Advanced mechanics of materials with microstructure

Attenuation or enhancement—a one-dimensional analysis on shock transmission in the solid phase of a cellular material

Micromechanical models for porous and cellular materials in linear elasticity and viscoelasticity

Due to the excellent specific energy absorption and high specific strength, cellular materials are widely used in impact protection fields. Higher energy absorption efficiency has always been pursued through designing various structures. According to the bio-inspired design from the growth of ticks and bamboo, this study proposes an easy-to-operate elongation-shortening strategy to improve the mechanical properties of Schwarz Primitive (P) and Schoen Gyroid (G) cells. After that, a gradient design is achieved by combining unit cells with different mechanical properties. The mechanical properties, deformation modes, deformation mechanisms and cyclic response behaviours of the proposed novel cellular materials are investigated by conducting compression testing and finite element analysis. The results show that the elongation-shortening strategy effectively adjusts the configuration of the unit cell, thereby altering the deformation model and optimising energy storage and energy dissipation. Specifically, tensile unit cells exhibit superior energy storage capability. The impact of the elongation-shortening ratio on energy absorption varies across different relative densities. Gradient structures with various elongation-shortening ratios facilitate steady and gradual energy absorption, akin to density-gradient structures. This approach enhances performance by altering the deformation mechanism and expands design possibilities for controlling energy absorption, providing a promising new direction for cellular material design.

Planar cellular materials, or honeycombs, are considered as two-phase materials where the properties of one of it phases (voids) degenerates to zero. They are characterized by a low relative density and herein we assume that the solid phase of the material can be modeled as an assembly of axially loaded rods or general flexural elements in infinite and repetitive truss or frame structures, respectively. For the analysis and evaluation of the effective mechanical properties of a 2D cellular material the repetitive structure representing the material is assumed to be in a repetitive stress state. This allows for the analysis to be performed on a single repetitive cell under appropriate boundary conditions. However, all published results refer to cellular materials with repetitive modules possessing at least two orthogonal axes of symmetry. It seems that no general method of analysis of cellular material construed as infinite repetitive structures under periodic stresses for arbitrary repetitive cells is available, unless, as said, the repetitive cell possesses at least two perpendicular axes of symmetry. This is the subject matter of this study - to present a general exact technique to analyze infinite repetitive structures, with nonsymmetrical repetitive cells, under periodic stresses.

The correct analysis of shocks in a cellular material

Uncertainties in material properties, geometry, manufacturing processes, and operational environments are clearly critical at all scales (nano-, micro-, meso-, and macro-scale). The incorporation of reliability analysis is critical in designing material structures when material properties are uncertain. The concept of mesostructured or cellular materials is motivated by the desire to put material only where it is needed for a specific application. Typically, the cellular materials have superior structural compliant performance per weight than parts with bulk material or foams. This research develops a reliability-based synthesis method to design cellular material structures under random fields. The efficiency of the proposed framework is achieved with the combination of topology optimisation and stochastic local regression by utilising polynomial chaos expansion and Karhunen–Loeve transform. The effectiveness of the proposed framework is demonstrated with two examples including a ground truss structure and an automotive component which is composed of cellular material.

Dynamic stress–strain states for metal foams using a 3D cellular model

In the Part I of this study, namely the analytical part in Mazor et al. (1992), the governing equations of the phenomenon in which a planar shock wave collides head-on with a cellular material and interacts with it were developed using a Lagrangian approach. In addition, the numerical approach adopted by us during the numerical course of this study was briefly outlined there. The present part reports on experimental and numerical results of the head-on reflection of a planar shock wave with an open cell polyurethane foam. Foams as mentioned by Gibson and Ashby (1988) and summerized in Part I of this study by Mazor et al. (1992), are one of the two general types of cellular materials.

Rationale:Most cases of foot drop are known to result from lower motor neuron pathologies, particularly lumbar radiculopathy and peripheral neuropathy, including common peroneal neuropathy. To improve the prognosis of foot drop, it is important to quickly and accurately diagnose the etiology and provide appropriate treatment.Patient concerns:A 65-year-old female patient with a history of L4-5 intervertebral disc herniation presented with right foot drop that had developed 1 month previously.Diagnosis:Electrodiagnostic examination revealed common peroneal neuropathy combined with L5 radiculopathy, with the former being the main cause of the foot drop. MRI of the right knee was performed to identify the cause of the peroneal nerve lesion, which revealed an intraneural ganglion cyst in the common peroneal nerve.Interventions:The patient was treated by ultrasound-guided percutaneous cyst aspiration and corticosteroid injection into the decompressed ganglion, followed by strengthening exercise, electrical stimulation therapy, and prescription of an ankle foot orthosis.Outcomes:We confirmed regeneration of the injured peroneal nerve at the follow-up electrodiagnostic examination 12 weeks after the intervention. In addition, the manual motor power test demonstrated an increase in the ankle dorsiflexor function score by one grade.Lessons:Diagnosing the cause of foot drop can be difficult with multiple co-existing pathologies, and consideration of various possible etiologies is the key for appropriate diagnosis and treatment. In addition to imaging modalities such as MRI, electrodiagnostic examination can help to improve diagnostic accuracy. Intraneural ganglion cyst of the common peroneal nerve is rare, but should be considered as a possible cause of foot drop.

The topology optimization (TO) process has the objective to structurally optimize products in various industries, such as in biomechanical engineering. Additive manufacturing facilitates this procedure and enables the utility of advanced structures in order to achieve the optimal product design. Currently, orthopedic implants are fabricated from metal or metal alloys with totally solid structure to withstand the applied loads; nevertheless, such a practice reduces the compatibility with human tissues and increases the manufacturing cost as more feedstock material is needed. This article investigates the possibility of applying bioinspired lattice structures (cellular materials) in order to topologically optimize an orthopedic hip implant, made of Inconel 718 superalloy. Lattice structures enable topology optimization of an object by reducing its weight and increasing its porosity without compromising its mechanical behavior. Specifically, three different bioinspired advanced lattice structures were investigated through finite element analysis (FEA) under in vivo loading. Furthermore, the regions with lattice structure were optimized through functional gradation of the cellular material. Results have shown that optimal design of hip implant geometry, in terms of stress behavior, was achieved through functionally graded lattice structures and the hip implant is capable of withstanding up to two times the in vivo loads, suggesting that this design is a suitable and effective replacement for a solid implant.

The paper gives an overview of issues relating to the characterisation of the progressive collapse of core cellular materials used in sandwich construction. The specific structural application addressed is foreign object impact, and in this case the core cellular material is subject to multi axial stresses, progressive collapse and possible rupture. Crushable foams have been used for many years as core materials. Possible foam materials are based on polymers (e.g. Divinycell, Rohacell), metals (e.g. Alporas) and graphite. It has been shown that the mechanical properties of cellular materials, e.g. elastic behaviour, uniaxial crush and densification, are dependent on the cell geometry, on the cell size (foam density) and on the parent material.

Contamination of various food samples became one of the critical issues in food pathogen infection. Food pathogen can be detected by using digital polymerase chain reaction (PCR) and sequencing. These methods were reliable but consuming and take a longer time for detection. The present work describes the innovation to develop a technology to extract double-stranded deoxyribonucleic acid (dsDNA) from food samples and then denatured dsDNA into and single-strand DNA (ssDNA) for further use on the chip using microfluidic device. Microfluidic device is a lab-on-chip device that consist of microfluidic channels that provide paths for biomolecules to flow to individual point of care. DNA extraction is the process by which DNA is separated from proteins, membranes, and other cellular material contained in the cell from which it is recovered. Lysis solution is used in the process of extraction the DNA to break up the cells containing DNA from protein and other cellular materials. This extraction firstly be done in the most labour-intensive in obtaining the DNA biomolecules. Extraction methods may require an overnight incubation, may be a protocol that can be completed in minutes or a couple of hours by using a commercial kit. The disadvantages of the laboratory and commercial kit is due to time-consuming, poor cost-effectiveness, the need to use big laboratory and a complicated process which need an expertise to conduct the experiment and interpret the data. This research is proposed to design and fabricate a microfluidic device that has DNA extraction capabilities. In this research DNA extraction using a commercial kit will be used as a comparison for the quality of the result. The microfluidic device can be used in health care delivery system and will help the doctors in diagnostic process to identify disease of a patient rapidly. Other than that, the output extracted from microfluidic device will be used for DNA probe target interaction for diagnostic kit. The major advantage of microfluidic device is that it consumes less time compared to the conventional chemical methods.

A cellular material was proposed as an ideal candidate for multifunctional material achieving various optimal properties in many length scales. The superior performances on mechanical, thermal, electrical, and fluidic properties have been explored in analytic, numerical, and experimental studies. Since the cellular materials have wide range of potential applications in microscopic devices, characterization in small length scale gains more attentions recently. For this assessment, the atomistic approach as well as continuum approach becomes crucial to characterize its performance in multiscales. One of the key multifunctional features of the nanoporous microstructures would be high fluidic performance. Some studies investigated macroscopic transport properties, but less has been done to address the scale- and shape-dependent transport properties for their microscopic fluidics applications. In this study, we investigated complex flow patterns and transport properties of porous structures in microscopic scales. To address the geometry-dependent transport properties, a non-equilibrium molecular dynamics was employed in the atomistic scale. Various flow channels in the porous materials were introduced to address the size and shape effect of the flow patterns in small length scales.

Due to their excellent properties, including low weight, high stiffness and strength and heat insulation, cellular materials are widely used in engineering applications, especially in the aerospace and defense industries, as energy absorption devices. To improve the performance of the cellular material, optimization of the material property has attracted considerable research interest. The present research aims to investigate the influence of the gradient on the behavior of graded cellular material under impact conditions. This research program has four parts.

In this study, a dynamic enhancement stress model for cellular materials was derived from kinematics perspective, which directly reflected the influence of inertia effect on dynamic stress. Based on the proposed dynamic enhancement stress model, a densification strain calibration (DSC) analytical model with wider applicability for cellular materials was established, in which stress-dependent densification strain was employed. FE simulations for linear hardening and power hardening material under dynamic impact were conducted to validate DSC model. Comparing with idealized model (rigid, perfectly-plastic, locking model), dynamic plateau stress obtained by using of DSC model matched better with numerical results. Moreover, experimental results in published literature were employed to further confirm the reliability of DSC model in predicting projectile deceleration and final crushing depth. Finally, DSC model was used to predict dynamic response of gradient PVC foam, and the relative errors of final crushing depth to numerical results was within 8%.