Round Specimens Research Articles

Local fatigue strength assessment of induction hardened components based on numerical manufacturing process simulation

Induction hardening as common heat treatment process for highly-stressed automotive components significantly affects the surface layer properties leading to a compressive residual stress condition and a local hardening of the material. The beneficial effect of the post-treatment is generally well investigated and already implemented in industrial applicable guidelines by considering nominal fatigue strength enhancement factors. However, as the fatigue strength improvement essentially depends on the applied manufacturing process parameters, the resulting local material properties and the local load stress distribution, an elaborated numerical fatigue assessment procedure based on a manufacturing process simulation of a notched round specimen is presented in this paper. Thereby, a two-dimensional axi-symmetric model is set-up, whereby the inductive heating process is performed in COMSOL® and the subsequent quenching process in SYSWELD®. The resulting axial residual stress condition at the notch area of the specimen reveals a sound accordance to X-ray measurements. Finally, a local fatigue strength assessment based on the local strain approach is shown. Herein, manufacturing dependent residual stress states are considered as mean stresses on the basis of the damage parameter by Smith, Watson, and Topper. The estimated fatigue data points agree well to results of four-point bending fatigue tests, which basically prove the applicability of the presented fatigue design methodology.

Mechanical properties of SFRC using blended manufactured and recycled tyre steel fibres

This paper investigates the mechanical properties of 10 steel fibre reinforced concrete (SFRC) mixes at fibre dosages of 30, 35 and 45 kg/m3. Manufactured Steel Fibres (MSF) are used on their own, or blended with sorted steel fibres recycled from end-of-life tyres (RTSF). To characterise the flexural behaviour of the mixes, two flexural test methods, BS EN 14651:2005 3-point notched prism tests and ASTM C1550-05 centrally loaded round panel tests are employed. A strong correlation is found in the flexural behaviour of the SFRC prism and round panel specimens, with corresponding conversion equations proposed. The mechanical properties of hybrid mixes using RTSF vary depending on dosages, but are comparable with those of MSF-only mixes at the same fibre dosage. A positive synergetic effect is derived from hybrid mixes containing 10 kg/m3 of RTSF.

Impact of the heating/quenching process on the mechanical, optical and thermodynamic properties of polyetheretherketone (PEEK) films

ObjectiveThe aim of this study was to investigate the impact of a heating/quenching process on the optical, mechanical and thermodynamic properties of filled (20%_4000) and unfilled PEEK films (0%_2000 and 0%_4000). Heating/quenching was performed to simulate thermoforming as possible method to process thermoplastic polymers for dental application. MethodsFor the investigation, films of different PEEK qualities (0%_2000, 0%_4000, 20%_4000) were produced using isostatic pressing (n=10/quality). From each PEEK film, round specimens (n=20/PEEK film) with a diameter of 34mm were cut and following parameters were determined: translucency (T%), Martens-Hardness (HM), indentation modulus (EIT), glass transition temperature (TG), melting temperature (TM) and enthalpy of fusion (ΔHf). Same specimens were exposed to heating/quenching using defined parameters. Afterwards, T%, HM, EIT, TG, TM and ΔHf were determined again. Data were analysed using Kolmogorov–Smirnov test, univariate ANOVA followed by post-hoc Scheffé test with partial eta squared (ηp2), Kruskal–Wallis and Mann Whitney U test. Level of significance was defined to 95%. ResultsMaterials showed significant differences for all investigated parameters in the initial state, except of TG (p=0.249). The heating/quenching process showed a significant increase on T% for the unfilled materials 0%_2000 and 0%_4000. HM and EIT decreased significantly through heating/quenching for all materials. Moreover, heating/quenching showed a reduction of TG for 0%_2000 and 20%_4000, while TM decreased for 0%_2000 and 0%_4000. ΔHf confirms different crystallinities of tested materials. SignificanceThe heating/quenching process showed a significant impact on all investigated parameters. The highest impact was found for mechanical properties resulting in decreased values of HM and EIT.

Stress relaxation behaviour in IN718 nickel based superalloy during ageing heat treatments

Designing microstructure of components made from Inconel 718 nickel based superalloy (IN718) with tailored mechanical properties for high temperature applications, require sequential thermo-mechanical processing. This often includes straining and annealing at solution annealing temperature (i.e. ≈ 980°C) followed by water quenching and subsequent aging heat treatments at lower temperatures. In addition to the microstructure development (i.e. precipitation) the aging heat treatment partially relieve the residual stresses generated at previous stages of forging and water quenching, however the stress field will not be completely relaxed.In this study, a series of experiments were conducted on round tensile specimens made from IN718 bar to investigate tensile stress relaxation behaviours at elevated temperatures used for aging heat treatments. The stress relaxation curves obtained can be described by a hyperbolic function with a non-zero asymptotic stress (σ∞), which seems to be proportional to the initially applied stress (σ0) for a fixed temperature. This behaviour is investigated at temperatures between 620°C and 770°C that is a temperature range used in industry to perform the aging heat treatments to obtain microstructures with tailored mechanical properties. It has been shown that the σ∞/ σ0 ratio has decreased rapidly with increasing temperature at this range. The relaxation behaviour has been assessed numerically and an empirical relationship has been defined for each temperature that can be used for modelling purposes.

Erratum to: A Novel Approach to Determination of Threshold for Stress Corrosion Cracking (KISCC) using Round Tensile Specimens

Due to an error by the authors, the reference R. Rihan, R.K. Singh Raman, and R.N. Ibrahim: Materials Science and Engineering A, 2006, vol. 425, pp. 272-77 should have been included in the list of references as well as cited as a source of the data in Figures 11, 12 and 16.

Microporosity and statistical size effect on the fatigue strength of cast aluminium alloys EN AC-45500 and 46200

This paper investigates the fatigue strength of two cast aluminium alloys, EN AC-45500 and 46200, dealing with the influence of microporosity and the statistical size effect. Small-scale round specimens are extracted from cylinder heads and crank cases as typical cast components in automotive industry. Uniaxial fatigue tests under alternating tension/compression loading are performed. Local microstructural properties, such as second dendrite arm spacing and microporosity, are characterized by means of metallography, fracture surface analysis utilizing scanning electron microscopy, and X-ray computed tomography. The measurements reveal significant differences in microporosity and microstructure depending on the extraction position and specimen type. These findings are reflected by the experimental test results showing that the microporosity majorly affects the fatigue behaviour with a maximum difference in fatigue resistance at ten million load-cycles of up to 39% in case of the EN AC-45500 specimens. Additional experiments involving two different EN AC-46200 specimen types exhibiting unequal highly-stressed volumes demonstrate a reduction of the high-cycle fatigue strength by 8% caused by the statistical size effect. Fatigue strength assessment incorporates the application of the model by Tiryakioğlu based on the extreme value distribution of the micropore sizes by Gumbel, as well as the √area approach by Murakami. The evaluated results agree well to the fatigue tests enabling a local fatigue strength assessment under consideration of manufacturing process dependent material characteristics.

Stress correction method for flow stress identification by tensile test using notched round bar

In this paper, a stress correction method for flow stress identification using notched round bar tensile test is proposed. Flow stress is evaluated in uniform elongation and local elongation until final fracture in a tensile test with circumference notched round bar tensile test specimens. Tensile load and change in the shape of the notch are measured by image analysis. In order to correct the average tensile stress to the flow stress, inverse analysis is applied to the tensile test. For the validation of the inverse analysis, numerical tensile tests are performed by FEM. As a result of applying the inverse analysis for the numerical tensile tests, the corrected flow stress completely reproduces the two types of reference flow stress curves which are determined by Swift’s and Voce’s law. On the other hand, the flow stress corrected by Bridgman’s method, which is a conventional stress correction method, overestimated these reference flow stress curves. In the case of the actual tensile test of low carbon steel SS400 (in JIS), the flow stress corrected by inverse analysis corresponds to Swift’s law determined in uniform elongation. As well as numerical tensile test results, the flow stress corrected by Bridgman’s method is higher than that of obtained by the inverse analysis.

A Validation Approach for Quasistatic Numerical/Experimental Indentation Analysis in Soft Materials Using 3D Digital Image Correlation.

A quasistatic indentation numerical analysis in a round section specimen made of soft material has been performed and validated with a full field experimental technique, i.e., Digital Image Correlation 3D. The contact experiment specifically consisted of loading a 25 mm diameter rubber cylinder of up to a 5 mm indentation and then unloading. Experimental strains fields measured at the surface of the specimen during the experiment were compared with those obtained by performing two numerical analyses employing two different hyperplastic material models. The comparison was performed using an Image Decomposition new methodology that makes a direct comparison of full-field data independently of their scale or orientation possible. Numerical results show a good level of agreement with those measured during the experiments. However, since image decomposition allows for the differences to be quantified, it was observed that one of the adopted material models reproduces lower differences compared to experimental results.

Methodology for assessing embryonic cracks development in structures under high‐cycle multiaxial random vibrations

AbstractThe myriad applicability of the frequency‐domain critical plane criterion is outlined in order to evaluate and track the progression of fatigue damage in metallic structures subjected to high‐cycle multiaxial random vibrations. The fatigue assessment using the given criterion is performed according to the following stages: (i) critical plane definition, (ii) power spectral density evaluation of an equivalent normal stress and (iii) computation of the damage precursor and fatigue life.The frequency‐domain critical plane criterion is validated using experimental results related to (a) AISI 1095 steel cantilever beams under nonlinear base vibration, (b) 18G2A steel and (c) 10HNAP steel round specimens under random non‐proportional combined flexural and torsional loads.

Efficient approach for cohesive zone based three-dimensional analysis of hydrogen-assisted cracking of a circumferentially notched round tensile specimen

An efficient ABAQUS based finite element (FE) analysis for hydrogen-assisted cracking is presented. Analysis of two dimensional (2-D) diffusion of hydrogen is coupled with three dimensional (3-D) stress analysis incorporating cohesive elements. The deleterious effect of hydrogen on crack growth is introduced through the hydrogen enhanced decohesion (HEDE) mechanism where modification to the cohesive energy is related to local hydrogen concentration. The proposed method is applied to hydrogen-assisted cracking of a circumferentially notched tensile (CNT) specimen under three different conditions of hydrogen supply and its performance is demonstrated through the close agreement between the corresponding computed critical stress intensity factors (SIFs) and the experimental results reported in the literature. The modelling duly accounts for the off-centre precracked ligament usually resulting from fatigue precracking of CNT specimens. The results clearly bring out the non-axisymmetric nature of concentration distribution and stress field, and reveal enhanced hydrogen diffusion at a point on the outer edge of the ligament profile where crack depth is the highest and wherefrom the crack extension is likely to initiate.

Microstructure-based assessment of creep rupture behaviour of cast-forged P91 steel

The work presented in this study was performed with the intent to characterize the microstructure evolution for short term creep exposure of cast-forged P91 steel. The short-term creep test was performed at temperature range of 620–650°C and stresses ranging from 120 to 200MPa. To characterize the sample after creep exposure, field emission scanning electron microscopy (FESEM) with energy dispersive X-ray spectroscopy (EDS), optical microscope and micro-hardness testing were utilized. Creep tests were performed on round creep specimens. For low temperature service condition, longer creep life was obtained. The fracture surface of creep ruptured specimen were characterized by using the FESEM. The transgranular fracture mode was noticed in all the tests condition. The creep rupture life was found to be decreased with increase in applied stress. The maximum rupture life was measured about to be 3329.28h for the sample exposed at 620°C for 120MPa. A negligible microstructural change was measured in gripping area compared to the gauge area (necking area) of crept sample. The laves phase formation was also noticed along the grain boundaries for creep exposure life of 3329.28h.

Multiaxial fatigue strength assessment of electroslag remelted 50CrMo4 steel crankshafts

This work investigates the fatigue strength of multiaxially-loaded gas engine crankshafts incorporating electroslag remelted 50CrMo4 steel. Uniaxial fatigue tests with small-scale round specimens before and after performing the ESR process are conducted. The results reveal that the high-cycle fatigue strength at the run-out region significantly decreases by 21% if no ESR-treatment is performed. Multiaxial fatigue tests under proportional normal and shear stress loading demonstrate that the elliptical model by Gough and Pollard leads to a minor underestimation of 5% compared to the test results. An application of several state-of-the-art equivalent stress hypotheses utilizing the critical plane approach is presented and the estimated results are compared to the experiments in terms of high-cycle fatigue resistance and crack initiation angle.

Strain controlled cyclic tests on miniaturized specimens

The paper is dealing with strain controlled cyclic tests using a non-contact strain measurement based on digital image correlation techniques on proportional sizes of conventional specimens. The cyclic behaviour of 34CrNiMo6 high-strength steel was investigated on miniaturized round specimens with diameter of 2mm that were compared with specimens in accordance with ASTM E606 standards. The cycle asymmetry coefficient was R= -1. This application is intended to be used for life time assessment of in service components in future work which enables to carried out a group of mechanical tests from a limited amount of the experimental material. The attention was paid to confirm the suitability of the proposed size miniaturization geometry, testing set up and procedure. The test results obtained enabled to construct Manson-Coffin curves and assess fatigue parameters. The purpose of this study is to present differences between cyclic curves and cyclic parameters which have been evaluated based on conventional and miniaturized specimens.

Dynamic Fracture Strength of 90% Tungsten Alloys

Dynamic fracture strength of tungsten alloys generated with a round bar Charpy specimen impacted at velocity ranging from 25 to 160 m/s has been reported to increase with loading rate. For as sintered alloys, the Charpy energy reached 1150 J/cm2 at 145 m/s, which is about 4 times the conventional Charpy energy obtained at 5 m/s. The analysis of the main failure process does not provide an explanation of this high level of failure energy.Additional post-mortem analyses have been conducted revealing a failure process involving multiple tensile cracks at the higher impact velocity. Consequent numerical simulations reproducing this failure process with the hydrocode AUTODYN have provided insights on the increase of the Charpy energy with impact velocity. The simulations were conducted with a modified Johnson-Cook model reproducing the observed strain rate dependence in the thermally and viscous regime, and with erosion strain criteria to trigger the failure process.

Experimental Investigation of Compressive Behaviour of Pier by Partial Replacement of Metakaolin

Objectives:The main focus of our experimental investigation is to study the behavior of a pier based on variations in compressive strength due to partial replacement of cement with metakaolin in order to attain maximum stiffness and strength, so as to withstand the shear forces, bending moments and other related structural response parameters efficiently. Analysis: The round and rectangular specimens were prepared by replacing cement with metakaolin up to 15%. The samples were tested after 7 and 28 days. Findings: Study reveals that with the replacement of 10% metakaolin in both circular as well as rectangular moulds, there is an increase in the load carrying capacity approximately about 19%, when compared with plain reinforced concrete moulds after 28 days. The most important finding is that the replacement of cement by metakaolin up to 10% helped us to attain higher strength after 7 as well as 28 days hence providing us a simple and efficient method of preventing the pier failure by attaining higher strengths. Improvement/Applications: Based on the test results there is remarkable increase in the load carrying capacity of pier which enhances the rigidity of pier in terms of strength and stiffness.

CrMoV鍛鋼環状切欠き試験片のクリープ破断強度

CrMoV鍛鋼環状切欠き試験片のクリープ破断強度

A DFT-based method for 3D digital image correlation

The present work describes an approach to digital image correlation (DIC) which is based on calculations performed on the image Fourier domain.The developed method uses the cross-correlation peak of image subsets computed through the discrete Fourier transform (DFT) to arrive at an estimation of the rigid translation between them, thus enabling the detection of three-dimensional shapes from stereo image pairs and the computation of their displacements between images captured at different loading conditions. The method is expected to offer possible advantages in terms of robustness to lighting conditions, displacement estimation precision, and computational speed.In order to verify that this method can reproduce results from conventional DIC, images of a quasi-static tensile test of a round specimen are used to compare the values obtained from the DFT based method with the results from commercial software using the traditional intensity field based approach to DIC.

Factors Affecting Direct Tension Pull-Off Test Results of Materials Bonded to Concrete

AbstractThe direct tension pull-off test (ASTM D7522/D7522M-15, ASTM D4541-09e1, ASTM C1583/C1583M-13 and others) is the only practical, in situ test to assess bond strength of materials bonded to a concrete substrate relatively. Although the method is prescribed, there are a number of variations anecdotally seen in practice which may affect the uniform interpretation of the test method results. In particular, it was hypothesized that both shear and normal stresses introduced by the drilling process damage the sample affecting results disproportionately with the depth of cut. This study systematically investigated this hypothesis with the aim of providing improved guidance associated with depth, and indeed method, of core drilling. Preformed, hand-drilled, and core-drilled specimens were tested, and the results were compared. Additionally, a system for applying a controlled torsional moment to the specimens was used to quantitatively investigate the effect of such force being applied during the specimen preparation. This study also investigated the effect of using square cuts. Hand-drilled and core-drilled specimens were observed to have reduced pull-off capacity—exhibiting a reduction of 0.03 MPa/mm depth and 0.04 MPa/mm depth, respectively—with increased core depth, although this was not attributed to the torsion that may be present during the drilling process. Square specimens exhibited marginally lower capacity than comparable round specimens and a similar increased reduction in capacity of 0.05 MPa/mm depth of cut. Finally, a discussion of the implications and interpretation of pull-off test results is presented.

Bonding quality of industrially produced cross-laminated timber (CLT) as determined in delamination tests

The resistance to delamination of cross-laminated timber (CLT) made from spruce has been investigated. The main goal was to examine if delamination results are influenced by the shape of test specimens as both square and round specimens may be evaluated according to the CLT standard EN 16351. Furthermore, the influence of the production parameters number of layers, layer thickness and bonding pressure on delamination behavior were investigated. The results show that specimen shape and number of layers affect the resistance to delamination. Square specimens and a high number of layers show significantly higher delamination than round specimens and specimens with low number of layers. Layer thickness and bonding pressure, however, have no influence. As the number of specimens which exceeded delamination or wood failure requirements given in the CLT standard was very high it is questionable, if the applied delamination procedure is suitable for evaluating the bond integrity of CLT. As a result, it is recommended to eliminate the option to use square or round specimens in delamination tests and to revise the CLT standard accordingly. Furthermore, we suggest either to adjust the delamination test parameters or to develop a new test method to be able to assess bond durability more realistically.

The history of the Royal Society for Public Health.

Developments over the last two centuries have shaped the public health specialty that we know today. The Royal Society for Public Health (RSPH) and its predecessors played a major part in this transformation. It is the oldest independent public health body in the world, and its history mirrors the increasing scope of this specialty since the mid-19th century.The first Public Health Act in the United Kingdom was passed in 1848, bringing Boards of Health and the beginning of organised state influence on welfare. The Act was spurred on by fears of cholera, which caused epidemics in Europe from the 1830s. Industrialisation, poverty, poor nutrition and rapid urban spread led to high death rates from infection and other causes. The 1848 Act encouraged districts with the highest rates of death to appoint a Medical Officer of Health (MoH). At that time, the average age of death, even for the affluent middle classes, was around 45 and children were lucky to survive their fifth birthday. Labourers and workmen died, on average, in their 20s. The Society of Public Health was formed in 1856 and by the late 19th century medical training in the science of public health had progressed, with germ theory replacing the idea that diseases were spread by 'miasmas', such as from the bad smells of poor and dirty environments. In the late 19th century, about three quarters of the population lived in towns or cities and while infection and various types of 'cleansing' still dominated MoH work, there was also increasing concern about diet, housing and education.Another Public Health Act in 1875 provided the impetus for The Royal Society of Health, established in 1876. It was initially known as the 'Sanitary Institute' as public health was often termed sanitary science. Although women were allowed to qualify in medicine at universities from the late 1870s in the United Kingdom, it was a long time before they worked in public health other than as sanitary inspectors for Boards of Health or in nursing. So the next organisation in our history was established as 'The Association of Medical Men with a Qualification in State Medicine, Public Health and Hygiene' in 1886. A stained glass window commemorating its founder, Dr. William Robert Smith, still hangs in the Portland Place premises of the RSPH.The Association was quickly renamed as the British Institute of Public Health and became the Royal Institute of Public Health (RIPH) in the year of Queen Victoria's Jubilee, 1897. The aims of promotion of learning and discussion included giving support for the often isolated role of the MoH. The RIPH meetings sometimes included passing round specimens and test tubes containing cultures of bacteria, presumably with attention to hygiene, as there are no reports of outbreaks resulting from these activities!In 1903, a group of 'sanitary' doctors formed the Institute of Hygiene and started to accredit products with 'hygienic merit', such as soap and disinfectants. …