1,720,995 research outputs found
XFEM for Composites, Biological, and Bioinspired Materials: A Review
No full textThe eXtended finite element method (XFEM) is a powerful tool for structural mechanics, assisting engineers and designers in understanding how a material architecture responds to stresses and consequently assisting the creation of mechanically improved structures. The XFEM method has unraveled the extraordinary relationships between material topology and fracture behavior in biological and engineered materials, enhancing peculiar fracture toughening mechanisms, such as crack deflection and arrest. Despite its extensive use, a detailed revision of case studies involving XFEM with a focus on the applications rather than the method of numerical modeling is in great need. In this review, XFEM is introduced and briefly compared to other computational fracture models such as the contour integral method, virtual crack closing technique, cohesive zone model, and phase-field model, highlighting the pros and cons of the methods (e.g., numerical convergence, commercial software implementation, pre-set of crack parameters, and calculation speed). The use of XFEM in material design is demonstrated and discussed, focusing on presenting the current research on composites and biological and bioinspired materials, but also briefly introducing its application to other fields. This review concludes with a discussion of the XFEM drawbacks and provides an overview of the future perspectives of this method in applied material science research, such as the merging of XFEM and artificial intelligence techniques
Editorial: Design and Fabrication Tools for Advanced Materials: Applications in Biomechanics and Mechanobiology
No full textDesigning tough isotropic structural composite using computation, 3D printing and testing
Full text linkStaggered platelet composites found in nature, such as nacre, bone, and conch-shell, exhibit a remarkable combination of high toughness, strength, and/or stiffness, and have inspired the development of bio-inspired composites mimicking their characteristic features. However, those excellent mechanical properties are primarily observed under specific loading conditions due to their mechanical anisotropy, which originates from the aligned microstructures consisting of high aspect ratio inclusions. In this study, we combine numerical simulations and 3D-printing to define a design strategy of isotropic two-dimensional structural composites consisting of stiff and soft constituents that are arranged in square, triangular, and quasicrystal lattices. For relatively isotropic structures, the soft tile/stiff boundary configuration significantly outperforms the stiff tile/soft boundary configuration in terms of normalized toughness, strength, and stiffness with respect to the simple rule of mixture estimates for each, because the former provides more extrinsic toughening mechanisms and effectively lowers the stress concentration near the crack tip. The quasicrystal lattice offers the best isotropy in elastic response, while its absolute values of stiffness, strength, and toughness turn out to be similar or lower than those of triangular lattice composites due to more irregular stress distribution. In contrast, for the highly anisotropic staggered platelet structure, the stiff tile/soft boundary configuration significantly outperforms the inverted one, owing to its unique load-transfer mechanism, which relies primarily on the shear-lag effect
Hierarchical bioinspired architected materials and structures
No full textDesigning new materials that are both lightweight, damage-tolerant, and sustainable is a primary requirement for the advancement of many technological fields. To date, lattice materials appear to be ideal candidates for achieving such multifunctionality at the material scale and leveraging the structural hierarchy can pave the way to amplify their performance. Nature teaches us that, by designing multiscale architectures through a "bottom-up"logic, it is possible to improve and fine-tune the properties of biological building blocks to get robust and multifunctional materials. Yet, we are still far from achieving such a level of perfection that Nature has. In an attempt to narrow this gap and understand the role of hierarchical strategies in lattice structures, we studied, by finite element modeling, 3D hierarchical lattice structures formed by "beam-based"elementary units. Specifically, we selected two types of unit cells with different mechanical behaviors, we combined them into different topological configurations - through hierarchy and engineering approach - and we studied their mechanical behavior under four-point bending loading. The results of this study are twofold: introducing structural heterogeneity by mixing different unit cell types can be beneficial in terms of mechanical properties, while introducing structural hierarchy does not lead to significant improvements in the deformation behavior of the lattice structures analyzed. The latter, however, significantly changes the surface-to-volume ratios of the lattice structures and thus extends their functionality. The evidence found may open new horizons for applications such as heat exchangers, mechanical filters, tissue regeneration scaffolds, energy storage systems, and packaging.(c) 2022 Elsevier Ltd. All rights reserved
Fatigue-caused damage in trabecular bone from clinical, morphological and mechanical perspectives
Full text linkBone quantity and quality are considered the main predictors of bone mechanical properties (i.e., strength and fracture resistance). These factors deal with the morphology and chemical composition of bone and can be assessed by non-invasive techniques such as dual-energy x-ray absorptiometry (DXA), providing the bone mineral density (BMD) and the trabecular bone score (TBS). These parameters, and in particular BMD, are currently used as clinical predictors of fracture risk but do not provide information regarding the fatigue life. Bone is continuously subjected to fatigue loading and fatigue-induced damage can be crucial in fragility fractures. To probe the effect of fatigue-induced damage on bone microarchitecture and elucidate the effect of such damage on the bone clinical parameters, we combined fatigue testing on ex-vivo porcine trabecular bone samples with DXA measurements and μCT imaging. In addition, we performed interrupted cyclic tests at different load levels and measured fatigue-induced damage accumulation in the form of stiffness degradation. We also highlighted the change of clinical and microstructural parameters during the accumulation of fatigue-induced damage in interrupted fatigue tests. Our results suggest that the parameters obtained from the current non-invasive diagnostic protocols (i.e. μCT and DXA) are not able to assess the amount of fatigue-induced damage. This can be due to the fact that such techniques provide global parameters, whereas fatigue-induced damage is a local phenomenon, closely connected to the microarchitecture.Accepted Author ManuscriptBiomaterials & Tissue Biomechanic
Plant Biomimetic Principles of Multifunctional Soft Composite Development: A Synergistic Approach Enabling Shape Morphing and Mechanical Robustness
No full textPlant tissues are constructed as composite material systems of stiff cellulose microfibers reinforcing a soft matrix. Thus, they comprise smart and multifunctional structures that can change shape in response to external stimuli due to asymmetrical fiber alignment and possess robust mechanical properties. Herein, we demonstrate the biomimetics of the plant material system using silk fiber-reinforced alginate hydrogel matrix biocomposites. We fabricate single and bilamellar biocomposites with different fiber orientations. The mechanical behavior of the biocomposites is nonlinear, with large deformations, as in plant tissues. In general, the bilamellar system shows increased modulus, strain UTS, and toughness compared to the single-lamellar system for most of the tested orientations. Overall, the biocomposites present a wide range of elastic modulus values (3.0 +/- 0.6-104.7 +/- 11.3 MPa) and UTS values (0.23 +/- 0.04-12.5 +/- 2.0 MPa). The bilamellar biocomposites demonstrated shape-transforming abilities with diverse morphing modes, emulating different plant tissues and creating complex shape-morphing structures. These multifunctional biocomposites possess tunable and robust mechanical properties, controllable shape-morphing deformations, and the ability to self-controlled encapsulation, grip, and release objects. By harnessing biomimetic principles, these soft, smart, and multifunctional materials hold potential applications spanning from soft robotics, medicine, and tissue engineering to sensing and drug delivery
3D-Printed Architected Materials Inspired by Cubic Bravais Lattices
Full text linkLearning from Nature and leveraging 3D printing, mechanical testing, and numerical modeling, this study aims to provide a deeper understanding of the structure-property relationship of crystal-lattice-inspired materials, starting from the study of single unit cells inspired by the cubic Bravais crystal lattices. In particular, here we study the simple cubic (SC), body-centered cubic (BCC), and face-centered cubic (FCC) lattices. Mechanical testing of 3D-printed structures is used to investigate the influence of different printing parameters. Numerical models, validated based on experimental testing carried out on single unit cells and embedding manufacturing-induced defects, are used to derive the scaling laws for each studied topology, thus providing guidelines for materials selection and design, and the basis for future homogenization and optimization studies. We observe no clear effect of the layer thickness on the mechanical properties of both bulk material and lattice structures. Instead, the printing direction effect, negligible in solid samples, becomes relevant in lattice structures, yielding different stiffnesses of struts and nodes. This phenomenon is accounted for in the proposed simulation framework. The numerical models of large arrays, used to define the scaling laws, suggest that the chosen topologies have a mainly stretching-dominated behavior- A hallmark of structurally efficient structures-where the modulus scales linearly with the relative density. By looking ahead, mimicking the characteristic microscale structure of crystalline materials will allow replicating the typical behavior of crystals at a larger scale, combining the hardening traits of metallurgy with the characteristic behavior of polymers and the advantage of lightweight architected structures, leading to novel materials with multiple functions
Effect of delamination on the fatigue life of GFRP: A thermographic and numerical study
Full text linkDelamination is the major failure mechanism in composite laminates and eventually leads to material failure. An early-detection and a better understanding of this phenomenon, through non-destructive assessment, can provide a proper in situ repair and allow a better evaluation of its effects on residual strength of lightweight structural components. Here we adopt a joint numerical-experimental approach to study the effect of delamination on the fatigue life of glass/epoxy composites. To identify and monitor the evolution of the delamination during loading, we carried out stepwise cyclic tests coupled with IR-thermography on both undamaged and artificially-damaged samples. The outcome of the tests shows that IR-thermography is able to identify a threshold stress, named damage stress ?D, which is correlated to the damage initiation and the fatigue performance of the composite. Additionally, we performed FE-simulations, implementing the delamination by cohesive elements. Such models, calibrated on the basis of the experimental fatigue results, can provide a tool to assess the effect of parameters, such as the delamination size and location and composite stacking sequence, on the residual strength and fatigue life of the composite material
Bone osteon-like structures: A biomimetic approach towards multiscale fiber-reinforced composite structures
No full textNatural materials show astonishing mechanical properties, despite their rather poor building blocks. This counterintuitive behavior can be traced back to their hierarchical organization that enhances the properties of the building blocks. A classic example is bone: lightweight, stiff, strong, yet tough. This property combination is attributed particularly to the microstructure, where osteons deflect and arrest cracks. In this work, we mimic the bone microstructure with fiber-reinforced composites: we perform a numerical parametric study, by varying the layup of the osteon-like structures (OLS) and interconnecting layers representing the interstitial bone lamellae, and we manufacture and test single OLS as proof of concept. Results show the key role of OLS and interconnecting layers in deflecting and arresting cracks, whereas the combination of diverse materials affects the elastic properties. Finally, the introduction of hollow OLS, not affecting fracture toughness, might be used to expand the material functionality, paving the way toward novel multifunctional composites
3D printing of bending-dominated soft lattices: numerical and experimental assessment
Full text linkPurpose
This study aims to investigate the behaviour of soft lattices, i.e. lattices capable of reaching large deformations, and the influence of the printing process on it. The authors focused on two cell topologies, the body-centred cubic (BCC) and the Kelvin, characterized by a bending-dominated behaviour relevant to the design of energy-absorbing applications.
Design/methodology/approach
The authors analysed the experimental and numerical behaviour of multiple BCC and Kelvin structures. The authors designed homogenous and graded arrays of different dimensions. The authors compared their technical feasibility with two three-dimensional-printed technologies, such as the fused filament fabrication and the selective laser sintering, choosing thermoplastic polyurethane as the base material.
Findings
The results demonstrate that multiple design aspects determine how the printing process influences the behaviour of soft lattices. Besides, a graded distribution of the material could contribute to fine-tuning this behaviour and mitigating the influence of the printing process.
Practical implications
Despite being less explored than their rigid counterpart, soft lattices are now becoming of great interest, especially when lightweight, wearable and customizable solutions are needed. This study contributes to filling this gap.
Originality/value
Only a few studies analyse design and printing issues of soft lattices due to the intrinsic complexity of printing flexible materials
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