Strength retention of self-reinforced,absorbable polyglycolide rods in hydrolytic environment

Absorbable polyglycolide suture fibers were sintered with the compression molding techniques to cylindrical rods at temperatures between 205°C and 232°C for 3–5 min with final pressures of 50–80 N/mm². The cylindrical rods had nominal diameters between 1.5–4.5 mm and a length of 50 mm. The initial bending moduli and the initial bending strengths of the rods were between 9–15 GPa and 220–430 MPa, respectively. The shear strengths of the rods were between 165–255 MPa. The hydrolytic loss of mechanical strength of the above self-reinforced, absorabable polyglycolide rods were studied in phosphate buffer at 37°C and 77°C. It was found that the rate of strength loss decreases with the increasing diameter of the rods. On the other hand, the rate of strength loss increases when the temperature of the buffer solution is raised. The strength, retention time at 37°C was between 7–10 weeks showing that the loss of mechanical strength of self-reinforced polyglycolide rods occurs more rapidly in vivo than in vitro.     

Induced anisotropic permeability due to drying of concrete

Structural strength, porous space, and permeability of concrete are strongly affected by mechanical, hydrous, and thermal loading. These various loadings may lead to drying shrinkage, one of the main characteristics of this type of material, which has to be involved in the behaviour modelling and experimental investigations being the subjects of this paper. Experimental devices and principal parameters studied are first presented. Drying shrinkage and loss of mass in time were measured on prismatic samples while uniaxial compression tests were performed on cylindrical samples. Gas permeability tests, carried out on a concrete cylinder 30 mm in diameter, form the second part of this study. The samples used for these measurements were cored from each prismatic sample at the end of 10 months or 2 years of drying, either from the transverse direction of sample (privileged direction of drying) or from the longitudinal direction. Gas permeability procedure, using micropulse test technique, is described as well as the experimental process. Experimental results are finally commented on and discussed with a view on induced anisotropy due to desiccation. Such an anisotropy is clearly observable in permeability, which is also increasing with drying time.     

Compressive response of PMMA microcellular foams at low and high strain rates

Microcellular foams are widely applied in various applications in both civil and military applications for barriers and energy absorption materials. Poly(methyl methacrylate) microcellular foams were fabricated via supercritical foaming method. Field emission scanning electron microscopy, differential scanning calorimetry, and mechanical test machine were used to visualize the foam structure and test the quasi‐static compression properties. Moreover, Split Hopkinson Bar (SHPB) setups were adopted to explore the dynamic compression properties. The experimental results show that the microcellular foams have homogeneous cell size distribution and exhibit superior compressive behavior at both quasi‐static and high strain rates. The mechanical properties depend on both foam density and strain rate. Strain rate effects are clearly observed. At quasi‐static strain rate and 7500 S^?1 regime, cell wall bucking and folding are the main failure mechanism. However, at high strain rate regime, softening phenomenon is observed. By roughly calculating the energy absorbed and the temperature rise, the temperature of the foams will rise up to as high as 130 °C after conducting high strain rate compression, and it is postulated that the generated heat will destroy the cell structure of the foams. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46044.     

Uniaxial compaction behaviour and elasticity of cohesive powders

The compression and compaction behaviour of bentonite, limestone and microcrystalline cellulose (MCC) — three cohesive powders widely used in industry were studied. Uniaxial compression was performed in a cylindrical die, 40 mm in diameter and 70 mm high, for three selected cohesive powder samples. The initial density, instantaneous density and tablet density were determined. The influence of maximum pressure and deformation rate was examined. The secant modulus of elasticity E_sec was calculated as a function of deformation rate v, maximum pressure p and powder sample. After compaction experiments in hydraulic press at three pressures - p = 30, 45 and 60 MPa - and two different deformation rates, the strength of the produced tablets was examined in a material strength testing machine.From uniaxial compression tests performed on the universal testing machine for loading and unloading, the modulus of elasticity E was calculated on the basis of the first linear phase of unloading. The total elastic recovery of tablets was also obtained.     

High temperature mechanical characterisation of an alumina refractory concrete for Blast Furnace main trough: Part I. General context

Blast Furnace main trough is an industrial structure submitted to severe high temperature cyclic loading applied on its inner lining made of refractory concrete. The attempt to increase the lifetime of such a structure by numerical simulation requires a proper experimental characterisation of all materials involved and particularly of the refractory concrete. The present paper exposes an analysis of the conditions required for an experimental setup in accountancy with the material working conditions. Then, the development of a performing high temperature mechanical testing device aimed at characterising the castable behaviour in its service conditions is introduced. In particular an original extensometer allowing high temperature direct measurement of the specimen height variation has been developed. Lastly, results of an uniaxiale compression test carried out at intermediate temperature are presented and discussed.     

Mechanical behaviour of MgO–C refractory bricks evaluated by stress–strain curves

In this work, the mechanical behaviour of a set of resin- and pitch-bonded MgO–C refractories containing metallic additives was evaluated in laboratory tests at high temperature in a non-oxidant atmosphere. Commercial bricks were used for this evaluation, and a comprehensive characterization of the as-received materials was performed using several techniques (mineralogical analysis by X-ray diffraction, density and porosity measurements, differential thermal and thermogravimetric analyses and microstructural analysis by reflected light microscopy coupled with cathodoluminiscence accessory and scanning electron microscopy). Stress–strain curves in compression were obtained at room temperature, 600, 1000 and 1400 °C under flowing N₂ gas. An Instron 8501 servo-hydraulic machine was used with a capacitive extensometer suitable for axial strain measurements at high temperatures. A constant displacement of 0.1 mm/min was applied until specimen failure. Several parameters were calculated from the stress–strain curves: failure stress, failure strain, yield stress and secant Young's modulus. Moreover, a comprehensive characterization of the tested specimens was carried out. The analysis of the mechanical behaviour has been based on previous research and the results have been interpreted in terms of the thermal evolution of the brick's microstructure. The resin-based refractory exhibited the higher values of mechanical strength and Young's modulus in the entire range of testing temperatures. Up to 1000 °C, the mechanical behaviour was controlled by the type of binder and the changes in porosity whereas at 1400 °C, the main differences between the responses of resin- and pitch-based refractories were mainly caused by the metallic additive reactions.     

Strain rate dependence of adhesive joints for the automotive industry at low and high temperatures

In this study the impact and quasi-static mechanical behaviour of single lap joints (SLJ) using a new crash resistant epoxy adhesive has been characterized as a function of temperature. Single lap adhesive joints were tested using a drop weight impact machine (impact tests) and using a universal test machine. Induction heating and nitrogen gas cooling was used in order to achieve a homogeneous distribution of temperature along the overlap of + 80 °C and ?20 °C, respectively. Adherends made of mild steel, similar to the steel used in automobile construction, were chosen in order to study the yielding effect on the strength of the SLJ. Results showed that at room temperature (RT) and low temperature (LT), failure was dictated by the adherends due to the high strength of the adhesive. At high temperature (HT), a decrease was found in the maximum load and energy absorbed by the joint due to the reduced strength of the adhesive at this temperature. The results were successfully modelled using the commercially available finite element software Abaqus^®. Good correlation was found between experimental and numerical results, which allows the reduction of experimental testing.     

Effect of High-Temperature Treatment on the Mechanical Properties of Rowan (Sorbus aucuparia L.) Wood

Heat treatment is a wood modification method that has been used to some extent in improving timber quality. The high temperature thermal treatment of wood is an environmentally friendly method for wood preservation. This technique has attracted considerable attention both in Europe and in North America in recent years.

This article presents the results of experimental studies on influence of heat treatment on the mechanical properties of Rowan (Sorbus aucuparia L.) wood performed in order to understand its role in wood processing. Samples were exposed to temperature levels of 120, 150, and 180°C for time spans ranging from 2 to 10 h. Mechanical properties including compression strength, modulus of elasticity, modulus of rupture, Janka hardness, impact bending strength, tension strength perpendicular to grain, tension strength parallel to grain, shear strength, and cleavage strength of heat-treated samples were determined. Maximum reduction values of 34.12, 28.40, and 26.37% were found for impact bending strength, tension strength parallel to grain, and cleavage strength for the samples exposed to 180°C for 10 h, respectively. Overall, the results showed that treated samples had lower mechanical properties than those of the control samples. Statistically significant difference was determined (P = 0.05) between mechanical properties of the control samples and those treated at 180°C for 10 h.     

Mechanical properties of layered silicate/starch polycaprolactone blend nanocomposites

The mechanical behavior of layered silicate/starch polycaprolactone blend nanocomposites was evaluated. Three different clays (Cloisite Na⁺, Cloisite 30B and Cloisite 10A) were used as reinforcement. Nanocomposites were prepared by melt intercalation followed by compression molding. These nanocomposites were characterized using X‐ray diffraction, scanning electron microscopy, dynamic mechanical analysis and tensile testing. X‐ray diffraction results showed that most of the clays were intercalated within the polymeric chains. In all cases, mechanical properties were improved with clay incorporation and the improvement was better as the clay content was increased. The best properties were achieved with Cloisite 10A due to their greatest compatibility with the matrix. A mechanical model, which takes into account the effective parameters of the clay, was used in order to estimate the dispersion of clay within the polymer. The highest dispersion was obtained for Cloisite 10A, which is in accordance with the experimental mechanical properties. Although dynamical‐mechanical properties improved with clay incorporation, the glass transition temperature was not affected. Copyright © 2006 Society of Chemical Industry     

Mechanical Response of Thermoset Polymers under High Compressive Loads, 2

Summary: A nonlinear viscoelastic material model was used to describe the experimental behaviour of thin vinyl ester specimens subjected to compression in thickness direction. The stress‐dependent material functions in the model were found in creep and strain recovery tests on thick cylindrical specimens. The elastic and creep response of thin thermoset polymer specimens subjected to compressive loads was simulated while varying the geometry of the test set samples. The calculated increase in the apparent elastic modulus and decrease of the creep‐strain rate due to reduced thickness‐to‐width ratio is in a good qualitative correlation with experimental results for corresponding geometries. The constraint due to friction and interaction with the material outside the loaded surface area were identified as the cause for high apparent stiffness, which converges with decreasing thickness to an asymptotic value dependent on the modulus and Poisson's ratio of the material.

The shape of a 2 mm‐thick specimen under compression.     

Investigate the influence of bonding temperature in transient liquid phase bonding of SiC and copper

Joining of ceramics to metals provide timeless challenges in nuclear engineering industries. There is a pressing need for developing a suitable technique for joining silicon carbide (absorber) to copper radio frequency structures in Compact Linear Collider. Transient liquid phase bonding is a promising candidate that could be employed for joining of dissimilar materials with high re-melt temperature. In the present work, experiments were carried out on Transient Liquid phase bonding of silicon carbide and copper using metal interlayer. Lead, which has high wettability, is selected as an interlayer in the Transient Liquid Phase (TLP) bonding process. Experimental results of mechanical testing reveal the strength of the SiC/Cu joints and its integrity. Since, the bonding temperature is the most important parameter to achieve sound joint with good mechanical properties, its influence is studied through experimental trials. From the experimental studies, it is found that the bonding temperature should be 230 °C to obtain the good quality SiC/Copper joints.Favorable temperature distribution is achieved at this bonding temperature and consequently, the joining efficiency of SiC/Copper joints is increased..     

Biodegradable composites of poly(butylene succinate‐co‐butylene adipate) reinforced by poly(lactic acid) fibers

Biodegradable composites of poly(butylene succinate‐co‐butylene adipate) (PBSA) reinforced by poly(lactic acid) (PLA) fibers were developed by hot compression and characterized by Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), dynamic mechanical analyzer, and tensile testing. The results show that PBSA and PLA are immiscible, but their interface can be improved by processing conditions. In particular, their interface and the resulting mechanical properties strongly depend on processing temperature. When the temperature is below 120 °C, the bound between PBSA and PLA fiber is weak, which results in lower tensile modulus and strength. When the processing temperature is higher (greater than 160 °C), the relaxation of polymer chain destroyed the molecular orientation microstructure of the PLA fiber, which results in weakening mechanical properties of the fiber then weakening reinforcement function. Both tensile modulus and strength of the composites increased significantly, in particular for the materials reinforced by long fiber. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43530.     

玻璃丝形状尺寸对玻璃软化点温度测量影响研究

通过机械拉丝工艺法制备不同直径(Φ0.50~Φ0.90 mm)、不同圆柱度(ΔΦ0.01~ΔΦ0.06mm)和不同圆度(ΔΦ0.01~ΔΦ0.2 mm)3种形态的玻璃丝,采用Littleton法测试玻璃软化点温度,探究玻璃丝直径、圆柱度和圆度对软化点测量结果的影响作用规律。研究结果表明:随着玻璃丝直径增大,测试的玻璃软化点温度逐渐降低;对于不同圆柱度的玻璃丝,上下两端直径差ΔФ增大,软化点温度变化量增大;对于不同圆度的玻璃丝,其软化点温度取决于玻璃丝断面最小直径,最小直径一定时,随着最大直径增大,软化点温度变化不大。     

Effect of Plug-Filling,Testing Velocity and Temperature on the Tensile Strength of Strap Repairs on Aluminium Structures

Abstract

In this work, an experimental study was performed on the influence of plug-filling, loading rate and temperature on the tensile strength of single-strap (SS) and double-strap (DS) repairs on aluminium structures. Whilst the main purpose of this work was to evaluate the feasibility of plug-filling for the strength improvement of these repairs, a parallel study was carried out to assess the sensitivity of the adhesive to external features that can affect the repairs performance, such as the rate of loading and environmental temperature. The experimental programme included repairs with different values of overlap length (L _O = 10, 20 and 30 mm), and with and without plug-filling, whose results were interpreted in light of experimental evidence of the fracture modes and typical stress distributions for bonded repairs. The influence of the testing speed on the repairs strength was also addressed (considering 0.5, 5 and 25 mm/min). Accounting for the temperature effects, tests were carried out at room temperature (≈23°C), 50 and 80°C. This permitted a comparative evaluation of the adhesive tested below and above the glass transition temperature (T _g), established by the manufacturer as 67°C. The combined influence of these two parameters on the repairs strength was also analysed. According to the results obtained from this work, design guidelines for repairing aluminium structures were recommended.     

Investigation of char strength and expansion properties of an intumescent coating exposed to rapid heating rates

An efficient and space saving method for passive fire protection is the use of intumescent coatings, which swell when exposed to heat, forming an insulating char layer on top of the virgin coating. Although the temperature curves related to so-called cellulosic fires are often referred to as slow heating curves, special cases where the protective char is mechanically damaged and partly removed can cause extremely fast heating of the coating. This situation, for a solvent based intumescent coating, is simulated using direct insertion of free films into a muffle oven. The char formed is evaluated with respect to the mechanical resistance against compression, degree of expansion, and residual mass fraction. Experimental results show that when using this type of shock heating, the mechanical resistance of the char against compression cannot meaningfully be correlated to the expansion factor. In addition, char properties, measured at room temperature, were dependent on the preceding storage conditions (in air or in a desiccator). The char was found to have the highest mechanical strength against compression in the outer crust facing the heat source. For thin (147 μm) free coating films, a tendency to contract in the horizontal plane was observed. The experimental approach is relevant for testing of intumescent coatings used in buildings where moving or falling objects may damage the char during a fire.     

Experimental investigation of heat transfer in an air duct with an inclined heating surface

In this paper some experimental results showing the influence of inclination of a cylindrical heating surface immersed in an air duct on heat transfer coefficient are presented. The experiments were performed in a laboratory-scaled apparatus of square cross section with dimensions 120 ‐ 120 mm and 1400 mm in height. Heat transfer surface was an electrical heater made of brass tube with outer diameter of 19 mm and 110 mm length. In each experiment the temperatures of the front and rear side of the heating surface, inclination angle, air velocity, inlet air temperature, and heater power were measured. It was concluded that heat transfer coefficient depends on flow conditions and angle of inclination. The maximum Nusselt number (Nu) was observed to occur about 45° inclination relative to the horizon, for the range of Reynolds numbers used in experiments. The values of heat transfercoefficients in the vertical position were very nearly the same as they were in the horizontal position. Based on the experimental results, a correlation was proposed for estimation of Nu at the desired flow velocity and inclination angle, relative to Nu at zero inclination.     

Compressive mechanical properties of HTPB propellant at low,intermediate, and high strain rates

Low, intermediate, and high strain rate compression testing (1.7 × 10^?4 to 2500 s^?1) of the hydroxyl‐terminated polybutadiene (HTPB) propellant at room temperature, were performed using a universal testing machine, a hydraulic testing machine, and a split Hopkinson pressure bar (SHPB), respectively. Results show that the stress linearly increases with strain at each condition; the increasing trend of stress at a given strain with the logarithm of strain rate changes from a linear to an exponential form at 1 s^?1. By combining these characteristics, we propose a rate‐dependent constitutive model which is a linearly elastic component as a base model, then multiplied by a rate‐dependent component. Comparison of model with experimental data shows that it can characterize the compressive mechanical properties of HTPB propellant at strain rates from 1.7 × 10^?4 to 2500 s^?1. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43512.     

Thermo-oxidative aging of acrylonitrile-butadiene rubber gaskets with real geometry used in plate heat exchangers

This study investigates the effects of aging on the physical and mechanical properties of commercially available acrylonitrile-butadiene rubber (NBR) gaskets while maintaining their original geometry. Thermo-oxidative cycles with 10 and 70 mm in length specimens were conducted from 80 to 170°C up to 180 days. The samples were analyzed employing compression set (CS), hardness, indentation modulus, cross-link density, total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), and thermogravimetry. The results showed that longer specimens presented better resistance to thermo-oxidative aging. Indentation results indicated regular oxygen permeability into the entire samples up to 110°C, while at higher temperatures, limited diffusion oxidation (DLO) effects promoted non-uniform aging. Time–temperature superposition (TTS) and Arrhenius methods were applied to predict the specimens' lifetime using CS as a failure criterion. Activation energies for 10 and 70 mm samples were 68.74 and 43.63 kJ mol⁻¹, respectively. Thus, the 70 mm specimen's lifetime was greater than 10 mm. For temperatures below ≈38°C, the response to the thermo-oxidative aging is independent of specimen length. Therefore, in determining the lifetime of gaskets with complex geometry, longer specimens are recommended to provide more reliable results than those suggested by the standards.     

Monotonic tension behavior of 2D woven oxide/oxide ceramic matrix composites at ultra-high temperature

The research on mechanical behavior and failure analysis of oxide/oxide CMC at ultra-high temperatures can broaden its application scope. The present work studied monotonic tension behavior of the oxide/oxide CMC at 800 °C～1200 °C and two tensile rates (i.e. 5 mm/min and 0.5 mm/min). The uniaxial tensile test, fracture morphology characterization and finite element analysis were preformed to reveal the deformation and failure mechanisms of the oxide/oxide CMC at ultra-high temperature. The results show that the mechanical properties of the oxide/oxide CMC are sensitive to the temperatures and tensile rates. The stress-strain curves are almost linear at the high tensile rate and nonlinear at the low tensile rate. The ultimate tensile strength decreases significantly at low tensile rate and for temperatures higher than 1100 °C. The mechanical properties of the material are principally determined by oxide fiber/oxide matrix interface strength under low temperature and high-stress conditions, while by interlayer bonding strength under high temperature and low-stress conditions.     

Thermoset lactic acid‐based resin as a matrix for flax fibers

Thermoset composites were produced from flax fibers and a novel lactic acid (LA)‐based thermoset resin. This resin is based on methacrylated, star‐shaped oligomers of LA. The main purpose of this work was to evaluate whether this resin can be used to produce structural composites from flax fibers. Composites were prepared by spray impregnation followed by compression molding at elevated temperature. The tests showed that composites can be produced with as much as 70 wt% fiber. The composites were evaluated by tensile testing, flexural testing, charpy impact test, dynamic mechanical thermal analysis (DMTA), and low‐vacuum scanning electron microscopy. The ageing properties in high humid conditions were evaluated, the Young's modulus ranged from 3 GPa to 9 GPa in the best case. This work shows that structural composites can be produced from renewable material. It is clear from the results that these composites have properties that make them suitable for furniture, panels, or automotive parts. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011