Takenobu Sakai

Evaluation of damage progression and mechanical behavior under compression of bone cements containing core-shell nanoparticles by using acoustic emission technique.

In this work, the effect of the incorporation of core-shell particles on the fracture mechanisms of the acrylic bone cements by using acoustic emission (AE) technique during the quasi-static compression mechanical test was investigated. Core-shell particles were composed of a poly(butyl acrylate) (PBA) rubbery core and a methyl methacrylate/styrene copolymer (P(MMA-co-St)) outer glassy shell. Nanoparticles were prepared with different core-shell ratio (20/80, 30/70, 40/60 and 50/50) and were incorporated into the solid phase of bone cement at several percentages (5, 10 and 15 wt%). It was observed that the particles exhibited a spherical morphology averaging ca. 125 nm in diameter, and the dynamic mechanical analysis (DMA) thermograms revealed the desired structuring pattern of phases associated with core-shell structures. A fracture mechanism was proposed taking into account the detected AE signals and the scanning electron microscopy (SEM) micrographs. In this regard, core-shell nanoparticles can act as both additional nucleation sites for microcracks (and crazes) and to hinder the microcrack propagation acting as a barrier to its growth; this behavior was presented by all formulations. Cement samples containing 15 wt% of core-shell nanoparticles, either 40/60 or 50/50, were fractured at 40% deformation. This fact seems related to the coalescence of microcracks after they surround the agglomerates of core-shell nanoparticles to continue growing up. This work also demonstrated the potential of the AE technique to be used as an accurate and reliable detection tool for quasi-static compression test in acrylic bone cements.

Damage accumulation behavior of non-crimp fabric-reinforced epoxy composite under static and cyclic tensile loading

A non-crimp fabric with a stacking sequence of [0°,+45°,90°,−45°] embedded in epoxy resin matrix was analyzed. Samples for mechanical test were obtained from laminates at different orientations depending on the textile architecture direction at 0°, 45°, and 90° in order to study the relationship between damage initiation and propagation with fabric geometry. Tension mode tests (static and cyclic) were carried out to evaluate the evolution of damage using as a main tool, the acoustic emission technique that allows monitoring the mechanical behavior of the materials during the test in ‘real time’. Results show that there is a remarkable mechanical influence of the reinforcement textile in the composite and that damage generation and progression (mechanisms of fracture) is highly dependent of the direction in which the stress is applied in relation with the architecture of the fabric. In static tensile mode, samples at 0° exhibited better mechanical parameters than samples at 90°, while at 45° orientation was lesser. The effect of textile geometry was demonstrated to have an influence in such mechanisms. In cyclic tensile mode, Kaiser effect is observed at low stresses, while the experimental results showed that the Felicity effect became clearer along with the increasing of stress level.

Evaluation of Mechanical Behaviour of Bone Cements by Using Acoustic Emission Technique

Biomaterials such as acrylic bone cements are widely applied in orthopaedic surgery for the fixation of artificial joints. Therefore, the mechanical behavior of such materials under external stresses is of special interest in order to achieve long-term in vivo performance. Fracture process can be attributed to diverse random microscopic damage modes. As the load increases, new damage modes appear and the existing ones can transition into others depending on the nature of the material. However, limitation exists in detailing the understanding of the micromanage initiation and development, and, consequently, in optimizing biomaterials performance. This paper focuses in the study of the emission of acoustic signals from bone cements in order to monitor the evolution of the internal defects that are believed to dominate in vivo failure.

Effect of Crystallinity and fiber volume fraction on Creep Behavior of Glass Fiber Reinforced Polyamide

Thermoplastic Polyamide (PA) is known as Nylon®, and its FRP are one of the engineering plastics. It is very important for them to reveal accurately the visco-elastic behavior. Furthermore, PA is a crystalline polymer, and it is necessary to consider the effect of crystallization on mechanical properties. The purpose of this study was to make clear the effect of crystallization and fiber volume fraction on creep behavior of PA and its composites. The creep test was performed using the materials which adjusted crystallinity on each fiber volume fraction. As a result, these materials conformed to Arrhenius type of time-temperature superposition principle, and these effects on creep behavior had the time retardation effect. To compare the creep behavior on these effects, we made the grand master curves for crystallinity and fiber volume fraction. Obtained two grand master curves were compared each other, the shapes of these curves are similarly, and we can superposed them. It is therefore, the creep behavior including each conditions have the same behavior. Using these curves and shift factors, we can calculate the creep behavior, and be able to estimate the creep behavior with the effect of arbitrary time, temperature, crystallinity and fiber contents.

Effect of Viscoelastic Behavior on Electroconductivity of Recycled Activated Carbon Composites

In the Waterworks Bureau, the activated carbon has been used for filtering water. After the life service of activated carbon, it is normally disposed. This work focuses on the processing of a composite material in order to recycle these wasted carbon particles. These activated carbons were used for the filler of composite materials, and a composite with carbon contents of 10% ~ 60% was manufactured and characterized. They exhibited electroconductive behavior because of the carbon particles used as fillers. The electroconductivity have an intimate relationship with the strain of the material. However, because of the composite viscoelasticity, the electroconductivity presented changes by their stress relaxation behavior with the same strain. In this study, it was revealed the relationship between the viscoelasticity and the electroconductivity of recycled activated carbon composites.

An Experimental-Numerical Hybrid Approach to Analysis of Fiber-Matrix Interfacial Stresses

In this study, the single fiber composite was used to evaluate the stress transfer between a single fiber and a matrix. Single steel fiber was inserted to the epoxy resin, and it was applied the tensile load. Applied load was from 0 N to 177 N, and then the photoelastic images were taken by a digital CCD camera. On the photoelastic analysis, the stress separation was carried out using an experimental-numerical hybrid method. The boundary conditions for a local finite element model, that is, the tractions along boundaries are inversely determined from photoelastic fringes. After determining the boundary conditions for the local finite element model, the stresses can be obtained by finite element direct analysis. Using this input data and the finite element model of analysis region, not only the stress but also the strain distributions were obtained. Consequently, by using the photoelasticity data and geometric data for input data of finite element analysis, accurate data was obtained by the hybrid method for stress separation.

Fracture behavior of wasted activated carbon powder composites

At the Waterworks Bureau (Tokyo Metropolitan Government), activated carbon has been used for filtering water. After being used for the filtering process, it is normally disposed or burned for thermal recycling. However, CO2 emissions occur during the thermal recycling. This work focuses on the identification of mechanical behavior of recycled wasted activated carbon (WAC) in order to elaborate smart materials having mechanical–electrical functions. Acoustic emission technique (AE) was used intensively as characterization support in which sensors were attached to detect microdamage during bending tests. At first, the resonant frequencies of the specimens were measured using the through-transmission test. The resonant frequencies of the specimens containing low weight fractions of WAC powder were less in comparison to the frequencies of the specimens with higher volume fraction. The frequency analysis was carried out with the projected wavelet transform on the signals detected during bending tests. Obtained data showed that, typically, the first major peaks showed the resonant frequency of the sensors, while the second major peaks exhibited signals indicative of resin cracking. The surfaces of the fractured specimens were analyzed by optical microscopy in order to visualize the crack formation and propagation on the activated carbon composite under flexural stresses. Consequently, fractographic and AE analyses provide better understanding of the failure mechanisms involved.

Biomechanical contribution of elastin on wound skin of hairless mice

Dynamic mechanical analysis (DMA) was carried out to understand the effect of the application of elastin on wound skin of hairless mice. Wound group, placebo group, and elastin group were selected to evaluate that effect. As the results of DMA testing, the wound and the placebo groups showed lower storage and loss moduli than the elastin group. On the result of loss tangent, there is a small difference between these groups, and the elastin group showed the lowest value. Consequently, the application of elastin on the wounded skin showed the possibility for recovery the skins.

Preliminary study of optimal measurement location on vibroarthrography for classification of patients with knee osteoarthritis.

[Purpose] The aims of the present study were to investigate the most suitable location for vibroarthrography measurements of the knee joint to distinguish a healthy knee from knee osteoarthritis using Wavelet transform analysis. [Subjects and Methods] Participants were 16 healthy females and 17 females with severe knee osteoarthritis. Vibroarthrography signals were measured on the medial and lateral epicondyles, mid-patella, and tibia using stethoscopes with a microphone while subjects stood up from a seated position. Frequency and knee flexion angles at the peak wavelet coefficient were obtained. [Results] Peak wavelet coefficients at the lateral condyle and tibia were significantly higher in patients with knee osteoarthritis than in the control group. Knee joint angles at the peak wavelet coefficient were smaller (more extension) in the osteoarthritis group compared to the control group. The area under the receiver operating characteristic curve on tibia assessment with the frequency and knee flexion angles was higher than at the other measurement locations (both area under the curve: 0.86). [Conclusion] The tibia is the most suitable location for classifying knee osteoarthritis based on vibroarthrography signals.

Observation of Fiber-Matrix Interfacial Stresses Using Phase-Stepping Photoelasticity

In this study, the single fiber composite was used to evaluate the stress transfer between a single fiber and a matrix. Single steel fiber was inserted to the epoxy resin, and it was applied the tensile load. Applied load was from 0 N to 177 N, and then the photoelastic images were taken by a digital CCD camera. In the photoelastic analysis, the phase-stepping and phase-unwrapping technique were used to measure the stress difference distribution more accurately. Obtained data were included the 3D information, therefore, we converted the stress difference data, including the 3D information to 2D photoelasticity using the geometrical information. The maximum shear stress was placed on the side surface of the steel fiber near the end of fiber, and the maximum normal stress difference was measured near the surface of the end of the fiber. The results of stress distribution on the interface between the fiber and the resin indicated that the stress concentration was observed in the middle part of the end of the fiber and the side surface near the end of the fiber.