Mechanical Compression Tests Research Articles

Utilization of agate powder residue for manufacturing ecological bricks

In recent years, it has become increasingly important to search for alternatives for the development of new materials with sustainable characteristics. This is due to the fact that the environmental problems faced by the whole world have become increasingly worrying due to their serious short and long term impacts. In view of this, the use of materials from reuse and the disposal of polluting waste shows itself as an excellent alternative for the development of new products. Considering the mineral sector as a major generator of solid waste, this study proposed the reuse of agate powder, a residue from the extraction and processing process of agate stone, for the manufacture of ecological bricks. Mechanical compression tests were performed on bricks with 7, 14, 21 and 28 days, thus obtaining a mechanical strength profile. The results obtained were compared with those proposed by NBR 8491 (2012), which proved very promising, being above the values proposed by the standard in all cases.

Nonlinearity of mechanical behavior of 3D-reinforced composites under compression

Modern technological capabilities make it possible to produce 3D spatially-reinforced for polymer composite materials. The tasks of experimental research and analysis of the deformation process of new composite materials for aviation purposes taking into account the nonlinearity of mechanical behavior become actual. The paper presents an experimental study of the mechanical compression behavior of composite material specimens made of 3D woven carbon fiber preforms using the pressure impregnation technology (Resin Transfer Molding method with a pairwise interlayer reinforcement and a longitudinal layer). Compression mechanical tests were carried out on specimens using a universal system of electromechanical testing Instron 5882 and a system of 3D analysis of displacement and strain fields on the surface. Tests were conducted in accordance with ASTM D 3410 recommendations and using specialized tooling. Consideration of nonlinearity parameter during experimental data processing is proposed. The importance of determining the values of critical deformation in compression as a parameter characterizing the moment of the beginning of fracture is noted. Comparison of carbon fiber composite materials made by the same technology from fibers and binders of different manufacturers has been carried out. The experimental diagrams "stress-strain" and their approximating dependences taking into account the nonlinearity function w are obtained. The type of functions w of the studied materials is defined, the linear approximation of dependence of functions w on deformation is substantiated. Values of strength limits, elastic modulus, nonlinearity coefficient and critical damage were obtained, statistical processing of the obtained results and their analysis were carried out.

Influence of Structure and Geometry on the Compressive Deformation Behavior of Macadamia Integrifolia and Bertholletia Excelsa Shells: A Validated Finite Element Simulation Study

Macadamia (Macadamia integrifolia) and Brazil nuts (Bertholletia excelsa) have an impressive mechanical resistance. To better understand the key structural features and foam‐like deformation behavior, mechanical compression tests coupled with numerical finite element simulations are performed. Models with different degrees of structural complexity highlight the effects of geometry where even small changes strongly influence the stress distribution and deformation behavior. Circumferential tensile stresses play a vital role in the failure process. Voids or vascular bundles in the shell wall redistribute stresses and bolster the overall strength of structures by preventing early crack propagation. The void arrangement has the potential to inspire the design of lightweight materials with strategically incorporated porosity, leading to improved mechanical performance. Linear elastic models, despite their oversimplification, are valuable for gaining crucial insights about the influence of geometry. The mechanical behavior is further influenced to different extents by isotropy and orthotropy. The distinctive architecture of nutshells offers valuable insights into the design of composite structures with controlled failure, capable of withstanding high compression loads combining foam‐like behavior and fibrous layers.

Study on dynamic mechanical properties and meso-damage mechanism of carbon fibers recycled aggregate concrete under freeze-thaw environment

The uniaxial compression mechanical properties tests of carbon fibers recycled aggregate concrete (CFRAC) were carried out in order to investigate the effect law of coupling freeze-thaw cycles (FTCs) and dynamic strain rates on the mechanical properties of CFRAC. Two cases of carbon fibers (CFs) doping of 0% and 0.3% were considered. The full CFRAC uniaxial compressive stress-strain curves at different strain rates (10−5/s, 10−4/s, 10−3/s, 10−2/s) after different FTCs (0, 50, 100) were obtained. The microscopic characteristics and microcrack propagation process of the specimens were analyzed by means of nuclear magnetic resonance (NMR), scanning electron microscope (SEM) and acoustic emission (AE). The results showed that the specimens still had significant strain rate sensitivity after FTCs. With the same amount of CFs doping and strain rate, the strength and elastic mode (E) of the specimens kept decreasing as the number of freeze-thaw cycles (N) increased. With the same N, the strength and E of the specimens increased and the deformation capacity decreased as strain rate increased. With the addition of 0.3% CFs, the frost resistance and crack resistance of the specimens were significantly enhanced. Combined with the statistical damage constitutive model, the influence of FTCs and dynamic strain rates coupling on the meso-damage mechanism of CFRAC was analyzed. The meso damage evolution process was characterized by five characteristic parameters E0, εa, εh, εb and H. The results showed that there was an obvious regularity between the change of characteristic parameters and CFs content, dynamic strain rate and the N. An effective link between the fine-scale damage mechanism and the macroscopic nonlinear intrinsic behavior was established. The phenomenon of AE signal lag in uniaxial compression was explained from the perspective of effective stress.

Utilizing halloysite nanotube to enhance the properties of cement mortar subjected to freeze-thaw cycles

This study investigates the impact of the long-term pozzolanic properties of halloysite nanotube (HNT) on the physical and mechanical properties, permeability, durability, and microstructural characteristics of cement mortar subjected to repeated freeze-thaw cycles. For this purpose, the two-year cured samples were exposed to 300 freeze-thaw cycles. Deterioration of the cement mortar surface was visually assessed and regularly quantified by mass loss and length change. Furthermore, helium porosity, electrical resistivity, and ultrasonic pulse velocity (UPV) were performed on cement mortar mixtures to elucidate the effect of repeated freeze-thaw cycles on permeability. In terms of mechanical properties, compressive and flexural strength tests were conducted; static elastic modulus and flexural toughness were also calculated. The frost durability of samples was analyzed using the relative dynamic modulus of elasticity and durability factor as the indexes to assess mortar's freeze-thaw resistance. Moreover, the microstructures of specimens before and after 300 freeze-thaw cycles were analyzed by scanning electron microscopy. Visual comparisons and experimental results demonstrated that the HNT introduction in cement mortars markedly enhances the frost resistance of plain mortar. It leads to the refinement of the cement paste pore structure and a reduction in its porosity due to the nucleating, filling, and long-term pozzolanic effects of HNT. It was found that the contribution of HNT's pozzolanic activity is the most important of these mechanisms. Therefore, less water penetration into the hardened cement composites occurs, which results in higher frost durability. The samples containing 2 wt.% HNT (by weight of cement) exhibited the lowest mass loss, expansion, porosity, and UPV loss due to repeated freeze-thaw cycles. The highest electrical resistivity and residual mechanical strengths also pertained to samples with 2 wt.% HNT. Hence, the HNT replacement dosage of 2 wt.% can be regarded as an optimal content for the cement mortars studied in this work. Finally, the two-way ANOVA revealed that HNT percentage is the factor with the greatest impact on mass loss, electrical resistivity, and compressive strength. In terms of length change, porosity, and flexural strength, the freeze-thaw cycle was the most statistically important factor.

Microstructure, Hardening, and Mechanical Properties of Hypoeutectic Al–Ce–Ni Alloys with Zr and Zr + Sc Additions and the Effect of Ultrasonic Melt Processing

Ternary Al–Ce–Ni alloys have a potential in the manufacture of automotive and airspace components, as well as in replacing traditional aluminum alloys in high‐temperature applications, which is determined by the formation of fine and thermally stable Al11Ce3 and Al3Ni eutectic. Herein, the microstructure and mechanical properties of a hypoeutectic Al4Ce2Ni alloy using Zr and Zr + Sc additions combined with ultrasonic melt processing and dispersion hardening are improved. As a result, the grain structure of the as‐cast alloys is significantly refined and the annealing at 350 °C leads to a considerable hardening effect, especially in the alloys with Zr + Sc additions (doubling the hardness). Al3Zr and Al3(Zr,Sc) coherent particles are identified as hardening nanoprecipitates. The compressive mechanical testing at room and elevated temperatures shows that the additions of Zr and Zr + Sc improve the strength with the additional increase caused by ultrasonic melt processing.

Mechanical and Environmental Assessment of Lathe Waste as an Addiction to Concrete Compared to the Use of Commercial Fibres.

The use of fibres applied to concrete in order to improve its properties is widely known. Nowadays, research is not only focused on improving mechanical properties but also on the environmental implications. The aim of this research was a mechanical and environmental comparison between different types of fibres. For this purpose, commercial fibres of three materials were used: low carbon steel, modified polyolefins, and glass fibre. In order to improve the sustainability of the sector, we also analysed and compared the performance of using a waste product, such as fibres from machining operations on lathes. For the evaluation of the mechanical properties, compression and flexural tests were carried out. The results show that the use of low carbon steel fibres increases the flexural strength by 4.8%. At the environmental level, and in particular for impact categories such as the Global Warming Potential (GWP), lathe waste fibres prove to be the most suitable. For instance, compared to glass fibres, CO2 emissions are reduced by 14.39%. This is equivalent to a total of 38 kg CO2 emissions per m3 of reinforced concrete. In addition to avoiding the consumption of 482 MJ/m3 of fossil fuels, the results of the research indicate the feasibility of using waste fibres as a substitute for commercial fibres, contributing to an improved environmental balance without losing mechanical performance.

Discovering the mechanics of artificial and real meat

Artificial meat is an eco-friendly alternative to real meat that is marketed to have a similar taste and feel. The mechanical properties of artificial meat significantly influence our perception of taste, but how precisely the mechanics of artificial meat compare to real meat remains insufficiently understood. Here we perform mechanical tension, compression, and shear tests on isotropic artificial meat (Tofurky® Plant-Based Deli Slices), anisotropic artificial meat (Daring™ Chick’n Pieces) and anisotropic real meat (chicken) and analyze the data using constitutive neural networks and automated model discovery. Our study shows that, when deformed by 10%, artificial and real chicken display similar maximum stresses of 21.0 kPa and 21.8 kPa in tension, -7.2 kPa and -16.4 kPa in compression, and 2.4 kPa and 0.9 kPa in shear, while the maximum stresses for tofurky were 28.5 kPa, -38.3 kP, and 5.5 kPa. To discover the mechanics that best explain these data, we consulted two constitutive neural networks of Ogden and Valanis–Landel type. Both networks robustly discover models and parameters to explain the complex nonlinear behavior of artificial and real meat for individual tension, compression, and shear tests, and for all three tests combined. When constrained to the classical neo Hooke, Blatz Ko, and Mooney Rivlin models, both networks discover shear moduli of 94.4 kPa for tofurky, 35.7 kPa for artificial chick’n, and 21.4 kPa for real chicken. Our results suggests that artificial chicken succeeds in reproducing the mechanical properties of real chicken across all loading modes, while tofurky does not, and is about three times stiffer. Strikingly, all three meat products display shear softening and their resistance to shear is about an order of magnitude lower than their resistance to tension and compression. We anticipate our study to inspire more quantitative, mechanistic comparisons of artificial and real meat. Our automated-model-discovery based approach has the potential to inform the design of more authentic meat substitutes with an improved perception of taste, with the ultimate goal to reduce environmental impact, improve animal welfare, and mitigate climate change, while still offering the familiar taste and texture of traditional meat. Our source code, data, and examples are available at https://github.com/LivingMatterLab/CANNs.

Mechanical characterization and modeling of microstructural deformation of Si anode sheet

Battery anodes generally have a layered structure consisting of an active material layer (including binder, conductive carbon, and active material) and a foil layer of the current collector (copper foil). Such layered structures bring grand challenges to our understanding of the mechanical behaviors of the Si-based anode sheets since the large deformation of the Si particles, and solid-solid interfacial interactions (particle-particle and particle-binder) are key knowledge in high-energy, safe, and durable batteries. Herein, we characterize a typical commercialized Si-based anode with detailed microstructure morphology. Representative mechanical tests, including tensile and compression tests, are conducted to characterize the constitutive behaviors of the anode materials. Further, we propose a 3D computational model with detailed descriptions of the microstructures of the active material is established to enable a fundamental understanding of the deformation behaviors. Results present a comprehensive understanding of the Si-based anode materials for the first time and provide a powerful model for the future design of the anode for the next-generation batteries.

Printing tissue-engineered scaffolds made of polycaprolactone and nano-hydroxyapatite with mechanical properties appropriate for trabecular bone substitutes

BackgroundBone tissue engineering, based on three-dimensional (3D) printing technology, has emerged as a promising approach to treat bone defects using scaffolds. The objective of this study was to investigate the influence of porosity and internal structure on the mechanical properties of scaffolds.MethodsWe fabricated composite scaffolds (which aimed to replicate trabecular bone) from polycaprolactone (PCL) reinforced with 30% (wt.) nano-hydroxyapatite (nHAp) by extrusion printing. Scaffolds with various porosities were designed and fabricated with and without an interlayer offset, termed as staggered and lattice structure, respectively. Mechanical compressive testing was performed to determine scaffold elastic modulus and yield strength. Linear regression was used to evaluate mechanical properties as a function of scaffold porosity.ResultsDifferent relationships between mechanical properties and porosities were noted for the staggered and lattice structures. For elastic moduli, the two relationships intersected (porosity = 55%) such that the lattice structure exhibited higher moduli with porosity values greater than the intersection point; vice versa for the staggered structure. The lattice structure exhibited higher yield strength at all porosities. Mechanical testing results also indicated elastic moduli and yield strength properties comparable to trabecular bone (elastic moduli: 14–165 MPa; yield strength: 0.9–10 MPa).ConclusionsTaken together, this study demonstrates that scaffolds printed from PCL/30% (wt.) nHAp with lattice and staggered structure offer promise for treating trabecular bone defects. This study identified the effect of porosity and internal structure on scaffold mechanical properties and provided suggestions for developing scaffolds with mechanical properties for substituting trabecular bone.

Novel 3D-Printed Biocarriers from Aluminosilicate Materials

The addition of biocarriers can improve biological processes in bioreactors, since their surface allows for the immobilization, attachment, protection, and growth of microorganisms. In addition, the development of a biofilm layer allows for the colonization of microorganisms in the biocarriers. The structure, composition, and roughness of the biocarriers’ surface are crucial factors that affect the development of the biofilm. In the current work, the aluminosilicate zeolites 13X and ZSM-5 were examined as the main building components of the biocarrier scaffolds, using bentonite, montmorillonite, and halloysite nanotubes as inorganic binders in various combinations. We utilized 3D printing to form pastes into monoliths that underwent heat treatment. The 3D-printed biocarriers were subjected to a mechanical analysis, including density, compression, and nanoindentation tests. Furthermore, the 3D-printed biocarriers were morphologically and structurally characterized using nitrogen adsorption at 77 K (LN2), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The stress–strain response of the materials was obtained through nanoindentation tests combined with the finite element analysis (FEA). These tests were also utilized to simulate the lattice geometries under compression loading conditions to investigate their deformation and stress distribution in relation to experimental compression testing. The results indicated that the 3D-printed biocarrier of 13X/halloysite nanotubes was endowed with a high specific surface area of 711 m2/g and extended mesoporous structure. Due to these assets, its bulk density of 1.67 g/cm3 was one of the lowest observed amongst the biocarriers derived from the various combinations of materials. The biocarriers based on the 13X zeolite exhibited the highest mechanical stability and appropriate morphological features. The 13X/halloysite nanotubes scaffold exhibited a hardness value of 45.64 MPa, which is moderate compared to the rest, while it presented the highest value of modulus of elasticity. In conclusion, aluminosilicate zeolites and their combinations with clays and inorganic nanotubes provide 3D-printed biocarriers with various textural and structural properties, which can be utilized to improve biological processes, while the most favorable characteristics are observed when utilizing the combination of 13X/halloysite nanotubes.

Poster 152: Detrimental Effects of Chlorhexidine on Articular Cartilage Viability, Matrix, and Mechanics

Objectives: Chlorhexidine gluconate (CHG) is commonly used in antiseptic irrigation solutions for bacterial decontamination during orthopaedic surgery. Although the chondrotoxicity of CHG to articular cartilage has been reported, CHG irrigation is utilized by some surgeons to limit surgical site infection and to salvage grafts after accidental contamination during joint surgery. The full extent of CHG irrigation-related chondrotoxicity, as well as its effects on articular cartilage extracellular matrix and mechanical properties, are unknown. The purpose of this study was to determine the in vitro effects of a single one-minute CHG exposure on the viability, biochemical content, and mechanics of native articular cartilage explants. Methods: Articular cartilage explants (n=6 per group) were harvested from the femoral condyles of the porcine stifle and sectioned at the tidemark. Explants were bathed in Irrisept® chlorhexidine solution (0.05% CHG in sterile water) at varying concentrations (0% control, 0.01% CHG, and 0.05% CHG) to stimulate surgical irrigation for 1 minute, followed by complete phosphate-buffered saline wash and culture. After seven days of culture in chondrogenic medium, the explants were analyzed for viability (live/dead assay); collagen content (hydroxyproline assay); glycosaminoglycan (GAG) content (dimethyl methylene blue assay); and compressive mechanical testing (creep indentation testing). Statistical analyses were performed using a one-way ANOVA with post hoc Tukey test. Results: Seven days after CHG exposure, a dose-dependent decrease in mean chondrocyte viability was observed in the CHG groups (p<0.001), with <3% viability observed in the 0.05% CHG group (Figure 1). There was no significant difference in mean collagen content per wet weight among groups. Conversely, 0.05% CHG exposure led to a decrease in mean GAG per wet weight compared to negative control (p=0.029) and 0.01% CHG (p=0.046) (Figure 2). These changes in GAG content corresponded to observed changes in the compressive mechanical properties of the explants. A dose-dependent decrease in mean aggregate modulus and shear modulus was observed after CHG exposure (p<0.029), indicating weakening of the cartilage matrix and increased deformation in response to compressive loads (Figure 3). Conclusions: One-minute CHG exposure to articular cartilage explants led to dose-dependent decreases in chondrocyte viability, GAG content, and compressive mechanical properties. These detrimental effects were observed for both 0.05% and 0.01% CHG concentrations. There is a paucity of literature examining the effects of CHG on articular cartilage matrix and mechanics, and the findings of this study suggest a lack of matrix maintenance following cell death, raising concern for risk of mechanical failure of the cartilage tissue. Clinicians should be judicious regarding the use of CHG irrigation at these concentrations in the presence of native articular cartilage.

Strength deterioration and energy dissipation characteristics of cemented backfill with different gangue particle size distributions

The particle size distribution of gangue is an important factor affecting the strength of backfill body. To uncover the strength deterioration law and energy dissipation characteristics of cemented backfill with different gangue particle sizes, the uniaxial compressive strength mechanical tests were carried out by scanning electron microscopy analysis combined with rock mechanics test system and acoustic emission monitoring equipment. The deformation failure mode, mechanical characteristics, acoustic emission response characteristics and energy dissipation characteristics of backfill samples with different particle size distribution under uniaxial compression were studied. The results shown that: The particle size distribution of gangue material is very important to the performance of backfill body. The compressive strength of the backfill sample with medium particle size was the largest. As the particle size of the gangue increases, the acoustic emission response degree of the backfill firstly increases followed by a subsequent decrease. The acoustic emission ringing count and energy rate reach the peak when the backfill was destroyed. Building upon the principle of energy dissipation and release, the defined energy dissipation ratio was used as the strength deterioration index of the backfill body. The energy dissipation ratio of fine grain size, medium grain size and coarse grain size filling was 19.64%, 7.85% and 12.93%, respectively. When the failure mode of the backfill shifts from tensile failure to shear failure, the energy dissipation ratio decreases from 19.64% to 7.85%. The storage capacity of elastic strain energy in the backfill gradually increases, and the strength degradation degree of backfill gradually decreases.

Ultra-flexible Al2O3 fibers: A novel catalyst support material for sustainable catalysis

Flexible aluminum oxide (Al2O3) fibers were prepared by the blow spinning method and their potential as a high-temperature catalyst support was investigated. The synthesized Al2O3 fibers exhibited remarkable flexibility in both mechanical compression and recovery tests, which remained intact in a wide temperature range from −196 °C to 1200 °C. Moreover, their low thermal conductivity of 0.030 W K−1∙m−1, demonstrated an outstanding thermal insulation. Subsequently, nickel nanoparticles were uniformly distributed on the surface of the Al2O3 fibers as a self-supporting catalyst using a conventional impregnation method. The resulting self-supporting Ni/Al2O3 catalyst demonstrated remarkable thermo-catalytic performance and re-activation capability at high temperatures for thermocatalytic reaction of dry reforming of methane (DRM). Our findings highlight the potential of pure Al2O3 flexible fibers as a versatile material for various industrial applications, including high-temperature catalysis.

Adjusting of the performance characteristics of the La(Fe,Si)13 compounds and their hydrides for multi-stimuli cooling cycle application

The use of multi-stimuli materials is a promising approach for increasing the cooling capacity of magnetic refrigerators. The working body undergoes both a magnetic field and an external compressive pressure during cooling. The proposed material must have outstanding magnetocaloric and mechanical properties. The magnetocaloric properties should provide a high adiabatic temperature change value in a limited field range. Mechanical stability at high pressures and adequate geometry are required to ensure high heat transfer values. The compounds La(Fe,Si)13 and their hydrides are the most suitable for the manufacture of such devices. They are able to work at both room and cryogenic temperatures. In the article, we present the results of direct measurements of the magnetocaloric effect and mechanical compression tests of the cast and hydrogenated La(Fe,Si)13Hδ rods. The samples were reinforced with a secondary alpha-iron phase, which ensured their mechanical integrity during hydrogenation and cycle performance. The addition of a secondary alpha-iron phase leads to a decrease in the magnetocaloric effect value. Therefore, we determine the optimal content of the secondary phase, which provides a balance between the caloric and mechanical alloy properties.

Making foam-like bioactive glass scaffolds by vat photopolymerization

This study explores the feasibility of bioactive glass scaffolds by using a stereolithographic technology (digital light processing-based vat photopolymerization) as fabrication method and the micro-tomographic reconstruction of an open-cell polymeric sponge as input virtual model to the printing system, in the attempt to replicate the trabecular architecture of cancellous bone. Additively-manufactured scaffolds were investigated from morphological (scanning electron microscopy), microstructural (X-ray diffraction), mechanical (compressive tests) and bioactive viewpoints (immersion studies in simulated body fluid (SBF)). Well-densified foam-like glass scaffolds were obtained after sintering, provided with suitable mechanical properties (compressive strength 21.9 ± 6.2 MPa, elastic modulus 4.8 ± 0.1 GPa, Weibull modulus 3.9) for bone-contact applications. The formation of a hydroxyapatite layer on scaffold struts after soaking in SBF also demonstrated the in vitro bioactivity of the printed structures.

Multi-scale deterioration mechanism of shear strength of gypsum-bearing mudstone induced by water-rock reactions

Investigation of water-rock reactions effects on the shear strength of gypsum-bearing mudstone is necessary for underground engineering design and assessment of engineering safety. A comprehensive study of the multi-scale deterioration effects and mechanisms of water-rock reactions on gypsum-bearing mudstone can contribute to developing better engineering applications. The 25 sets of laboratory dissolution tests and 30 sets of conventional rock mechanical compression tests conducted in this study demonstrate the progressive modification of rock properties on multiple scales, including changes in mineralogy, porosity, grain structure, microstructures, and complexity of micropores, with sodium sulfate and gypsum being the most active minerals. Water-rock reactions cause irreversible morphological changes in microstructures. For instance, the number of intracrystalline pores increased, the contact between grains changed from face-to-face contact to line-to-line contact, and the volume of micropores, mesopores and macropores inside the rock increased by a maximum of 80.0%, 59.9% and 71.4% respectively. The maximum increase in the porosity of the samples was 5.33%. The increasing number of microphysical changes leads to defects that develop into weak areas, significantly decreasing the shear strength of gypsum-bearing mudstone. The maximum decrease in the cohesion of the samples was 79.06% throughout the dissolution process. It was found that the decrease in the cohesion of the samples c at the early stage of dissolution is mainly affected by the increase in the micropore volume. In the middle and late stages, the cohesion c of the samples decreased in a straight line, which is mainly caused by the increase in the macropore volume and porosity. The fluctuation in the cumulative pore volume during the whole dissolution process leads to fluctuation in the internal friction angle φ. The multi-scale degradation model of rock samples induced by water-rock reactions should be formulated to accurately evaluate the effect of water-rock reactions on rock shear strength.

Reliability Evaluation of Board-Level Flip-Chip Package under Coupled Mechanical Compression and Thermal Cycling Test Conditions.

Flip Chip Ball Grid Array (FCBGA) packages, together with many other heterogeneous integration packages, are widely used in high I/O (Input/Output) density and high-performance computing applications. The thermal dissipation efficiency of such packages is often improved through the use of an external heat sink. However, the heat sink increases the solder joint inelastic strain energy density, and thus reduces the board-level thermal cycling test reliability. The present study constructs a three-dimensional (3D) numerical model to investigate the solder joint reliability of a lidless on-board FCBGA package with heat sink effects under thermal cycling testing, in accordance with JEDEC standard test condition G (a thermal range of -40 to 125 °C and a dwell/ramp time of 15/15 min). The validity of the numerical model is confirmed by comparing the predicted warpage of the FCBGA package with the experimental measurements obtained using a shadow moiré system. The effects of the heat sink and loading distance on the solder joint reliability performance are then examined. It is shown that the addition of the heat sink and a longer loading distance increase the solder ball creep strain energy density (CSED) and degrade the package reliability performance accordingly.

Investigation on Mechanical and Thermal Properties of 3D-Printed Polyamide 6, Graphene Oxide and Glass-Fibre-Reinforced Composites under Dry, Wet and High Temperature Conditions

This study is focused on 3D printing of polyamide 6 (PA6), PA6/graphene oxide (PA6/GO) and PA6/glass-fibre-reinforced (PA6/GF) composites. The effect of graphene oxide and glass-fibre reinforcement on 3D-printed PA6 is explored for improvement of the interfacial bond and interlaminar strength in ambient, wet and high temperature conditions relating to electric car battery box requirements. The influence of environmental conditions and process parameters on the 3D-printed polymer composites quality is also examined. Commercial PA6 filament was modified with GO to investigate the thermal and mechanical properties. The modified composites were melt-compounded using a twin-feed extruder to produce an improved 3D-printing filament. The improved filaments were then used to 3D-print test samples for tensile and compression mechanical testing using universal testing machines and thermal characterisation was performed following condition treatment in high temperature and water for correlation to dry/ambient samples. The study results show the studied materials were mostly suitable in dry/ambient conditions. PA6/GF samples demonstrated the highest strength of all three samples in ambient and high-temperature conditions, but the least strength in wet conditions due to osmotic pressure at the fibre/matrix interface that led to fibre breakage. The introduction of 0.1% GO improved the tensile strength by 33%, 11% and 23% in dry/ambient, dry/high temperature and wet/ambient conditions, respectively. The wet PA6/GO samples demonstrated the least strength in comparison to the ambient and high-temperature conditions. Notwithstanding this, PA6/GO exhibited the highest tensile strength in the wet condition, making it the most suitable for a high-strength, water-exposed engineering application.

Reliable Methods for Classification, Characterization, and Design of Cellular Structures for Patient-Specific Implants.

In our research, our goal was to develop a characterization method that can be universally applied to periodic cell structures. Our work involved the accurate tuning of the stiffness properties of cellular structure components that can significantly reduce the number of revision surgeries. Up to date porous, cellular structures provide the best possible osseointegration, while stress shielding and micromovements at the bone-implant interface can be reduced by implants with elastic properties equivalent to bone tissue. Furthermore, it is possible to store a drug inside implants with a cellular structure, for which we have also prepared a viable model. In the literature, there is currently no established uniform stiffness sizing procedure for periodic cellular structures but also no uniform designation to identify the structures. A uniform marking system for cellular structures was proposed. We developed a multi-step exact stiffness design and validation methodology. The method consists of a combination of FE (Finite Element) simulations and mechanical compression tests with fine strain measurement, which are finally used to accurately set the stiffness of components. We succeeded in reducing the stiffness of test specimens designed by us to a level equivalent to that of bone (7-30 GPa), and all of this was also validated with FE simulation.