Ring Specimens Research Articles

Theoretical and experimental study on the mechanical measurement of rock tensile fracture by ring radial compression

Conventional Brazilian disc splitting tests are hampered by stress concentration at the loading points, leading to test outcomes that do not truly represent the engineering failure strength of rocks. To enhance the accuracy of these tests, the specimen shape has progressed from the Brazilian disc to a circular ring. This study presents a theoretical analysis of the compression deformation process in circular rings, followed by platform-radial compression tests conducted on various types of rocks and metals, employing the digital speckle correlation method alongside an improved mechanical extensometer. The findings indicate that circular ring specimens failed under a combination of tensile and compressive stresses. The main crack originates along the loading direction on the inner wall of the ring and propagates outwards, resulting in the failure of the entire ring structure. While maximum tensile strain may serve as an indicator of rock failure, tensile stress alone should not be considered a definitive criterion for failure.

Early Cracking of Cementitious Materials Based on Stress Concentration Method

Abstract The traditional ring constraint shrinkage test method for detecting shrinkage cracking of cementitious materials has been found to have low cracking sensitivity and random occurrence of cracks. To address these problems, this study proposed an improvement ring constraint shrinkage test apparatus. The apparatus was used to analyze the stress distribution at key nodes and cross sections by theoretical and finite element methods. The study also counted the cracking time and crack location distribution of the improvement ring constraint specimens by test results. The findings showed that the average cracking time of the cement mortar that improved ring specimens was 52.4 % shorter than that of the conventional ring specimen. This significant reduction in the test observation period indicates that the improvement ring constraint shrinkage test method is highly efficient. Moreover, 98 % of the crack offset was within 27.35 mm of the expected cracking location, and the offset distance was negligible compared with the conductive coating length. These results suggest that the improvement ring constraint shrinkage test method can effectively limit the location of specimen cracking.

Numerical Analysis on Frictional Heat Effect in Polyether-Ether-Ketone (PEEK)/Steel Pair by using OpenFOAM Model

The PEEK material has been applied to a sliding bearing system in a power plant system because of its high mechanical durability. In the solid friction of the PEEK materials, the frictional heat becomes the important factor because the temperature increase due to the frictional heat causes the rapid increase of the frictional coefficient of the specimen. To maintain the low frictional coefficient of the PEEK materials, an effective cooling method for the PEEK materials needs to be developed. In this study, the passive cooling method, which attaches the heat sink to the PEEK materials, was suggested. For evaluating the suggested cooling method of the PEEK materials, the calculation model adopting OpenFOAM, which is open-source software, has been developed. Adopting some functions and libraries of OpenFOAM, the frictional heat, heat resistance, and heat transfer coefficient on the heat sink were modelled. The sliding bearing experiment was conducted and time variation of the temperature and friction coefficient in the ring specimen were measured. The temperature variation in the ring specimen was compared with the calculation result. From the numerical calculation results, the developed calculation model could simulate the temperature-time variation of the ring obtained in the experiment, when the variation of the frictional coefficient, heat resistance, and heat transfer coefficient was modelled appropriately. Based on the friction and wear test results, by applying a heat dissipation mechanism to the ring test piece, the calorific value of the PEEK material can be reduced, and it is stable. It was suggested that the friction was maintained.

Design and validation of a new ring hoop plane strain test for characterizing the anisotropic plastic behavior of tubular materials

The accurate characterization of the plastic behavior of tubular materials is challenging due to the difficulties in acquiring proper specimens for mechanical testing. In this study, we propose a novel testing technique, namely the ring hoop plane strain Test (RHPST), as a supplementary test for characterizing materials experiencing distinct strain paths compared to standard uniaxial tensile tests. To design a suitable ring specimen’s geometry that satisfies the necessary plane strain conditions, we developed a meta-modelling approach merging response surface method (RSM) and the finite element method (FEM). Experimental tests are conducted on RHPST specimens, and 3D digital image correlation (DIC) technique is used to monitor the strain fields within the specimen's gauge section. However, observations indicate the presence of edge effects on the gauge specimen. These edge effects significantly influence and limit the homogeneity of the plane strain field. To tackle this limitation, a correction procedure is developed for separating the authentic plane strain area, constituting approximately 78% of the RHPST specimen's width. Furthermore, we successfully fabricated a novel grooved ring specimen (GRHPST), which exhibits a wider region of the plane strain state encompassing up to 90% of the gauge width, while minimizing the impact of edge effects. The true stress-true strain curve obtained from the GRHPST specimen exhibits exceptional agreement with the curve predicted using the Hill48 yield criterion. Notably, no additional corrections are required for the measured true stress-true strain curve, thereby affirming the efficacy of the GRHPST specimen as an adept test for characterizing the anisotropic plastic behavior of AA6063 tubes.

Research on Damage Evolution in Ultra-thin Sheet Material under Deep Drawing and Ironing Process

In this paper, the effect of damage induced in deep drawing and ironing processes on the subsequent service performance of deep drawn cups was investigated. To obtain the cups with different amount of deformation damage, three kinds of drawing tests including one-stage deep drawing, two-stage deep drawing, and two-stage deep drawing and ironing were conducted using a 0.3 mm interstitial-free steel sheet. With help of the DF2015 ductile fracture model, the damage evolution of the drawn cups was calculated. Moreover, ring specimens cut from the side walls of the drawn cups were tested in a specially designed tension platform. The load F max and displacement x corresponding to the maximum load point, and the difference in displacement dx from the maximum load point to the fracture initiation point of ring tensile specimens were used as indicators to evaluate the effect of accumulated damage on the subsequent service performance of the parts.

Large Ring Test for Evaluation of Restrained Shrinkage Cracking: Calibration and Experimental Trial

The durability of shotcrete tunnel linings is significantly affected by restrained shrinkage cracking. Given the unique characteristics of shotcrete applied in tunnel linings, especially when dealing with accelerated shotcrete containing reinforcement fibres, it is necessary to upscale the ring test commonly used. This paper presents a comprehensive experiment using large ring tests with cast concrete to investigate the impact of upscaling ring test geometry. The two ring specimens demonstrated comparable cracking age (22 days) and strain measured in the steel ring, suggesting that consistent results can be obtained through the proposed instrumentation, calibration, and correction methods. Moreover, the estimated induced tensile stresses of the concrete rings (2.8 and 2.7 MPa) are slightly lower than the predicted tensile strength (3.3 MPa) at the age of cracking, which indicates that some driving forces contributing to restrained shrinkage cracking were not indicated in the strain gauge readings. Furthermore, the study identified multi-crack formation and additional potential causes for crack initiation, which include self-restraint due to the moisture gradient in the vertical direction, deflection of the concrete ring caused by its self-weight, and friction on the contact surface of the support. Therefore, optimising the geometry of the ring specimens and the apparatus is imperative to minimise additional driving forces and unmeasurable restraints for crack initiation, especially when employing the stress rate method to assess cracking potential.

Dynamic and Energy Consumption Characteristics of Sandstone Ring Specimens under Dry and Wet Cycling

The aim of this study was to examine the effects of sandstone ring specimens with different inner diameters on dynamic compression mechanical characteristics after dry and wet circulation. To carry out our study, we subjected a sandstone ring specimen with a 50 mm outer diameter and a 0~25 mm inner diameter to 10 cycles of dry and wet circulation. Afterward, we recorded the specimen’s basic physical parameters and used a split-Hopkinson pressure bar (SHPB) test device to perform an impact compression test. Following dry and wet circulation, our results showed that the mass loss rate increased and the volume expansion rates and density decreased with the increase in the inner diameter of the sandstone ring sample. Simultaneously, with the increase in the inner diameter of the specimen ring, the dynamic compressive strength of the specimen presented an exponential negative correlation, the dynamic elastic modulus presented a quadratic negative correlation, and the dynamic peak strain presented a quadratic positive correlation. Concurrently, the average particle size of the specimen decreased, and the degree of breakage increased with the increase in the sandstone sample’s inner diameter. Regarding the energy analysis performed in this study, the sandstone ring sample’s energy dissipation increased, and its kinetic performance evidently weakened with the increase in the ring sample’s inner diameter. The results of this study have certain reference values for the construction and maintenance of natural cavity rock and underground hard rock roadways.

Research on the Tensile Mechanical Properties and Fracture Characteristics of GFRP Mortar Tubes under Impact Loads

To investigate the protective effect of glass fiber-reinforced plastic (GFRP) pipes on cement mortar, dynamic splitting tests were carried out on cement mortar and GFRP-mortar pipe specimens by using a 74 mm diameter Hopkinson pressure bar (SHPB) test device combined with a high-speed video camera device to obtain the crack expansion process and rupture and fragmentation morphology of the specimens. The results show that the tensile strength of cement mortar rings is lower and that the stress?strain curve is single-peaked. Compared with cement mortar rings, the tensile strength of GFRP-mortar ring specimens increases significantly, and the stress-strain curve is bimodal. For 0.5 MPa air pressure and wall thicknesses of 0, 2, 3, and 4 mm, the hollow rate of the 0.187 specimen peak stress is 3.21, 1.02, 1.05, and 1.26 times that of the 0.292 specimen. For 0.5 MPa air pressure and a hollow rate of 0.187, the wall thickness of the 2, 3, and 4 mm specimen peak stress is 1.06, 1.31, and 1.69 times that of the 0 mm specimen. The increase in the wall thickness, the decrease in the hollow rate and the increase in the strain rate make the dynamic tensile strength of the specimens increase. The dynamic modulus of elasticity of the GFRP-mortar pipe specimens was lower than that of the mortar specimens, and the increase in strain rate and the thickness of the GFRP pipe wall resulted in an increase in the dynamic modulus of elasticity of the specimens. The cement mortar specimen under impact load was split and tensile damage occurred; the GFRP-mortar specimen suffered tensile damage at the two ends of the applied force, and the upper and lower ends were crushed. With the increase in the strain rate, the GFRP-mortar specimens transitioned from cracks to the formation of “V” area damage, and the specimen crushing degree increased, but the existence of GFRP pipe can have a protective effect on the mortar, reducing the degree of specimen rupture and crushing. The increase in the hollow ratio reduces the ability of the specimen to resist the external load, and the degree of specimen rupture and fragmentation increases.

Study on acoustic emission parameter fusion-based NOL ring damage assessment method for modeling hydrogen storage cylinder shells

In this study, we examined the damage progression in the NOL ring of fiber-reinforced composites during axial failure, utilizing an acoustic emission methodology. The NOL ring is used to simulate the destruction process of the fiber-woven material of the shell of a hydrogen storage cylinder during pressurization. We constructed three combined eigenvalues (AERA, AER, and AEb) derived from the parameters of acoustic emission amplitude, energy, and rise time to characterize and evaluate the damage status of the NOL rings. In the first instance, we analyzed NOL ring specimens at varying tensile stages using AERA values, discovering that these values could delineate the tensile damage of the NOL ring into three distinct phases. Following this, we employed the AERA and AER values to substantiate the demarcation of the NOL ring damage phases. Additionally, we analyzed the AEb values using the consistent load-bearing segment at different junctures of the cyclic loading experiment to confirm the validity of the AE parameter fusion. The findings indicated that the AERA and AER values were highly responsive to the early damage and the cumulative damage changes in the specimens. In the third phase of NOL ring extension, the AERA values displayed a high degree of variability and complexity. On the other hand, the AEb values declined rapidly beyond 0.85Fmax. This evidence corroborated the appropriateness of the three fused characteristic values—AERA, AER, and AEb —in evaluating the NOL ring damage progression.

Analysis of fracture state and fatigue life of high modulus carbon fiber wrapped composite barrel

High-modulus Carbon Fiber-reinforced Polymer composites are widely used in critical industries due to their exceptional mechanical properties. However, the fatigue and fracture of high modulus carbon fiber materials are currently poorly studied. For this purpose, the NOL ring fatigue tensile testing is referenced and improved to investigate the performance and service life of high-modulus carbon fiber wound barrels. NOL ring specimens, made of M40 carbon fiber material, are subjected to quasi-static tensile and fatigue tests. The fracture state and characteristics of high modulus materials during fatigue are analyzed. Two-parameter Weibull distribution function is used to analysis statistically the fatigue life results of composite samples. Then, the life curve is drawn for different stress amplitudes. Additionally, the fiber fracture surface is observed under a high-power microscope. The fiber fracture model under brittle fracture is established. The results indicate that the fracture characteristics and mechanisms of high-modulus materials differ from those of high-strength materials, necessitating different fatigue life assessment methods. The fatigue failure of high modulus fibers exhibits brittle fracture similar to quasi-static loss, with flat fracture surfaces and minimal cumulative damage. The failure mechanism is accompanied by brittle fractures with a small amount of fiber pulled out.

Mechanical Behavior of Seamless Pipes Using Ring Expansion Technique and Novel Hoop Stress Correlation Factor (K)

This study investigated the stress–strain behavior of seamless pipes in the hoop direction using the ring expansion test, which is a non-standardized mechanical testing technique used for evaluating the mechanical properties of round tubes. However, this technique has limitations, such as unidentified specimen geometry, strain measurement, and the estimation of friction coefficients. The study employed experimental, numerical, and analytical methodologies to address these limitations and throughout the study, a novel hoop stress correlation factor (K) was identified to be multiplied by the hoop stress derived equation for reduced section ring specimens. The experimental strain was measured using a newly derived analytical equation, and a mathematical predictive model was developed to estimate the K-factor using the Design of Experiment (DoE) and Design-Expert statistical software. The study concluded that the ring expansion test is a promising technique for evaluating the mechanical properties of seamless pipes similar to the unified axial tensile stress–strain behavior. However, future research is needed to estimate the hoop stress correlation value (K) for all ring geometries. The study's finding of the novel hoop stress correlation factor (K) in the case of a reduced section ring specimen is particularly noteworthy, as it addresses a significant research gap in the field.

Lateral ring compression test applied to a small caliber steel jacket: Identification of a constitutive model

The evolution of threats and scenarios requires continuous performance improvements of ballistic protections for armed forces. From a modeling point of view, it is necessary to use sufficiently precise material behavior models to accurately describe the phenomena observed during the impact of a projectile on a protective equipment. In this context, the goal of this paper is to characterize the behavior of a small caliber steel jacket by combining experimental and numerical approaches. The experimental method is based on the lateral compression of ring specimens directly machined from the thin and small ammunition. Various speeds and temperatures are considered in a quasi-static regime in order to reveal the strain rate and temperature dependencies of the tested material. The Finite Element Updating Method (FEMU) is used. Experimental results are coupled with an inverse optimization method and a finite element numerical model in order to determine the parameters of a constitutive model representative of the jacket material. Predictions of the present model are verified against experimental results and a parametric study as well as a discussion on the identified material parameters are proposed. The results indicate that the strain hardening parameter can be neglected and the behavior of the thin steel jacket can be described by a modeling without strain hardening sensitivity.

Magneto-mechanical coupling effect of ferromagnetic materials: Test characteristics and theoretical model

The magneto-mechanical coupling effect of ferromagnetic materials is the result of macroscopic influence of mechanical properties on magnetic properties under the combined action of stress field and applied magnetic field, which essentially can be attributed to the change of material properties caused by the transformation of microscopic magnetic domain structures. The effect of applied magnetic field is mainly manifested as the change of magnetic moment cluster (direction and size) inside microscopic magnetic domain; The stress field mainly causes the movement and rotation of the domain walls inside the ferromagnetic material, and further causes the change of magnetic moment cluster. Taking Q235 low carbon steel as an example, the effects of tensile stress σt on some important magnetic parameters of ferromagnetic materials under different excitation intensities (i.e., H0), such as the maximum value of applied magnetic field Hmax, intrinsic coercive field Hcj, hysteresis loss power per unit volume ph and anhysteretic magnetization Man, were obtained by setting macroscopic magneto-mechanical coupling test and fully considering the influence of demagnetizing field Hd (The standard ring specimen was used for demagnetization correction of the non-standard strip specimen). Meanwhile, the basic magnetization characteristics of ferromagnetic materials were discussed by introducing the basic magnetization curve F(H0, Ban) and considering the effect of σt as the equivalent stress field Hσ based on the theory of microscopic magnetic domain and the principle of thermodynamic. In the range of 635.4 A/m ≤ H0 ≤ 928.6 A/m and 0 MPa ≤ σt ≤ 350 MPa, the theoretical calculation models Man(H0, σt) and Hσ(H0, σt) in the magneto-mechanical coupling effect were obtained, which are in good agreement with the experimental results.

A novel procedure to determine the hoop mechanical properties of pipe materials using ring elongation testing technique

In this study, experiments including axial tensile tests and ring elongation tests, as well as analytical analyses were developed to determine the mechanical properties of ASTM A106 Grade B seamless carbon steel (A106-B) pipe material. Ring elongation tests were performed on the ring specimens to determine the mechanical properties of the A106-B pipe material in the hoop direction. Whereas axial tensile tests were carried out on standard axial tensile specimens to determine the axial stress-strain behavior of the A106-B pipe material. The axial stress-strain curve of the A106-B pipe material was used as a reference to validate the ring elongation test results. Besides, Analytical analyses using curved and straight beam formulas were developed. Directly from the ring elongation tests experimental results, both the curved and straight beam formulas accurately predicted the young's modulus and hoop yield strength of the A106-B pipe material. Moreover, the A106-B pipe material's plastic stress-strain behavior in the hoop direction was also successfully determined directly from the ring elongation test results with high accuracy.

Gas gun driven dynamic expansion of 3D-printed AlSi10Mg rings

This paper presents a new experimental setup to study dynamic fragmentation of metallic rings manufactured by 3D-printing technology. The ring is inserted over a ductile thin-walled tube which is impacted axially by a conical-nosed cylindrical projectile fired by a single-stage light–gas gun. The diameter of the projectile is larger than the internal diameter of the thin-walled tube, which expands as the projectile advances, pushing radially outwards the metallic ring, that eventually breaks into multiple fragments. The impact velocities considered in the present experimental campaign range from 197 m/s to 385 m/s. The AlSi10Mg ring specimens are printed by Selective Laser Melting technique, with an inner diameter of 14 mm and square cross section of 2 × 2 mm2. To obtain time-resolved information on the mechanics of fragmentation, the number of fractures, and the size of the fragments, the tests have been recorded with two-high speed cameras. A tunnel-shaped soft casing made of polymer foam is placed around the specimen to softly recover the ejected fragments, that have been weighted and sized to determine the statistics of the fragments size distribution. In addition, the predictions of the fragmentation theory of Kipp and Grady (1985) for the evolution of the number of fragments with the impact velocity have been compared with the experimental evidence, and an excellent quantitative agreement has been found within the whole range of loading rates investigated. Compared to other available techniques for dynamic fragmentation of rings, in which the expansion of the specimen is driven by electromagnetic or explosive loading, this experimental setup stands out for its simplicity, fast operation, quick assembly, and flexibility to test different engineering materials, which facilitates performing extensive experimental campaigns (34 successful tests have been carried out in this research). To the authors’ knowledge, this paper presents the most comprehensive data set to date on the fragmentation of dynamically expanded printed rings, including the first high-resolution video recordings of the formation of multiple cracks throughout the circumference of the samples, and scanning electron microscopy images of the fractures showing the porous microstructure on the cracks surface.

Long-term high-temperature exposure effects on mechanical properties and structure of the 42XNM alloy after neutron irradiation in the VVER-1000. Part 1. Mechanical tests

The paper presents the results of mechanical tests of ring specimens made of the 42XNM alloy after irradiation as part of the control and protection system of the VVER-1000 reactor to a damaging dose of ~12 dpa at a temperature of ~350°C and subsequent isothermal annealings in the temperature range of 400– 1150°C (heating and holding for ~2 h). A model was constructed and validated by the finite element method, it describes the mechanical characteristics of irradiated and non-irradiated samples from the 42XNM alloy during tests in the temperature range from 500 to 1000°C. The model was used to plot the temperature dependences of the maximum local plastic deformation and the yield strength of the material under study.

Long-term high-temperature exposure effects on mechanical properties and structure of the 42XNM alloy after neutron irradiation in the VVER-1000. Part 2. Structural studies

The paper presents the results of structural studies of ring specimens made of the 42XNM alloy after irradiation as part of the control and protection system of the VVER-1000 reactor to a damaging dose of ~12 dpa at a temperature of ~350°C and subsequent isothermal annealings in the temperature range of 400– 1150°C (heating and holding for ~2 h). It is shown that during long-term isothermal annealing, a change in the phase composition of the alloy is observed, dislocation structures and grain-boundary segregations are annealed, and porosity evolves. It has been confirmed that decrease in the plastic properties of the 42XNM alloy after irradiation and subsequent isothermal annealing in the temperature range of 400–1000°C could be explained by the formation of precipitates of the second phases (zones of discontinuous decomposition of the solid solution with the release of α-Cr particles along the grain boundaries) and pores at the grain boundaries.

Model-experiment comparison for transverse loading of metal–composite ring specimen (Part 1)

As a building block towards improved understanding and design of Composite Overwrapped Pressure Vessels (COPV), this paper presents simulations and experimental validation of a 3D finite element model for a metal–composite ring structure subjected to quasi-static indentation, used as a proxy for low velocity impact (LVI). The focus of the work is to model composite ply delamination as well as metal–composite separation, using cohesive elements. A methodology is presented to determine the parameters used for the traction-separation law that controls the cohesive elements. The model was calibrated and validated using a hybrid metal–composite ring at reasonable engineering length-scales, corresponding to structures with 159 mm outer diameter and 50 mm length. Each ring specimen was loaded in displacement controlled compression up to 20 mm, i.e. the point at which composite delamination and plastic deformation of the metallic layer has occurred. Validation is performed by comparing experimental force–displacement curves, strain fields and damage mechanisms to results obtained from the finite element (FE) model. Results from the numerical modelling are in good agreement with experimental values.

Performance improvement strategy of the TBM disc cutter ring material and evaluation of impact-sliding friction and wear performance

Tunnel Boring Machine (TBM) cutter ring is prone to collapse, fracture, wear, and other types of failures when dealing with hard rock/extremely hard rock. In order to address the above issue, performance enhancement strategies including electroslag remelting and increased number of tempering cycles in the heat treatment process have been implemented. These strategies lead to improvements in the comprehensive performance of the cutter rings. To evaluate the effectiveness of these enhancements, a comparison was made between the mechanical properties of the cutter rings made by H13 and W360 steels, based on the parameters including microhardness, impact toughness, and impact-sliding resistance. The results show that the microhardness of W360 cutter ring specimen has increased by 9.99%, while the impact toughness has also increased by 54.2%. According to the impact-sliding wear experiment, the impact region of the W360 specimen has a smaller wear depth under the impact angles, reflecting that the impact resistance of the W360 specimen is better. However, when the impact angle is 60°, the wear volume of the sliding region of W360 specimen is larger than that of H13 specimen, which may be related to the fact that H13 specimen contains a higher proportion of martensite. To sum up, better comprehensive performance could be obtained by choosing a reasonable metallurgical method and an optimizing heat treatment process.

Experimental and theoretical studies on the lateral collapse of mechanically lined pipes

The mechanically lined pipe, which consists of a thin non-corrosive liner and a carbon steel pipe, is an economical way to transport acidic fluid in offshore applications. However, it is prone to lateral loading and potentially develops plastic collapse and liner separation during the operational stage. The present study examines its crushing performance using small-scale 2-inch lined pipes manufactured by a customized hydroforming facility. The lined pipes comprised a seamless GB45 carbon steel tube and a grade T2 copper liner. Four ring specimens extracted from lined pipes and two single-layer rings were crushed on a universal testing machine in a quasi-static manner. The tube was found to develop an ovalized shape initially and then changed into a "∞" shape in the end. The carrier and liner were found to stay together throughout the crushing process, with slight liner separation taking place. The manufacture and lateral collapse processes were also reproduced with finite element models and nonlinear analytical formulation. The analytical model was established based on the principle of virtual work and nonlinear ring theory, assuming small strain and finite rotation. It showed that the analytical and numerical simulation results agreed with the experimental results. The influence of major parameters of the problem was also studied based on the full-scale lined pipe. Amongst other findings, manufacture-related plastic hardening is shown to affect the load-carrying capacity and the growth of separation during lateral collapse.