bluuebunny/crossref_metadata_2025 huggingface dataset:
Time-temperature dependence of the fracture toughness of a poly(phenylene sulphide) polymer
Authors: Adachi T , Osaki M , Yamaji A , Gamou M
Published: April 2011

The time-temperature dependence of the fracture toughness of poly(phenylene sulphide) (PPS) resin was examined. The fracture toughness was measured at several deflection rates and ambient temperatures in a three-point bending test. On the basis of these experimental results, the master curve of fracture toughness was determined from the shift factor of the thermoviscoelastic characteristics. The time-temperature dependence equivalent law can be applied to the fracture toughness by conducting a fracture test at a variety of rapidly changing deflection rates. The results clearly showed that the fracture passes from brittle to ductile near the glass transition temperature, and that the fracture of PPS is strongly dependent on the thermoviscoelastic characteristics. Therefore, the fracture toughness can be predicted for a wide range of temperatures and over a long time span.
An analytical approach to water absorption based in situ test procedures for concrete
Authors: Wilson M A
Published: April 2011

There are several procedures that are used to assess empirically the in situ water absorption properties of concretes. All of these are based on complex absorption geometries involving both surface cap and drilled hole sources. In this paper, analyses are presented that show that the absorption from any radially symmetrical source may be described by a polynomial in (time)1/2 in which the sorptivity is the coefficient of the leading term. Application of the analyses thus enables the fundamental measure of water absorption, the sorptivity, to be calculated, so allowing valid and accurate comparisons to be made between data from different materials and also from different test geometries. The analyses can also define the extent to which the simple application of these tests for comparative purposes is acceptable and the cases in which such empirical comparisons may be misleading. Other considerations relating to the in situ testing of cementitious materials generally are considered briefly.
Crystallization and physical properties of polyvinyl acetate/polyvinylidene fluoride blends
Authors: Tawansi A , Badr S I , Abdelaziz M
Published: April 2011

Structural and thermal characterizations and dc resistivity measurements were performed for polyvinyl acetate (PVAc)/polyvinylidene fluoride (PVDF) blends. The ferro- to para- electric transition temperature ( TFP) and the melting temperature of PVDF were detected by DTA. X-ray diffraction and infrared analysis evidenced the presence of α- and β-PVDF crystalline phases for the studied blends. IR spectra revealed some structural defects such as difluorinated alkenes and head-to-head segments. The optical absorption spectra suggested the presence of two optical gaps. The electrical resistivity results were discussed on the basis of the modified interpolaron hopping model. The calculated values of the charge carrier hopping distance were in the range of 5.5-7.5 nm. The present blends are suggested to be used as pressure and microwave sensors and to produce a surface acoustic wave diffraction grating of variable order for laser optical communications.
Fatigue properties of a TiNi shape-memory alloy wire subjected to bending with various strain ratios
Authors: Furuichi Y , Tobushi H , Ikawa T , Matsui R
Published: April 2011

A fatigue-test machine for alternating bending of a wire under strain-controlled conditions was developed. Bending-fatigue tests on a TiNi shape-memory alloy wire were then performed for various strain ratios. The results obtained can be summarized as: (1) the fatigue life curves under alternating bending and pulsating bending, as expressed by the relationship between maximum strain and the number of cycles to failure, systematically follow the order of strain ratio; (2) the larger the strain ratio, the longer the fatigue life; (3) the fatigue life under rotating bending is shorter than that under alternating bending; (4) the increase in temperature during cyclic bending becomes larger in the order: rotating bending, alternating bending, pulsating bending. The fatigue life decreases in proportion to the increase in temperature; and (5) the fatigue limit of strain for alternating bending, pulsating bending and rotating bending is in the region of R-phase transformation.
Stress analysis and structural modifications of a polyester double-tape seam
Authors: Tang W , Keefe M
Published: April 2011

In this paper, a polyester double-tape seam is studied both experimentally and numerically. In the numerical analysis, the seam components are described with layered models containing fabric composite layers. The in-plane and out-of-plane elastic constants of the fabric composite layers are derived using a crimp model and a stacked model respectively. An existing finite element code, ANSYS 5.7, is used to perform two-dimensional stress analysis of the seam under tension. Numerical results identified the stress concentration causing strength loss in the seam. Finally, two structural modifications are proposed to improve the seam strength. The modifications are evaluated by both simulations and tests.
Selection of arbitrarily scaled cross-sections in bending stiffness design
Authors: Pasini D , Smith D J , Burgess S C
Published: April 2011

Performance indices can be used to model the relative structural efficiency of different cross-sectional shapes. Performance indices have been previously defined mainly for structural cross-sections that are scaled proportionally in size. This paper extends the method of performance indices by allowing scaling of cross-sections in any direction. A novel feature of the method described in this paper is the inclusion of the space envelope as a design parameter. The first part of the paper gives a derivation of the general solution for the performance index. The second part presents a graphical selection procedure and discusses the efficiency limits of cross-sections due to buckling instability. It concludes with a case study to demonstrate the method.
Design of laminated plate with account taken of strength
Authors: Kolpakov A G , Kalamkarov A L
Published: April 2011

A new approach to the problem of the discrete design of laminated composite plate with account taken of strength is presented. The solution of the design problem for a laminated plate possessing the required set of stiffnesses and strength is developed. A mathematical solution of the problem and the algorithms to compute the designs are provided. The developed algorithms make it possible to solve a new type of design problem. Several numerical examples illustrating the possibilities of the developed algorithms and programs are presented.
Shape fixity and shape recovery of polyurethane shape-memory polymer foams
Authors: Tobushi H , Shimada D , Hayashi S , Endo M
Published: April 2011

The thermomechanical properties of polyurethane shape memory polymer (SMP) foams were investigated experimentally. The results obtained can be summarized as follows. (1) By cooling the foam after compressive deformation at high temperature, stress decreases and the deformed shape is fixed. Stress decreases markedly in the region of temperature below the glass transition temperature Ts during the cooling process. (2) By heating the shape-fixed foam under no load, the original shape is recovered. Strain is recovered markedly at the temperature region in the vicinity of Tg. (3) The ratio of shape fixity is 100 per cent and that of shape recovery 98 per cent. Neither ratio depends on the number of cycles. (4) Recovery stress increases by heating under constraint of the fixed shape. Recovery stress is about 80 per cent of the applied maximum stress. Relaxed stress at high temperature is not recovered. (5) The shape deformed at high temperature is maintained for six months under no load at Tg’60 K without depending on maximum strain, and the original shape is recovered by heating thereafter. (6) If the deformed shape is kept at high temperature, the original shape is not recovered. The factors influencing the shape irrecovery are the holding conditions of strain, temperature, and time.
Cumulative fatigue damage assessment and life predictions of as-forged vs QT V-based MA steels using two-step loading experiments
Authors: Yang L , Fatemi A
Published: April 2011

This study examines the fatigue damage accumulation process associated with a commonly produced forged vanadium-based microalloyed (MA) steel and its comparison with its quenched and tempered (Q&T) counterpart at the same hardness level. The advantage of MA steels compared to the traditional Q&T steels is the elimination of the costly quenching and tempering processes. Completely reversed strain-controlled two-level block loading tests were conducted on smooth axial specimens at room temperature. Under multi-level block cycling, the two steels displayed different characteristics, though they showed similar behaviour in constant amplitude fatigue. Therefore, a key to successful assessment of fatigue damage accumulation under variable amplitude service loading is selection of an appropriate cumulative fatigue life prediction model which reflects the material's damage characteristics. The effectiveness of several cumulative fatigue damage models and their life prediction capabilities are evaluated using the experimental data.
Physically based damage models for laminated composites
Authors: McCartney L N
Published: April 2011

The computing power that is available for engineering calculation continues to grow at a dramatic pace. Engineers in industry want to have seamless models that can be used to design across the scale range from atoms to structures, including simulation of the manufacturing process. A limited aspect of this wish is the requirement to deal effectively with the progressive growth of microstructural damage in composites and its effect on both property degradation and the catastrophic failure event. This paper reviews progress that is being made at the National Physical Laboratory (NPL) with the development and validation of physically based damage growth models for laminated composites. The review includes:

(a) prediction of undamaged ply properties determined from the properties of the fibre and the matrix, with emphasis on comparison of analytical models with each other, and with finite and boundary element solutions; (b) discussion of various stress transfer models, and their validation, that have been developed for application to the prediction of the properties of composite laminates having ply crack damage; (c) prediction of ply cracking in multiple-ply cross-ply laminates subject to triaxial loading (without shear) and bending; (d) prediction of ply cracking in general symmetric laminates subject to combined triaxial loading and in-plane shear loading; (e) consideration in a damage mechanics context of progressive ply crack formation in general symmetric laminates subject to thermal residual stresses and general in-plane loading, where an important new methodology is described that results from attempting to develop a continuum damage model from a physically based discrete ply cracking model based on energy concepts; (f) discussion of how the models might be integrated into finite element analysis (FEA) systems to enable strain softening in structures to be adequately modelled.

The paper also includes statements concerning the status of the various models in relation to alternative approaches, and to model validation.
Mechanical properties and fracture mechanism of ZA-27/TiO2 particulate metal matrix composites
Authors: Seah K H W , Sharma S C , Krishna M
Published: April 2011

The mechanical properties and the fracture mechanism of composites consisting of ZA-27 alloy reinforced with titanium dioxide particles were investigated with the primary objective of understanding the influence of the particulate reinforcement on the mechanical behaviour of the ZA-27 alloy. The titanium dioxide particle content in the composites ranged from 0 to 6 per cent, in steps of 2 wt %. The composites were fabricated by the stir casting technique in which the reinforcement particles were dispersed in the vortex created in the molten matrix alloy. The study revealed improvements in Young's modulus, ultimate tensile strength (UTS), compressive strength, yield strength and hardness of the composites as the titanium dioxide content was increased, but at the expense of ductility and impact strength. The fracture behaviour of the composite was also significantly influenced by the presence of titanium dioxide particles. Eventual fracture was a result of crack propagation through the matrix as well as through the reinforcing particles. Scanning electron microscopy and fractography analyses were carried out to provide suitable explanations for the observed phenomena.
Structural efficiency maps for beams subjected to bending
Authors: Pasini D , Smith D J , Burgess S C
Published: April 2011

The structural efficiency of different cross-sections subjected to bending is considered in this paper. An envelope efficiency parameter, λ, is defined in terms of two shape transformers, A and 1. These transformers describe the relative ratio of the area and the second moment of area of the cross-sectional shape with respect to a rectangular envelope surrounding the shape. It is shown in a structural efficiency map that the mass efficiency of all cross-sectional shapes subjected to bending is bounded by two limiting curves. One limit curve represents cross-sections with material as far as possible from the neutral axis, the other limit curve is for cross-sections with material close to the neutral axis. The application of the map to two practical cases is also considered, together with scaling of the rectangular envelope.
Experimental analysis of the effect of grain size on the mechanical behaviour of thin copper sheet in pure moment bending
Authors: Kocańda A , Prejs T
Published: April 2011

During the bending process, both tensile and compressive stresses act on material layers. An estimation of the stress values can be based on information taken from a standard tensile test, but this method cannot take into account some of the complex effects that take place during bending. However, it is possible to obtain experimental material characteristics from a pure moment bending test. Such characteristics include the complexity of the process, as well as the material elastic and plastic properties. A special device was developed to carry out pure moment bending tests on microspecimens. In the case of very small elements, the microstructure of the workpiece plays a key role in the mechanism of plastic deformation. The influence of grain size has been investigated and analysed for a 0.1 mm thick copper sheet.
Crystallinity control in parts produced from stereolithography injection mould tooling
Authors: Harris R A , Hague R J M , Dickens P M
Published: April 2011

The use of moulds produced by stereolithography (SL) for injection moulding provides a quick route to manufacturing a low volume of parts without expensivehard tooling. However, these parts have been shown to exhibit different material property characteristics than those produced from metal tooling. The aim of the present work is to research methods that would allow SL moulds to produce parts of similar material property characteristics to those from conventional metal tools. This work has identified that the different part characteristics are due to differing levels of crystallinity developed in the parts from the comparative mould varieties (SL and metal). These crystallinity differences have been associated with the cooling rates imparted owing to the thermal properties of the mould material. The latter part of this work concerns controlling and manipulating this degree of crystallinity. After a discussion of possible methods, two approaches are taken to modifying the crystalline content of parts produced by SL moulds. One of the approaches is material based, the other concerns the injection moulding process. Differential scanning calorimetry (DSC) is used to quantify the resulting levels of crystallinity in the parts. The results show that by process modification it is possible to produce parts by SL moulding that possess a similar crystalline content to those moulded from metal tooling. The use of modified materials allows parts created in SL and metal tools to be of a consistent crystalline content. The work concludes that not only are SL moulds capable of producing parts that are more like those from metal moulds but also present some unique opportunities that have been demonstrated to be unachievable in metal moulds.
Filament wound container made of natural fibres and rubber: Conceptual design
Authors: van Rijswijk K , Koussios S , Bergsma O K
Published: April 2011

In the transportation sector, the search for cost reduction has led to the introduction of composite materials. This paper focuses on filament wound containers made of natural fibres and rubber. These containers show great potential for application in developing countries, where usage of locally grown materials is often justified considering the high prices and mediocre quality of the locally available synthetic fibres, if already available. Where containers reinforced with synthetic fibres will not be able to compete with existing steel containers, which are often imported, the ones made of sustainable natural fibres show great potential. The cost reduction is primarily based on the philosophy of making use of the local situation: local manufacturing of locally designed products with locally grown materials for transportation of local consumables for the local market. In this article, the integrated design procedure of a natural fibre wound container taking these local aspects into account is discussed. A feasibility study on such a container for the Vietnamese market is described, showing significant improvements in economy and sustainability.
Fatigue crack propagation of aluminium panels repaired with adhesively bonded composite laminates
Authors: Daghyani H R , Sayadi A , Hosseini H Toudeshky
Published: April 2011

The fatigue crack propagation of aluminium panels when repaired with unidirectional glass fibre composite laminates was investigated. The stress intensity factor at the crack tip of cracked panels repaired with single-sided and double-sided composite patches was evaluated by developing three-dimensional finite element models (FEMs). A particular surface preparation was used to bond the patches to the aluminium panels, resulting in a cohesive failure mechanism in the specimens. The results show that the stress intensity factor in the aluminium specimens was considerably decreased for double-sided repair, although for single-sided repair specimens the fatigue life was almost doubled compared with the specimens before repair.
Early-age finite element modelling of industrial ground floors
Authors: Robins P J , Bishop J W , Austin S A
Published: April 2011

A series of finite element (FE) models of ground floor slab behaviour has been developed and validated against in situ data from site instrumentations. Good agreement was obtained for thermal flow models, and the negative impact of air movement over the top of the slab has been highlighted. Plane stress models of slabs exposed to uniform and differential thermal gradients representing hydration and shrinkage effects demonstrated that the stresses resulting from frictional restraint are significantly less than those caused by warping restraint, even though the latter are currently not considered in design.
Stress and failure analysis of thick-walled conical composite rotors
Authors: Hufenbach W , Gude M , Zhou B , Kroll L
Published: April 2011

The high specific strength and stiffness of composite materials, as well as the possibility of creating a load-adapted property profile of them are ideally suited for the design of high-speed lightweight rotors. With respect to a load-adapted reinforcement structure of composite rotors, the rotor geometry has a significant influence on the optimum fibre orientation. In the case of conical rotors—the structural behaviour is strongly influenced by centrifugally induced bending effects in the rotor structure, which cause complex three-dimensional stress states in combination with the ordinary tangential and radial stresses. For analysis of the resulting complex stress states, an analytical method has been developed and verified numerically as well as experimentally. The novel method presented here is the basis for a realistic failure analysis and, in particular, serves as an efficient tool for extensive parameter studies and optimizations within the design process.
Acoustic emission from the tension fatigue of glass fibre reinforced plastics
Authors: Steel J A , Reuben R L , Hamlin M , Brown E R
Published: April 2011

This work investigates acoustic emission (AE) generated during tension fatigue tests carried out on a glass fibre reinforced plastic (GFRP) composite specimen. Continuous acquisition of AE events during measurements enables mapping of AE events with fatigue cycle time. The results allow analysis of the event rate obtained during parts of the fatigue cycle so that crack propagation events, at the peak of each load cycle, and crack closure events, on the unloading stage of each cycle, can be identified. The event rate in each of these parts of the cycles is also examined with respect to various test parameters, and qualitative results are shown that suggest some distinct correlations between event rate and crack length. The results can be applied as a diagnostic technique for modelling cumulative composite damage in critical composite structures such as pressure vessels and machine structures. The crack closure event rate is strongly correlated to crack length. The results can be used without the need to consider more sophisticated AE parameters in the design of a composite damage monitoring system.
Experimental and numerical analysis of loading rate and temperature effects on matrix cracking in CFRP laminates
Authors: Lafarie-Frenot M C , Gamby D , Nguyen T H
Published: April 2011

As a consequence of their use in structural parts of supersonic aircraft, laminated composite materials have to withstand long periods at high temperature. The study presented here aims to characterize the transverse matrix cracking of a carbon/epoxy material subjected to tensile loading. Tensile tests have been performed on {03/903}s laminates at three temperatures (20, 70 and 120°C) and three crosshead velocities (0.01, 1 and 10mm/min). Transverse matrix crack development is described for the nine corresponding experimental conditions. An LEFM approach is used to analyse the results concerning the first crack onset. After the validity of such an approach has been discussed, the focus is placed upon variations in the material resistance to transverse matrix cracking with temperature and loading rate.
Thermal stress induced by the adhesion topology of a semiconductor integrated circuit package
Authors: Lee D C , Kim M G , Lee J I
Published: April 2011

In the semiconductor integrated circuit (IC) package, the top surface of the silicon chip is directly attached to the lead frame by a double-sided adhesive layer. Under the functional operation, the IC package has been known to encounter such thermomechanical failure as delamination. This failure is due to the thermal residual strain and stress of the adhesive surface on the silicon chip in the curing-cooling process. The induced thermal effects in the curing process affect the fatigue life of the IC package. Thus, it is necessary to reduce the thermal stress induced on the silicon chip. In this paper, to reduce the surface failure and improve the durability of the silicon chip, the adhesive topologies and thermal stresses on the silicon chip at curing temperature are studied by finite element analysis (FEA).
Cost as a driver in advanced composites aerospace research
Authors: Clayton G , Howe C
Published: April 2011

This paper describes the influences of manufacturing cost reduction on Australian aerospace advanced composites research and development. Cost reduction is seen to be one of the prime drivers, alongside new product and services evolution and market growth, for undertaking research. Some recent research and development work conducted at Hawker de Havilland on a leading-edge flap control serves as an illustration of the methods employed to evaluate article cost across different manufacturing processes. Production flow diagrams are used together with applicable cost, equations to estimate product cost, and a summary is given on cost comparisons.
Fracture and tensile fatigue properties of stitched fibreglass composites
Authors: Mouritz A P
Published: April 2011

The effect of through-thickness stitching on the in-plane fracture toughness and tensile fatigue properties of a glass reinforced polymer composite is investigated. A large improvement in the fracture toughness of fibreglass composites can be achieved by stitching. It is discovered that stitching can force the crack to follow a tortuous path from stitch to stitch, and this improves the fracture resistance. However, the ability of stitching to increase the fracture toughness is critically dependent on the stitch pattern. Stitching is found to shorten the tensile fatigue life of the fibreglass composite. The fatigue damage mechanisms are investigated, and it is shown that crimping and distortion of load-bearing fibres by the stitches results in the early formation of cracks which is the cause of the reduced fatigue life. As with the in-plane fracture toughness, the fatigue performance is affected by the stitch pattern.
Selective generation of Lamb wave modes and their propagation characteristics in defective composite laminates
Authors: Su Z , Ye L
Published: April 2011

Techniques for the generation of Lamb waves with purpose of non-destructive inspection (NDI) were briefly reviewed. An active excitation control circuit was designed and instrumented with an online damage diagnosis system, by which the desired fundamental symmetric Lamb mode, shear mode and antisymmetric mode can be selectively stimulated. A signal processing and identification algorithm in the time-scale domain, using spectrographic analyses based on the wavelet transform technique, was developed to assist the wave signal interpretation. The proposed excitation methodology was applied to the study of the dispersion and propagation characteristics of Lamb waves in quasi-isotropic CF/EP composite laminates with delamination. For validation, numerical simulations were conducted in parallel with experimental investigations.
Prediction of non-linear electromagnetoelastic properties for piezoelectric/piezomagnetic fibre reinforced composites
Authors: Tan P , Tong L
Published: April 2011

In this paper, the constitutive equations for the non-linear electromagnetothermoelastic properties of piezoelectric/piezomagnetic fibre reinforced composites (PEMFRC) materials are presented. These equations are derived on the basis of the thermodynamic principle using Gibbs free energy expanded into a Taylor series, emphasis being placed on quadratic non-linearities. The coupling effects between any two independent variables such as the preload and the electric and magnetic fields are included in these equations. Subsequently, the non-linear constitutive equations and isofield assumptions are employed to derive the closed-form formulae required for the present XY PEMFRC non-linear model and YX PEMFRC non-linear model. These two models can be used to predict the effective non-linear electromagnetoelastic properties of PEMFRC materials. Single- and double-loading conditions are introduced when deriving the required closed-form formulae for the effective non-linear electromagnetoelastic constants of PEMFRC materials. Using the present models, a parametric study is conducted for both LiNbO3/CoFe2O4 and PZT-5H/CoFe2O4 PEMFRC materials. For the effective non-linear electromagnetoelastic properties along the fibre direction, the corresponding closed-form formulae proposed in this paper are consistent with those derived using the rule of mixtures. For the case of the piezoelectric fibre volume fraction Vf = 1 and the electric field Hn = 0, the constitutive equations proposed in this paper for the non-linear behaviour of PEMFRC materials are the same as those available in the literature for purely piezoelectric materials.
Advanced bobsleigh design. Part 1: Body protection, injury prevention and performance improvement
Authors: Dabnichki P , Motallebi F , Avital E
Published: April 2011

Bobsleigh is one of the most popular Olympic winter sports where technology and engineering play a major role. The technological advances in the sport over the last two decades have been notable. However, the introduction of the female bobsleigh competition highlighted some noticeable shortcomings in the current sled design. The present work proposes ergonomic modifications to the existing bobsleigh design, with specific focus on women, aiming to address these issues by simultaneously reducing the injury rate and delivering improved performance. Two main aspects are discussed: bobsleigh interior design, i.e. the introduction of internal padding, footrests, etc., and modifications to the push handles. It is shown that such modifications would not cause any deterioration in the performance but could theoretically bring some performance benefits such as improved driving stability and better aerodynamics owing to the reduced size of the cavity. The possibility of rule alterations concerning the size and weight of sleds is briefly discussed.
Advanced bobsleigh design. Part 2: Aerodynamic modifications to a two-man bobsleigh
Authors: Motallebi F , Dabnichki P , Luck D
Published: April 2011

The aim of the present study is to improve the aerodynamic performance of the bobsled as a function of its shape and the relative position of the athletes inside the bobsled. This performance optimization problem is studied by means of wind tunnel testing. The aerodynamic responses of the manned and unmanned bobsleigh are analysed in terms of overall drag force measurements. Experimental results show that the proposed modifications to the sidewalls and the nose section of the bobsled improve its drag performance. The relative position of the driver and the brakeman has a great influence on the drag of the bobsled.
Processing of all-polypropylene composites for ultimate recyclability
Authors: Cabrera N , Alcock B , Loos J , Peijs T
Published: April 2011

This paper describes the development of so-called all-polypropylene composites, namely polypropylenes (PPs) reinforced with oriented polypropylene fibres rather than glass or natural fibres. These all-polypropylene composites have specific economic and ecological advantages since, upon recycling, a polypropylene blend is obtained that can be reused to make all-PP composites again or, alternatively, be used for other PP-based applications. One of the main challenges in the development of all-PP composites is to create a processing window that is large enough to keep the oriented PP reinforcement intact while this is combined or impregnated with PP resin. The technological breakthrough in the processing of all-PP composite that has been established is based on the hot compaction (welding) of coextruded tapes. These coextruded tapes consist of an oriented polymer core, providing strength and stiffness, and a polymer skin with a lower melting temperature than the core material forming the matrix and bonding the tapes together. Consolidation is achieved by simply ‘welding’ the tapes together, thus avoiding typical impregnation problems encountered in traditional thermoplastic composite manufacturing. Pilot studies have already shown the potential of a wide range of manufacturing technologies including thermoforming and filament winding.
Influence of process parameters on residual stress in thermoplastic filament-wound parts
Authors: Schlottermöller M , Schledjewski R , Mitschang P
Published: April 2011

Owing to the existence of residual stresses, working stresses can have a smaller effect. The present paper reports on an investigation of the influence of process parameters on the induced residual stress in filament-wound test samples. It describes the necessary machinery and measuring devices for a repeatable process. The process parameters were identified and their influence on the implemented residual stress during the production of thermoplastic filament-wound parts was determined using a design of experiments approach with a fractional factorial concept. As a result of this sensitivity study on the established process, the winding angle, the annealing, the number of layers, the mandrel temperature and, to a slightly smaller extent, the tape tension were identified to have a significant influence. However, only the applied tape tension provides the possibility of controlling the residual stress independently from the parameters that are fixed by the mechanical design or simply the geometry of the part.
Dielectric and mechanical studies of the durability of adhesively bonded aluminium structures subjected to temperature cycling. Part 2: Examination of the failure process and effects of drying
Authors: Armstrong G S , Banks W M , Pethrick R A , Crane R L , Hayward D
Published: April 2011

Additional dielectric measurements and mechanical tests on adhesively bonded joints are reported for bonds having been aged by complete immersion in water at 50 and 65 °C and by changing between these temperatures. Dielectric frequency domain measurements are discussed in terms of the effects on the adhesive and the oxide layer as a result of water ingress to the bond line. Initially, the moisture adsorption follows a pseudo-Fickian behaviour, and correlation with the mechanical properties would suggest that the initial loss in mechanical strength is consistent with plasticization of the adhesive layer. In all the cases studied, acceleration in the rate of increase in the permittivity was observed consistent with the moisture converting the interfacial oxide layer to hydroxide. X-ray diffraction measurements indicate that the hydroxide formed was predominantly of the boehmite [λ-A1O(OH)] form, but also with some of the diaspore [α-A1O(OH)] form. The change of the oxide to hydroxide changes the bond line characteristics and is clearly identifiable in the time domain reflectometry (TDR) measurements. Further analysis of the high-frequency dielectric data indicate that the changes in the adherend surface resistivity that occur in the latter stages of ageing may be indicative of the conversion of oxide to hydroxide. Comparison of the TDR measurements with ultrasonic and optical images indicated that the dramatic loss of shear and cleavage strength is coincident with the observation of defects having been created in the interfacial layer. The ability for a joint to recover on drying was investigated, and the data indicate that, depending on the distribution of the moisture in the bond, recovery of mechanical properties is or is not possible. In the initial stages, when moisture is in the adhesive, recovery is in principle possible. However, once moisture has changed the interfacial layer, recovery becomes more difficult.
Oxide fibres in a nickel-base matrix—do they degrade or become stronger?
Authors: Mileiko S T , Sarkissyan N S , Kolchin A A , Kiiko V M
Published: April 2011

The fibre/matrix interface in fibrous composites with brittle fibres can play a synergetic role in developing creep resistance of the composites. Increasing the interface strength, which is accompanied with a better fibre/matrix contact, results firstly in a decrease in the fibre critical length, which enhances the fibre strength as a result of the scale effect, and secondly in an increase in the characteristic fibre strength as a result of the healing of defects on the fibre surface. Such behaviour of the fibres is the most important argument in favour of producing heat-resistant metal matrix composites with high interface strength. An additional argument is the stability of such an interface under variable loading. It is shown that oxide fibres in Ni-base matrices can be sufficiently strong to provide Ni-base composites with high creep resistance up to a temperature of at least 1150°C.
Design of composite laminates with low thermal expansion
Authors: Bressan F , De Bona F , Somà A
Published: April 2011

A procedure for the design of structural elements made of carbon-epoxy laminates with low thermal expansion in the main direction has been developed. By using an interferometric technique, the influence of material characteristics and process parameters on the thermal expansion behaviour was assessed. In order to minimize the interval of uncertainty of the thermal expansion coefficient, using the lamination theory, a laminate with layers at 0° and 30° coupled with layers with an orientation chosen between 45° and 60° was proposed. Prototypes were constructed following a standard manufacturing process. Interferometric measurements were performed, showing that the proposed procedure permits a low thermal expansion with a reduced uncertainty to be achieved.
Creep properties and failure assessment of new and fully repaired P91 pipe welds at 923 K
Authors: Hyde T H , Sun W , Becker A A , Williams J A
Published: April 2011

A creep testing programme was conducted at 923 K to identify the properties for new and repaired welds fabricated in a 9CrMoNbV grade P91 steel using a 9CrMoNbV weld metal. The material data obtained were assessed and used to determine the material creep and damage constitutive equations for the parent material (PM), weld metal (WM) and heat-affected zone (HAZ) materials in the P91 welds. Steady state creep and continuum damage finite element analyses were performed to assess the failure behaviour of the circumferential welds in the pipes, under two internal pressures and a range of end load levels. A full post-weld heat treatment is assumed to have been carried out, and any effects of welding-induced residual stresses were neglected. The results obtained have illustrated the main features of life reduction of a P91 pipe owing to the presence of welds, an additional life reduction due to repair and the more limited life reduction due to geometry difference, for the particular set of material properties used.
Damage zone characterization of composite panels with a modified crack growth model
Authors: Lexian H , Daghyani H R , Toudeshky H H
Published: April 2011

In the present study a modified crack growth model (MCGM) is introduced to analyse the crack propagation status in the damaged zone of fibre reinforced composites. The damaged zone is modelled on the basis of a virtual crack being subjected to a cohesive closure stress. The residual strengths of composite laminates are evaluated characterizing the matrix crack density at the damaged zone and defining a relationship between the plate stiffness before and after damage. Experimental tests were performed employing epoxy/glass fibre reinforced composite laminates to determine the residual strength of centre cracked specimens. The residual strength of composite panels using the new model correlates well with experimental results when compared with previous models.
Effect of the properties of the polymer materials on the quality of selective laser sintering parts
Authors: Shi Y , Li Z , Sun H , Huang S , Zeng F
Published: April 2011

The effect of the properties of the polymer materials, such as molecular weight, molten viscosity, crystallization rate and the particle size of the powder, on the quality of selective laser sintering (SLS) parts is researched. The results indicate that the molecular weight affects the quality of the SLS parts through the melting viscosity. SLS parts of higher density can be fabricated with polymer materials of lower melting viscosity. Crystallinity largely affects the precision of the SLS part—shrinkage is more serious with increasing crystallinity. SLS parts sintered with polymer powder materials, whose melting peak and crystalline peak differ greatly, have high dimensional precision. The particle size of the powder affects not only the precision but also the density of the SLS part. The appropriate particle size is about 75-100 μm.
Characterizing alloy additions to carbon high-nitrogen steel
Authors: Rawers C J
Published: April 2011

Alloy compositions are designed for specific industrial needs and applications. In this study, alloying elements that are known to enhance specific material properties of commercial Fe-Cr-Ni stainless steels were found to be similarly successful when added to Fe-15Cr-15Mn stainless steels. Unique to this study is the alloy addition of both carbon and nitrogen in excess of approximately 0.4 wt%. The nitrogen and carbon remained as interstitials without the formation of nitride or carbide precipitates even in carbon and nitrogen concentrations as high as 2wt%. Nitrogen and carbon alloying increased hardness, strength (σYIELD 850 MPa and σTMAX 2 GPa), toughness and wear resistance. Precipitate formers such as niobium and solid solution additives such as silicon and molybdenum enhanced σYIELD but to a much smaller extent than interstitial alloying. Additions of silicon and molybdenum significantly improved oxidation protection at all temperatures and are necessary to prevent spallation at temperatures above 800 K. In corrosion tests, alloys form a passive region, but small concentrations of nickel are necessary to ensure repassivation.
Development and application of advanced textile composites
Authors: Bannister M K
Published: April 2011

Three-dimensional fibre-reinforced polymer composites made by the textile processes of weaving, braiding, stitching and knitting have tremendous potential for improving the performance of composite structures and reducing their cost of manufacture. Current applications of three-dimensional composites are described, including examples in the aerospace, maritime, automotive, civil infrastructure and biomedical fields. However, to date the use of three-dimensional textile composites has not been exploited for many potential applications, and some of the issues impeding the widespread use of three-dimensional textile composites are identified.
Fracture toughness tests of wheelset materials used in the Japanese Shinkansen express trains
Authors: Dzugan J , Ito Y , Kwon S , Ogawa K , Shoji T
Published: April 2011

The present study is part of a project dealing with the service life extension of Japanese Shinkansen superexpress train wheelsets. This paper deals with fracture toughness behaviour evaluation of wheelset materials. Two wheel materials and one axle material were investigated. The fracture toughness under quasi-static as well as under dynamic loading conditions was evaluated. The results were summarized and the fracture toughness velocity dependence was evaluated.
Monitoring the polymerization of a diglycidyl ether bisphenol-A/2,2′-dimethyl-4,4′-methylenebis (cyclohexylamine) matrix with a Fourier transform infrared optical fibre sensor
Authors: Fouchal F , Knight J A G , Dickens P M
Published: April 2011

An optical fibre sensor (OFS) for the online monitoring of the polymerization reaction is described in this paper. The sensor, based on Fourier transform infrared (FT-IR) and differential scanning calorimetry (DSC) analysis, was used to study the reaction between diglycidyl ether bisphenol-A (DGEBA) and 2,2′-dimethyl-4,4′-methylenebis(cyclohexylamine) (DMMB-CHA). Changes in concentrations of reactants and products were monitored over the curing period at different temperatures by the FT-IR technique, and from DSC runs the variation in the enthalpy of reaction over time for different curing temperatures was determined. Plots of fractional conversions versus time from the two methods were produced and compared. An attempt to deduce glass transition temperatures from the fractional conversion curves produced by FT-IR is also described. This involved the use of the fitting polynomial calculated from the DSC results. As a result, a sensor designed for embedding into a system curing at elevated temperature was constructed and tested.
Transformation-induced creep and stress relaxation of TiNi shape memory alloy
Authors: Matsui R , Tobushi H , Ikawa T
Published: April 2011

The subloop deformation behaviour of a TiNi shape memory alloy (SMA) under various loading conditions was investigated. Creep and stress relaxation were induced for stress-controlled subloop loadings. The results obtained can be summarized as follows:

1. In the case of subloop loading under stress-controlled conditions, strain increases under constant stress in the loading process and decreases in the unloading process. Creep and creep recovery appear owing to martensitic transformation (MT). 2. In the case of subloop loading under stress-controlled conditions, stress decreases under constant strain in the loading process and increases in the unloading process. Stress relaxation and stress recovery appear owing to martensitic transformation. 3. In the case of subloop loading under strain controlled-conditions with a low strain rate, the reloading stress-strain curve passes through the unloading start point. In the case of stress-controlled conditions, return-point memory does not appear. 4. The above behaviour of the return-point memory and pseudoviscoelastic behaviour of creep and stress relaxation appear according to the martensitic transformation and the reverse transformation, based on variations in stress and temperature.
Evaluation of test regimes for stab-resistant body armour
Authors: Walker C A , Gray T G F , Nicol A C , Chadwick E K J
Published: April 2011

Modern lightweight stab-resistant body armour has been developed in response to the operational requirements and the experiences of police forces. While a high degree of protection may be afforded to the wearer, this has usually been achieved at the expense of weight, stiffness, and comfort. The use of a test method to measure the protection level of a proposed design against a target specification is inherent in the design and development process. This study reviews data used to establish recent improvements in standard test methods, and shows that deficiencies in current standards may well lead to over-specification of body armour. It is shown that more detailed characterization of real human stabbing actions is needed and the test situation needs to be viewed as a multibody, dynamic interaction if results are to be obtained that reflect the reality of an attack. The information will be of particular interest to body armour manufacturers and researchers working to improve armour design.
Geometric modelling of industrial preforms: Woven and braided textiles
Authors: Robitaille F , Clayton B R , Long A C , Souter B J , Rudd C D
Published: April 2011

Predictive calculations of the physical properties of fibrous preforms and composite parts require an appropriate description of the preform geometry. Most internal dimensions of a preform are set during its manufacturing through mechanical interactions occurring between the tows and threads. However, the global shape and the interlacing patterns of the constituent textiles are determined independently. In this paper, a formal procedure for the description of the interlacing patterns is proposed. This procedure, which is based on the individual textile manufacturing processes, is general in the textiles considered and in the possible applications. The interlacing patterns are expressed by a series of vectors that follow a universal set of criteria and are generated from the values taken by the processing parameters. Defining examples are given for three-dimensional woven textiles and three-dimensional tubular braided textiles, and geometrical applications are also presented. Further examples for warp-knitted textiles and multiple-layer stacks will be given in a subsequent paper, together with examples of physical applications.