Mechanical Characterization Studies Research Articles

Bone neoformation of a novel porous resorbable Si-Ca-P-based ceramic with osteoconductive properties: physical and mechanical characterization, histological and histomorphometric study.

The aims of the present work were to study a new porous Nurse's A ceramic (Si-Ca-P-based material) bone substitute and examine its mechanical properties invitro and the biocompatibility, osteoconductivity and resorption process invivo. Porous ceramic scaffolds were prepared by solid-state reaction and implanted in critical-sized defect created in 15 NZ rabbits. Strength values were determined by the diametrical compression of disk test. Weibull analyses were performed following the European Standard for technical ceramics EN-843-5: 1996, considering 90% of confidence intervals. Results were correlated with scanning microscope observations of fracture surfaces. Implanted scaffolds were characterized by histological and histomorphometric point of view. The parameters of the Weibull distribution of strength, determined by diametrical compression of disks, were modulus m=13, and characteristic strength σ0 =0.60 MPa (90% confidence limit: m=7.2-17.6, σ0 =0.570-0.578). Porous calcium silicophosphate scaffolds showed significantly more bone formation in the pores and in the periphery of the implant than the control group. Histomorphometric analysis revealed that the ceramic scaffold (62.23±0.34*) produced higher values of bone-to-implant contact (BIC) percentages (higher quality, closer contact); moreover, defect closure was significative in relation with control group. The porous calcium silicophosphate ceramic is biocompatible, partially resorbable and osteoinductive material. This rabbit study provides radiological and histological evidences confirming the suitablity of this new material for bone tissue regeneration on critical defects.

Mechanical characterization and fractographic study of epoxy–kaolin polymer nanocomposites

In this work the mechanical behavior of composite materials formed by a diepoxy–diamine (epoxy) thermosetting matrix filled with kaolin intercalated with ethylenediamine (K–EDA) was studied. Fracture toughness experiments showed that an addition of 2wt% K–EDA to the epoxy matrix causes an approximately 24% increase in the critical stress intensity factor (KIC). The study of fracture mechanisms was completed using the double-notch four-point-bending test. The presence of kaolin particles in the matrix induces crack branching and deflection mechanisms. Furthermore, observation of the fracture surface revealed the presence of tails near kaolin particles, which is consistent with crack-pinning. The present study indicates that kaolin clay can be effective in toughening epoxy at small quantities if it is reasonably well dispersed.

Mechanical characterizations of composite material with short Alfa fibers reinforcement

This paper presents an experimental study of mechanical characterization of composite materials, reinforced with short vegetable fibers and obtained by a new implementation of their extraction from Alfa bundles. From many previous studies on the chemical treatments of these fibers, to improve the interfacial adhesion; an alkaline chemical treatment optimization under different durations was applied to the fibers and a fatigue behavior analysis was conducted under an acoustic control of polypropylene matrix samples with different volume fiber fractions. An SEM observation of the fibers morphology and of the interfacial characteristics of the material during the test before and after the optimized alkaline treatment showed the impact of this treatment by the important increase of the Young module from 28.67% to 132.22% with respect to the virgin PP and of the traction resistance from 11.34% to 30.14% with respect to the non treated fibers for 30%.

29pm2-F-2 微小引張試験片の2次元歪解析による機械特性評価技術の検討

29pm2-F-2 微小引張試験片の2次元歪解析による機械特性評価技術の検討

The mechanical characterization study of mitral annulus at different sites in normal adults using ultrasonic dual pulse-wave Doppler

Objective To define the mechanical features of mitral annulus at various sites,and to investigate the specific mechanics characterization at different mitral annulus sites in evaluation consequences of left ventricular function by dual pulse-wave Doppler (DPW) technology.Methods The DPW spectrums were obtained at lateral and aboral interval,anterior and inferior and posterior mitral annular from 112 normal adults.The peak systolic velocity (Sm),peak early diastolic velocity (Em),peak late diastolic velocity (Am),the beginning time of the peak and the time to peak were measured,and E/A,Em/Am,E/Em,left ventricular ejection fraction (LVEF) and left ventricular fractional shortening (LVFS) were computed.Results 1)Sm,Em,Am and Em/Am measured in the free wall annulus were significantly greater than measured in the interval annulus of mitral annular sites.However,E/Em was opposited (P ＜ 0.05).Sm of the posterior wall mitral annulus accelerated frist and experienced shortest duration in all the mitral annular sites (P ＜ 0.01).There were no significant differences of Em time parameters among different mitral annulus sites.Am of the beginning time and peak time in the free wall annulus were significantly longer than that in the interval annulus of anterior mitral annular sites.However,the acceleration time was opposited(P ＜0.05).2) Sm was correlated with LVEF and LVFS (r =0.243 and r =0.227,P ＜0.01) only at the posterior mitral annular site,Em/Am of anterior and posterior wall mitral annulus had the highest correlations with mitral orifice flow E/A(r =0.545 and 0.545 respectively,P ＜ 0.01).Conclusions There are significant differences among the mechanics patterns at different mitral annulus sites in normal adults.The mechanics characterization at different mitral annulus sites have different conclusions of left ventricular function. Key words: Echocardiography; Ventricular function,left; Mitral annulus; Dual pulse-wave Doppler

Continuum Damage Mechanics (CDM) Based Local Approach to the Sheet-Bulk Metal Formability Prediction

Since sheet-bulk metal forming processes inherit properties of both sheet and bulk metal forming processes, their analysis requires on one side following certain methods conventionally devised in these process classes analyses whereas on the other side leaving certain customs out. For instance, inherent anisotropy of the rolled sheet has to be taken into account whereas due to non-vanishing out of plane stress component, analysis with thin shells using the plane stress state assumption is no more applicable. Similarly, methods based on necking instabilities, i.e. forming limit diagrams, which are typically used in sheet metal formability assessment; fall short in sheet-bulk metal formability prediction. In the present study, we propose a local approach to fracture, more specifically a phenomenologically based Lemaitre variant CDM model, devised frequently in bulk metal forming analysis, as an alternative. For this purpose, a combined nonlinear isotropic-kinematic hardening plasticity with Hill48 type initial anisotropy is fully coupled with isotropic damage. Together with the concept of effective stress and equivalent strain principle, quasi-unilateral damage evolution is used, where the energetic contribution of the compressive stress state to the damage driving force is scaled with a so-called crack closure parameter, . For the quasi unilateral damage evolution is inactive whereas for it is fully active which completely suppresses the development of damage under compressive stress states. The framework devises state coupling between elasticity and damage and kinematic coupling between plasticity and damage which increases the relative effect of on the eventual damage development. To this end, a direct extension to the finite strains for metal forming analysis is realized using a corotational formulation and the developed framework is implemented as a VUMAT subroutine for ABAQUS Explicit. For evaluation of the predictive capability of the model, teeth forming process results for DC04 reported in Soyarslan et al. 2011, An Experimental and Numerical Assessment of Sheet-Bulk Formability of Mild Steel DC04, Journal of Manufacturing Science and Engineering, Vol. 133 6, (2011) S. (061008) 1-9, are used. Mechanical material characterization studies are realized using a hybrid experimental-numerical procedure. This methodology relies on minimizing the difference between the experimentally handled global clamp force demand diagrams and the diagrams from the simulations at the complete range of the experiments involving fracture. As known finite element solutions with softening material models are prone to pathological mesh dependence. For this fact, a crack band method is used where the minimum element size, as a controlling parameter of the localization size, is also fitted through the characterization studies and identically used in the process simulations. The simulations show that a correct prediction of the zone and time of fracture is possible for the selected process whereas since the teeth formation process is mainly a compressive process, once the quasi-unilateral damage development is not used, i.e. for , a premature crack prediction is recorded which is not compatible with the experimental findings.

Influence of Y2O3 particles on mechanical properties of magnesium and magnesium alloy (AZ91D)

Nowadays, research studies and industrial requirements are directed toward the goals of achieving environmental friendliness, energy savings, and reduced weight. Magnesium and magnesium alloys are well suited for structural and automotive applications owing to their lightweight. However, the reduced hardness and strength of these alloys do pose problems in exploiting their usage. These impediments of lightweight metal matrix can be alleviated by reinforcing hard-phase particles. Different volume percentages of Y2O3 particles (average grain size 5 µm) were added as reinforcements in pure magnesium and magnesium alloy (AZ91D) and the composites were processed through the two-step stir-casting technique. Mechanical and metallurgical characterization studies were carried out on the stir-cast composites under as-cast and heat-treated conditions. Uniform distribution of yttria particles in magnesium and magnesium alloy matrix was observed through scanning electron micrographs. Macro and microhardness tests revealed the increased hardness with the increased amount of yttria reinforcement.

FATIGUE BEHAVIOR CHARACTERIZATION OF NITINOL FOR PERIPHERAL STENTS

Nitinol stents are nowadays widely used for the treatment of occlusions in peripheral arteries. However, the expansion of this indication has also highlighted some complications. In particular, the patient daily activities expose the peripheral arteries to large and cyclic deformations which may cause long-term failure of the device and consequently re-occlusion of the artery. Accordingly, the assessment of the stent fatigue rupture is of primary importance to assure the effectiveness of stenting procedure. However the fatigue behavior characterization of Nitinol for peripheral stent is a quite difficult problem because of the complexity of the in vivo solicitations the stent is subjected to and the strong nonlinearity in the material response. In this paper we approached the problem in two steps: (i) in the first step the study of the stent solicitations under realistic (physiological) conditions was performed through the use of numerical simulations which allowed sophisticated patient-specific models of the stenting procedure; (ii) in the second step, the previous results were used for the design of an experimental campaign and the following execution of the tests for the material mechanical characterization and fatigue life study. The tests were performed on Nitinol specimens derived from the same tubes used for producing a commercial peripheral stent and created following the same procedure employed for the device. As a consequence of the small dimension of the specimens, a preliminary design of the experimental test set-up was also required. The obtained results allowed a sufficiently accurate characterization of the stent material fatigue behavior in the range of interest.

Fabrication and design aspects of high-temperature compact diffusion bonded heat exchangers

Abstract The Very High Temperature Reactor (VHTR) using gas-cooled reactor technology is anticipated to be the reactor type for the Next Generation Nuclear Plant (NGNP). In this reactor concept with an indirect power cycle system, a high-temperature and high integrity Intermediate Heat Exchanger (IHX) with high effectiveness is required to efficiently transfer the core thermal output to a secondary fluid for electricity generation, hydrogen production, and/or industrial process heat applications. At present, there is no proven IHX concept for VHTRs. The current Technology Readiness Level (TRL) status issued by NGNP to all components associated with the IHX for reduced nominal reactor outlet temperatures of 750–800 °C is 3 on a 1–10 scale, with 10 indicating complete technological maturity. Among the various potential IHX concepts available, diffusion bonded heat exchangers (henceforth called printed circuit heat exchangers, or PCHEs) appear promising for NGNP applications. The design and fabrication of this key component of NGNP with Alloy 617, a candidate high-temperature structural material for NGNP applications, are the primary focus of this paper. In the current study, diffusion bonding of Alloy 617 has been demonstrated, although the optimum diffusion bonding process parameters to engineer a quasi interface-free joint are yet to be determined. The PCHE fabrication related processes, i.e., photochemical etching and diffusion bonding are discussed for Alloy 617 plates. In addition, the authors’ experiences with these non-conventional machining and joining techniques are discussed. Two PCHEs are fabricated using Alloy 617 plates and are being experimentally investigated for their thermal-hydraulic performance in a High-Temperature Helium Facility (HTHF). The HTHF is primarily of Alloy 800H construction and is designed to facilitate experiments at temperatures and pressures up to 800 °C and 3 MPa, respectively. Furthermore, some preliminary microstructural and mechanical property characterization studies of representative diffusion bonded Alloy 617 specimens are presented. The characterization studies are restricted and less severe from an NGNP perspective but provide sufficient confidence to ensure safe operation of the heat exchangers in the HTHF. The test results are used to determine the design operating conditions for the PCHEs fabricated.

Dynamic mechanical characterization of asphalt concrete mixes with modified asphalt binders

The primary objective of this work is to characterize and compare the dynamic mechanical behavior of asphalt concrete mixes with styrene butadiene styrene (SBS) polymer and crumb rubber modified asphalt binders with the behavior of mixes with unmodified viscosity grade asphalt binders. Asphalt binders are characterized for their physical and rheological properties. Simple performance tests like dynamic modulus, dynamic and static creep tests are carried out at varying temperatures and time. Dynamic modulus master curves constructed using numerical optimization technique is used to explain the time and temperature dependency of modified and unmodified asphalt binder mixes. Creep parameters estimated through regression analysis explained the permanent deformation characteristics of asphalt concrete mixes. From the dynamic mechanical characterization studies, it is found that asphalt concrete mixes with SBS polymer modified asphalt binder showed significantly higher values of dynamic modulus and reduced rate of deformation at higher temperatures when compared to asphalt concrete mixes with crumb rubber and unmodified asphalt binders. From the concept of energy dissipation, it is found that SBS polymer modification substantially reduces the energy loss at higher temperatures. Multi-factorial analysis of variance carried out using generalized liner model showed that temperature, frequency and asphalt binder type significant influences the mechanical response of asphalt concrete mixes. The mechanical response of SBS polymer modified asphalt binders are significantly correlated with the rutting resistance of asphalt concrete mixes.

Study of Mechanical Characterization of Ceramic Specimens from a Brazilian Test Adaptation

The Brazilian Test is easy to perform and its result is the tensile strength of the material provided certain ratios are fulfilled between the diameter of the sample, the load bearing width and the characteristic length of the material. In this paper we present experimental results obtained from 8 mm-thick ceramic cylinders whose diameter was 40 mm in length. The cylinders were obtained from a standard type of clay by pressing and subsequent baking at 900 oC. We made a complete mechanical characterization of the material, which included obtaining fracture properties, and a numerical simulation of the Brazilian test based on the cohesive crack model. Numerical results confirm that the size and boundary conditions chosen for the test are adequate to get the actual tensile strength of construction ceramics, which prove that this type of test is useful to compare the strength of several types of construction ceramics in a simple and convenient way. Besides, it requires a very small amount of material to prepare the specimen

Nanoengineering Ultra-High-Performance Concrete with Multiwalled Carbon Nanotubes

Ultra-high-performance concretes (UHPCs) are characterized by extremely high packing densities. These densities can be achieved with optimization of grain size distribution by incorporating a homogeneous gradient of fine and coarse particles during mixing. Addition of steel fibers can increase the ductility under tensile loading tremendously. The packing density is a key parameter for the high bond strength between steel fibers and the UHPC matrix. The objective of this study is twofold: to enhance the behavior of the bond between the steel fibers and the matrix by increasing packing density with the inclusion of nanometer-sized particles while preserving the workability of the concrete mix. Multiwalled carbon nanotubes (MWNTs) were chosen for their unique physical and impressive mechanical properties (i.e., ultimate strength, stiffness, and ductility). However, because of the nanotubes’ inherent tendency to agglomerate, an extensive study was conducted to optimize their dispersion in solutions suitable for concrete mixing. An experimental validation study was then conducted to explore the effects of incorporating MWNTs in mixes with only 0.022% by cement weight and how they affect the bond behavior of two different high-strength steel fibers. Mechanical characterization studies revealed that low concentrations of MWNTs can significantly improve the bonding behavior of single pulled-out high-strength steel fibers. No conclusive evidence can be drawn with regard to MWNTs’ influence on the UHPCs’ compressive and bending strengths [i.e., 200 and 13 MPa (30 and 1.9 ksi), respectively].

Characterization of Q & T Steel Poleshoes Manufactured by Sand Casting

Abstract This paper presents a study of the microstructural and mechanical characterization of the GS 35 CrMoV 10 4 alloy employed in the manufacture of sand-cast poleshoes for 4-pole synchronous electric power generators working at a frequency of 60 Hz. In addition, the most appropriate treatment for ensuring compliance with the technical specifications defined in DIN Standard No. 1.7755 has been designed.

Growth and characterization studies of ferroelectric diglycine nitrate (DGN) single crystals

Single crystals of diglycine nitrate [(NH 2CH 2COOH) 2HNO 3] (DGN), a ferroelectric material with Curie temperature 206 K, were grown in silica gel at room temperature by the solubility reduction method at room temperature (39 °C). Bulk crystals of dimension 21 mm × 18 mm × 11 mm have been grown by optimizing the growth conditions. The grown crystals have been characterized by structural, optical and mechanical characterization studies. Fourier transform infrared (FTIR) spectral analysis reveals that the crystal consists of all functional vibrational groups. FT-Raman spectrum, which is complement to FTIR studies, has also been recorded. Surface analysis by SEM reveals that the crystal absorbs water from the moisture. The optical transparency range and the lower cut-off of UV transmission were identified from the recorded UV–vis spectrum of DGN. The UV cut-off wavelength of DGN is 286 nm. Thermal analysis of the crystalline sample was performed by TGA and DTA methods. The crystal is thermally stable up to 217 °C. The Vicker's microhardness value of DGN crystal is decreases with increase of load. The work hardening coefficient ( n) of diglycine nitrate was determined using the least squares fit method and found to be 1.5.

Influence of the yttria content on the mechanical properties of Y 2O 3-ZrO 2 thin films prepared by EB-PVD

A mechanical characterization study of the whole range (ZrO 2) 1− x –(Y 2O 3) x system is presented for thin film samples. Films have been prepared by Electron Beam Physical Vapour Deposition (EB-PVD) on Si(1 0 0) substrates. The mechanical characterization, obtained from nanoindentation and Brillouin Light scattering (BLS) techniques, shows a monotonous behaviour between the two pure compounds of the series except for the film with 0.08 Y 2O 3 molar content of yttria-stabilized zirconia (YSZ) solid solution that presents an anomalous hard value. Additionally, BLS is presented as an alternative technique to the study of the mechanical properties of this system.

Improving mechanical properties of magnesium using nano-yttria reinforcement and microwave assisted powder metallurgy method

In the present study, magnesium nanocomposites were fabricated by using magnesium as matrix and nano-yttria as reinforcement. Composites with 0.5 and 2.0 wt.% of Y 2O 3 were synthesized through powder metallurgy route incorporating microwave assisted rapid sintering technique followed by hot extrusion. Microstructural characterization revealed reasonably uniform distribution of Y 2O 3 particulates in the matrix and the presence of nanopores. Thermomechanical analysis revealed significant reduction in CTE of magnesium as a result of presence of yttria nanoparticulates. Mechanical characterization studies revealed that hardness, 0.2% yield strength, ultimate tensile strength, work of fracture and ductility increased with increasing amount of reinforcement from 0.5 to 2.0 wt.%. The studies revealed that the best combination of mechanical properties is realized from the composite containing 2.0 wt.% of yttria.

Enhancing the mechanical properties of pure aluminum using hybrid reinforcement methodology

In this study, novel aluminum based hybrid composite was synthesized using a cost effective disintegrated melt deposition technique followed by hot extrusion. Coupled use of continuous and interconnected galvanized iron mesh and SiC particulates in aluminum matrix was explored. Microstructural characterization revealed good interfacial integrity between the matrix and reinforcements. Results of thermal mechanical analysis indicate a decrease in the average coefficient of thermal expansion of the aluminum matrix with the use of both singular and hybrid reinforcements. Mechanical characterization studies revealed that the coupled use of galvanized iron mesh and SiC particulates in aluminum matrix led to better improvement in the macrohardness, 0.2% yield strength and UTS when compared to unreinforced aluminum and singularly reinforced composites. An attempt is made to correlate the presence of hybrid reinforcements in the aluminum matrix with the physical and mechanical behavior of the end composite.

Development of hybrid Mg/Al2O3 composites with improved properties using microwave assisted rapid sintering route

In the present study, hybrid magnesium based composites reinforced with an equivalent of 5 vol.% of micron and nano-sized Al2O3 particulates were synthesized using powder metallurgy technique incorporating an innovative microwave assisted rapid sintering technique. Microstructural characterization revealed near equiaxed grain morphology and the presence of minimal porosity in all the samples. Mechanical characterization studies revealed that the coupled addition of micron and nano-sized particulate reinforcements in magnesium matrix leads to a significant increase in hardness, elastic modulus, 0.2% yield strength, ultimate tensile strength and a decrease in ductility when compared to pure magnesium. Tensile testing results further revealed an increase in elastic modulus and ductility with no apparent change in the 0.2% yield strength and ultimate tensile strength of the hybrid composites upon the addition of nano-sized alumina particulates from 0.5 to 0.75 volume percent. With an increase in nano-sized alumina particulates from 0.75 to 1%, the overall mechanical properties of the hybrid composites were enhanced with an increase being observed in the elastic modulus, 0.2% yield strength and ductility of the composites. An attempt is made in this study to investigate the feasibility of the processing methodology and to study the effects of the addition of particulate reinforcements of different sizes on the microstructure, physical and mechanical properties of magnesium.

Nano-biotechnology: carbon nanofibres as improved neural and orthopaedic implants

For the continuous monitoring, diagnosis, and treatment of neural tissue, implantable probes are required. However, sometimes such neural probes (usually composed of silicon) become encapsulated with non-conductive, undesirable glial scar tissue. Similarly for orthopaedic implants, biomaterials (usually titanium and/or titanium alloys) often become encapsulated with undesirable soft fibrous, not hard bony, tissue. Although possessing intriguing electrical and mechanical properties for neural and orthopaedic applications, carbon nanofibres/nanotubes have not been widely considered for these applications to date. The present work developed a carbon nanofibre reinforced polycarbonate urethane (PU) composite in an attempt to determine the possibility of using carbon nanofibres (CNs) as either neural or orthopaedic prosthetic devices. Electrical and mechanical characterization studies determined that such composites have properties suitable for neural and orthopaedic applications. More importantly, cell adhesion experiments revealed for the first time the promise these materials have to increase neural (nerve cell) and osteoblast (bone-forming cell) functions. In contrast, functions of cells that contribute to glial scar-tissue formation for neural prostheses (astrocytes) and fibrous-tissue encapsulation events for bone implants (fibroblasts) decreased on PU composites containing increasing amounts of CNs. In this manner, this study provided the first evidence of the future that CN formulations may have towards interacting with neural and bone cells which is important for the design of successful neural probes and orthopaedic implants, respectively.

Mechanical strength improvement of electrical discharge machined cemented carbides through PVD (TiN, TiAlN) coatings

Electrical discharge machining (EDM) is an alternative shaping route for manufacturing complex component shapes of hard and brittle materials as WC–Co cemented carbides (hardmetals). However, it results in a heat-affected surface layer with poor surface integrity that often leads to mechanical degradation of these materials. This work focuses on assessing the feasibility of physical vapor deposition (PVD) of hard coatings as a technique for improving surface integrity and mechanical strength of EDMed hardmetals. In doing so, the influence of PVD of TiN and TiAlN coatings on the flexural strength of cemented carbides substrates shaped using multi-pass sequential EDM was investigated. For comparison purposes, coating effects on a reference surface condition attained through grinding and polishing using diamond as abrasive were also evaluated. Experimental results show that hard coating deposition markedly decreases the lessening effect of EDM on the fracture resistance of hardmetals. However, no flexural strength differences between coated and uncoated abrasive-machined samples are discerned. The mechanical characterization studies were complemented by detailed fractographic examination and the results were analyzed by linear-elastic fracture mechanics. It is concluded that, although coated EDMed cemented carbides exhibit an effectively larger critical defect size, a mechanical strength improvement is finally achieved because an overcompensating effect ascribed to beneficial changes on intrinsic severity (nature) of the critical flaw and residual stress state at the surface.