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Humanitarian actors involved in physical rehabilitation, such as the International Committee of the Red Cross (ICRC), usually provide their beneficiaries with lower-limb prostheses comprising Solid Ankle Cushion Heel (SACH) feet as these are considered appropriate (price, durability, low profile to fit a majority of patients, appearance) and reliable for all ambulation levels. However, individuals in low-resource settings having higher ambulation abilities would greatly benefit from dynamic prosthetic feet with improved biomechanics and energy storage and release. Some attempts tried to address this increasing need (e.g. Niagara Foot) but most products proposed by large manufacturers often remain unaffordable and unsuitable to the context of low-resource settings. The design requirements and a price target were defined in partnership with the ICRC according to their initial assessment and used as a starting point for the development process and related technological choices. Numerical simulation and modeling were used to work on the design and to determine the required materials properties (mechanical, chemical, wear), and a cost modeling tool was used to select suitable materials and relevant processing routes (price vs. performance). A prosthetic foot comprising an internal keel made of composite materials, a filling foam, and a cosmetic shell with a foot shape was developed. Manufacturing processes meeting the cost criteria were identified and prototype feet were produced accordingly. These were successfully tested using a compression testing system before gait analyses were performed in the laboratory with non-amputees wearing testing boots. After validation in laboratory conditions, the prototype foot was tested in the field (Vietnam) with 11 trans-tibial unilateral amputees, who showed an increased mobility compared with the SACH foot. The collaboration of different research fields led to the development of a prosthetic foot which met the technical requirements determined by the ICRC's specific needs in its field of operation. The materials and selected production processes led to a manufacturing cost of less than 100 USD per part., Competing Interests: The authors have declared that no competing interests exist.

Hygro-thermal ageing of composite materials introduces a modification in the material properties of its constituents and the development of stresses that can lead to severe local damage like fracture of the reinforcing fibers and de-bonding of the latter from the matrix. The study of the complex stress field generated by this induced damage is helpful in designing more resistant materials. Modelling strain-stress filed in the vicinity of these discontinuities has led to the development of different analytical models like for instance shear lag models based on simplification assumptions. Recently the development of embedded optical sensors allowed to shed light on the assumptions made, since they can be used, at the same time, as reinforcement and sensors and thus being capable to give information on the strain distributions during the evolution of the damage. In this work a single fiber composite, whose reinforcement is an optical sensor, is used in order to investigate the complex strain field generated by the fiber fracture caused by the matrix swelling during water uptake.

This work validates the use of integrated polyvinylidene fluoride (PVDF) film sensors for dynamic testing, even after being subjected to UV-thermo-hygro-mechanical accelerated ageing conditions. The verification of PVDF sensors’ survivability in these environmental conditions, typically confronted by civil and military aircraft, is the main concern of the study. The evaluation of survivability is made by a comparison of dynamic testing results provided by the PVDF patch sensors subjected to an accelerated ageing protocol, and those provided by neutral non-aged sensors (accelerometers). The available measurements are the time-domain response signals issued from a modal analysis procedure, and the corresponding frequency response functions (FRF). These are in turn used to identify the constitutive properties of the samples by extraction of the modal parameters, in particular the natural frequencies. The composite specimens in this study undergo different accelerated ageing processes. After several weeks of experimentation, the samples exhibit a loss of stiffness, represented by a decrease in the elastic moduli down to 10%. Despite the ageing, the integrated PVDF sensors, subjected to the same ageing conditions, are still capable of providing reliable data to carry out a close followup of these changes. This survivability is a determinant asset in order to use integrated PVDF sensors to perform structural health monitoring (SHM) in the future of full-scale composite aeronautical structures. [ABSTRACT FROM AUTHOR]

The durability and reliability of lead-free solder joints depends on a large number of factors, like geometry, processing parameters, microstructure and thermomechanical loads. In this work, the nature and influence of the plastic constraints in the solder due to joining partners have been studied by parametric finite element simulation of solder joints with different dimensions. The apparent hardening due to plastic constraints has been shown to strongly depend on the solder gap to thickness ratio with an inversely proportional evolution. Due to interaction of several parameters, the macroscopic stress–strain constitutive law of lead-free solder materials should be determined in the most realistic conditions. In order to identify the elasto-plastic constitutive law of Sn–Ag–Cu solders, a sub-micron resolution Digital Image Correlation technique has been developed to measure the evolution of strain in solder joints during a tensile test. Experimental results of the stress–strain response of Sn–Ag–Cu solder joints have been determined for several solder gaps. The measured load–displacement curves have been used in an inverse numerical identification procedure to determine the constitutive elasto-plastic behaviour of the solder material. The effects of geometrical constraints in a real solder joint with heterogeneous stress and strain fields are then studied by comparing the apparent (constrained) and constitutive (non-constrained) stress–strain relationships. Once the size dependant constraining effects have been removed from the stress–strain relationship, the scale effects can be studied separately by comparing the constitutive elasto-plastic parameters of joints with a variable thickness. Experimental stress–strain curves (constrained and unconstrained) for Sn–4.0Ag–0.5Cu solder in joints of 0.25–2.4 mm gap are presented and the constraining and the size effects are discussed. [ABSTRACT FROM AUTHOR]

Long term durability of osseointegrated implants depends on bone adaptation to stress and strain occurring in proximity of the prosthesis. Mechanical overloading, as well as disuse, may reduce the stability of implants by provoking bone resorption. However, an appropriate mechanical environment can improve integration. Several studies have focused on the definition of numerical methods to predict bone peri-implant adaptation to the mechanical environment. Existing adaptation models differ notably in the type of mechanical variable adopted as stimulus but also in the bounds and shape of the adaptation rate equation. However, a general comparison of the different approaches on a common benchmark case is still missing and general guidelines to determine physically sound parameters still need to be developed. This current work addresses these themes in two steps. Firstly, the histograms of effective stress, strain and strain energy density are compared for rat tibiae in physiological (homeostatic) conditions. According to the Mechanostat, the ideal stimulus should present a clearly defined, position and tissue invariant lazy zone in homeostatic conditions. Our results highlight that only the octahedral shear strain presents this characteristic and can thus be considered the optimal choice for implementation of a continuum level bone adaptation model. Secondly, critical modeling parameters such as lazy zone bounds, type of rate equation and bone overloading response are classified depending on their influence on the numerical predictions of bone adaptation. Guidelines are proposed to establish the dominant model parameters based on experimental and simulated data., (Copyright © 2016 IPEM. Published by Elsevier Ltd. All rights reserved.)

Objectives: (i) To assess the effects of mechanical overloading on implant integration in rat tibiae, and (ii) to numerically predict peri-implant bone adaptation., Materials and Methods: Transcutaneous titanium implants were simultaneously placed into both tibiae of rats (n = 40). After 2 weeks of integration, the implants of the right tibiae were stimulated daily for 4 weeks with loads up to 5N (corresponding to peak equivalent strains of 3300 ± 500 με). The effects of stimulation were assessed by ex vivo mechanical tests and quantification of bone mineral density (BMD) in selected regions of interests (ROIs). Specimen-specific finite element models were generated and processed through an iterative algorithm to mimic bone adaptation., Results: Bilateral implantation provoked an unstable integration that worsened when mild (2-4N) external loads were applied. In contrast, a stimulation at 5N tended to "counterbalance" the harmful effects of daily activity and, if applied to well-integrated specimens, significantly augmented the implants' resistance to failure (force: +73% P < 0.01, displacement: +50% P < 0.01 and energy: +153% P < 0.01). Specimen-specific numerical predictions were in close agreement with the experimental findings. Both local and overall BMD variations, as well as the implants' lateral stability, were predicted with small errors (0.14 gHA/cm 3 and 0.64%, respectively)., Conclusions: The rats' daily activity detrimentally affects implant integration. Conversely, external stimulations of large magnitudes counterbalance this effect and definitively improve integration. These changes can be predicted using the proposed numerical approach., (© 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Laminates are produced by stacking prefabricated plies composed of fiber products. Within the aerospace industry, a ply thickness of 125 μ m is commonly regarded as the standard. Ply thicknesses of less than 100 μ m are generally considered as thin plies. Due to their ability to provide superior mechanical properties relative to conventional laminates thin-ply (TP) laminates are gaining interest in several high-tech industries. Although the research on TP laminates increased over the past few years, a comprehensive evaluation of the mechanical behavior of TP laminates accounting for the ply-thickness is an ongoing challenge due to the intricacies of ply interactions, and experimental difficulties. The mechanical response of fiber reinforced polymer laminates is governed by damage progression during loading, with the thickness of individual plies playing a crucial role in influencing the initiation and evolution of local cracks and failures. Therefore, in this study, the effective mechanical properties of carbon fiber reinforced polymer composite with varied ply thicknesses have been experimentally evaluated and the accumulation of the damage events has been monitored using acoustic emission measurements, utilizing a contactless laser vibrometer. In this experimental study, the ply thickness is increased in a systematic manner (ranging from 50 μ m to 200 μ m). Experimental investigation has been carried out in quasi-static tension and compression. The results show that unnotched TP laminates subjected to tensile loading demonstrate enhanced effective strength, attributed to less premature failure. Conversely, as the thickness of the lamina increases, there is a reduction in the overall strength of the laminate. However, in the case of the notched specimen lowest strength has been observed at a ply-thickness of 100 μ m in this study. Under compressive loading, unnotched and notched specimen tends to show similar mechanical behavior to unnotched specimens under tensile loading. The overall strength is raised with decreasing ply thickness. The findings from this study may be valuable for incorporating ply-thickness considerations into models for predicting the mechanical performance of laminates under dynamic loading. [ABSTRACT FROM AUTHOR]

In the present work, glass fiber-reinforced (GFR) composite specimens were fabricated using the vacuum-bag molding process. The properties related to the vibrational response of the fabricated composite plates, such as natural frequency, modal density, and damping loss factor (DLF), were investigated through both experimental and numerical approaches. The effects of different parameters, including boundary conditions (BCs), fiber orientations, laminate layer numbers, and aspect ratios, were comprehensively studied. It was found that the experimental and numerical results were in close agreement. For each case, finite element analysis was performed to determine the natural frequencies and mode shapes. Regarding the various BCs, the DLF was observed to be highest (0.47) for fully clamped BC and lowest (0.12) for free-free BC, whereas the modal density was highest (0.068) for cantilever BC and lowest (0.037) for fully clamped BC. In terms of different lamination schemes, the DLF was highest (0.42) for a plate with quasi-isotropic fibers and lowest (0.25) for a plate with unidirectional fibers, while the modal density was highest (0.068) for quasi-isotropic fibers and lowest (0.047) for unidirectional fibers. Regarding the plates with different laminate layers, the highest DLF (0.47) was observed for a plate with 16 layers, while the lowest DLF (0.33) was found in a plate with 8 layers. Conversely, the highest modal density (0.067) was observed for a plate with 8 layers, and the lowest (0.057) was noted for a plate with 16 layers. Lastly, considering aspect ratios, the highest DLF (0.48) was observed for an aspect ratio of 0.5, and the lowest (0.26) for an aspect ratio of 1.5. The highest modal density (0.09) was also observed for an aspect ratio of 0.5, while the lowest modal density (0.045) was for an aspect ratio of 1.5. [ABSTRACT FROM AUTHOR]

It is widely known that glass–epoxy laminates are renowned for their high stiffness, good thermal properties, and economic qualities. For this reason, composite materials find successful applications in various industrial sectors such as aerospace, astronautics, the storage sector, and energy. The aim of this study was to investigate the mechanical and thermal properties of composite materials comprising two different types of epoxy resin and three different hardeners, both at room temperature and under cryogenic conditions. The samples were produced at IZOERG (Gliwice, Poland) using a laboratory hot-hydraulic-press technique. During cyclic loading–unloading tests, degradation up to a strain level of 0.6% was observed both at room temperature (RT) and at 77 K. For a glass-reinforced composite with YDPN resin (EP_1_1), the highest degradation was recorded at 18.84% at RT and 33.63% at 77 K. We have also investigated the temperature dependence of thermal conductivity for all samples in a wide temperature range down to 5 K. The thermal conductivity was found to be low and had a relative difference of up to 20% among the composites. The experimental results indicated that composites under cryogenic conditions exhibited less damage and were stiffer. It was confirmed that the choice of hardener significantly influenced both properties. [ABSTRACT FROM AUTHOR]

This work examines the effects of varying weight percentages (0.1, 0.3, and 0.5 wt%) of pristine and functionalized graphene (–COOH, –OH, and –NH2) on the compression and impact strength of carbon fiber-reinforced polymer (CFRP) composite laminates. The laminates were fabricated in two different stacking sequences of carbon fiber in composite laminates, i.e., 0/90° and 0/90/ ± 45° by hand layup technique. Experimental results showed that the inclusion of graphene in epoxy matrix enhances the compressive strength and impact characteristics, namely impact force, displacement, energy profile, and damage behavior of CFRP laminates. Moreover, the orientation of carbon fiber layers in laminates affects the internal damage behavior of specimens and the delamination between fiber layers. The maximum improvements of 38.65 and 76.82% are noticed in the compressive strengths of 0/90° and 0/90/ ± 45° stacked laminates with the reinforcement of 0.1 wt% of pristine and 0.3 wt% of –COOH functionalized graphene to epoxy, respectively. In summary, the test results have shown that using graphene as a reinforcing filler can significantly improve the impact performance of CFRP composites. [ABSTRACT FROM AUTHOR]

Implanted rat bones play a key role in studies involving fracture healing, bone diseases or drugs delivery among other themes. In most of these studies the implants integration also depends on the animal daily activity and musculoskeletal loads, which affect the implants mechanical environment. However, the tissue adaption to the physiological loads is often filtered through control groups or not inspected. This work aims to investigate experimentally and numerically the effects of the daily activity on the integration of implants inserted in the rat tibia, and to establish a physiological loading condition to analyse the peri-implant bone stresses during gait. Two titanium implants, single and double cortex crossing, are inserted in the rat tibia. The animals are caged under standard conditions and divided in three groups undergoing progressive integration periods. The results highlight a time-dependent increase of bone samples with significant cortical bone loss. The phenomenon is analysed through specimen-specific Finite Element models involving purpose-built musculoskeletal loads. Different boundary conditions replicating the post-surgery bone-implant interaction are adopted. The effects of the gait loads on the implants integration are quantified and agree with the results of the experiments. The observed cortical bone loss can be considered as a transient state of integration due to bone disuse atrophy, initially triggered by a loss of bone-implant adhesion and subsequently by a cyclic opening of the interface., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Biomaterials are constructed from limited sets of building blocks but exhibit extraordinary and versatile properties, because hierarchical structure formation lets them employ identical supramolecular motifs for different purposes. Here we exert a similar degree of structural control in synthetic supramolecular elastomers and thus tailor them for a broad range of thermomechanical properties. We show that oligopeptide-terminated polymers selectively self-assemble into small aggregates or nanofibrils, depending on the length of the oligopeptides. This process is self-sorting if differently long oligopeptides are combined so that different nanostructures coexist in bulk mixtures. Blends of polymers with oligopeptides matching in length furnish reinforced elastomers that exhibit shear moduli one order of magnitude higher than the parent polymers. By contrast, novel interpenetrating supramolecular networks that display excellent vibration damping properties are obtained from blends comprising non-matching oligopeptides or unmodified polymers. Hence, blends of oligopeptide-modified polymers constitute a toolbox for tailored elastomers with versatile properties.

The authors propose a protocol to derive finite element (FE) models from micro computer tomography scans of implanted rat bone. A semi-automatic procedure allows segmenting the images using specimen-specific bone mineral density (BMD) thresholds. An open-source FE model generator processes the segmented images to a quality tetrahedral mesh. The material properties assigned to each element are integrated from the BMD field. Piecewise, threshold-dependent density-elasticity relationships are implemented to limit the effects of metal artefacts. A detailed sensitivity study highlights the coherence of the generated models and quantifies the influence of the modelling parameters on the results. Two applications of the protocol are proposed. The stiffness of bare and implanted rat tibiae specimens is predicted by simulating three-point bending and inter-implant displacement, respectively. Results are compared with experimental tests. The mean value and the variability between the specimens are well captured in both tests.

Purpose: To assess the effect of external mechanical microstimuli of controlled magnitude on the microarchitecture of the peri-implant bone beds in rat tibiae., Materials and Methods: Tibiae of forty rats were fitted with two transcutaneous titanium cylinders. After healing, the implants were loaded to 1 to 3 N, five days/week for four weeks. These force levels translated into intraosseous strains of 700 ± 200 με, 1400 ± 400 με, and 2100 ± 600 με. After sacrifice, the implants' pullout strength was assessed. Second, the bone's microarchitecture was analyzed by microcomputed tomography (μCT) in three discrete regions of interest (ROIs). Third, the effect of loading on bone material properties was determined by nanoindentation., Results: The trabecular BV/TV significantly increased in an ROI of 0.98 mm away from the test implant in the 1 N versus the 3 N group with an opposite trend for cortical thickness. Pull-out strength significantly increased in the 2 N relatively to the nonstimulated group. Higher values of E-modulus and hardness were observed in the trabecular bone of the 2 N group., Conclusion: The in vivo mechanical loading of implants induces load-dependent modifications in bone microarchitecture and bone material properties in rat tibiae. In pull-out strength measurements, implant osseointegration was maximized at 2 N (1400 ± 400 με).