Mechanical Properties In Order Research Articles

Characterization of repair mortars for the assessment of their compatibility in restoration projects: Research and practice

Repair mortars used for restoration are assumed to be highly compatible with historic materials in terms of physical, chemical and mechanical properties in order to assure the durability of masonry on the long term. Compatibility criteria are defined based on the original mortar characteristics but the quality and the performance of the repair mortar after application on masonry are not generally evaluated. From this perspective, historic mortars and repair mortars from three historic masonry structures were analyzed in terms of chemical, mineralogical, and physical point of view. A methodology is given taking into account the added value of analytical techniques and the basic requirements from both practical and scientific point of view.

Influence of High-Pressure Hydrogen Exposure on Increase in Volume by Gas Absorption and Tensile Properties of Sealing Rubber Material

When a rubber O-ring was used as a sealing material of a pressure vessel for high-pressure hydrogen gas such as 70MPa, which is the hydrogen pressure for fuel cell electric systems, the O-ring was extruded from the pressure vessel due to an increase in volume by gas absorption, and consequently cracks initiated in the previous study. Therefore, it is important to clarify the influence of hydrogen pressure on the increase in volume and mechanical properties in order to design the rubber O-ring for high-pressure hydrogen gas. From this viewpoint, unfilled and carbon black-filled sulfur-vulcanized NBR composites were exposed to hydrogen gas at a maximum pressure of 100MPa ; then, the influence of hydrogen exposure on volume increase and tensile properties of the composites was investigated. The residual hydrogen content which was measured 35 min after decompression increased with an increase in the hydrogen pressures ranging from 0.7 to 100MPa for the unfilled composite (NF) and the filled composite (CB). In contrast, the volume of NF and CB was hardly changed less than 10MPa, and the increase in volume by gas absorption was observed more than 10MPa. The elastic modulus of NF and CB decreased with an increase in volume, and this tendency can be successfully explained in term of the decrease in the crosslink density and elongation by volume increase. Although the tensile strength of NF hardly depended on the volume of specimen, the tensile strength of CB clearly decreased with an increase in volume. This is considered to be because a boundary structure between carbon black and rubber matrix was changed by hydrogen exposure.

Forming of C45 Steel at Critical Temperature

An important measure in steel processing industry is achieving the required mechanical properties and micro structure of the material. A new phenomenon has been discovered recently which allows to refine ferrite grain significantly and to spheroidise carbides over a very short time compared to conventional heat treatment techniques. The newly developed technology based on the ASR (Accelerated Spheroidisation and Refinement) effect consists in heating a steel workpiece through thickness to a temperature no higher than Ac1 and in subsequent plastic deformation. The energy introduced through plastic deformation causes the workpiece temperature to increase. This temperature increase, however, is not uniform throughout the workpiece cross-section, leading to substantial inhomogeneity. Fully austenitized regions, partially austenitized regions, and areas where no phase transformation occurred, coexist. In locations previously subjected to intensive plastic deformation, cementite lamellae disintegrate and globular carbides form. In regions subjected to milder plastic deformation, spheroidisation does not occur directly in the course of the thermomechanical treatment. Despite, the cementite lamellae show a stronger tendency to spheroidise during subsequent annealing. The combination of a suitable pre-heating temperature, an appropriate amount of strain and a possible reheating leads to transformation of initial ferrite-pearlite micro structure with lamellar pearlite into desired ferrite matrix with spheroidised carbides. Key microstructure parameters governing the properties of ferrite-pearlite steels include exactly the ferrite grain size, the distribution of defects within the ferrite grain and the distribution and morphology of carbides. The present article describes a new thermomechanical treatment technique which allows controlling these microstructure parameters and related mechanical properties in order to achieve their favourable combination in structural carbon steel C45. The processing time is very short when compared to several-hour conventional heat treatments. This offers potential for achieving desired mechanical properties with time and energy savings.

Design and characterization of microstructure evolution during creep of 12% Cr heat resistant steels

12% Cr heat resistant steels with a fine dispersion of nano precipitates were designed supported by thermodynamic modeling. A detailed characterization of the microstructure evolution at different creep times (100 MPa/650 °C/8000 h) was carried out by scanning transmission electron microscopy (STEM). The results of the microstructure analysis are correlated with the mechanical properties in order to investigate the influence of different precipitates (especially M 23C 6) on the creep strength of the alloys. Precipitation of Laves phase and Z-phase was observed after several hours creep time. Very few Z-phase of the type Cr(V,Ta)N nucleating from existing (V,Ta)(C,N) was observed. Both alloys show growth and coarsening of Laves phase, meanwhile the MX carbonitrides present a very slow growth and coarsening rate. Alloys containing Laves phase, MX and M 23C 6 precipitates show best creep properties.

Influence of microstructure and phase composition on the nanoindentation characterization of bioceramic materials based on hydroxyapatite

The aim of the study was to investigate the influence of microstructure and phase composition on the mechanical behaviour of hydroxyapatite (HAp) and biphasic HAp/β-tricalcium phosphate (β-TCP) bioceramic materials using nanoindentation. The formation of β-TCP phase in the HAp ceramic had the predominant influence on the nanomechanical properties of compact ceramics. For investigated microstructures there appear to be a slight decrease in the elastic modulus with increasing load and a higher decrease in hardness, which are in agreement with upper bounds of the results reported in literature. Maximal value of reduced modulus and hardness is yielded with pure HAp, and is measured to be 133.76 GPa for average grain size of 3 μm and 12.18 GPa for average grain size of 140 nm, respectively. The average modulus and hardness results for HAp/β-TCP ceramics with higher (101.61 GPa, 6.76 GPa) and lower grain size (115.72 GPa, 8.76 GPa) show sufficient mechanical properties in order to serve as hard tissue replacement material.

Damage development in a noncrimp‐glass fabric reinforced epoxy composite material

AbstractThe relationship between textile architecture and the damage sequence under tensile loading has been investigated experimentally for a composite material reinforced with a noncrimp glass‐fiber textile of configuration [0°, +45°, 90°, −45°] stacking sequence based on epoxy resin matrix cured with high‐temperature hardener. The system chosen for this work consists of a bifunctional epoxy, diglycidyl ether of bisphenol A, cured with a tetrafunctional amine, diaminodiphenyl sulfone (DDS). This system ensures to obtain a rigid material with excellent mechanical properties in order to observe, analyze, and identify the process and progress of the generated damage and the failure mechanism which leads to the materials fracture. The properties have been studied for each ply direction at 0°, +45°, 90°, and −45° in order to make a comparative assessment of the influence of the polyester (PES) yarns in zig‐zag and unidirectional geometry, that hold together the four plies in the textile, in the composite damage generation. The laminates were uniaxially tensile loaded until final fracture occurred. It was found that PES threads have an effect on cracking progression depending on the textile orientation. POLYM. COMPOS., 2009. © 2009 Society of Plastics Engineers

Mechanical Properties of Nanocrystalline HVOF Coatings

Thermal spraying (TS) is increasingly used to deposit thick wear resistant coatings on machine and equipment parts. Therefore, it is of uttermost importance to know their mechanical properties in order to tailor and optimize the coatings for various applications. Typically properties of the thermal sprayed coatings are inferior as compared to corresponding bulk materials for various reasons. Furthermore, measurement of mechanical properties of coatings is much more tedious and difficult than deriving bulk properties. In this paper, mechanical properties of alumina based nanocrystalline coatings and the measurement techniques developed are reported. A model relating the microstructure of the sprayed coatings and their properties is introduced and discussed.

Aged bovine chondrocytes display a diminished capacity to produce a collagen-rich, mechanically functional cartilage extracellular matrix

Most fundamental studies in cartilage tissue engineering investigate the ability of chondrocytes from young animals to produce cartilaginous matrix under various conditions, while current clinical applications such as autologous chondrocyte implantation, use chondrocytes from donors that are decades past skeletal maturity. Previous investigations have suggested that several characteristics of primary chondrocytes are age-dependent but none have quantified cell proliferation, proteoglycan synthesis and accumulation, collagen synthesis and accumulation, compressive and tensile mechanical properties in order to examine the effects of donor age on all of these parameters. We enzymatically isolated primary bovine chondrocytes from fetal, young and aged animals and cultured these cells in agarose gels to assess the above-mentioned properties. We found that fetal and young (but still skeletally mature i.e. 18-month-old bovine) chondrocytes behaved similarly, while aged chondrocytes (5- to 7-year-old bovine) displayed diminished proliferation ( approximately 2x less), a slightly reduced proteoglycan accumulation per cell ( approximately 20%), and significantly less collagen accumulation per cell ( approximately 55%) compared to the younger cells. Histological observations and mechanical properties supported these findings, where a particularly significant reduction in tensile stiffness produced by aged chondrocytes compared to younger cells was observed. Our findings suggest that donor age is an important factor in determining the outcome and potential success when tissue-engineered cartilage is produced from articular chondrocytes. More specifically, primary chondrocytes from aged donors may not possess sufficient capacity to produce the extracellular matrix that is required for a mechanically resilient tissue.

Preparation and characterization of novel fast disintegrating capsules (Fastcaps) for administration in the oral cavity

The objective of this study was to prepare novel capsule-based fast disintegrating dosage forms for the oral cavity (Fastcaps). First, cast films were prepared from various additive-containing gelatin solutions and evaluated with respect to disintegration time and mechanical properties in order to identify suitable formulations for the capsule preparation. The disintegration time of films decreased with decreasing bloom strength and could be further decreased by the addition of sugars or PEGs. Fast disintegrating capsules were successfully prepared by a dipping process, whereby parameters such as the viscosity and temperature of the dipping solution and the dipping velocity of the steel pins were optimized. The required viscosity range of the dipping solution for Fastcap manufacturing was 500–600 cP. The addition of the hydrophilic additives (xylitol, sorbitol or PEG 1500) did not significantly affect the viscosity and gelation temperature of the dipping solution. The in vitro disintegration of Fastcaps (30–45 s) was twice as rapid as the one of regular hard gelatin capsules. In vivo, Fastcaps disintegrated rapidly (9–13 s) and their content was spread throughout the oral cavity within seconds. Lactose and/or microcrystalline cellulose were suitable fillers for Fastcaps. The mechanical properties of Fastcaps were similar to commercially available gelatin capsules, which assures good processability and handling.

Aged bovine chondrocytes display a diminished capacity to produce a collagen-rich, mechanically functional cartilage extracellular matrix

Most fundamental studies in cartilage tissue engineering investigate the ability of chondrocytes from young animals to produce cartilaginous matrix under various conditions, while current clinical applications such as autologous chondrocyte implantation, use chondrocytes from donors that are decades past skeletal maturity. Previous investigations have suggested that several characteristics of primary chondrocytes are age-dependent but none have quantified cell proliferation, proteoglycan synthesis and accumulation, collagen synthesis and accumulation, compressive and tensile mechanical properties in order to examine the effects of donor age on all of these parameters. We enzymatically isolated primary bovine chondrocytes from fetal, young and aged animals and cultured these cells in agarose gels to assess the above-mentioned properties. We found that fetal and young (but still skeletally mature i.e. 18-month-old bovine) chondrocytes behaved similarly, while aged chondrocytes (5- to 7-year-old bovine) displayed diminished proliferation (∼2× less), a slightly reduced proteoglycan accumulation per cell (∼20%), and significantly less collagen accumulation per cell (∼55%) compared to the younger cells. Histological observations and mechanical properties supported these findings, where a particularly significant reduction in tensile stiffness produced by aged chondrocytes compared to younger cells was observed. Our findings suggest that donor age is an important factor in determining the outcome and potential success when tissue-engineered cartilage is produced from articular chondrocytes. More specifically, primary chondrocytes from aged donors may not possess sufficient capacity to produce the extracellular matrix that is required for a mechanically resilient tissue.

Development of sialon ceramics for lubricated sliding applications

AbstractMicrostructural design and characterization of mechanical as well as tribological properties of sialon ceramics are the aim of this work. A potential application for these materials are fuel injection pumps for gasoline engines. The currently used metal parts face severe tribological damage with increasing pumping pressures and thus a replacement is needed. Sialon ceramics offer a wide variety of compositional parameters which allow to tailor microstructure and mechanical properties in order to meet the tribological requirements. Since phase boundaries in the sialon system shift depending on the additive elements used, investigations of the phase relations have been performed for two different sintering additives in order to gain informations about reasonable starting compositions. Then, the ratio of the sialon modifications, the amount of grain boundary phase and the grain morphologies have been correlated with the initial composition and the amount of sintering additives. For high hardness values an increase of the fraction of the α‐sialon modification in mixed α/β‐sialon materials is beneficial. The fracture toughness can be raised by promoting growth of elongated grains. It can be done either by achieving higher β‐sialon fractions in mixed α/β‐sialon ceramics or by sintering with an excess of additive in pure α‐sialon materials. Under lubricated sliding with isooctane, sialon ceramics showed a more advantageous behaviour with regard to friction coefficients and wear than commercial silicon nitride and coarse‐grained alumina.

Preface: phys. stat. sol. (b) 242/3

AbstractThis special issue of physica status solidi (b) is dedicated to papers presented, or in a few cases additional to, the Workshop on Auxetics and Related Systems held during 27–30 June 2004 at Będlewo near Poznań, Poland. There were around 40 participants at the workshop from Poland, the United Kingdom, Japan, USA, Belarus, China, Denmark, Germany, Greece, Italy, Malta, Russia, Slovakia and Ukraine. More details on the workshop can be found at http://www.ifmpan.poznan.pl/zp10/auxet/main.html.Auxetic materials exhibit negative Poisson's ratio behaviour. In other words, they expand (contract) transversely when stretched (compressed) lengthwise. They are, thus, examples of one class of 'negative' materials which are currently attracting significant interest. Other negative materials include those having negative stiffness, negative thermal expansion, negative refractive index, negative permittivity and negative permeability. Naturally‐occurring auxetic materials are known and continue to be discovered. However, it was the production of the first synthetic auxetic material (polyurethane foam) by Lakes, closely followed by the discovery of auxetic behaviour in a preconditioned commercially‐available expanded form of polytetrafluoroethylene by Evans, both in the late 1980s, which provided the impetus for the current research into auxetic materials. The range and diversity of attendees at the workshop in Poland reflects the extent to which the field has subsequently developed.Auxetics are of interest both intellectually and also from the point of view of potential applications. From the fundamental perspective, research activities concentrate on structure–property relationships through consideration of materials and mechanisms leading to auxetic behaviour from the nanoscale to the macroscale. The effect of a negative value of Poisson's ratio on the enhancement of related properties is also of keen interest. A combination of theoretical and experimental approaches is being pursued in this respect. In terms of applications‐based research for auxetics, the emphasis is on processing and fabrication of an increased range of auxetic materials, and characterisation of their mechanical and other physical properties (e.g. vibroacoustic damping properties). The papers presented here cover auxetic metals, ceramics, polymers, composites, foams and honeycombs in a variety of forms (e.g. bulk, fibre and thin film).Auxetics represent only one of many materials currently being developed as a result of counterintuitive properties. Papers presented here and also at the workshop include those relating to liquids at negative pressure, nanocrystalline magnets, negative thermal expansion polymer thin films, fractal structures containing negative stiffness components, and nanomechanical properties of metals. It is clear that there are considerable challenges and potential benefits to be gained from the development of multifunctional materials having one or more of the novel properties relating to the materials presented here (and elsewhere). The workshop was successful in achieving the aim of gathering scientists from a range of disciplines from across the world to exchange information relating to materials with unusual mechanical properties in order to provide greater insight into such materials and also to define future research perspectives and priorities. The collection of papers in this special issue captures the current state‐of‐the‐art in this area and provides clear indicators for future developments.We would like to gratefully acknowledge the support by the sponsors of the workshop (Centre of Excellence MMMFE, European Union 6th Framework Programme; Institute of Molecular Physics, Polish Academy of Sciences; State Committee for Scientific Research; UK EPSRC Auxetic Materials Network (AuxetNet)), the Scientific Committee, the Local Organising Committee, and the participants of the workshop.

Optimization of Propellant Binders – Part Two: Macroscopic Investgation of the Mechanical Properties of Polymers

AbstractThe development of new propellant binder systems requires the thermodynamic calculation of physico‐chemical data as well as the adaption of the mechanical properties in order to achieve a reliable innerballistic profile of the resulting propellant. Therefore, this study focuses on the mechanical properties of a binder system comprising GAP, NC as well as the energetic plasticizer DNDA and the curing agent Desmodur N100. By applying statistical methods, the mechanical properties of the binder can be predicted as a function of its composition. A macroscopic analysis of the interrelations between the E‐modulus, the ultimate tensile strength as well as the elongation at break and the specific deformation energy lead to the creation of failure master curves, which can be used as a rule of thumb criterion for the formulation of propellant binders.

Optimization of Propellant Binders – Part I: Statistical Methodology

AbstractThe development of new propellant binder systems requires the thermodynamic calculation of physico‐chemical data as well as the adaption of the mechanical properties in order to achieve a reliable innerballistic profile of the resulting propellant. However, in most cases the mechanical data may not be easily predicted due to the complex interactions between the components of the binder like the resin, the curing agent or possibly plasticizers and curing catalysts. Therefore, this study focusses on the capability of the multivariate analysis on the prediction of the E‐modulus of a system comprising nitrocellulose as well as GAP, Desmodur N100 and an energetic plasticiser. Using this method, an equation has been derived which, within the regression intervall, may be used for the prediction of the E‐modulus as a function of the components mentioned above.

Bioresorbable devices made of forged composites of hydroxyapatite (HA) particles and poly l-lactide (PLLA). Part II: practical properties of miniscrews and miniplates

Miniscrews and miniplates made of forged composites composed of raw hydroxyapatite (u-HA) particles (particle size 0.2–20 μm, averaging 3.0 μm, Ca/p=1.69 and containing CO 3 2−) and a poly l-lactide (PLLA, M ̄ v : about 180 kDa, containing residual 0.05 wt% lactide) with osteological bioactivity such as direct bonding to bone and osteoconductivity, total resorbability and radiopacity were examined for various mechanical properties in order to evaluate their usefulness for cranio-, oral and maxillo-facial as well as plastic and reconstructive surgeries with PLLA-only or titanium devices. The composites containing u-HA particles at 30 wt% for miniscrews and 40 wt% for miniplates were selected based on total mechanical strengths and bioactivity, respectively. It was found that the composite devices generally had slightly different mechanical properties than forged PLLA-only devices of which strengths are ranked the highest among the reinforced PLLA-only ones that having been used in many clinical cases to date, in spite of their approximate 2 or 3 times lower absolute strengths than those of titanium ones. However, a remarkable distinction that makes the composite miniplates stand above the titanium ones was confirmed on their fatigue resistance to alternate bendings such that they retained 70% of their initial strength even after 60 times without revealing any damage, whereas the metallic devices fully broke off at only 8 times. This behavior was similar to that of forged PLLA-only devices but is unique as composites made of organic polymers divided by inorganic particles. In addition, profile plates such as L-, T-, X, T, C-, Mesh-, Box-, and Barhole types which were processed by forging twice exhibited nearly directional isotropy in strength and could be deformed in situ at ordinary temperatures to adjust their shapes along the surface undulations of the skull, mandible, maxilla, zygomatic bone and the like without thermoforming and did not return to their original shapes inside an alive body due to the high PLLA’s T g (65°C) over an alive body temperature (37°C). Since it had already been confirmed in previous papers that these stiff and tough composites have the osteological bioactivity which is missing from both PLLA-only and titanium ones, and radiopacity which is wanting in PLLA-only ones, these various small and thin screws and plates have conclusively less objectionable practicality for use in oral-maxillo and craniofacial as well as plastic and reconstructive surgeries.

Thermal and dynamic mechanical properties of metallocene polyethylene

A comprehensive study has been made of a metallocene polyethylene (m-PE) characterising the isothermal crystallisation kinetics, melting and crystallisation behaviour, crystal growth and dynamic mechanical properties in order to understand the relationship between molecular structure and mechanical properties of this new class of polyethylene. The melting behaviour after step-wise crystallisation showed that m-PE consisted of molecular fractions with different molecular weight and branch distribution. Dynamic mechanical property studies showed that three transitions existed in m-PE with the α-transition increasing in intensity and shifting to higher temperatures in samples crystallised at higher temperature compared with rapidly cooled samples.

Das Konservieren von Baudenkmalen: eine neue Methode, um die Wirksamkeit einer stein festigenden Massnahme nachzuweisen / The conservation of monuments: A new method to evaluate consolidating treatments

Abstract The degradation of monumental stones is the result of the interaction between the material and environmental factors, such as water, heat, atmospheric pollutants and living organisms. This interaction starts at the stone surface, progresses inwards and may reach several millimetres in depth. The common decay processes may lead to significant losses of the strength properties of the outermost layer of some stone materials which results in erosion, cohesionless appearance and disintegration. At present there is no method to measure stone hardness, both at the superficial surface and at larger depths (few centimetres), with the same sensitivity and reliability, which can be used both in laboratory and in situ. The aim of this paper is to present the application of a new methodology for measuring the Drilling Resistance (DR) of natural stones, by the use of the new portable system (DFMS) that can operate in the laboratory and in situ. The results obtained so far show that this new method is highly promising for in situ evaluation of the mechanical properties in order to assess the consolidating treatment applied for the conservation of monuments.

Study of sand particle erosion of magnetron sputtered multilayer coatings

Sand particle erosion remains a crucial problem in aeronautical engines. Blades are made out of titanium alloy known for its poor erosion resistance. To protect these pieces, tungsten-based multilayer coatings deposited by magnetron sputtering were developed. They were tested on a specific erosion rig. Tests allowed to choose deposition parameters leading to extremely resistant films. Impact tests were performed on several monolayer coatings to determine their mechanical properties in order to simulate erosion by finite element method.

Correlation between the mechanical properties and the homogeneity of some photopolymerized acrylic/methacrylic networks1

Proton T 1ρ data obtained by CP/MAS solid-state 13 C NMR at 100.56 MHz for different polyacrylate networks were correlated with their mechanical properties in order to determine the best mixture in terms of stress-at-break (σ), Young's modulus of elasticity (Y), and homogeneity of the monomers that are forming the solid network. The mixtures were formed by the photopolymerization of 40% trimethylolpropane triacrylate (TMPTA), 40% dipentaerythritol pentaacrylate (DPHPA), and 20% of a monomer from a series of poly(ethylene glycol) and poly(ethylene) dimethacrylate. Proton T 1ρ 's in networks were not quite averaged to a single value by spin diffusion as in polymer blends, indicating extensive intermixing of TMPTA and DPHPA in forming the network, but with phase separation between the dimethacrylate homopolymer and the rest of the network that is dependent on the laser power. The stress-at-break and the Young's modulus of elasticity were determined for each of the mixtures at different values of the laser power used for the polymerization.

Correlation between the mechanical properties and the homogeneity of some photopolymerized acrylic/methacrylic networks1

Proton T1ρ data obtained by CP/MAS solid-state 13C NMR at 100.56 MHz for different polyacrylate networks were correlated with their mechanical properties in order to determine the best mixture in terms of stress-at-break (σ), Young's modulus of elasticity (Y), and homogeneity of the monomers that are forming the solid network. The mixtures were formed by the photopolymerization of 40% trimethylolpropane triacrylate (TMPTA), 40% dipentaerythritol pentaacrylate (DPHPA), and 20% of a monomer from a series of poly(ethylene glycol) and poly(ethylene) dimethacrylate. Proton T1ρ's in networks were not quite averaged to a single value by spin diffusion as in polymer blends, indicating extensive intermixing of TMPTA and DPHPA in forming the network, but with phase separation between the dimethacrylate homopolymer and the rest of the network that is dependent on the laser power. The stress-at-break and the Young's modulus of elasticity were determined for each of the mixtures at different values of the laser power used for the polymerization. © 1996 John Wiley & Sons, Inc.