technology. It can be more efficient and completely harmless to the environment and people. In the first part of this work, the basics of the elastocaloric effect (eCE) and the state-of-the-art in the field of elastocaloric materials and devices are presented. In the second part, we are addressing crucial challenges in designing active elastocaloric regenerators, which are currently showing the largest potential for utilization of eCE in practical devices. Another key component of elastocaloric technology is a driver mechanism that needs to provide loading for active elastocaloric regenerators in an efficient way and recover the released energy during their unloading. Different driver mechanisms are reviewed and the work recovery potential is discussed in the third part of this work.

Structural fatigue is the major obstacle that prevents practical applications of the elastocaloric effect (eCE) in cooling or heat-pumping devices. Here, the eCE and fatigue behaviour of Ni-Ti plates are systematically investigated in order to define the fatigue strain limit and the associated eCE. Initially, the eCE was evaluated by measuring adiabatic temperature changes at different strain amplitudes and different mean strains along the loading and unloading transformation plateaus. By comparing the eCE with and without pre-strain conditions, the advantages of cycling an elastocaloric material at the mean strain around the middle of the transformation plateau were demonstrated. In the second part of this work, we evaluated the fatigue life at the mean strain of 2.25% at the loading plateau and at the unloading plateau after initial pre-straining up to 6% and 10%, respectively, It is shown that on polished samples, durable operation of 10(5) cycles can be reached with a strain amplitude of 0.50% at the loading plateau, which corresponds to adiabatic temperature changes of approximately 5 K. At the unloading plateau (after initial pre-strain of 10%), durable operation was reached at a strain amplitude of 1.00%, corresponding to adiabatic temperature changes of approximately 8 K. The functional fatigue was analysed after the cycling and it is shown that once the sample has been stabilized there is no further degradation of the eCE, even after 10(5) cycles. These results present guidelines for the design and operation of efficient and durable elastocaloric devices in the future. (C) 2018 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

In the paper, the influence of the yield-point phenomenon (YPP) on cyclic plasticity of the console beam is presented with the objective to demonstrate the impact of the YPP on the local cyclic plasticity. The influence of the YPP and its dependence on cyclic material hardening or softening was studied through experiments and numerical simulations. Console beams are made from the low-alloy EN 42 CrMo 4 steel in its normalized state (184 HV), which exhibits cyclic hardening, and in its tempered state (296 HV), which is subject to cyclic softening. Numerical simulations were performed on constitutive model of cyclic plasticity taking into account the kinematic hardening, isotropic hardening or softening and formulations of the YPP which are based on the change of the elastic region surface in the stress space at first transition into the stress plateau. Analysis of the results shows the importance of taking into account the YPP equations in constitutive models of cyclic plasticity as well as the influence of the YPP on cyclic plasticity of the console beam.