Mechanical Loading Tests Research Articles

Thermo-mechanical stress modelling and fracture analysis on ultra-thin silicon solar cell based on super multi-busbar PV modules

Thinning of crystalline silicon (c-Si) wafers will reduce material cost and improve productivity, which significantly impacts the development of solar photovoltaic (PV) industry. However, this process leads to reduction in mechanical strength of the cell and increased solar cell fracture during the manufacturing process. This study investigates the mechanical property of full wafers and half wafers with varying thicknesses, both before and after the slicing process. Thermo-mechanical stress in half cells was analyzed using finite element modeling (FEM) to clarify the origin of cracks, the influence of Si thickness on cracking and the process impacts on eventual cell breakage. Fracture analysis was implemented not only in soldering process but also during lamination and dynamic mechanical loading (DML) tests. Our findings reveal that the thinner solar cells become even more fragile and susceptible to fracture or power attenuation during the module manufacturing process and operation as well. FEM simulations also verify that the highest stress occur in the thinnest Si wafers after soldering, lamination and DML processes, respectively. However, the choice of 16 Cu ribbons with a diameter of 0.26 mm, which is verified and confirmed as the optimal super multi-busbar (SMBB) technology for the ultra-thin solar cells based PV module, can help to reduce the cell stress and improve the module reliability in mass production.

Investigation of static and dynamic mechanical loads on light-weight PV modules for offshore floating applications

Photovoltaic (PV) systems are significant for the transition towards renewable energy. However, their expansion is constrained by the scarcity of suitable land in proximity to electric grids. To address this issue, floating PV is a promising solution. Ensuring the robustness of floating PV installations remains a major concern, particularly regarding the mechanical load due to strong winds in open water. This study aims to assess the impact of wind on floating PV modules, by considering real wind speed values occurring at the North Sea. To achieve this objective, the influence of PV module configuration, such as inclination, is examined. Moreover, different thicknesses of PV glass are considered to find an optimum between mechanical stability and material consumption. Lastly, a resonance vibration test is performed and compared to simulations to estimate the effects of vibration on PV module stress. The findings indicate that a low inclination installation is preferable, and a glass-glass PV module with a 2.5 mm glass thickness can withstand static and dynamic mechanical loads, although long-term durability requires further investigation. Additionally, it is crucial for the standard Dynamic Mechanical Load (DML) test to include higher pressure values and an extended vibration test at the resonance frequency with the highest measured acceleration, identified after a frequency sweep.

Distraction Enterogenesis in Rats: A Novel Approach for the Treatment of Short Bowel Syndrome.

Surgeons often encounter patients with intestinal failure due to inadequate intestinal length ("short bowel syndrome"/SBS). Treatment in these patients remains challenging and the process of physiologic adaptation may take years to complete, which frequently requires parenteral nutrition. We propose a proof-of-concept mechanical bowel elongation approach using a self-expanding prototype of an intestinal expansion sleeve (IES) for use in SBS to accelerate the adaptation process. IESs were deployed in the small intestines of Sprague Dawley rats. Mechanical characterization of these prototypes was performed. IES length-tension relationships and post-implant bowel expansion were measured ex vivo. Bowel histology before and after implantation was evaluated. IES mechanical studies demonstrated decreasing expansive force with elongation. The deployment of IES devices produced an immediate 21 ± 8% increase in bowel length (p < 0.001, n = 11). Mechanical load testing data showed that the IESs expressed maximum expansive forces at 50% compression of the initial pre-contracted length. The small-intestine failure load in the rats was 1.88 ± 21 N. Intestinal histology post deployment of the IES showed significant expansive changes compared to unstretched bowel tissue. IES devices were scalable to the rat intestinal model in our study. The failure load of the rat small intestine was many times higher than the force exerted by the contraction of the IES. Histology demonstrated preservation of intestinal structure with some mucosal erosion. Future in vivo rat studies on distraction enterogenesis with this IES should help to define this organogenesis phenomenon.

Machine learning-augmented multi-arrayed fiber bragg grating sensors for enhanced structural health monitoring by discriminating strain and temperature variations

AbstractFiber optic sensors (FOS) in long-term structural health monitoring (SHM) have drawn significant attention due to their pivotal role in detecting defects and measuring structural performance in diverse infrastructures. While using FOS, temperature variation due to environmental factors is still considered one of the major challenges to isolating sensing parameters. To address this issue, we reported a machine learning (ML)-augmented multi-parameter sensing system that enables simultaneous detection of strain and temperature effects based on one single fiber Bragg gratings (FBGs) sensor for SHM. The initial phase entailed designing, fabricating, and characterizing a novel FBG sensor in the laboratory, incorporating a set of four FBGs, each distinguished by distinct Bragg wavelengths. In the next phase, ML algorithms are employed to separate temperature effects from strain variations. As a proof of concept, mechanical loading tests are conducted on the sensor, exposing the FBG portion to various temperature conditions. In the final phase, data collected from a post-tensioned concrete bridge embedded with both strain and temperature FBG sensors are utilized, and the developed ML models are applied to observe real-environment outcomes. Despite the limited feature points of collected FBG spectrums, the developed ML models effectively address cross-sensitivity issues induced by temperature perturbations. The long-term benefit of using FOS is that it will enable a better understanding and utilization of aging infrastructure. This will potentially reduce embodied carbon of infrastructure in the future and assist in the global efforts to achieve Net-Zero.

Degradation of structural safety levels in prototype balanced beam systems

Post-tensioned balanced beam structures are very sensitive to natural deterioration and excessive environmental attacks, which can lead to relatively rapid drops in safety levels. Since partial failure or corrosion of pre-stressing tendons can be difficult to detect, the strategy of last resort to ensure that safety levels are acceptable remains to perform a mechanical load test, with the risks that this entails. In the case of some iconic balanced beam systems, destructive investigations are further limited by the need to comply with the deontological standards valid for cultural heritage structures. The capacity and robustness of balanced beam systems can therefore be estimated by relying primarily on accurate mechanical models and sensitivity analyses against scenarios that may degrade safety. To this end, reference models can be corroborated by information from various sources, including experimental campaigns and archives. This study, in particular, focuses on the evaluation of the residual capacity offered by Morandi's prototype balanced beam scheme, to aid prognosis, and possibly support “decision-making” for possible reuse. Finally, an experimental and numerical application to the most complex post-tensioned concrete balanced beam system ever designed by Riccardo Morandi is presented, i.e. the roofing system of Pavilion V of Torino Esposizioni dating back to the late 1950 s.

Wind turbine load optimization control and verification based on wind speed estimator with time series broad learning system method

AbstractWith the rapid development of wind power, the power performance and mechanical load characteristics of wind turbine are simultaneously considered and focused. Normally, wind turbine senses the incoming flow characteristics through the nacelle mounted anemometer, due to the inability to perceive the characteristics of wind speed in advance, the control strategy makes the wind turbine itself to be at a passive state during the operation process. In this paper, a wind turbine mechanical load optimization control strategy based on an accurate wind speed estimator with time series Broad Learning System Method (BLSM) is designed, simulated and also verified. Firstly, the basic control theory of the BLSM and also a mechanical load optimization controller is designed. Then the OpenFAST is used to conduct a full‐life cycle simulation comparison study on mechanical load characteristics of wind turbine before and after the implementation of the optimization control strategy. Finally, a field empirical mechanical load test is performed on the wind turbine, which is configured with BLSM mechanical load optimization control technology. The findings indicate that the implementation of this control strategy can significantly mitigate the ultimate and fatigue loads of wind turbines, particularly the fatigue loads of tower base tilt and roll bending moments, with a reduction rate of approximately 6.2% and 4.3%, respectively.

The impact of high temperature on mechanical properties and behaviors of sandstone

The impact of high temperature environments on the physical and mechanical properties of rocks is a significant factor to consider. The investigation into the impact of elevated temperatures on the physical and mechanical characteristics of rocks holds great importance in the advancement and exploitation of deep-seated mineral reserves, as well as in ensuring the safety and stability of subterranean engineering projects. This study utilizes the state-of-the-art GCTS Mechanical Loading Test System to conduct uniaxial and triaxial compression tests on sandstone after thermal treatment from 25°C to 650°C. In addition, XRD, SEM and nuclear magnetic resonance experiments were carried out on the sandstone after thermal treatment. The aim of the experiments is to provide a quantitative characterization of mechanical properties and behaviors of the rock samples. The results show that the mass, density, and wave velocity of sandstone decrease with increasing temperature, while volume and porosity increase. The mass, volume, and rate of density change of sandstone exhibit a significant increase when subjected to temperatures above 500°C. The uniaxial compressive strength and elastic modulus exhibit an initial increase followed by a subsequent decrease as the temperature rises, with 300°C serving as the critical turning point. The axial peak strain and Poisson’s ratio increase with increasing temperature. The cohesion decreases with increasing temperature, while the internal friction angle increases. Additionally, it is observed that the rate of change for both properties exhibits an increase beyond the temperature threshold of 400°C.

TESTING OF ZIRCONIA FPD FRAMEWORKS FOR FIXED PROSTHESES: MODEL DESIGN AND EVALUATION OF FRACTURE LOAD.

In our previous test model, the abutment teeth and the model base were printed with resin and bonded with a polyether material. Some abutment teeth were fractured during the mechanical load test. Therefore, the aim was to develop and evaluate a new model under mechanical loading until fracture with zirconia FPD frameworks. At a fracture load of up to 1,636 N, neither the artificial abutment teeth nor the base model fractured. Furthermore, the artificial abutment teeth did not detach from the base model. Therefore, the model should be suitable for mechanical testing of most ceramic-based framework materials for three-unit FPDs.

Impact of restorative material on fracture behaviors of class II restoration in endodontically treated deciduous molars.

The purpose of this study was to investigate the fracture behavior of endodontically treated (ET) deciduous molar when directly restored with different restorative materials in Class II (MO) cavities in comparison with permanent teeth. MO cavities were prepared with 2.4-2.5 mm and 1.9-2.0 mm in buccolingual width, and mesiodistal width of each cavity walls, respectively, followed by direct restoration with different materials: resin-modified glass ionomer cement (RMGIC), composite resin (CR), and composite resin containing 25% short glass-fiber (SFRC). All specimens were subjected to mechanical loading tests at a speed of 1 mm/min and evaluated fracture resistance and fracture modes. A one-way ANOVA followed by a Tukey multiple comparisons analysis was used. Deciduous-SFRC (3,310.5±396.2 N) were significantly higher fracture resistance than permanent-RMGIC (1,633.8±346.8 N) (p<0.001), and permanent-CR (1,400.0±381.3 N) (p<0.001). For the direct restoration of MO cavity after endodontic treatment, SFRC demonstrated its promising performance in load-bearing capacity and failure mode, especially in ET deciduous molars.

A Method of Producing Low-Density, High-Strength Thin Cement Sheets: Pilot Run for a Glass-Free Solar Panel

This paper presents an innovative method of producing a low-density, high-strength, thin cement sheet. A seaweed powder was mixed with Portland cement, a foaming agent, calcium sulfoaluminate (CSA), and a quantity of water to create an A4-sized thin sheet with a thickness of 7 mm, which can withstand 1.5 kg in weight. This sheet was then covered with ethylene vinyl acetate and a backsheet to create a sandwiched cement sheet. The advantages of this sandwiched cement sheet are two-fold. First, it can support up to 13 kg in a static mechanical loading test, without bending, for over eight hours. Second, it can be quickly recovered at the end of its life cycle. This was a preliminary experiment to produce a large cement sheet that could satisfy the loading requirements for a solar panel. The purpose of the large, thin cement sheet is to replace the glass in a conventional solar panel and create a lightweight solar panel of less than 10 kg, which would mean that the installation of solar panels would become a one-person operation rather than a two-person operation. It would also increase the efficiency of the solar panel installation process.

Study on the performance of titanium alloy-lined thin-walled vacuum chamber

HIAF-BRing, the main synchrotron accelerator of the High Intensity Heavy-Ion Accelerator Facility, requires an average pressure lower than 1 × 10 −9 Pa and the magnetic field increase rate of no less than 12 T/s to fulfill radioactive beam physics and high energy density physics experiments. To reduce the eddy current effect and the gap size of dipoles, a titanium alloy-lined thin-walled vacuum chamber with a wall thickness of 0.3 mm is proposed by IMP, which has been developed from the initial ceramic-lined vacuum chamber. By mechanical loading testing, when the internal stress of titanium alloy rings made by 3D selective laser melting (SLM) reaches 639 MPa, it is still within the elastic deformation range, in fact, the yield strength of the 3D printed titanium alloy material is 912 MPa. In order to reduce the pressure gradient inside the thin-walled vacuum chamber caused by the surface outgassing of the rings, TiZrV thin films have been deposited on the rings by planar target magnetron sputtering. Through TiZrV deposited on the rings, the pressure at the middle of the thin-walled vacuum chamber has been dropped from 1.5 × 10−9 Pa to 1.0 × 10−9 Pa. At the same time, as the magnets are continuously energized, the actual heating state of the thin-walled vacuum chamber has been also measured.

Effect of the long-term storage methods on the stability of cartilage biomechanical parameters

Long-term stability of the tissue product in terms of mechanical parameters is a key factor for its expiration date. For the investigation of storage effects on the cartilage tissues the experimental mechanical loading test combined with XCT scanning for the irregular shape inspection was performed. The samples were preserved according to three different protocols using the deep-freezing and two types of saline solution preservation. The stability of the biomechanical parameters was tested within annual intervals. All samples were subjected to uni-axial compression loading using the in-house developed compact table top loading device in displacement-driven mode. Based on the measurements, the results are represented in the form of stress-strain curves and quantified as elastic modulus and ultimate compression stress. It can be concluded that no significant difference was found in neither the mechanical properties of the samples nor in the effects of each preservational method.

Electrically conductive adhesive-free interconnection of shingle solar cells

This work deals with the usage of electrically conductive adhesives (ECA) for the interconnection of shingle solar cells. In a detailed study on small-format shingle modules characterized by current-voltage, electroluminescence and magnetic field imaging measurements, the impact of an ECA reduction (usage of ECA dashes instead of a continuous ECA line) as well as the complete omission of ECA is investigated with regards to the electrical interconnection quality. Inter alia, it is demonstrated that lamination can improve interconnection quality in ECA-containing shingle joints and establish interconnection in ECA-free shingle joints by pressing adjacent shingles together and thereby forming a busbar-to-busbar contact of decent electrical quality. In a follow-up experiment, the approach of simply omitting the usage of ECA for shingle interconnection is tested with regards to thermal cycling, damp heat and dynamic mechanical load tests finding only minor compromises, if at all, in terms of long-term stability.

Modeling the dynamic magneto-mechanical response of magnetic shape memory alloys based on Hamilton’s principle: The numerical algorithm

This paper is the second part of a variational modeling work on the dynamic magneto-mechanical response of magnetic shape memory alloys (MSMA). In the first part of this series work, the governing equations system for modeling the dynamic response of MSMA samples has been derived based on Hamilton’s principle, which contains the Maxwell’s equations, the magneto-mechanic equations, the evolution equations of internal variables and the twin interface motion criteria. In this paper, we aim to conduct comprehensive numerical simulations on the dynamic magneto-mechanical response of MSMA samples. To solve the governing system, the space–time finite element method is applied and a double-loop iterative numerical algorithm is proposed. By using this algorithm, the independent variables in the governing system and the motion of twin interfaces in the MSMA sample can be determined separately and iteratively. Besides that, a specific discretization of the sample is adopted to simplify the calculation of variant state distribution in the sample. To show the efficiency of the numerical algorithm, the magneto-mechanical response of a MSMA sample in stress-assisted dynamic field loading tests and field-assisted dynamic mechanical loading tests are studied. Based on the numerical results, some global response curves of the MSMA sample are plotted, which show good consistency with the experimental results. Furthermore, the current configuration of the sample and the distributions of some important physical fields in the sample can be simulated. The current work will be helpful for the design of novel actuators or energy harvesters with MSMA.

Reliability study on the half-cutting PERC solar cell and module

In the photovoltaic industry, there are three critical parameters such as module power, cost and reliability. For increasing module power, half-cutting technology on the cell is one of the technologies because this can reduce the heating power by reducing the current. Therefore, laser scribing and mechanical cleaving (LSMC) technology have been implemented. As a result, the power of the module did not show any loss during standard test conditions when electrical luminescence and powers were monitored for the laser dicing process. However, in field conditions, the cut side of the cells with the laser process can cause cell breakage by wind or snow if the side has cracks. And then these crack cells can finally cause module power loss. Therefore, in this study, the laser process quality of the cell has been investigated by microscope image and scanning electron microscopy with laser process parameters such as laser power, frequency, and pulse width. In addition, cell strength was also checked by the four points of bending force to find the optimized laser process condition. The module power loss was analyzed with a static mechanical load test (MLT), which can represent snow or wind effect in the field. Our analyses show a strong correlation between crack width by laser, cell bending force, and module power loss. This correlation can explain the module power loss estimation, which can affect the reliability in the field without making module-level tests for the first time. In addition, the encapsulant thickness combination test and the mid-rail effect were also presented to reduce the power loss. As a result, the module power loss reached -1.34%. Finally, this study can contribute to the better reliability of the big wafer size products with LSMC technology.

Joining of Composites with Metals using Graded Metal Fabric Interfaces

A major challenge in the implementation of fibre-reinforced plastics (FRPs) is the provision of stress-appropriate joints with other materials. Establishing a high-strength, graded metal fabric interface using industrially established joining methods is a target-oriented approach in this context. For this purpose, a novel solution based on a textile transition structure in combination with the evaluation of different joining methods is presented in this article. A process chain was developed that depicts both the design and production of textile transition structure as reinforcement material of the FRP component and the further processing to metal FRP composites. Within the textile transition structure, the hybrid fabrics combine glass fibre yarns and metal flat wires, where the latter enable the joining process and transfer loads into the reinforcing glass fibres. The manufacturing implementation of this new joining interface from the textile to the hybrid component is described in detail within the paper. Furthermore, results of mechanical load tests of the graded metal fabric interface are presented. The research results make a significant contribution to the development of innovative graded metal fabric interface with a benign failure behaviour and a great potential especially with regard to the efficient joining of mixed material constructions in large-scale applications.

Development of an Integrated Powered Hip and Microprocessor-Controlled Knee for a Hip-Knee-Ankle-Foot Prosthesis.

Hip-knee-ankle-foot prostheses (HKAF) are full lower-limb devices for people with hip amputations that enable individuals to regain their mobility and move freely within their chosen environment. HKAFs typically have high rejection rates among users, as well as gait asymmetry, increased trunk anterior-posterior lean, and increased pelvic tilt. A novel integrated hip-knee (IHK) unit was designed and evaluated to address the limitations of existing solutions. This IHK combines powered hip and microprocessor-controlled knee joints into one structure, with shared electronics, sensors, and batteries. The unit is also adjustable to user leg length and alignment. ISO-10328:2016 standard mechanical proof load testing demonstrated acceptable structural safety and rigidity. Successful functional testing involved three able-bodied participants walking with the IHK in a hip prosthesis simulator. Hip, knee, and pelvic tilt angles were recorded and stride parameters were analyzed from video recordings. Participants were able to walk independently using the IHK and data showed that participants used different walking strategies. Future development of the thigh unit should include completion of a synergistic gait control system, improved battery-holding mechanism, and amputee user testing.

Flexible Wearable Nanomaterial-Based Sensing Device for Back Pain and Injury Prevention

Poor trunk posture during daily activity is known to increase the risk of low back pain and decrease quality of life. Monitoring trunk posture is a promising, proactive way to help prevent low back pain. A flexible, wearable, posture-monitoring sensor has been developed and tested in this letter. The device, referred to as “spine tape,” consists of flexible carbon nanotube composite strain sensing elements, which are screen-printed onto athletic tapes, along with a customized microcontroller-based data collection system. The spine tape possesses highly customizable dimensions and can be readily applied onto the human body, while maintaining a discreet and comfortable user experience. A series of sensing tests, including mechanical loading tests and human subject tests, was performed to characterize the performance of the spine tape. In addition, human motion analysis was used to validate the prototype and identify future improvements.

Manufacturing of pedestal supporting error field correction coil in JT-60SA

Eighteen error field correction coils (EFCCs) consisting of copper conductor and epoxy resin are installed in the vacuum vessel of JT-60SA in order to correct magnetic fields caused by manufacturing and installation errors of superconducting coils. Pedestals consisting of plate and spring bars for supporting the EFCCs were designed to withstand electromagnetic force during plasma operations and allow relative displacement between the EFCC at 40 °C and the vacuum vessel at 200 °C during baking operations. Feasibility of fixing the ends of the spring bars to the plates with plug welding and clearance of 50 μm was investigated using mechanical load test and trial manufacturing. Design for manufacturing was decided based on the results. Structural integrity of the design was confirmed through structural analysis with finite element method (FEM). Manufacturing of the pedestals has successfully completed.

Polymer-Metal Adhesion of Single-Lap Joints Using Fused Filament Fabrication Process: Aluminium with Carbon Fiber Reinforced Polyamide

Additive manufacturing (AM) is often used for prototyping; however, in recent years, there have been several final product applications, namely the development of polymer-metal hybrid (PMH) components that have emerged. In this paper, the objective is to characterize the adhesion of single-lap joints between two different materials: aluminium and a polymer-based material manufactured by fused filament fabrication (FFF). Single-lap joints were fabricated using an aluminium substrate with different surface treatments: sandpaper polishing (SP) and grit blasting (GB). Three filaments for FFF were tested: acrylonitrile butadiene styrene (ABS), polyamide (PA), and polyamide reinforced with short carbon fibers (PA + CF). To characterize the behaviour of these single-lap joints, mechanical tension loading tests were performed. The analysis of the fractured surface of the joints aimed to correlate the adhesion performance of each joint with the occurred failure mode. The obtained results show the impact of surface roughness (0.16 &lt; Ra &lt; 1.65 µm) on the mechanical properties of the PMH joint. The ultimate lap shear strength (ULSS) of PMH single-lap joints produced by FFF (1 &lt; ULSS &lt; 6.6 MPa) agree with the reported values in the literature and increases for substrates with a higher surface roughness, remelting of the primer (PA and PA + CF), and higher stiffness of the polymer-based adherent.