bluuebunny/crossref_metadata_2025 huggingface dataset:
Sintering of 316L stainless steels to high density via the addition of chromium—molybdenum dibromide powders Part 1: Sintering performance and mechanical properties
Authors: Becker B S , Bolton J D , Eagles A M
Published: April 2011

Single and mixed additions of both chromium diboride and molybdenum diboride powders were effective in raising the sintered density of water-atomized 316L stainless steel to 98 per cent of the full density at sintering temperatures in the range 1250-1300°C. Chromium diboride was more effective than molybdenum diboride in reducing the sintering temperature.

The mechanical properties in terms of tensile strength and ductility were superior to those obtained with normal sintered stainless steel and the alloys exhibited considerable ductility despite the presence of a grain boundary boride eutectic phase. Mixed additions of both chromium plus molybdenum diboride gave the best overall levels of strength and ductility.
The mechanical properties of lead-containing and lead-free solders—meeting the environmental challenge
Authors: Plumbridge W J , Gagg C R
Published: April 2011

Reliability is a principal objective in electronics equipment. This imposes a significant challenge, particularly in the face of continued miniaturization, which results in more severe conditions for the interconnection. At present, no sound methodologies exist for reliable life prediction of solder joints and, for lead-free alloys, this problem is accentuated by a shortage of data on mechanical behaviour appropriate to service. To meet the demands of forthcoming environmental legislation, a new generation of lead-free solder alloys is being developed. The paper presents a comparison of the mechanical behaviour of the conventional Sn-37Pb solder with that of Sn-3.5Ag and Sn-0.5Cu alloys (where the compositions are in weight per cent) which are potential replacements. It is demonstrated that the mechanical properties of the lead-free alloys may be better or worse than those of the eutectic Sn-Pb alloys. The ranking of the alloys may change according to the test conditions. Strengths fall to quite low levels with decreasing strain rate and increasing temperature. The Sn-3.5Ag solder has substantially superior creep resistance although, for creep lives less than 1000 h at 75°C, prior ageing impairs this performance, as is the case for Sn-37Pb. During high-strain fatigue, the lead-free alloys are marginally inferior, and the presence of a dwell in the strain cycle generally causes a significant reduction in life. The implications of these findings in relation to the implementation of lead-free technology are considered.
Determination of materials design values for the use of fibre-reinforced polymer composites in civil infrastructure
Authors: Karbhari V M
Published: April 2011

Fibre-reinforced polymer composites used in civil infrastructure are significantly different in material form and process than the autoclave cure prepreg-based composites used in the aerospace and defence sectors and hence lack the substantial well-established materials database required for routine civil engineering design. This paper provides recommendations for the development of an approach within an overall methodology of partial reduction factors expressed as Md = ϕ Mk, which enables design with emerging materials that may not have databases sufficient for statistical determination of materials design values. The approach is such that it enables its future incorporation into a load and resistance factor design (LRFD) methodology using techniques of statistical analysis and reliability theory. The method enables the use of reduction factors for the purposes of design while allowing for the derivation of routine design parameters based on either incomplete data records, or records of other comparable but intrinsically different systems. Examples are provided to illustrate the use of the methodology in specific cases, and results are compared with well-known empirical factors used in conventional handbook-based design.
On the nature, properties and wear response of s-phase (nitrogen-alloyed stainless steel) coatings on AISI 316L
Authors: Dahm K L , Dearnley P A
Published: April 2011

Nitrogen-alloyed AISI 316L coatings with nitrogen contents, [N], between 1.2 and 80 nitrogen atoms per 100 metal atoms (N/100 Me) were obtained by reactive sputter deposition. Coatings comprising only a nitrogen supersaturated metastable face-centred cubic (fcc) phase (s-phase) were obtained for 8.6 ≤ [N] ≤ 48 N/100 Me. For [N] ≤ 5.8 N/100 Me body-centred cubic (bcc) phases were present in the coatings while at [N] ≤ 65 N/100 Me the coatings comprised unidentified high nitrogen phases in addition to s-phase. The lattice parameter of the fully s-phase coatings increased linearly with increasing [N] according to a = 0.3585 + 0.00075 [N] nm The hardness of the s-phase coatings attained a maximum value of ≈20 GPa at [N] ≈ 30-40 N/100 Me. The nitrogen in the s-phase coatings reduced the wear of the coatings by 1-2 orders of magnitude compared to the wrought material by promoting an oxidational wear mechanism.
A Monte Carlo simulation for the study of three-dimensional Cartesian braided composites failure
Authors: Bigaud D , Hamelin P
Published: April 2011

The failure behaviour modelling of three-dimensional Cartesian braided composites is presented. Two main parameters are considered to be predominant in the failure behaviour: the variations of the yarns orientation, which generates a complex field of stresses, and the scattering of internal values of strength partly due to damages induced in the yarn during the manufacturing and consolidation steps. Thus, the internal geometry of the braided composite first needs to be identified. A subcell modelling solution based on a multiscale analysis allowing the mechanical influence of each constituent (fibre or resin) to be considered within the composite is next proposed. Finally, the analysis of the braided composite mechanical behaviour leads to the study of an aggregate of multiscale subcells with randomly distributed individual mechanical properties. The theoretical results obtained show good agreement with the experiments carried out on carbon/PA 12 three-dimensional Cartesian braided composites.
Studies on refractory bonding systems used in vitrified silicon carbide grinding wheels
Authors: Jackson M J
Published: April 2011

The performance of vitrified silicon carbide grinding wheels is dependent on the molten properties of their bonding systems. The erosion of silicon carbide during the manufacture of grinding wheels is enhanced by the action of high glass content vitrified bonding systems that reduces their wear resistance during the grinding process. Replacing the glass content of the bond with a clay that does not vitrify can improve their wear resistance. However, the harmful effects of quartz particles that are found in clay minerals need to be eliminated during the firing process before the grinding wheels are used to grind precision engineering components. A mathematical model describing the dissolution of quartz in refractory bonding systems was compared with experimental data using X-ray diffraction techniques. It was found that when grinding wheels were isothermally heat treated, the residual mass fraction of quartz was found to be a function of time. When compared with experimental data, the model was found to be accurate for short periods of heat treatment that are associated with vitrified silicon carbide firing cycles. The model is of practical use for predicting the complete dissolution of quartz in vitrified bonding systems used for high-performance silicon carbide grinding wheels.
Lower bound of the fracture toughness relation in biaxial loading
Authors: Radhakrishnan V M
Published: April 2011

Many studies have been carried out to relate KI and KII at fracture in biaxial loading. In the present investigation, the Mohr type of stress intensity factor (SIF) circles in uniaxial and pure shear type of loading are presented and discussed for the ‘no fracture’ relation between KI and KII for inclined cracks in biaxial loading. This ‘no fracture’ relation forms the lower bound for the fracture toughness relation between KI and KII. The experimental data points are seen to lie outside this lower bound for different materials.
Permanent deformation in idealized bituminous composites
Authors: Collop A C , Khanzada S
Published: April 2011

This paper describes tests undertaken to characterize the deformation behaviour of idealized bituminous mixtures and the development of a model to describe the permanent deformation exhibited by these mixtures in a wheel-tracking test. Steady state uniaxial and triaxial tests are used to characterize the deformation behaviour of the idealized mixtures over a range of stress levels, strain rates and temperatures. Results show that at low stress levels the deformation mechanism is linear viscous flow whereas at high stress levels the deformation mechanism is non-linear viscous flow with a power-law creep exponent of approximately 2.4. Wheel tracking tests have been performed over a range of applied stress levels and temperatures. Results indicate that the accumulation of permanent deformation in these idealized mixtures is non-linear. The measured uniaxial and triaxial properties have been used in a viscous model to predict the permanent deformation measured from wheel tracking tests. A method is presented for incorporating the observed non-linear behaviour of these materials in a linearized viscous approach. The results indicate good agreement between predictions and measurements, indicating the applicability of this type of model.
New formulations for the Hopkinson bar technique to extract a response of the constituent material in composite specimens
Authors: Mahfuz H , Al Mamun W , Austin L , Haque A , Jeelani S
Published: April 2011

During stress wave propagation through a composite material, the wave velocities through the fibre and matrix are different because of the differences in the respective moduli and densities. The stresses and strains generated in the constituent material are accordingly related to the wave velocities. In a typical split Hopkinson pressure bar (SHPB) experiment, the composite coupon is held in between the incidence and transmitter bars and a global response is obtained. While this provides a basis of comparison between various material systems, the information is not sufficient to predict failure of the composite precisely. Knowledge of the individual responses of the fibres and the matrix is needed for accurate failure analysis. However, the existing SHPB formulations are not capable of extracting individual responses from a regular test set-up. In the current investigation, a new set of mathematical formulations has been derived from the momentum concept so that the individual strain and stress responses of the fibres and the matrix can be estimated from regular SHPB tests. Coaxial cylindrical coupons have been designed and fabricated for this purpose. Test results indicate that there is good correlation between the predicted and experimental data, especially at lower strain rates. Details of the mathematical derivations and experimental procedures are described in the paper.
Experimental and numerical analyses of thermomechanical refractory lining behaviour
Authors: Gasser A , Boisse P , Dutheillet Y , Poirier J
Published: April 2011

Refractory linings are used in order to protect the steel structure in industrial applications such as coal-fired power plants or steel ladles. These linings are subjected to important thermal loading that can lead to cracking (due to the difference between the thermal expansion of steel and the thermal expansion of the refractory). The aim of this study is to build a tool that allows the structural design to be improved so as to decrease the refractory cracking. The first approach is developed on a local scale. A special furnace allows the reproduction of the thermal conditions in a coal-fired plant. Acoustic emission is employed to detect when the refractory is cracking. A finite element analysis, using three-dimensional elements and a smeared-crack model, is conducted to reproduce the experimental observations. The material behaviour is identified using an inverse method. This local approach can be directly used for structural analyses when the geometry of the lining is sufficiently simple. For instance, the computation of a steel ladle is presented. When the geometry of the lining is very complex, it is not possible to compute it with this three-dimensional model. In this case, a simplified approach using a two-layered composite shell, the behaviour of which is equivalent to the three-dimensional behaviour, is briefly described.
A study of the coefficients of thermal expansion of Al alloy 6061-albite composites
Authors: Sharma S C , Seah K H W , Krishna M , Ramesh A
Published: April 2011

The change in the coefficients of thermal expansion (CTEs) of albite particulate-reinforced Al alloy 6061 metal-matrix composites was investigated with respect to temperature. The composites were prepared by the ‘compocasting’ technique and the albite contents were 2, 4 and 6 wt % respectively. A comparison was made with the unreinforced matrix material. The results show that the CTE significantly increased with increasing temperature but decreased with increasing albite content. These phenomena are explained.
The contribution of advanced high-temperature materials to future aero-engines
Authors: Winstone M R , Partridge A , Brooks J W
Published: April 2011

Improvements in the performance and efficiency of gas turbine engines have been intimately linked to the development of materials technologies for the high-temperature components. This paper reviews some of the recent research that will ensure that the engines for the next generation of aircraft deliver world class performance at an affordable cost.
Finite element analysis model of the cumulative damage failure process in a continuous-fibre ceramic composite loaded in flexure
Authors: Jenkins M G , Mark K Y
Published: April 2011

A finite element analysis (FEA) using macro-based input commands was used to model the cumulative damage failure process of a continuous-fibre ceramic composite loaded in flexure. The modelling was predicated by the subject material which exhibited asymmetric stress-strain response for uniform uniaxial monotonic tensile and compressive loading. The FEA model of the prismatic rectangular flexural beam was composed of separately meshed fibre and matrix elements loaded in four point flexure. The cumulative damage process was modelled using a macro-based input code combined with an element ‘kill’ command that was used to change the stiffnesses of those fibre and matrix elements whose respective ultimate tensile strengths were exceeded by the resulting tensile stresses. Matrix elements were allowed to support compressive stresses up to the ultimate compressive strength of the matrix material. However, unsupported fibre elements (i.e. those coincident with ‘killed’ matrix elements) were not allowed to support compression. Even though the model did not explicitly include the behaviour of the interphase material, good agreement between the FEA results and experimental test results was found for the subject three-dimensionally braided NicalonTM fibre-reinforced β-SiC matrix composite.
The effect of ageing duration on the mechanical properties of Al alloy 6061-garnet composites
Authors: Sharma S C
Published: April 2011

A well-consolidated composite of Al alloy 6061 reinforced with 4, 8 and 12 wt% garnet was prepared by a liquid metallurgy technique, the composite was heat treated for different ageing durations (T6 treatment), and its mechanical properties were determined by destructive testing. The results of the study indicated that, as the garnet particle content in the composites increased, there were marked increases in the ultimate tensile strength, compressive strength and hardness but there was a decrease in the ductility. There was an improvement in the tensile strength, compressive strength, and hardness with ageing due to precipitation. Precipitation in Al alloy 6061, with and without garnet particulate reinforcement, was studied using transmission electron microscopy. The fracture behaviour of the composites was altered significantly by the presence of garnet particles and the crack propagation through the matrix, and the reinforcing particle clusters resulted in final fracture.
Stress computation methods for hybrid inorganic phosphate cement-concrete cross-section
Authors: De Roover C , Vantomme J , Wastiels J
Published: April 2011

After more than 10 years of study, researchers at the Vrije Universiteit Brussel have developed a new non-alkaline mineral polymer named inorganic phosphate cement (IPC). This ceramic is reinforced by glass fibres in order to increase the toughness, the tensile strength and the stiffness of the resulting composite material. This new material is combined with a traditional material such as concrete to result in a new concept of bridge cross-section. The deck is made of concrete and the box girder is made of IPC sandwich panels. This paper presents two stress calculation models regarding the mechanical behaviour of hybrid IPC-concrete elements. The first considers the bilinear tensile behaviour of the IPC material. The second constitutive model simplifies the bilinear behaviour of the material by an equivalent linear behaviour. Comparison of the two calculation models shows that approximation of the complex behaviour of the IPC composite by an equivalent linear behaviour induces limited errors on the maximal normal stresses and deflection values. Therefore, the equivalent linear method is an easy way to determine the parameters necessary for the first global design at the ultimate limit state and serviceability limit state of the structure. Moreover, this method is safe, and therefore is appropriate for determining the dimensions of a hybrid IPC-concrete structure in the preliminary design stage.
Effective materials properties: Determination and application in mechanical design and optimization
Authors: Grujicic M , Cao G , Fadel G M
Published: April 2011

A finite element procedure for determination of effective mechanical, thermal and thermomechanical properties of multi-phase materials is developed in this paper. To account for the variation in phases contiguity with the change in volume fractions, a computer-based procedure is proposed for generation of the materials microstructure. The procedure is applied to the cobalt-tungsten carbide (Co-WC) two-phase material. The results show significantly better agreement with their experimental counterparts compared with analytical methods of predicting effective materials properties. Finally, the case of flywheel optimization is used to demonstrate that accurate determination of effective materials properties can be very critical in heterogeneous-materials design problems.
Strengthening of tunnel supports using carbon fibre composites
Authors: Moy S S J , Hill P , Moriarty J , Dier A F , Kenchington A , Iverson B
Published: April 2011

A research programme into the strengthening and life extension of tunnel supports using carbon fibre composites is presented. Details are given of a carbon fibre reinforced polymer (CFRP) beam that will be used to relieve the load on the existing tunnel support and also provide an alternative load path to support the loads above the tunnel. The progressive damage non-linear finite element analysis of the beam is explained, as is the static and fatigue testing of the beam. A complementary test programme of coupon testing to examine the degradation of CFRP in aggressive conditions is also briefly described. It is shown that the technology developed is applicable to other infrastructure applications.
Comparison of the mechanical properties of A356-SiC particle-reinforced metal matrix composites produced by two melting routes
Authors: Akbulut H , Yalcin Y , Yilmaz F
Published: April 2011

SiC particle-reinforced metal matrix composites (MMCs) were produced by a common liquid-phase technique in two different melting routes. In the first route, 5, 10, 15 and 20 vol % SiC-reinforced A356-based MMCs were produced. In the second route, an Alcan A356 + 20 vol % SiC composite billet was diluted to obtain 5, 10, 15 and 20 vol % SiC-reinforced MMCs. In both cases the average particle size was 12 μ. The microstructural and mechanical property relationships of these composites were investigated. Vortex-produced MMCs showed a fairly good particle distribution accompanied by approximately 5-8 vol % porosity. Diluted Alcan composites produced excellent particle distribution and finer eutectic silicon crystals. Compressive and tensile properties were compared between vortex-produced and diluted composites. The results showed that diluted MMCs showed better properties compared with composites produced by the vortex method. Both composite groups were subjected to a T6 ageing heat treatment. The rate of increase in the yield, and tensile and compressive strength values were always higher in the as-cast materials than in T6 heat-treated composites with increasing SiC particle content. This difference was attributed to accelerated nucleation of precipitation and, therefore, overageing caused by ceramic particles. SEM investigations on the fracture surfaces showed that good particle bonding existed in the diluted composites.
Superelastic deformation of a TiNi shape memory alloy subjected to various cyclic loadings
Authors: Gong J M , Tobushi H , Takata K , Okumura K
Published: April 2011

Superelasticity is one of the important mechanical properties of shape memory alloys (SMAs). In the present paper, the superelastic deformation behaviour of a TiNi SMA under various loading conditions with different experimental temperatures and strain rates was investigated. The characteristics of transformation stress during cyclic deformation were analysed. The relationship between the residual stress and strain accumulated during cyclic loading is expressed by a straight line. After mechanical training with cyclic deformation, two-way deformation appears on account of R-phase transformation. The starting and finishing conditions of the transformation become unclear after cyclic deformation at high temperature.
Electrochemical assessment of erosion-corrosion of commercially pure titanium and a titanium alloy in slurry impingement
Authors: Neville A , McDougall B A B
Published: April 2011

The economic and effective operation of machinery and plant involved in fluids handling is increasingly dependent on the utilization of materials that combine high corrosion resistance and good wear resistance. This paper focuses on erosion-corrosion where mechanical wear is due to impacting solid particles entrained in a liquid flow. The characteristics of commercially pure (CP) titanium (grade 2) and titanium alloy (Ti 5111) in erosion-corrosion conditions are assessed. There is much literature available on the corrosion behaviour of titanium and titanium alloys but little has been reported on corrosion in wear environments. The erosion-corrosion characteristics of each material at 18 and 50°C were assessed using an impinging jet apparatus. The tests were performed in a 3.5% NaCl saline solution. Experiments were conducted to determine the mass loss by combined erosion-corrosion processes before independently determining the electrochemical corrosion mass loss and the mechanical mass loss. It has been shown that under erosion-corrosion conditions titanium and its alloys exhibit active corrosion behaviour, in contrast to passive behaviour when the tenacious oxide film remains intact in static conditions. The synergistic effect between erosion and corrosion is significant and is dependent on the material.
A new approach to integrated instruction in mechanics and materials science
Authors: Khanna S K , Jenkins C H , Roylance D
Published: April 2011

Educating student engineers in the total design of structures should involve an integrated approach. Hence a new course linking mechanics, materials science and design has been developed. The course, titled ‘Mechanics and Materials in Structural Design’, educates students in the total design of structures. One important aspect of this approach to teaching is to develop multimedia-based virtual laboratory modules. This paper focuses on one such module, namely the ‘tension test of metals’ module. This module links the mechanics experiment with the fundamentals of materials science and highlights its usefulness in generating design information. With this approach to teaching, using an apparently simple tension test, the students can better visualize the linkages between mechanics, materials response at the macro and atomic levels, and design. Preliminary evaluation of the course suggests that this philosophy of teaching an integrated course on design is valid.
Design optimization of silo structures made from composite materials Part 1: Design of the vertical cylindrical section
Authors: Morozov E V , Henshall J L , Brown C J
Published: April 2011

This study implements the general design optimization procedures that have been formulated for composite materials to the design of silo structures. Recent Eurocodes and other guides have presented a thorough summary of the necessary procedures for steel silo design. However, design guidance for composite silos is less readily available. While the use of a composite material requires consideration of the anisotropy of the material properties, it also allows a greater degree of interaction between the material and the design requirements. This paper, and its companion, present a genera) approach to the optimized design of the main parts of a cylindrical silo structure, i.e. the upper cylindrical section (Part 1) and the hopper (Part 2) respectively. The general methodology is outlined, and the effectiveness of the optimization is demonstrated using a particular example. In this case, the resultant optimized design produced a 16 per cent saving in wall thickness, and thus material cost, in comparison with the non-optimized wall thickness.
Design optimization of silo structures made from composite materials Part 2: Optimum design of the composoite conical hopper
Authors: Morozov E V , Henshall J L , Brown C J
Published: April 2011

This study implements the general design optimization procedures that have been formulated for composite materials to the design of silo structures. Recent Eurocodes and other guides have presented a thorough summary of the necessary procedures for steel silo design. However, design guidance for composite silos is less readily available. While the use of a composite material requires consideration of the anisotropy of the material properties, it also allows a greater degree of interaction between the material and the design requirements. This paper, and its companion, present a general approach to the optimized design of the main parts of a cylindrical silo structure, i.e. the upper cylindrical section (Part 1) and the hopper (Part 2) respectively. The present paper develops the structural optimization of multilaycred and multizonal composite shells further for this particular application. Using the particular silo design outlined in Part 1, it is shown that a reduction in material of more than 50 per cent is achieved compared with the equivalent single-zone design for the conical hopper.
Time-temperature dependence of fracture toughness for bisphenol a epoxy resin
Authors: Araki W , Adachi T , Gamou M , Yamaji A
Published: April 2011

The relationship between the curing conditions and the time-temperature dependence of fracture toughness was investigated for bisphenol A epoxy resin. The glass transition temperature and Angell's fragility parameter, which are obtained from thermoviscoelasticity measurements, were used to characterize epoxy resins cured under various conditions. Examination of the fracture toughness at various temperatures and displacement rates showed that it depends on both temperature and time, and that it follows the time-temperature equivalence principle. The time-temperature dependence of the fracture toughness was greatly affected by the fragility parameter. The fracture toughness of the resin with a smaller fragility parameter increased from lower temperatures to the brittle-ductile transition temperature than that of the resin with a larger fragility parameter when their glass transition temperatures were approximately 400 K. It was also found that the brittle-ductile transition temperature did not depend on the fragility parameter. This means that epoxy resin with a smaller fragility parameter has better fracture characteristics than epoxy resin with a larger fragility parameter if their glass transition temperatures are approximately 400 K.
Influence of microstructural voids on the mechanical and impact properties in commingled E-glass/polypropylene thermoplastic composites
Authors: Santulli C , Brooks R , Rudd C D , Long A C
Published: April 2011

In recent years, the compression moulding of E-glass/polypropylene commingled composites has been thoroughly investigated. In particular, in the University of Nottingham, a number of studies have been carried out, trying to correlate moulding parameters with mechanical properties and microstructural void content. However, some aspects of commingled composites have received less coverage so far and are therefore dealt with in this paper. These concern the effect of the processing conditions of these materials on interlaminar shear strength and impact properties and the influence of the synergy between processing, microstructure and properties on the impact performance of commingled composite structures. With this aim, flat plaques of E-glass/polypropylene commingled composites with a different fibre architecture (two-and three-dimensional) were non-isothermally compression moulded under various moulding conditions and then tested. The test programme included falling weight impact tests with a staircase procedure, Charpy impact tests and interlaminar shear strength (ILSS) tests. To evaluate the consolidation of the laminates, void content measurement using optical microscopy was related to ILSS and impact test results. In particular, the specific issues arising in moulding laminates with added three-dimensional fibres were studied. These include correct placement of the tow, sufficient preheating of thick laminates and nesting of the layers during moulding. The results of these tests are discussed in the light of the moulding conditions and quality, and conclusions are drawn regarding optimum moulding conditions for impact performance. Finally, indications on the reliability and possible improvement of the moulding procedure to yield a sufficient moulding quality, even with large thickness, are also provided. The knowledge acquired on material consolidation properties is applied in the manufacture of an automotive side intrusion beam: problems due to the scale effect are also discussed.
Effect of thermal plasma heating on the dielectric properties of Al-Zr composites
Authors: Sahu D R , Roul B K , Singh S K , Chaudhury R N P
Published: April 2011

A low-cost extended arc thermal plasma heating (EATPH) source has been used for the sintering of Al-Zr high-temperature ceramic oxides, and their dielectric properties have been studied. Pellets of Al-Zr composites were sintered using optimum sintering parameters such as sintering time, plasma power and plasmagen gas flow rate in an EATPH reactor. Samples of similar composites were also sintered using a conventional resistive heating furnace at 1500°C for 20 h, and their dielectric properties were studied and compared with the plasma sintered sample. Sintered pellets were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and dielectric measurement, carried out as a function of frequency and temperature. Highly dense sintered products were obtained by the plasma heating route within a very short sintering time compared with the conventional sintering schedule. Dielectric measurements (both dielectric constant and loss factor) showed a significant reduction in the dielectric constant, K, at room temperature under different test frequencies and also as a function of temperature. However, the change in dielectric loss factor, tan Δ, was not as pronounced as the change in K. The behaviour of the K and tan Δ curves changes drastically compared with the conventional sintered material. The reduction in K and the crossover behaviour of tan Δ in the plasma sintered specimen may be due to the action of non-reactive Ar plasmagen gas during plasma sintering, which favours mobile oxygen for the polarization network under the influence of frequency and temperature.
Influence of modal coupling on the buckling of concentrically loaded pultruded fibre-reinforced plastic columns
Authors: Lane A , Mottram J T
Published: April 2011

An experimental investigation concerning the buckling behaviour of pultruded fibre-reinforced plastic (PFRP) columns is presented. Full-sized tests were performed on wide-flange pultruded members across a range of lengths where local, global and combined buckling modes were expected. Combined buckling describes the situation where the local and global buckling modes occur concurrently in a violent and unstable manner. The research aims to provide test data that increase understanding of modal coupling in concentrically loaded columns. Modal coupling effects cause a reduction in the buckling load of imperfect columns and can lead to combined buckling. The extent to which mode interaction reduces the column buckling load is highly dependent on the magnitude of the imperfections present. Great care was taken during the experiments to ensure that the applied load was truly concentric, so that any interaction would be due to column imperfections alone. The geometrical column imperfections were measured prior to testing. The influence of mode interaction observed during the tests was found to be less than previous research had suggested. The experimental results will be used in future to prepare guidance for code writers and designers.
Strengthening of casilina bridge with carbon fibre reinforced polymer sheets
Authors: Arduini M , Napolitano P , Gottardo R
Published: April 2011

Advanced composite materials [fibre-reinforced polymers (FRP)] are becoming one of the major innovations in the construction field. After a relatively short research phase, they are now commonly used for repair and strengthening for many types of structure. The keys to the success of this technology are the reduction in labour cost, the speed of the application and the high durability of the system. This paper presents the largest FRP application carried out in Italy in 1999. The structure is a 30 year old, two-span, reinforced concrete (RC) bridge. Beams were reinforced in bending and columns in shear and confinement. The design aspect and working schedule are included in the paper, as well as indication of the construction time schedule in order to verify the assumption of lower cost in a real situation.
Prediction of the mechanical properties of polyethylene parts produced by different moulding methods
Authors: Godinho J S , Cunha A , Crawford R J
Published: April 2011

The properties of moulded plastic products are dependent on the processing technology used in their manufacture and in particular on the structural morphology resulting from the thermomechanical environment experienced by the melt. This paper presents a unified approach to predict the mechanical properties of moulded parts. A linear medium-density polyethylene (LMDPE) was processed using injection moulding, rotational moulding and compression moulding in order to induce different thermomechanical conditions (i.e. shear rates and cooling rates). Two models were then developed to predict the mechanical properties of the parts produced by the quite different moulding methods. One model is based on laminate theory, in which the mechanical properties of the individual layers through the wall thickness are used to predict the tensile and flexural properties of the full-thickness moulding. The other approach is more generic in that it predicts the properties as a function of two thermomechanical indices. A good agreement is achieved between the experimental data and the values predicted by the models. It is also shown that the combined use of the thermomechanical indices concept and the laminate analysis permits good predictions to be made for the mechanical properties of plastic mouldings with complex microstructures. It is proposed that this approach could provide a very valuable addition to existing melt flow simulation packages. This would provide a valuable tool for designers in that not only would it be possible to optimize processing conditions but also the properties of the end product could be predicted.
Optimum design of multilayer composite plates using simulated annealing
Authors: Rao Ananda M , Ratnam Ch , Srinivas J , Premkumar A
Published: April 2011

This paper proposes the use of a simulated annealing (SA) approach to the optimal design of multilayered composite plate structures. The orientation fibres and the number of layers in laminated composites play a major role in determining strength and stiffness. Therefore, the basic design problem is to determine the optimum stacking sequence of the composite laminate. The SA technique is employed to obtain the optimum fibre orientation of multilayered composite plates, so as to maximize fundamental natural frequency. The composite plate is discretized and analysed by a finite element (FE) analysis procedure using a computer program written in C language. The inverse iteration method is employed to obtain the fundamental frequency of a laminated plate with a given number of layers and fibre orientations in each layer. Both symmetric and antisymmetric fibre angles are considered. The optimum results of fibre orientations are compared with the conventional random walk (RW) method.
Microstructural analysis of non-woven fabrics using scanning electron microscopy and image processing. Part 1: Development and verification of the methods
Authors: Ghassemieh E , Acar M , Versteeg H
Published: April 2011

This paper reports image analysis methods that have been developed to study the microstructural changes of non-wovens made by the hydroentanglement process. The validity of the image processing techniques has been ascertained by applying them to test images with known properties. The parameters in preprocessing of the scanning electron microscope (SEM) images used in image processing have been tested and optimized. The fibre orientation distribution is estimated using fast Fourier transform (FFT) and Hough transform (HT) methods. The results obtained using these two methods are in good agreement. The HT method is more demanding in computational time compared with the Fourier transform (FT) method. However, the advantage of the HT method is that the actual orientation of the lines can be concluded directly from the result of the transform without the need for any further computation. The distribution of the length of the straight fibre segments of the fabrics is evaluated by the HT method. The effect of curl of the fibres on the result of this evaluation is shown.
Microstructural analysis of non-woven fabrics using scanning electron microscopy and image processing. Part 2: Application to hydroentangled fabrics
Authors: Ghassemieh E , Acar M , Versteeg H K
Published: April 2011

The image analysis techniques developed in Part 1 to study microstructural changes in non-woven fabrics are applied to measure the fibre orientation distribution and fibre length distribution of hydroentangled fabrics. The results are supported by strength and modulus measurements using samples from the same fabrics. It is shown that the techniques developed can successfully be used to assess the degree of entanglement of hydroentangled fabrics regardless of their thickness.
Probabilistic finite element analysis of residual stress formation in shrink-fit ceramic/steel gun barrels
Authors: Grujicic M , DeLong J R , DeRossett W S
Published: April 2011

The development of residual stresses in a hybrid α-SiC lining/CrMoV steel jacket gun barrel during shrink fitting of the jacket over the lining is studied using a probabilistic finite element analysis. Particular attention is given to understanding the development of the axial compressive stress in the ceramic lining, since this stress (if sufficiently high) can prevent lining failure caused by formation and growth of circumferential cracks near the barrel ends. To quantify the effect of variability in various design, material and process parameters on the magnitude and the distribution of the axial residual stress, a probabilistic structural analysis approach, known as the advanced mean value (AMV) method, is used, enabling determination of the cumulative distribution function for failure of the lining. The results obtained are validated using the adaptive importance sampling (AIS) method, an efficient direct statistical sampling technique. Lastly, the corresponding sensitivity factors which quantify the effect of variability in each parameter on the magnitude of axial residual stresses in the ceramic lining are computed. The results indicate that the loss of the compressive axial stress in the lining near the barrel ends is affected to the greatest extent by the magnitude of the friction coefficient at the lining/barrel interface.
Determination of non-linear, large, equal biaxial stresses and strains in thin elastomeric sheets by bubble inflation
Authors: Johannknecht R , Clauss G , Jerrams S
Published: April 2011

This paper presents a method for investigating the axisymmetric bubble inflation of elastomers by an optical measuring system and determining local stress and strain properties in biaxial deformation. In particular, the local stretch ratios on the bubble shell are evaluated by an element grid [1,2]. Both the pattern and the bubble contour are observed optically on-line during a continuous inflation process. The relations between internal pressure, bubble height and local shell stresses and strains are analysed. Additionally, free and tube-guided inflation using hydraulic and pneumatic pressure systems are compared. As stresses toward the pole of the bubble gradually increase during the inflation process, the experimental method permits an investigation into material properties at high equibiaxial loadings and the determination of constants for different material models. The conclusion of this investigation is that simple assumptions that relate local stress and strain levels to the bubble inflation height cannot be made.
Local plastic surfaces for cracking and crushing in concrete
Authors: Jefferson A D
Published: April 2011

The experimental failure envelope for concrete has the form of a curved Coulomb failure surface, which can reasonably be assumed to be related to a principal plane of shearing. This assumption is used in the development of a multiple surface plasticity model for concrete, in which the same local yield function is used to simulate directional fracture and isotropic compressive behaviour. A function is derived from experimental data that provides the transition from directional cracking behaviour to isotropic compressive behaviour. The local responses from all active plastic surfaces are coupled in a multisurface plasticity formulation, which provides the interaction between compressive and tensile behaviour in a natural way. The model is validated against experimental data from uniaxial and multiaxial compressive tests as well as tensile fracture tests. The model has been implemented in the finite element (FE) program LUSAS, and a summary of the implementation algorithm is provided. A number of stress path examples are considered, and the results from two FE analyses are presented.
Dental root implants produced by the combined selective laser sintering/melting of titanium powders
Authors: Tolochko N K , Savich V V , Laoui T , Froyen L , Onofrio G , Signorelli E , Titov V I
Published: April 2011

Preliminary experiments were carried out for the fabrication of dental root implants using an improved technique of laser processing of Ti powders. The properties of produced samples were characterized for various processing parameters. Samples with rod and cone shapes were formed. A combined selective laser sintering (SLS) and selective laser melting (SLM) process was utilized. With this combination, the samples possessed a structure composed of two different zones, namely a remelted compact core and a sintered porous shell. The results of these experiments show that it is possible to produce dental root implants possessing the required geometry, structure and strength by appropriate laser processing of Ti powder.
Structural integrity—whose responsibility?
Authors: Miller K J
Published: April 2011

Structural Integrity (SI) as a single distinct subject has now come of age. It has grown, sometimes painfully, through the activities of many different engineering and scientific disciplines, numerous professional institutions, separate industrial organizations, several university engineering departments and national and international societies. An accelerated impetus has been derived from severe engineering problems and accidents, some of which are briefly reviewed.

In the UK and elsewhere the numerous but separate disciplines initially involved in SI have each made valuable contributions. Engineers and scientists attempted to solve practical problems, but without accurate knowledge of the applied stress levels. They were followed by metallurgists, who focused attention on a materials microstructure. Design engineers and manufacturers were unable to incorporate defects of the order of grain size, or less, into their calculations. All were eventually assisted by two important developments.

First came the rapid advances in two-and three-dimensional finite element analyses of stress distributions in complex-shaped geometries, and second, the study of cracks by elastic and then elastic-plastic fracture mechanics. When combined, these computer-assisted developments focused attention on the all-important synergistic parameter a. En-route to this improved state of affairs several alternative approaches were investigated to quantify the SI of structures, components and materials, many of these alternatives effectively delaying progress for many years, at great cost.

Although the UK has made numerous positive contributions to SI investigations, sometimes due to unfortunate although avoidable accidents, of which many recent incidents are well-documented, future pitfalls and false trails have to be avoided wherever and whenever possible. To achieve this, individual discipline approaches now need to be better integrated at national and international levels. The increasing complexity of engineering components and structures intended to work at higher temperatures, in more aggressive environments, and with greater efficiency, will demand a higher degree of synthesis of effort. Society will demand nothing less Failures due to inappropriate and/or incorrect SI assessments leading to increasing costs to the nation in terms of human, animal and plant life, environmental damage to land sea and air, disruption to societal activities, not to mention the associated Government-sourced budget losses, need to be dramatically reduced.

By looking at some industry-university collaborations in SI studies, it is hoped that the issues raised in this lecture will help in plotting the way forward and answering the question

‘Structural Integrity-whose responsibility?’