Shear tests of rivet fastened rectangular hollow flange channel beams

The intermittently rivet fastened Rectangular Hollow Flange Channel Beam (RHFCB) is a new cold-formed hollow section proposed as an alternative to welded hollow flange channel beams. It is a monosymmetric channel section made by intermittently rivet fastening two torsionally rigid rectangular hollow flanges to a web plate. This process enables the end users to choose an effective combination of different web and flange plate sizes to achieve optimum design capacities. Recent research studies focused mainly on the shear behaviour of the most commonly used lipped channel beam and welded hollow flange beam sections. However, the shear behaviour of rivet fastened RHFCB has not been investigated. Therefore a detailed experimental study involving 24 shear tests was undertaken to investigate the shear behaviour and capacities of rivet fastened RHFCBs. Simply supported test specimens of RHFCB with aspect ratios of 1.0 and 1.5 were loaded at mid-span until failure. Comparison of experimental shear capacities with corresponding predictions from the current Australian cold-formed steel design rules showed that the current design rules are very conservative for the shear design of rivet fastened RHFCBs. Significant improvements to web shear buckling occurred due to the presence of rectangular hollow flanges while considerable post-buckling strength was also observed. Such enhancements to the shear behaviour and capacity were achieved with a rivet spacing of 100 mm. Improved design rules were proposed for rivet fastened RHFCBs based on the current shear design equations in AISI S100 and the direct strength method. This paper presents the details of this experimental investigation and the results.

Influence of initial texture on the microstructural instabilities during compression of commercial ?-Titanium at 25 °C to 400 °C

Cylindrical specimens of textured commercial pure alpha-titanium plate, cut with the cylinder axis along the rolling direction for one set of experiments and in the long transverse direction for the other set, were compressed at strain rates in the range of 0.001 to 100 s-1 and temperatures in the range of 25-degrees-C to 400-degrees-C. At strain rates greater-than-or-equal-to 1 s-1, both sets of specimens exhibited adiabatic shear bands, but the intensity of shear bands was found to be higher in the rolling direction specimens than in the long transverse direction specimens. At strain rates -0.1 s-1, the material deformed in a microstructurally inhomogeneous fashion. For the rolling direction specimens, cracking was observed at 100-degrees-C and at strain rates -0.1 s-1. This is attributed to dynamic strain aging. Such cracking was not observed in the long transverse specimens. The differences in the intensity of adiabatic shear bands and that of dynamic strain aging between the two sets of test specimens are attributed to the strong crystallographic texture present in these plates.

Micro and macroscopic features of impact failed defect induced carbon-epoxy composites

Laminated composite structures are susceptible to damage under impacts with attendant properly degradation. While studies on damage tolerance behaviour are emphasised and the findings reported, the citations correlating impacts with the fracture features are limited. In the present study, therefore, attempts have been made to depict how the transition of the fracture features take place depending on the type and extent of defect introduced onto the carbon-epoxy system. The test specimens were subjected to differing levels of low energy pendulum impacts with a view to have specimens with varying levels of intial impacts history. Into such specimens, additional defect in the form of slits of varying depths were introduced by a mechanical process. The test coupons were then allowed to fail by impact. The fracture surface was studied under scanning electron microscope. The fractographic features that appear, based on the induced/inserted defects, are presented in this paper. It was noticed that the energy absorbed for final fracture could be associated with the defect introduced into the system. It was also observed that the size of the mechanically inserted defect had a significant influence on the features of the fracture surface.

On the characterisation of syntactic foam core sandwich composites for compressive properties

Sandwich structures, especially those with honeycomb and grid structures as the core material, are very commonly employed in aircraft structures. There is an increasing use of closed-pore rigid syntactic foams as core materials in sandwich constructions because they possess a number of favourable properties. The syntactic foams, owing to their structure and formation, behave differently under compression compared to other traditionally used core materials. In the present study, therefore, syntactic foam core sandwich constructions are evaluated for their behaviour under compression in both edgewise and flatwise orientations. Further, the work characterises the relative performance of two sets of sandwich materials, one containing glass-epoxy and the other, glass/carbon hybrid-epoxy skins. As non-standard geometry test specimens were involved, only a comparative evaluation was contemplated in this approach. The experiments indicate that the nature of the reinforcement fabric in the skin has a bearing on the test results in edgewise orientation. Thus, the tendency towards initiation of vertical crack in the central plane of the core material, which is a typical fracture event in this kind of material, was found to occur after a delay for the specimens containing the glass fabric in the skin. Attempts are made to establish the correlation between observations made on the test specimen visually during the course of testing and the post-compression microscopic examinations of the fracture features.

Novel piezoelectric thin film impact sensor: application in non-destructive material discrimination

We report on the design, development, and performance study of a packaged piezoelectric thin film impact sensor, and its potential application in non-destructive material discrimination. The impact sensing element employed was a thin circular diaphragm of flexible Phynox alloy. Piezoelectric ZnO thin film as an impact sensing layer was deposited on to the Phynox alloy diaphragm by RF reactive magnetron sputtering. Deposited ZnO thin film was characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM), and Scanning Electron Microscopy (SEM) techniques. The d(31) piezoelectric coefficient value of ZnO thin film was 4.7 pm V-1, as measured by 4-point bending method. ZnO film deposited diaphragm based sensing element was properly packaged in a suitable housing made of High Density Polyethylene (HDPE) material. Packaged impact sensor was used in an experimental set-up, which was designed and developed in-house for non-destructive material discrimination studies. Materials of different densities (iron, glass, wood, and plastic) were used as test specimens for material discrimination studies. The analysis of output voltage waveforms obtained reveals lots of valuable information about the impacted material. Impact sensor was able to discriminate the test materials on the basis of the difference in their densities. The output response of packaged impact sensor shows high linearity and repeatability. The packaged impact sensor discussed in this paper is highly sensitive, reliable, and cost-effective.

Small-scale mechanical testing of materials

Small-scale mechanical testing of materials has gained prominence in the last decade or so due to the continuous miniaturization of components and devices in everyday application. This review describes the various micro-fabrication processes associated with the preparation of miniaturized specimens, geometries of test specimens and the small scale testing techniques used to determine the mechanical behaviour of materials at the length scales of a few hundred micro-meters and below. This is followed by illustrative examples in a selected class of materials. The choice of the case studies is based on the relevance of the materials used in today's world: evaluation of mechanical properties of thermal barrier coatings (TBCs), applied for enhanced high temperature protection of advanced gas turbine engine components, is essential since its failure by fracture leads to the collapse of the engine system. Si-based substrates, though brittle, are indispensible for MEMS/NEMS applications. Biological specimens, whose response to mechanical loads is important to ascertain their role in diseases and to mimic their structure for attaining high fracture toughness and impact resistance. An insight into the mechanisms behind the observed size effects in metallic systems can be exploited to achieve excellent strength at the nano-scale. A future outlook of where all this is heading is also presented.

Adesão dos cimentos Epiphany SE e iRoot SP: Resistência à tração e mapeamento dentinário por microscopia digital

O objetivo deste estudo foi avaliar o efeito da microestrutura dentinária na adesão de cimentos endodônticos modernos através: do desenvolvimento de uma metodologia para caracterizar microestruturalmente a dentina; da avaliação da resistência de união (através de ensaios de tração) dos cimentos endodônticos Epiphany SE, iRoot SP e AH Plus; da correlação dos dados obtidos da caracterização da microestrutura dentinária e dos ensaios de tração. Trinta terceiros molares inclusos, recém extraídos, foram embutidos em resina epóxi e seccionados 0,5mm abaixo da junção esmalte-dentina. Doze amostras foram eliminadas durante à preparação metalográfica devido à exposição da câmara pulpar. De cada dente, uma área de análise (AA) com 3,25 mm de diâmetro foi mapeada utilizando técnicas de microscopia ótica digital para: captura de ~400 imagens formando um mosaico; análise digital de imagens, obtendo os resultados de quantidade de túbulos (QT) e de fração de área de túbulos (FAT) do mosaico; conversão da imagem do mosaico em um mapa colorido em que as cores estão diretamente relacionadas à densidade de área tubular. As dezoito amostras restantes foram divididas em 3 grupos (N=6), de acordo com o cimento utilizado, para confecção dos corpos de prova para os ensaios de tração. Os valores de da resistência de união (RU) obtidos foram analisados estatisticamente com teste não-pareado t com correção de Welch e pelo teste F para comparar variâncias Os dados de FAT e de QT foram submetidos ao teste de D'Agostino & Pearson revelando-se não normais (P>0,05), o que indica grande variabilidade da amostragem. O cimento Epiphany SE apresentou uma resistência de união significativamente menor que o cimento AH Plus (P <0,05). Os corpos de prova do iRoot SP falharam prematuramente e não foram analisados. A aplicação do teste r de Spearman não demonstrou correlação significativa entre FAT e RU (P>0,05). O MEV de pressão variável foi utilizado para avaliar qualitativamente a superfície de fratura após os ensaios de tração. A análise revelou um padrão de fratura mista para o AH Plus e o Epiphany SE, além de diferenças no tamanho e na forma das partículas desses cimentos, o que pode influenciar no comportamento mecânico. Dentro da amostragem realizada, não se encontrou correlação significativa entre microestrutura dentinária e a resistência de união.

Use of enriched live prey in promoting growth and maturation of tiger shrimp (Penaeus monodon)

This study was undertaken to determine the effect of nutritional management of broodstock of Penaeus monodon on growth and maturation. Test specimens were obtained from a grow-out pond before attainment of maturity and were reared in hatchery tanks. Four types of dietary treatments (M1–M4) were given to separate batches that were run in duplicate. Feeding trials continued for five months. A diet with live bloodworm, bioencapsulated to contain tricalcic phosphate as its major component, was found to be the most efficient. Specimens of this particular batch assimilated food more efficiently, grew at a faster rate and attained maturity earlier than other groups. Bloodworm provided the lipid fractions for which there is no de novo synthesis in shrimp. The enrichment product acted by promoting somatic growth and increasing transfer of biochemical constituents needed by the ovary for develop

Residual properties of an injection-molded poly(phenylene ether ketone) carbon composite during flexural fatigue

The present work investigates the effects of cyclic fatigue loading on the residual properties of an injection-molded composite, carbon-fiber-reinforced poly(phenylene ether ketone) (CF/PEK-C), and damage development in this material under fatigue lending. Test specimens, which had been conditioned to various preselected fatigue damage stages, were measured for their residual properties. The results indicated that cyclic fatigue loading alters the constitutive behavior of the injection-molded composite, especially in the non-linear portion of the stress/strain curve. The residual strength decreases with increase in the number of fatigue cycles as a consequence of the accumulation of fatigue damage, which is dominated by the growth of microcracks. While the residual modulus increases slightly with cyclic fatigue loading, this is probably due to the oriented hardening resulting from creep deformation which is induced during cyclic loading. (C) 1997 Elsevier Science Limited.

The effect of formulated molecular weight on temperature resistance and mechanical properties in polyimide based composites

This experimental study examines the role of formulated molecular weight between crosslink sites on the temperature resistance and mechanical properties of composites based on a polyimide containing a diphenyl thioether unit (PTI). The composites are fabricated by in situ polymerization of monomer reactants (PMR) using three monomeric ingredients: bis(3,4-dicarboxyphenyl) sulfide dianhydride (TDPA); 4,4'-methylene dianiline (MDA); and the monomethyl ester of norbornene anhydride (NE). By changing monomeric molar ratio, three formulations are prepared, in which formulated molecular weight between crosslink sites varies from 1487 to 3446 g mol(-1). Unidirectional composite laminates from each formulation and T300 carbon fibres are compression moulded and cut into a series of test specimens. By measuring the glass transition temperature (T-g), Mode I interlaminar fracture toughness (G(IC)) and other mechanical properties at room and elevated temperatures, the influences of formulated molecular weight on the temperature resistance and mechanical properties of PTI-based composites are investigated.

Effect of mechanical deformation on permeation of hydrogen in iron

Rate of hydrogen permeation was measured under static as well as dynamic mechanical deformation conditions, Cylindrical tensile test specimens were used for the study and hydrogen permeation was measured electrochemically, It was observed that the hydrogen diffusivity decreased as plastic deformation increased for the static deformation experiments while elastic deformation had no significant effect on diffusivity but increased the steady state permeation flux, For the dynamic loading experiment, an elastic deformation increased the hydrogen permeation rate almost linearly. Onset of plastic deformation led a sudden decrease of permeation rate and the reduced rate was rapidly recovered when the plastic deformation ceased. These rapid changes in the permeation rates were explained that the absorbed hydrogen was trapped by dislocations and creation rate and density of dislocations changed drastically when plastic deformation started and stopped.

Comparisons between “sand blast” and “centripetal effect accelerator” type erosion testers

There are two major types of erosion testing devices that are used throughout the world for quantifying particle impact erosion against a solid surface. The first of these uses pressurised air to accelerate abrasive particles through a nozzle so that they impinge upon a target specimen. The second adopts a rotating disc to accelerate abrasive particles using the centripetal effect so that they impinge upon a series of targets arranged around the periphery of the disc. This paper reports the findings of a collaborative project that was designed to compare the performance and results obtained from a rig of each of the two types mentioned above. The sand blast type rig was provided by The Department of Powder Science Technology (POSTEC) at The Telemark Technological Research and Development Centre (TEL-TEK), Porsgrunn, Norway while the centripetal effect accelerator was provided by The Wolfson Centre for Bulk Solids Handling Technology, University of Greenwich, London, UK. The test programme included tests against a wide range of materials that are commonly used in pneumatic handling facilities. (Pneumatic handling is a means of conveying and transporting powders and granular solid materials in bulk in industrial process plant, through pipelines using a gas as the carrier medium.) Olivine sand was used as the abrasive and it was projected against the test specimens at velocities and concentrations commensurate with those seen in pneumatic conveyors. In all instances the materials used in the test programme were taken from the same batch so that scatter of experimental results due to specimen variation was minimised. The paper contains a series of recommendations for erosion testing equipment. A discussion based on the results and their applicability to the prediction of wear in pneumatic conveyors concludes the paper.

Degradation of poly-L-lactide. Part2 : increased temperature accelerated degradation

Poly-L-lactide (PLLA) is one of the most significant members of a group of polymers regarded as bioresorbable. The degradation of PLLA proceeds through hydrolysis of the ester linkages in the polymer's backbone; however, the time for the complete resorption of orthopaedic devices manufactured from PLLA is known to be in excess of five years in a normal physiological environment. To evaluate the degradation of PLLA in an accelerated time period, PLLA pellets were processed by compression moulding into tensile test specimens, prior to being sterilized by ethylene oxide gas (EtO) and degraded in a phosphate-buffered solution (PBS) at both 50°C and 70°C. On retrieval, at predetermined time intervals, procedures were used to evaluate the material's molecular weight, crystallinity, mechanical strength, and thermal properties. The results from this study suggest that at both 50°C and 70°C, degradation proceeds by a very similar mechanism to that observed at 37°C in vitro and in vivo. The degradation models developed also confirmed the dependence of mass loss, melting temperature, and glass transition temperature (Tg) on the polymer's molecular weight throughout degradation. Although increased temperature appears to be a suitable method for accelerating the degradation of PLLA, relative to its physiological degradation rate, concerns still remain over the validity of testing above the polymer's Tg and the significance of autocatalysis at increased temperatures.

Delamination Fracture Related to Tempering in a High-Strength Low-Alloy Steel

The delamination or splitting of mechanical test specimens of rolled steel plate is a phenomenon that has been studied for many years. In the present study, splitting during fracture of tensile and Charpy V-notch (CVN) test specimens is examined in a high-strength low-alloy plate steel. It is shown that delamination did not occur in test specimens from plate in the as-rolled condition, but was severe in material tempered in the temperature range 500 °C to 650 °C. Minor splitting was seen after heating to 200 °C, 400 °C, and 700 °C. Samples that had been triple quenched and tempered to produce a fine equiaxed grain size also did not exhibit splitting. Microstructural and preferred orientation studies are presented and are discussed as they relate to the splitting phenomenon. It is concluded that the elongated as-rolled grains and grain boundary embrittlement resulting from precipitates (carbides and nitrides) formed during reheating were responsible for the delamination.

The influence of reusing ‘Formtex’ controlled permeability

The effects of the reuse of ‘Formtex’ Controlled Permeability Formwork (CPF) liner on strength and durability properties of concrete were investigated at two different water-cement ratios and the results are reported in this paper. Test blocks were cast using the CPF on one side and impermeable formwork (IF) on the opposite side of the mould so that direct comparisons could be made between the two. The strength was assessed using the Limpet pulloff tester and both the air permeability and the water absorption (sorptivity) were measured using the Autoclam Permeability System. Both these instruments measured the ‘covercrete’ properties. In addition, cores cut from the test specimens were subjected to an accelerated carbonation test and a chloride exposure test. The results showed that the ‘Formtex’ CPF increases the surface strength and the durability of concrete compared to the IF. There was an almost complete elimination of blowholes. The permeability of concrete decreased and its resistance to the ingress of both carbon dioxide and chlorides increased when CPF was used. The beneficial effects of the Formtex CPF were most evident in concrete of higher water-cement ratio. With the reuse of the Formtex liner twice, that is a total of three uses, the performance of the CPF to improve the properties of concrete remained almost the same. In this research the CPF liner was cleaned thoroughly between each use, which must be adhered to for site applications for reproducing the beneficial effects observed in the laboratory.