Ring Specimens Research Articles

Fatigue damage criteria for antivibration systems with filled natural rubber under negative and positive R ratios

A shape change can initiate fatigue damage in rubber components, which has led to the development of the effective shear strain γt criterion in this investigation. Referring to the previous damage criterion, i.e., effective tensile strain εt, the relation between the two was revealed. To benchmark the effectiveness of different damage criteria, six damage criteria, including the commonly used maximum principal strain, stress, and strain energy density, were compared using cylindrical dumbbell samples in 30 fatigue cases under ± R ratios. A large scatter was generated using either the maximum principal strain or the stress criterion. The strain energy density was in excellent agreement in uniaxial tension loadings but failed in torsional loadings with R = −1. To save significant cost in producing a completed new S–N curve for each rubber material, the derived S–N base functions using both εt and γt have been successfully validated on three independent experiments, i.e., the cylindrical dumbbell specimens, the ring specimens, and the industrial mount MDS. To fully verify the applicability of both εt and γt, the prediction of the crack orientation was performed for the first time using the proposed criteria, to the knowledge of the author, and the results were consistent with the experimental observations. The proposed criteria are useful for antivibration product design.

Effect of polypropylene fiber on early-age properties and stress relaxation of ultra-high-performance concrete under different degrees of restraint

This paper aimed to investigate the effect of polypropylene (PP) fibers on mechanical properties, shrinkages, cracking potential, and stress relaxation of ultra-high-performance concrete (UHPC) at early age. The proportion of PP fibers was 0%, 1%, 2%, and 3% by the volume of concrete. Two types of restrained ring specimen (DR-1 and DR-2) were also employed to consider the effect of degrees of restraint. The results indicated that the cracking age of UHPC with PP fiber proportion from 0% to 2% was postponed, but further incorporation of PP fibers showed the inconspicuous benefits. Relaxed stress decreased with the incorporation of PP fibers. Moreover, the difference of stress relaxation was less pronounced between UHPC with 1% and 2% PP fibers. The influential factors for stress relaxation were analyzed. Both DR-1 and DR-2 demonstrated a high degree of restraint. This was attributed to the dominant role of autogenous shrinkage in total free shrinkage of UHPC, which eclipsed the effect of volume-to-surface ratio of specimen.

Frictional behavior of severe plastic deformed copper sample by using friction calibration curves

Equal Channel Angular Pressing (ECAP) known as one of the most significant methods involving in severe plastic deformation. There are not many investigations which focus on the design of dies and its analysis by FEM, considering friction coefficients as die geometry parameters; likewise, only few studies have been reported in which the effect of die shape has been analyzed, for example. One of the challenging problems in industrialization of ECAP is designing and manufacturing of die. To avoid trial and error in the next designs, the measurement of right friction coefficient plays a key role, which is used in finite element method to prevent doing experimental test. The main objective of this study was to investigate and find generalized friction calibration curves utilizing the ring compression test. To perform the ring compression test, which is oxygen-free copper with 99.7%, (BS EN 15079 standard) the standard ring specimen ratio of 6:3:2 was used. With use of different lubricants during the ring compression test the relations between friction coefficients and changes of inner and outer diameters was revealed. To solve complicated plasticity equations with complex geometries and boundary conditions with various friction coefficients, finite element method was used. To use more accurate frictional coefficient values with considering different ECAP passes, friction calibration curves were updated.

Investigation of differential shrinkage stresses in a revolution shell structure due to the evolving parameters of concrete

Abstract The article focuses on the influence of differential shrinkage linked by drying at the early-age displacements and strain distribution of a concrete ring specimen. Depending on the gradient of dimension changes through the thickness, tensile stress occurs near the exposed surface where drying is greater and thus results in strain gradients development. An experimental design was carried out on a concrete ring cast in laboratory conditions in order to monitor strains and displacements. Subsequently, a finite element method was used to simulate the ring’s behaviour in drying conditions. The gradient development linked by a non-uniform moisture distribution in the thickness is established by solving the non-linear partial differential drying equation with Mensi’s diffusion law. The stress and displacement analysis was modeled by three nodes curved shell FEM (CSFE-sh) based on strain approximation with the shell theory. Finally, the ring’s behaviour includes both differential shrinkage resulting in the mechanical and physical properties of gradients development in the thickness and the influence of prestressing, in which the tensile creep effects have a great influence. The comparison of experimental results with numerical simulation shows that drying and tensile creep phenomena have the most important influence on the early-age stress development in the walled ring.

Influence of Acetone and Primer on Strength and Ductility of Chlorinated Poly(vinyl chloride).

Primer is widely used to prepare bonding of chlorinated poly(vinyl chloride) (CPVC) pipe. The study examined the influences of primer and its major component, acetone, on CPVC's mechanical properties. Two types of CPVC product, sheet and pipe, were used in the mechanical testing. Sheet specimens were immersed in acetone or primer for 40 and 10 min, respectively, i.e., the maximum allowable time without mass loss, and then dried in air before the mechanical testing. Pipe (ring) specimens were treated either through immersion in acetone or primer for 30 min or in contact with these solvents locally on the inner surface for 2.5 h, and then air dried for 10.5 days before the mechanical testing. Results showed that CPVC's strength decreased after the absorption of these solvents, and air dry could remove acetone but not completely primer. The study also showed that pipe specimens by local contact with primer could generate brittle fracture. In view that sheet specimens always fractured in a ductile manner, brittle fracture of the pipe specimens could not be caused by CPVC degradation. Rather, strength decrease in the local region could provide a plausible explanation for the brittle fracture behavior, though further investigation is needed.

A correlation-based approach for evaluating mechanical properties of nuclear fuel cladding tubes

The present work offers and evaluates a correlation-based approach to determine the tensile properties of nuclear fuel cladding tubes. A set of model materials with known properties (i.e., austenitic and ferritic steels, fcc- and hcp-alloys) were tested to build a correlation between conventional tensile tests and ring (hoop) and tube (axial) tests. It was shown that close-to-linear relationships exist for the basic mechanical properties (i.e., yield and ultimate stress, uniform and total elongation) between the uniaxial tensile test data and the ring and tube test data. Using the ring and tube specimen geometries, the feasibility of the approach was demonstrated via manufacturing and testing specimens from irradiated Zr and FeCrAl nuclear fuel cladding tubes. Limitations caused by specific deformation mechanisms (e.g., high ductility of 304L steel) were discussed in detail. The approach can be extended to other tubular products with different geometry and dimensions.

Enhancing the sensitivity of a tribological testing method to enable development of lubricants for cold forging

Because of environmental issues, new water-based lubricants are being developed to replace the conventional lubrication approach in cold forging—phosphation plus soap coating. To support the development and application of water-based lubricants, a new testing method that is highly sensitive, accurate, and easy to use was established on the basis of the ring with boss compression test. The dimensions of ring specimens were optimized, and the method’s high sensitivity was demonstrated by obtaining scatter calibration curves and determining the distortion of the outer boss. The effectiveness and high sensitivity of the method were experimentally validated using two strategies. The method was then successfully employed to evaluate a commercial water-based lubricant; the effect of lubricant amount and lubrication mode was investigated.

The Estimation of Taylor-Quinney Coefficients Using Small Ring Specimens

BackgroundThe use of the Taylor-Quinney coefficient for introducing a thermal dissipation term into material models relies on understanding its dependencies. These are usually determined through extensive experimentation, wherein temperature variations are monitored in a test piece during mechanical loading.ObjectiveThis study aims to reduce the cost and time necessary to determining the dependencies of the Taylor-Quinney coefficient by proposing a novel small specimen inverse testing method and demonstrating its use on aluminium alloy 7175.MethodsThe method proposed is based on mechanical testing of a novel small ring specimen in parallel with FEA simulations. In the experiments, small rings of 7175-T7351 aluminium alloy, 20 mm in outer diameter, were loaded between two pins for different pin displacement rates (namely 1, 1.5 and 2 mm/s) at room temperature and the local specimen temperature field was monitored using an infra-red thermal camera. Fully coupled thermal-mechanical simulations of the tests were performed using a range of Taylor-Quinney coefficients, and the resulting temperature evolutions compared to the experimental results in order to determine appropriate coefficient values for the material.ResultsThe method presented shows good repeatability and allows for clear observation of thermal dissipation. Taylor-Quinney values ranging 0.51-0.59 are reported for the 7175 alloy, in line with values reported in the literature for similar alloys. Density, specific heat capacity and thermal conductivity, fundamental thermal material properties necessary for the simulations, are also reported for the alloy.ConclusionsThe method detailed shows promise for determining Taylor-Quinney coefficients in a wide range of experimental conditions and is proposed as a cheap and fast alternative to full-scale specimen testing of Taylor-Quinney coefficients. Taylor-Quinney values obtained for 7175 aluminium are shown to be much lower than the value of 0.9 often proposed for materials.

Studying the Electromagnetic Properties of Ring Specimens of the Magnetic Phase of a Dual-Phase Magnetic Material Based on Iron–Cobalt Steel

Studying the Electromagnetic Properties of Ring Specimens of the Magnetic Phase of a Dual-Phase Magnetic Material Based on Iron–Cobalt Steel

A comprehensive study on ring shape specimens under compressive and tensile loadings for covering the full range of I+II fracture modes of gypsum material

Using ring-shape specimens containing two aligned cracks on the internal surface of the ring, two test configurations subjected to tensile or compressive loads namely (i) diametrically compressed ring (DCR) and (ii) diametrically tensile ring (DTR) specimens were suggested to investigate the full mixed-mode I/II fracture problem. The fracture parameters, including modes I and II stress intensity factors and T-stress, were determined numerically for these two test specimens with different crack lengths and crack angles. Also, the ability of the specimens was examined by conducting experimental fracture tests on gypsum material. In addition, the direction of fracture kinking was investigated both experimentally and theoretically. The experimental results were then compared and predicted using the mixed mode fracture criteria such as maximum tangential stress (MTS) and generalized maximum tangential stress (GMTS). The normalized fracture toughness (KIIc/KIc) ratios of the tested DCR and DTR specimens were about 0.72 and 0.95, respectively. Such difference was related to the considerable effect of T-stress values and it was shown that the GMTS criterion provides more accurate predictions for the test results of both DCR and DCT samples compared to the MTS criterion.

A Method to Measure Permeability of Permalloy in Extremely Weak Magnetic Field Based on Rayleigh Model.

In order to solve the problem that the relative permeability of the permalloy is missing and difficult to measure accurately in an extremely weak magnetic field (EWMF, <1 nT), a method to measure the permeability in EWMF based on the Rayleigh model is proposed in this paper. In this method, the Rayleigh model for the magnetic material was first introduced. Then, the test system for measuring the permeability of permalloy for the standard ring specimen was set up. Based on the test data and the Rayleigh model, the functional expression applied to obtain the permeability in EWMF is achieved. Finally, the feasibility and accuracy of the method are verified by the permeability measurement of the custom large-size ring specimen in EWMF (<1 nT) and residual field measurement based on the four-layer shielding cylinder. This method can obtain the relative permeability in any EWMF and avoid test errors caused by extremely weak magnetization signals.

Routine pathologic evaluation of circular stapler anastomotic rings is not useful after resection for colorectal cancer: retrospective study and systematic review with meta-analysis.

BackgroundCircular staplers are commonly used for reconstruction after radical resection for colorectal cancer. Pathological analysis of the anastomotic rings is common practice, although the benefits are unclear. The purpose of this study was to evaluate the usefulness of routine histopathological analysis of anastomotic rings in an original series and in a systematic review of the literature.MethodThe retrospective study was performed at two university-associated academic hospitals in Winnipeg, Canada, including patients investigated for colorectal cancers (within 30 cm of the anal verge) who underwent resection between 2007 and 2020. The systematic review involved Ovid MEDLINE, Embase, Scopus, and Web of Science databases, selecting for adult human studies involving analysis of anastomotic rings in elective colorectal cancer resections. The main outcome measure was the proportion of patients with cancer in the anastomotic ring specimens. The frequency of benign pathology findings and changes to patient management were also examined.ResultsOut of 673 eligible patients, 487 were included in the retrospective analysis. No patients had cancer within the anastomotic ring specimens. Twenty-five patients (5.1 per cent) had benign pathological findings within the anastomotic ring specimens, and patient management was never affected. In the systematic review, 27 articles were included in the final analysis out of 5848 records reviewed. The rate of cancer within anastomotic ring specimens was 0.34 per cent, and the rate of change in patient management was 0.19 per cent.ConclusionThe likelihood of finding cancer within anastomotic rings is rare and their histopathological examination seldom changes patient management.

Calofolic Acid-A from Calophyllum scriblitifolium Bark Has Vasorelaxant Activity via Indirect PKA Activation Caused by PI-3 Kinase Inhibition in Rat Vascular Smooth Muscle Cells.

Previously, we isolated 2R,3S,15R-calofolic acids (CAs) from Calophyllum scriblitifolium bark, which showed vasorelaxant activity on phenylephrine (PE)-precontracted rat aortic rings. Although the effect was suggested to be induced via an extracellular Ca2+-independent manner and mainly acts on vascular smooth muscle, the exact mechanism of action of CAs remained unclear. Thus, this study investigated the detailed mechanism of calofolic acid-A (CA-A) induced vasorelaxation in an aortic ring specimen using rat vascular smooth muscle cells (VSMCs). The levels of PE-induced phosphorylation on MLC Ser19 decreased in VSMCs pretreated with CA-A. CA-A also decreased the phosphorylation of MYPT1 Thr696 and MYPT1 Thr853. On the other hand, CA-A increased the PE-induced phosphorylation of MYPT1 Ser695 and MYPT1 Ser668, which are reported to be phosphorylated by a cAMP-dependent protein kinase (PKA). CA-A slightly increased PKA substrate phosphorylation in a concentration-dependent manner. Furthermore, CA-A enhanced isoproterenol (ISO)-induced cAMP accumulation and PKA substrate phosphorylation. Treatment with PI-3 kinase (PI3K) inhibitor, LY294002, enhanced ISO-induced cAMP accumulation and PKA substrate phosphorylation in the same manner as CA-A treatment. Furthermore, CA-A was found to directly inhibit PI3K enzyme activity in a dose-dependent manner. Taken together, the present study indicated that CA-A induces vasorelaxation through an indirectly activated PKA-MYPT1 pathway caused by inhibition of PI3K activity.

Strength, durability and shrinkage behaviours of steel fiber reinforced rubberized concrete

Many studies have recently been conducted to reduce the environmental influences of construction in industrial sectors. Recycling rubber as aggregate in concrete helps to reduce the environmental effects of waste automobile tires, and enhances the deformability of the concrete in structural applications such as slabs on grade and concrete pavements. This study aims at examining the reinforcement of rubberized concrete by a hybrid system of fibers comprising industrial steel fibers and steel fibers from waste tires. Six concrete mixtures with/without steel fibers were investigated, using 0, 20% and 40% by volume of waste tire rubber (WTR) particles as a substitute for natural aggregates. The fresh properties of these concrete mixes were evaluated using concrete slump and air content tests, as well as unit weight. Compressive and splitting tensile strengths at 7 and 28 days and flexural strength at 28 days were used to evaluate the hardened concrete properties. Concrete porosity and rapid chloride permeability tests were conducted to evaluate the concrete’s permeability, and its volume stability was assessed by examining free-drying shrinkage and restrained shrinkage. The results showed that, although the mechanical properties of the concrete were negatively impacted when a portion of the crushed rock and sand aggregates were replaced by rubber particles, it was possible to produce rubberized concrete with comparable mechanical properties and durability to conventional concrete when 40 kg/m3 of steel fibers was used in conjunction with 20% rubber. The flexural strain capacity and post-peak properties of the rubberized concrete containing 20% rubber and 40 kg/m3 steel fibers were substantially better than conventional concrete. In addition, the free drying shrinkage strain after 56 days for all mixes was low, below 457 micro-strain or 0.046%, and the presence of high quantities of rubber particles and/or steel fibers in the concrete ring specimens subjected to restrained shrinkage testing prevented the initiation and propagation of cracks. The outcome of this study highlights the potential of these combinations for use in concrete pavement and slab on grade applications.

Shear modulus-based prediction of the fatigue life of antivibration rubber components

A potential novel approach was proposed to predict fatigue damage based on the shear modulus of the rubber material and the effective tensile strain. This methodology was validated in three independent fatigue programs. An S-N base curve was generated from cylindrical dumbbell specimens from 30 fatigue cases covering different R ratios in both negative and positive values. The curve was then applied to ring specimens with 90 fatigue cases and a Metacone suspension component mount. The results have shown that different S-N curves could be correlated with the shear modulus based on the effective tensile strain.

Analytical and Numerical Study of the Ring Expansion Testing Technique

Abstract This article presents a design development for the ring expansion test as an alternative technique of burst test to determine the mechanical properties of circular homogeneous thin-walled tubes in the hoop direction where it is supposed to fail. This is done by replacing the internal fluid pressure in burst test by a solid mandrel partitioned into an equal number of pieces. The numerical analyses were carried out using the commercial finite element method (FEM) package ABAQUS/CAE. The testing system consists of a multispecies mandrel assembled with two identical cones from top and bottom, and the ring specimen circumscribes the mandrel, which expands radially as a result of the cone’s axial displacement. The FEM was used to optimize the proposed design in terms of the minimum number of pieces in use. In addition, the effects of friction between the cones/the mandrel and between the ring/the mandrel are investigated. The FEM revealed that eight mandrel pieces or more are needed to preserve a uniform hoop stress throughout the ring circumference. Moreover, the FEM results in conjunction with theoretical formulas revealed that eight mandrel pieces at a minimum are required to minimize the power dissipated because of friction to a nuance value of 2 %. It is concluded that the higher the number of pieces used, the more uniform the hoop stress generated in the ring specimen. Moreover, it can effectively decrease friction effect at the ring/mandrel interface. The FEM also makes a great contribution in estimating the friction coefficients as it is restricted to be evaluated experimentally.

A micromechanical analysis of swelling-induced embrittlement in neutron-irradiated austenitic stainless steels

Swelling is commonly observed in austenitic stainless steels irradiated at high doses and high temperatures, such as fuel claddings in Fast-Breeder Reactors (FBR), as a consequence of the formation of irradiation-induced nanovoids. Macroscopic embrittlement has been reported above a critical swelling level. Several physical explanations have been proposed such as void-related fracture mechanisms and phase transformation associated with local changes of microchemistry. In addition, structural effects can affect the critical swelling level, tentatively explained by local corrosion, swelling gradient and bending effects. In order to address these phenomena, an extended experimental database is first presented, based on fuel pins irradiated in the Phénix fast reactor, showing the evolution of conventional tensile properties with swelling. In the present database, 15-15Ti specimens were irradiated from 30 to 120 dpa, with irradiation temperatures ranging from 400 °C to 625 °C and a maximum swelling of 11%. Other data published in scientific literature were also included in the analysis to extend the swelling range up to 30%. SEM and TEM analysis are also summarized to highlight specific embrittlement mechanisms related to the presence of voids. Theoretical analysis and finite element simulations are then performed based on porous materials constitutive equations in order to rationalize the experimental observations. Analytical and numerical results show that swelling-induced embrittlement can be understood from a mechanical perspective as a transition from void growth to void coalescence deformation mode. The effect of the spatial heterogeneity of void distribution is quantified and shown to be a key parameter. Structural effects coming from tests performed on ring and axial tensile specimens and from the presence of a swelling gradient in cladding thickness are also quantified. Numerical results are compared to experimental data, and a good agreement is observed.

Ring Hoop Tension Test for yield strength estimation: Numerical analysis for a novel correlation method and applicability for mechanical testing of tubes and pipes

The tubes and pipes manufacturing industry characterizes the mechanical properties of their products with a wide selection of standards, but most of them are qualitative testing methodologies. To estimate the mechanical properties from a quantitative point of view there are limited options in standards. In that sense, the standard tensile test is the preferred alternative by the manufacturers, but this option limits the mechanical estimation for the longitudinal direction of the tube–pipe product. Particular efforts have been made to design an alternative mechanical testing procedure to characterize the mechanical properties in the hoop direction of pipes and tubes. The Ring Hoop Tension Test (RHTT) was designed to fill this gap, but it shows limitations related to the required tooling and the influence of the frictional contact between the tooling and the ring specimen. In the nuclear industry, the Small Ring Test (SRT), a miniature test derivated from the RHTT, has been investigated in recent years. In this investigation, a novel RHTT was designed to overcome the limitations of SRT and RHTT, and a new procedure was implemented to estimate the yield strength of tubes and pipes. Numerical FEM simulations were performed to reach an optimum estimation method for the yield strength with the specific geometry of the SRT and a wide selection of pipe geometries with the RHTT. A set of hypothetical materials were designed to perform these analyses, taking into account the influence of Young’s modulus, proportional limit, hardening coefficient (based on the Ramberg–Osgood law), and presence of Lüders bands straining. To verify the results obtained from this numerical FEM analysis, experimental tests (standard tensile tests and RHTTs) and metallographic analysis were performed on aluminum Al 6063 T6 and copper C12200 R360 tubes, showing the capability of this optimized RHTT to estimate the yield strength in the hoop direction for anisotropic tubes and pipes.

Rubber fatigue prediction for filled natural rubber under positive and negative R ratios

An effective tensile strain εt for rubber fatigue under positive and negative ratios was proposed for the design of rubber products in the industry. It was applied to the cylindrical specimens over 30 fatigue cases: achieved the predicted points within a scatter band of 0.5 with R2 = 0.85. Further application to the ring specimens on 90 fatigue cases including different loading modes and phase angles: achieved the prediction within a scatter band of 1.7. Critical locations were correlated with the maximum values of εt. The novel approach without additional fitting variables can be used in engineering design and applications.

Effects of lubricant additives on tribological properties of poly-acetal under boundary lubrication

The objective of this study was to elucidate the effect of lubricant additives on the tribological properties of poly-acetal (POM) and steel materials under boundary lubrication. To investigate the effects of lubricant additives on the tribological properties of POM and structural changes at the friction interface, friction tests and surface analyses were conducted using friction modifiers and anti-wear additives among the lubricant additives under uniform atmosphere conditions other than the additives. The test materials used were POM ring specimens and S45C discs as mating materials. This test was conducted using a ring-on-disk friction test configuration in which the POM ring was rotated by a motor while the POM ring was pressed against the S45C disc at a constant load. As a result, it was found that lubricant additives inhibited the friction-reducing effect of POM regardless of the type of additives. In addition, it was inferred that the friction-reducing effect of POM was due to the POM transfer film formed on the steel material.