Gradient Of Mechanical Properties Research Articles

Effects of aging on the microstructure and mechanical properties of metastable β-type Ti-23.6Nb-5.1Mo-6.7Zr alloy with low elastic modulus

In this study, the influence of thermomechanical treatments on the microstructure and mechanical properties of a new metastable β-titanium Ti-23.6Nb-5.1Mo-6.7Zr alloy was assessed. The objective was to determine if the alloy is a potential candidate for a future fabrication of orthopedic implants, in particular prosthetic hip stems with a functional gradient of mechanical properties. Two thermomechanical processing routes were investigated: (a) 90% cold-rolled, (b) 90% cold-rolled, followed by annealing at 950 °C for 1 h. After these initial processing steps, samples were aged between 300 °C and 500 °C from 0.5 h to 4 h. Microstructural characterization was conducted by optical microscopy, transmission electron microscopy and x-ray diffraction. Young's modulus and microhardness were measured. Young's modulus of the sample annealed after cold rolling is lower than that after the cold rolled one. Aging was effective at increasing hardness but also increasing Young's modulus. The hardening during aging resulted from fine ωiso and α precipitation. The transmission electron microscopy investigations indicated that an aging treatment at 500 °C leads to a fine (α + β) microstructure, avoiding brittle ωiso precipitation. For these reasons, this alloy is a potential candidate for the manufacture of a hybrid hip prosthetic stem by employing localized aging treatment at 500 °C in the neck region, creating a functional strength gradient and maintaining a low Young's modulus in the distal part, which is needed to mitigate the stress shielding of the bone.

The puncture mechanics: an example from the bed bug Cimex lectularius showing traumatic insemination using the paramere.

Cimicidae are well-known for traumatic insemination, and males pierce females with their parameres and transfer sperm through them. The shape of parameres is relatively stable in the family, but in some genera, the paramere is elongated, appearing less resistant against lateral deflection. To understand the mechanical limitations of the paramere, we studied its penetration mechanics of the common bed bug, Cimex lectularius. We examined the post-abdominal morphology, paramere geometry and material properties and conducted breaking stress experiments on the paramere under wet and dry conditions. Mechanical property gradients are present with the paramere tip as the stiffest region and the base as the most flexible one. These mechanical properties relate to the presence of Ca, Zn and Si. The basal wing-shaped structure is flexible, enabling it to interlock with the anal region during mating. The paramere is slightly twisted; the tip region is circular in cross-section, and the geometry of the rest is rather complex. In the mechanical tests, wet parameres mainly buckled, while dried parameres broke off. The level of structural failures depended on directions from which the compression forces were applied. Structural, material and mechanical strengthening mechanisms preventing the paramere from mechanical failure are discussed.

Controlled Mechanical Property Gradients Within a Digital Light Processing Printed Hydrogel-Composite Osteochondral Scaffold.

Tissue engineered scaffolds are needed to support physiological loads and emulate the micrometer-scale strain gradients within tissues that guide cell mechanobiological responses. We designed and fabricated micro-truss structures to possess spatially varying geometry and controlled stiffness gradients. Using a custom projection microstereolithography (μSLA) system, using digital light projection (DLP), and photopolymerizable poly(ethylene glycol) diacrylate (PEGDA) hydrogel monomers, three designs with feature sizes < 200μm were formed: (1) uniform structure with 1MPa structural modulus ( ) designed to match equilibrium modulus of healthy articular cartilage, (2) = 1MPa gradient structure designed to vary strain with depth, and (3) osteochondral bilayer with distinct cartilage ( = 1MPa) and bone ( = 7MPa) layers. Finite element models (FEM) guided design and predicted the local mechanical environment. Empty trusses and poly(ethylene glycol) norbornene hydrogel-infilled composite trusses were compressed during X-ray microscopy (XRM) imaging to evaluate regional stiffnesses. Our designs achieved target moduli for cartilage and bone while maintaining 68-81% porosity. Combined XRM imaging and compression of empty and hydrogel-infilled micro-truss structures revealed regional stiffnesses that were accurately predicted by FEM. In the infilling hydrogel, FEM demonstrated the stress-shielding effect of reinforcing structures while predicting strain distributions. Composite scaffolds made from stiff μSLA-printed polymers support physiological load levels and enable controlled mechanical property gradients which may improve in vivo outcomes for osteochondral defect tissue regeneration. Advanced 3D imaging and FE analysis provide insights into the local mechanical environment surrounding cells in composite scaffolds.

Mechanical and elemental characterization of ant mandibles: consequences for bite mechanics.

Mandible morphology has an essential role in biting performance, but the mandible cuticle can have regional differences in its mechanical properties. The effects of such a heterogeneous distribution of cuticle material properties in the mandible responses to biting loading are still poorly explored in chewing insects. Here, we tested the mechanical properties of mandibles of the ant species Formica cunicularia by nanoindentation and investigated the effects of the cuticular variation in Young's modulus (E) under bite loading with finite-element analysis (FEA). The masticatory margin of the mandible, which interacts with the food, was the hardest and stiffest region. To unravel the origins of the mechanical property gradients, we characterized the elemental composition by energy-dispersive X-ray spectroscopy. The masticatory margin possessed high proportions of Cu and Zn. When incorporated into the FEA, variation in E effectively changed mandible stress patterns, leading to a relatively higher concentration of stresses in the stiffer mandibular regions and leaving the softer mandible blade with relatively lower stress. Our results demonstrated the relevance of cuticle E heterogeneity in mandibles under bite loading, suggesting that the accumulation of transition metals such as Cu and Zn has a relevant correlation with the mechanical characteristics in F. cunicularia mandibles.

Mandible mechanical properties and composition of the larval Glossosoma boltoni (Trichoptera, Insecta)

Insect feeding structures, such as mandibles, interact with the ingesta (food or/and substrate) and can be adapted in morphology, composition of material and mechanical properties. The foraging on abrasive ingesta, as on algae covering rocks, is particularly challenging because the mandibles will be prone to wear and structural failure, thus suggesting the presence of mandibular adaptations to accompany this feeding behavior. Adaptations to this are well studied in the mouthparts of molluscs and sea urchins, but for insects there are large gaps in our knowledge. In this study, we investigated the mandibles of a grazing insect, the larvae of the trichopteran Glossosoma boltoni. Using scanning electron microscopy, wear was documented on the mandibles. The highest degree was identified on the medial surface of the sharp mandible tip. Using nanoindentation, the mechanical properties, such as hardness and Young’s modulus, of the medial and lateral mandible cuticles were tested. We found, that the medial cuticle of the tip was significantly softer and more flexible than the lateral one. These findings indicate that a self-sharpening mechanism is present in the mandibles of this species, since the softer medial cuticle is probably abraded faster than the harder lateral one, leading to sharp mandible tips. To investigate the origins of these properties, we visualized the degree of tanning by confocal laser scanning microscopy. The autofluorescence signal related to the mechanical property gradients. The presence of transition and alkaline earth metals by energy dispersive X-ray spectroscopy was also tested. We found Ca, Cl, Cu, Fe, K, Mg, Mn, P, S, Si, and Zn in the cuticle, but the content was very low and did not correlate with the mechanical property values.

Analysis of crystallographic orientation and crack behavior in armor wire with spheroidized pearlite: Simulation and modeling with linear elastic fracture mechanics

This study investigates crack propagation in a pearlitic armor flexible riser subjected to CO2-rich marine environments, employing Scanning Electron Microscopy (SEM), Electron Backscatter Diffraction (EBSD), and Finite Element Modeling (FEM). A gradient in mechanical properties across the material's depth reveals a balance between surface strength and inner shear stress resistance, transitioning from γ-fiber and (001) texture at the surface to {110〈uvw〉 texture deeper. Our study revealed that Mode I (KI) fracture predominantly influences the failure, emphasizing the critical role of tensile stress in crack resistance. Analysis shows that crack growth is most susceptible at the midsection pit (z/a = 0), with pit size significantly affecting stress intensity. The study highlights the importance of material processing and microstructural orientation in determining mechanical properties, contributing to the development of robust materials for challenging marine applications.

Measurement of three-dimensional volumetric displacement fields in structural porous adhesive joints, under tensile and tensile-shear load, by means of in-situ X-ray microtomography

Nowadays, structural bonding is increasingly used for its advantages over conventional joining methods such as riveting or welding. Bonding defects (incomplete polymerization, gradient of mechanical properties, and presence of pores, among others.) can significantly impact the mechanical behavior of these assemblies. Among these defects, the presence of pores, detectable by means of X-ray microtomography measurements, could have a significant influence on the mechanical strength of a bonded structure (reduction of the useful section, questioning of the continuity of the joint, and stress concentration, among others). The study of these pores populations by means of microtomographic measurements, as well as their evolution under mechanical stress, can therefore provide valuable information regarding the mechanical behavior. These data can provide information on (i) the mechanical behavior on a microscopic scale, (ii) the identification of mechanisms of damage and failure of the adhesive joint, or (iii) the measurement of volume displacement fields. In this work, a method for calculating volume displacement fields in an adhesive joint is presented, using the detected pores as markers. The robustness, limits, and effects of different parameters (noise, voxelization, among others.) on this algorithm are identified on synthetic data representative of an adhesive joint. Finally, the validation of the method is based on interrupted tests on relatively small bonded specimens (called mini-Scarf) under tensile and tensile-shear loads.

An effective route to the additive manufacturing of a mechanically gradient supramolecular polymer nanocomposite structure

3D Printing techniques are additive methods of fabricating parts directly from computer-aided designs. Whilst the clearest benefit is the realisation of geometrical freedom, multi-material printing allows the introduction of compositional variation and highly tailored product functionality. The paper reports a proof-of-concept additive manufacturing study to deposit a supramolecular polymer and a complementary organic filler to form composites with gradient composition to enable spatial distribution of mechanical properties and functionality by tuning the number of supramolecular interactions. We use a dual-feed extrusion 3D printing process, with feed stocks based on the supramolecular polymer and its organic composite, delivered at ratios predetermined. This allows for production of a graded specimen with varying filler concentration that dictates the mechanical properties. The printed specimen was inspected under dynamic load in a tensile test using digital image correlation to produce full-field deformation maps, which showed clear differences in deformation in regions with varying compositions, corresponding to the designed-in variations. This approach affords a novel method for printing material with graded mechanical properties which are not currently commercially available or easily accessible, however, the method can potentially be directly translated to the generation of biomaterial-based composites featuring gradients of mechanical properties.

Sound Continuous Production of Thermosets

AbstractExisting manufacturing technologies for thermoset components are limited by long cycle times, simple structures, limited material, and poor controllability, making it difficult to realize complex structures with functionally graded properties. Herein, a sound continuous production (SCP) technology is proposed for the rapid manufacture of thermosets by accelerating the gelation through the mechanical, physical, and chemical effects of ultrasound. SCP is shown to enable the continuous production of homogeneous and heterogeneous thermosets. Its combination with a robotic arm allows for 360° omnidirectional continuous production, which is demonstrated by the successful construction of lateral and vertical‐oriented spiral structures via unsupported fabrication. Multiscale filaments with diameters ranging from 150 µm to 2 cm are manufactured and are shown capable of producing functionally graded materials with mechanical property gradients of up to five. The direct fabrication via SCP of a set of functional composites is demonstrated and a novel fabrication technique for multilayer carbon fiber‐reinforced plastic laminates is presented. This method can bring technological innovation to the rapid manufacture of thermosets for several emerging fields.

Magneto-active composites with locally tailored stiffness produced by laser powder bed fusion

Additive manufacturing technologies enable the production of complex and bioinspired shapes using magneto-responsive materials, which find diverse applications in soft robotics. Particularly, the development of composites with controlled gradients in mechanical properties offers new prospects for advancements in magneto-active materials. However, achieving such composites with gradients typically involves complex multi-material printing procedures. In this study, a single-step laser powder bed fusion (LPBF) process is proposed that enables precise local adjustments of the mechanical stiffness within magneto-active composites. By utilizing distinct laser parameters in specific regions of a composite containing thermoplastic polyurethane and atomized magnetic powder derived from hard magnetic Nd-Fe-B, the stiffness of the composite can be modified within the range of 2–22 MPa. Various magneto-responsive actuators with locally tailored stiffness are fabricated and their magnetic performance is investigated. The enhanced response exhibited by actuators with locally adjusted mechanical properties in comparison to their homogeneous counterparts with identical geometries is shown. As a demonstration of a biomedical application, a magnetically responsive stent with localized adjustment is presented with the ability to meet specific requirements in terms of geometry and local stiffness based on an individual's anatomy and disease condition. The proposed method presents an approach for creating functionally graded materials using LPBF, not only for magneto-active materials but also for several other structural and functional materials.

Fabrication of thin-walled hat-shaped beams from ultrahigh strength steel by laser-assisted robotic roller forming

Laser-assisted robotic roller forming (LRRF) can be applied to forming ultrahigh strength sheets to products with high geometrical accuracy. In this study, the geometrical profiles and three-point bending performance of thin-walled hat-shaped beams formed by LRRF and robotic roller forming (RRF, i.e., without laser heating) were experimentally investigated. It is found that the geometrical distortion resulted from the accumulation of longitudinal tension during multi-pass roller forming is significantly alleviated by LRRF. In addition, the bending performance of LRRF beam assembly is ameliorated at the initial deformation stage of three-point bending. The improvement is ascribed to a smaller bending radius and the alter of mechanical properties at the laser heat-affected zone. The lower geometrical precision of beams formed without laser heating results in early failure of spot welds of the beam assembly during three-point bending. LRRF beam assembly exhibits larger displacements at failure, and the failure mode is cracking at the edge of the laser-irradiated region. The pronounced microstructure differences on both sides of the crack suggest that the obvious laser-induced mechanical property gradients are responsible for the failure of LRRF beam assembly during three-point bending.

High-Entropy FeCoCrNiMn and FeCoNiCrAl Alloys Coatings: Structure and Properties

High-entropy alloys are a new class of materials consisting of at least five elements in an equiatomic or close to equiatomic ratio, which provides them with unique properties. Non-equiatomic high-entropy Fe-Co-Cr-Ni-Mn and Fe-Co-Cr-Ni-Al alloy coatings were applied to the 5083 alloy substrate using wire arc additive manufacturing and the cold metal transfer process. The structure, elemental composition, mechanical and tribological properties of coating / substrate systems were analyzed using modern methods of materials physics. The deposition of FeCoCrNiMn and FeCoNiCrAl HEA coatings on the surface of 5083 alloy was accompanied by the formation of gradients of elemental composition and mechanical properties. A transition layer with a thickness up to 450 μm was formed at the coating / substrate interface located at the coating-substrate boundary. The elemental composition gradient of the transition layer was studied, and a high level of chemical homogeneity of the coating was revealed. Alloying of the coating with substrate elements was observed. The alloying of the substrate with coating elements is accompanied by nonmonotonic changes of element composition in the 500 μm depth layer.

Variation in enamel mechanical properties throughout the crown in catarrhine primates

Enamel mechanical properties vary across molar crowns, but the relationship among mechanical properties, tooth function, and phylogeny are not well understood. Fifteen primate lower molars representing fourteen taxa (catarrhine, n = 13; platyrrhine, n = 1) were sectioned in the lingual–buccal plane through the mesial cusps. Gradients of enamel mechanical properties, specifically hardness and elastic modulus, were quantified using nanoindentation from inner (near the enamel-dentine junction), through middle, to outer enamel (near the outer enamel surface) at five positions (buccal lateral, buccal cuspal, occlusal middle, lingual cuspal, lingual lateral). Cuspal positions had higher mechanical property values than lateral positions. Middle enamel had higher mean hardness and elastic modulus values than inner and outer locations in all five crown positions. Functionally, the thicker-enameled buccal cusps of lower molars did not show evidence of increased resistance to failure; instead, lingual cusps—which show higher rates of fracture—had higher average mechanical property values, with no significant differences observed between sides. Preliminary phylogenetic results suggest there is relatively little phylogenetic signal in gradients of mechanical properties through the enamel or across the crown. There appears to be common mechanical property patterns across molar crowns in Catarrhini and potentially among primates more broadly. These results may allow more precise interpretations of dental biomechanics and processes resulting in mechanical failure of enamel in primates, such as wear and fracture.

Multimaterial and multiscale scaffold for engineering enthesis organ.

Tendon and ligament injuries are relevant clinical problems in modern society, and the current medical approaches do not guarantee complete recovery of the physiological functionalities. Moreover, they present a non-negligible failure rate after surgery. Failures often occur at the enthesis, which is the area of tendons and ligaments insertion to bones. This area is highly anisotropic and composed of four distinct zones: tendon or ligament, non-mineralized fibrocartilage, mineralized fibrocartilage, and bone. The organization of these regions provides a gradient in mechanical properties, biochemical composition, cellular phenotype, and extracellular matrix organization. Tissue engineering represents an alternative to traditional medical approaches. This work presents a novel biofabrication approach for engineering the enthesis. Gradient-based scaffolds were fabricated by exploiting the combination of electrospinning and three-dimensional (3D) bioprinting technologies. Studies were conducted to evaluate scaffold biocompatibility by seeding bone marrow-derived mesenchymal stem cells (BM-MSCs). Then, the scaffold's ability to promote cellular adhesion, growth, proliferation, and differentiation in both tenogenic and osteogenic phenotypes was evaluated. Fabricated scaffolds were also morphologically and mechanically characterized, showing optimal properties comparable to literature data. The versatility and potentiality of this novel biofabrication approach were demonstrated by fabricating clinical-size 3D enthesis scaffolds. The mechanical characterization highlighted their behavior during a tensile test was comparable to tendons and ligaments in vivo.

Suspension feeding in Copepoda (Crustacea) - a numerical model of setae acting in concert.

Suspension feeding via setae collecting particles is common within Crustacea. Even though the mechanisms behind it and the structures themselves have been studied for decades, the interplay between the different setae types and the parameters contributing to their particle collecting capacities remain partly enigmatic. Here, we provide a numerical modeling approach to understand the relationship among the mechanical property gradients, the mechanical behavior and the adhesion of setae, and the feeding efficiency of the system. In this context, we set-up a simple dynamic numerical model that takes all of these parameters into account and describes the interaction with food particles and their delivery into the mouth opening. By altering the parameters, it was unraveled that the system performs best when the long and short setae have different mechanical properties and different degrees of adhesion since the long setae generate the feeding current and the short ones establish the contact with the particle. This protocol can be applied to any system in the future as the parameters (i.e., properties and arrangement of particles and setae) can be easily altered. This will shed light on the biomechanical adaptations of these structures to suspension feeding and provide inspiration for biomimetics in the field of filtration technologies.

Hybrid materials with continuous mechanical property gradients that can be 3D printed

Here, we show tough materials with continuous composition and stiffness gradients, without interfaces between regions, using inorganic/organic hybrid materials that can also be 3D printed. Sol-gel hybrid materials have interacting and interpenetrating organic and inorganic co-networks and can deliver a synergy of the properties of those constituents. Their mechanical behaviour can be tuned through inorganic/organic content and cross-linking density. We describe hybrids of covalently linked silica-poly (tetrahydrofuran) (SiO2/PTHF) that show an unprecedented range of mechanical properties. SiO2/PTHF hybrids were formed with different silica contents, producing materials ranging from elastomeric to glassy, with a compressive stiffness at 10% strain of between 2 and 200 MPa: at an SiO2 content of 9 wt%, hybrids show a failure stress in compression of 8 MPa, at 70% strain, and tensile strength of 2 MPa at 80% strain. Gradual sol-gel gelation was employed to generate monoliths with composition and stiffness gradients without visible joins or points of weakness, and for development of ‘inks’ for additive manufacturing of 3D structures through direct ink writing. Monoliths with gradients were at least as strong, in tension and compression, as those made by casting a single sol. Cytocompatible materials with seamless stiffness gradients will have many applications: one is biomimicry of natural cartilaginous structures of the body, such as the intervertebral disc, which has a natural radial stiffness gradient.

Gradient characterization of steel-concrete interface at early ages

Steel-Concrete Interface (SCI) refers to the porous weak area at the interface between steel bar and cement matrix. This study proposes sophisticated methods for quantifying gradient properties and their evolution of SCI using back-scattered electron (BSE) imaging and nano-indentation. The gradient of SCI is identified through a robust statistical analysis. Distinct stratification structure of SCI is discovered, which can be demonstrated from the grayscale of BSE as well as the indentation modulus and hardness. The thickness of SCI increases with age and the increasing rates roughly decline with the increase of w/c. SCI can be divided into highly porous layer I and transition layer II according to the hierarchically porosity. The layer II is subdivided into II(a) and II(b) based on the gradient of mechanical properties, which is mainly caused by the spatial distribution of cement particles within SCI.

Quenching of Carbon Steel Plates with Water Impinging Jets: Differential Properties and Fractography

The demand for steel components with tailored properties is constantly growing. To obtain a specific variation of microstructures and mechanical properties along the component it must undergo a controllable cooling. One way to control the cooling rates along the component is by using different simultaneous water jet impingements on a hot austenitized surface. This can be done by a newly developed test rig for water Impinging Jet Quenching Technique (IJQT). This work discusses the effect of IJQT on mechanical properties and fracture behavior of 15 mm steel plates containing 0.27 and 0.38 mass-% carbon. The samples were cooled in a specifically designed setup of the technique to obtain simultaneous water and air cooling resulting in diverse microstructures. The mechanical property gradients of both steels were analyzed through hardness measurements and tensile tests. The fracture surfaces and the near fracture regions were observed using scanning electron microscope and light optical microscope respectively.The results from tensile tests showed that the larger part of the sample with higher carbon content was fully hardened, however smoothly transitioning to a more ductile region. The sample with lower carbon content combined various degrees of hardening and transitioned from higher to lower ultimate tensile strength values. Fracture behavior of higher carbon steel was predominantly brittle transitioning to a ductile, while the lower carbon steel had a small region showing brittle fracture transitioning to a larger region of predominant ductile fracture behavior.

Cartilage biomechanics: From the basic facts to the challenges of tissue engineering.

Articular cartilage (AC) is the thin tissue that covers the long bone ends in the joints and that ensures the transmission of forces between adjacent bones while allowing nearly frictionless movements between them. AC repair is a technologic and scientific challenge that has been addressed with numerous approaches. A major deadlock is the capacity to take in account its complex mechanical properties in repair strategies. In this review, we first describe the major mechanical behaviors of AC for the non-specialists. Then, we show how researchers have progressively identified specific mechanical parameters using mathematical models. There are still gaps in our understanding of some of the observations concerning AC biomechanical properties, particularly the differences in extracellular matrix stiffness measured at the microscale and at the millimetric scale. Nevertheless, for bioengineering applications, AC repair strategies must take into account what are commonly considered the main mechanical features of cartilage: its ability to withstand high stresses through three main behaviors (elasticity, poroelasticity and swelling). Finally, we emphasize that future studies need to investigate AC mechanical properties at different scales, particularly the gradient of mechanical properties around cells and across the cartilage depth, and the differences in mechanical properties at different scales. This multi-scale approach could greatly enhance the success of AC restorative approaches.

Comprehensive studies of SS316L/IN718 functionally gradient material fabricated with directed energy deposition: Multi-physics & multi-materials modelling and experimental validation

Metallic Functionally gradient materials (FGMs) are featured by gradually distributed metallic compositions generating unique mechanical and physical property gradients. As a major metal additive manufacturing process, Directed Energy Deposition (DED) has become an important process for manufacturing multi-materials parts. Fabricating metallic FGMs with the DED process has been studied experimentally in recent years. However, there is a lack of an effective modelling tool to predict the material composition gradients, FGM geometry, and the FGMs building process. The goal of this research is to fill this gap by establishing a novel multi-physics & multi-material thermal fluid model to fundamentally investigate the building process of FGMs with DED. In addition to the thermal distribution, phase change, and molten pool dynamics, the material distribution and geometry of the FGM part can be predicted with the model. As a demonstration, a DED fabrication process for Stainless Steel 316L/Inconel 718 FGM structure was simulated with this modelling tool. After that, the simulation results were validated with experimentally observed material composition and FGM geometry. The novelty of this study is the simulation of FGM part fabricated with DED process by fully considering multiple physics and multiple materials.