Tensile Stress Intensity Research Articles

Изучение возможностей углеродного материала в паре трения эндопротеза тазобедренного сустава при помощи математического моделирования и стендовых испытаний

INTRODUCTION: One of the most effective methods of surgical treatment of late-stage coxarthrosis is total hip replacement. However, the steady increase in the number of primary endoprosthetics results in the increase of revision surgeries. Our proposed solution to use carbon material in bearings will decrease the number of revision surgeries due to component wear, and may also significantly reduce the risk of aseptic loosening. AIM: To compare stress and torque of the head and liner structures with bearings made of carbositall with diameters of 28 mm and 38 mm using mathematical modeling and to compare the volume wear of bearings made of ceramics and carbositall using bench tests. MATERIALS AND METHODS: Mathematical modeling was used to assess the stresses in the proposed design. The mathematical model was created by software-based methods in ANSYS 5.7 environment. Structures with diameters of 28 mm and 38 mm were studied. A physical model of a bearing made of carbositall was made for bench testing. In accordance with requirements of GOST 31621-2012, a torque test of a carbositall bearing was performed. In accordance with GOST R ISO 14242-3-2013, a study of volume wear of bearings made of ceramics and carbositall was performed. RESULTS: Mathematical modeling of a bearing made of carbositall with a size of 38 mm in comparison with a bearing with a diameter of 28 mm showed a decrease in intensity of compressive and tensile stresses with a natural increase in the safety factor for components made of carbositall. Based on the results of the torque test of bearing for hip arthroplasty, the torque was 1.1 Nm. This indicator is 26.6% lower than the maximum permissible according to GOST 1.5 Nm. The torque index was 1.10 Nm. As a result of a comparative test for wear of bearing made of ceramic and carbositall, the mass loss of the ceramic head was 0.009 g, the mass loss of the ceramic liner was 0.013 g. The head made of carbositall lost 0.006 g, while the liner lost 0.009 g. In total, the mass loss of the carbon bearing is 31.8% less than that of the ceramic one. CONCLUSION: A large-diameter bearing showed the best strength characteristics of the carbon part of the structure, however, the strength limit of the titanium sleeve decreased. The torque of the carbon bearing was 1.1 Nm, which is 26.6% lower than the maximum permissible index, and the volume wear of the bearing made of carbositall is 31.8% less than the volume wear of the bearing made of ceramics.

Comparative analysis between size and mass ratio of nano-Al2O3 in the performance of dental composite and finding the optimum composition

Dental composites provide better bonding with tooth tissue as compared to other traditional materials such as amalgam. However, the development of dental composites relies on experimental results of physical, mechanical and thermal properties of the dental composite obtained after applying the strategy of filler technology, i.e., changing size, shape, surface modification and mass ratio of filler or reinforcement. In the present research, nano-Al2O3 particle size and filler mass ratio were varied to study their effect on the physical, mechanical and thermal behaviour of dental composite. The particle size was varied in the range of 30 nm, 50 nm and 70 nm. Nano-Al2O3 filler mass ratio was varied in the range of (0, 5, 10 and 15 wt. %). Fourier transform infrared analysis was done to check variations in absorption peak and band in the spectrum due to variation in the filler mass ratio and size. Physical properties, mechanical properties and thermal properties were investigated. It was observed that hardness, compressive strength, diametral tensile strength, flexural strength and stress intensity factor were increased by 133%, 13.6%, 27.4%, 25% and 20%, respectively, on adding 5 wt. % of nano-Al2O3 and decreased by 13.5%, 8.1%, 15.3%, 13.9% and 10.3%, respectively, on increasing particle size from 30 nm to 50 nm. The thermal degradation temperature was increased by 31.8% and 36% on adding 5 wt. % and increasing particle size from 30 nm to 50 nm, respectively. It can be concluded that in the case of nano-sized particulate filler, mass ratio played a more significant role than filler size in regards to optimization of physical, mechanical and thermal properties.

Prediction of hydrogen-assisted fracture under coexistence of hydrogen-enhanced plasticity and decohesion

This work presents a novel strategy to model the coexistence of HELP & HEDE mechanisms. The proposed method accounts for ductile and brittle damage with a competitive fracture criterion to describe the competition effect between HELP & HEDE mechanisms. The cooperation aspect is addressed by a dislocation-enhanced hydrogen accumulation model, which agrees with the HELP-mediated HEDE mechanism. The tensile, fracture toughness, and threshold stress intensity factor tests are simulated in different hydrogen environments. The results demonstrate that the proposed method reproduces the hydrogen-dependent ductile to brittle transition phenomenon. Under different hydrogen conditions, the dominating damage mechanism and degradation trends agree with experimental observations. Furthermore, for the investigated 4130 steel, the predicted value of fracture toughness and threshold stress intensity factor match the experiment results. The difference in damage kinetics inherent in the two test methods is captured, which supports the rationality of the proposed strategy for HELP and HEDE interaction.

Investigation of the crack evolution characteristics of coal and rock bodies around boreholes during progressive damage based on stress threshold values

The stress threshold is a key stress indicator of crack evolution of coal and rock bodies around boreholes during progressive damage. To investigate the crack evolution characteristics of coal and rock bodies around boreholes, digital speckle correlation method tests were conducted on intact specimens, specimens with boreholes, and specimens with grouted boreholes, and the characteristic parameters, such as the stress threshold, surface deformation field, crack opening and shear, and strain energy density, were quantitatively analyzed. The results show that (1) the distribution characteristics of surface cracks on the specimen are affected by the borehole structure and grouting; (2) the crack displacement evolution of coal and rock specimens remain basically stable at the initial stage of loading. In the middle and later stages, the cracks are continuously opening and shearing, which directly leads to the damage of the specimen; (3) the energy accumulation and release law of coal and rock bodies is related to the evolution of localization zone. In different areas outside the localization zone, the strain energy density shows different characteristics; (4) the tensile crack is the main reason for the destruction of coal and rock bodies around boreholes. During the progressive damage, the tensile cracks at the upper and lower ends of specimen experience the process of opening, closing and reopening. The presence of cohesion g(x) reduces the crack tensile stress intensity factor, so that the crack is in a balanced state before penetration, which is conducive to the connection and penetration of other cracks. The results provide theoretical guidance for the optimization design of gas extraction boreholes construction and grouting.

Microstructure size-dependent contact behavior of a thermoelectric film bonded to an elastic substrate with couple stress theory

Thermoelectric films linked to elastic substrates are typical engineering structures and have applications in heat recovery systems. This article uses the nonlocal heat conduction and couple stress theory to investigate the electric-thermal-elastic behavior of the thermoelectric film placed on the elastic half-plane. The internal characteristic lengths of both the thermoelectric film and the elastic substrate are introduced to reveal the scale effects. The coupling governing integro-differential equations in terms of the interface shear stress and tensile stress are derived for the thermoelectric film and the elastic substrate. The numerical results show how the distribution of the tensile and shear stress intensity factors is affected by the stiffness ratio of the substrate to the thermoelectric film, the internal characteristic lengths of the thermoelectric film and the elastic substrate, and the thickness to length ratio of the thermoelectric film. Compared with the classical model for a thicker thermoelectric film and stiffer elastic substrate, the present study demonstrates the necessity of taking into account the microstructure lengths of the thermoelectric film and the elastic substrate.

A systematic study of interface properties and fracture behavior of graphene/aluminum: Insights from a first-principles study

In-depth study of graphene/aluminum interface properties with different structures is of great significance for improving the toughness and strength of next-generation aluminum alloys. In this paper, different structural models of Al matrix and graphene/Al composites were studied by first-principles calculations, revealing the interface strength and fracture behavior mechanism. The stability, fracture energy and tensile strength of different surfaces of Al(1 0 0), Al(1 1 0), and Al(1 1 1) were investigated by first-principles calculations, and the interfacial strength and fracture behavior of three common surfaces were revealed. The Al(1 1 1) surface has the lowest surface energy, lowest fracture energy and lowest tensile stress intensity. On this basis, we considered coating graphene on Al(1 1 1) surface, and then investigated the effects of C vacancies and Si doping on the fracture energy and tensile strength of the composites. The results show that with the increase of C vacancies and the increase of Si introduction concentration, the fracture energy and tensile stress strength of the system tend to increase. The density of states calculations show that there is a certain hybridization effect between Al-3s, Al-3p and C-2p, Si-3p orbitals, forming s-p hybrid orbitals. The most stable interfaces contain low-energy state electrons with the most uniform electron distribution, which is a key factor for interface stabilization and strengthening. Our theoretical research results have certain guiding significance for the experimental synthesis of graphene-reinforced aluminum matrix composites and the improvement of the strength of aluminum and aluminum alloys.

Diverse angle-length-width model for 3D/4D/5D steel fiber reinforced concrete under tension

The most important characteristic of steel fiber reinforced concrete (SFRC) is its excellent post-cracking behavior. An analytical diverse angle-length-width model (DAM) was proposed to calculate the tensile stress-crack width (σ-w) constitutive behavior of SFRC members subjected to tension and to evaluate its post-cracking behavior. In the proposed model, the tensile stress in SFRC members with end-hooked steel fibers was generated from the straight fiber part, the end-hooked fiber part, and the concrete part. The effects of straight and end-hooked parts were separately considered, and three cases for different crack width ranges were analyzed for each part. The model was derived by considering all of the possible fiber inclination angles, fiber embedded lengths, and crack widths. It was found that SFRC members with new types of 4D and 5D steel fibers possessed a higher tensile stress than those with 3D steel fibers, and the tensile stress intensity increased with the increasing fiber volume fraction. Finally, the accuracy of the model was verified by comparing the values by DAM with the experimental results based on the sectional analysis.

Fracture and fatigue of the surface layer of layered media due to adhesive sliding contact

Layer cracking in a layered medium consisting of an elastic-perfectly plastic half-space (substrate) and a relatively stiff, elastic surface layer in adhesive sliding contact with a rigid asperity was analyzed with the finite element method using linear elastic fracture mechanics. The directions of tensile and shear mode fracture were determined from the maximum tensile and shear stress intensity factors (SIFs), respectively, whereas the directions of tensile and shear mode fatigue crack growth were determined from the maximum range of tensile and shear SIFs, respectively. The effects of asperity position, interfacial adhesion (Maugis parameter), crack depth, asperity interaction distance, layer thickness, and material properties of the elastic layer and the elastic-plastic substrate on fracture and fatigue crack growth in the layer are interpreted in the context of simulation results. It is shown that the propensity for fracture and fatigue in the layer is enhanced with increasing asperity interaction distance and Maugis parameter and decreasing crack depth and layer thickness. The numerical results of this study reveal that, for similar tensile and shear fracture toughness, layer fracture in adhesive sliding contact predominantly occurs by the out-of-plane tensile mode of fracture, whereas fatigue crack growth in the layer is a manifestation of the in-plane shear and out-of-plane tensile modes of fatigue crack growth.

A fracture mechanics analysis of asperity cracking due to sliding contact

Microfracture of surface protrusions residing on contacting surfaces, known as asperities, due to normal and shear surface traction occurs at various scales affecting the durability and performance of many mechanical components. In this study, microfracture of an asperity due to sliding against a rigid asperity was examined using a two-dimensional (plane strain) finite element model and linear elastic fracture mechanics. The effects of the asperity interference depth, sliding friction, crack position, and crack-face friction on the rate, direction, and dominant mode of crack growth were determined by the ranges of the maximum tensile and shear stress intensity factors. The asperity interference depth and sliding friction exhibited the most pronounced effects on the rate and direction of crack growth. A transition from shear to tensile dominant mode of crack growth was encountered with increasing asperity interference depth and/or sliding friction coefficient. Crack mechanism maps revealing the evolution of opening, slip, and stick between the crack faces are presented for a range of crack-face friction coefficient, asperity interference depth, and sliding friction coefficient. The simulation results provide insight into the underlying microfracture mechanics of asperities residing on sliding surfaces that exhibit different friction characteristics.

Structural Evolution During Cyclic Glacier Surges: 2. Numerical Modeling

The mesoscale structures of a glacier express the history of flow, temperature, and stress. Thus, in principle, numerical ice dynamics models have sufficient physics to examine the formation and transport of these structures. In this study we use a vertically integrated thermomechanical ice dynamics model to simulate the temporally evolving patterns of surficial moraine, stratification, foliation, and folding of glacier ice, and the density and orientation of traces of former crevasses. The modeled glaciers are simplified versions of Trapridge Glacier in northwest Canada that allow diagnostic modeling of influences on glacier structure and help to clarify the physics and numerics. In the model, surges occur every 50 years in response to a prescribed cyclic change in bed friction. Medial moraine patterns are simulated by tracking the englacial and supraglacial trajectory of debris injected at fixed points in the accumulation region. Stratification is assumed to be associated with isochronal surfaces, and vertical foliation is explained in terms of horizontal flattening of strain ellipsoids. Crevasses form when and where the intensity of tensile stress exceeds a prescribed threshold; crack damage is cumulative so that crevasse traces observed at sampling sites are a superposition of the damage accumulated en route. Folding is parameterized but not resolved. By evaluating the deformation gradient tensor along ice particle trajectories and applying the polar decomposition to this tensor, we isolate the cumulative effects of rotation and stretching by ice flow and calculate strain ellipsoids as well as other practical indicators of deformation.

Iron-based shape memory alloy for the fatigue strengthening of cracked steel plates: Effects of re-activations and loading frequencies

The paper discusses the application of an iron-based shape memory alloy (Fe-SMA) for the fatigue strengthening of steel plates. The shape memory effect (SME), which is the characteristic behavior of the Fe-SMAs, was used for the prestressed strengthening of steel plates. One steel plate without any pre-cracks and two steel plates with pre-cracks were retrofitted with Fe-SMA strips. The SMA-strengthened specimens along with a reference unstrengthened specimen were then subjected to high cycle fatigue (HCF) loading. The effect of multiple re-activations and different loading frequencies (e.g., fr = 0.005, 5, 10, and 15 Hz) on the HCF behavior of the Fe-SMA was investigated. The test results showed that the achieved prestressing level (i.e., recovery stress) in the Fe-SMAs for an activation temperature of 260 °C was in the range of 330–410 MPa, resulting in compressive stresses in the range of 35–72 MPa in the steel plates. Furthermore, it was observed that the recovery stress decreases slightly during cyclic loading, which should be considered in the design. The loss in the prestressing level was approximately 17–20% of the original prestressing; however, the re-activation (i.e., a second activation) process could retrieve a significant portion of the loss. The test results showed that the activated Fe-SMA strips could apply considerable compressive stresses to the cracked steel plate, which reduce the tensile stresses and stress intensity factors (SIFs) at the vicinity of the crack tip, resulting in a significant increase in the fatigue life of the specimens and a complete fatigue crack arrest in some cases.

Effect of thermal stress on wellbore integrity during CO2 injection

Wellbore integrity is a critical component of long-term carbon storage. Depleted reservoirs that are potential CO2 storage sites, typically contain several wells. Due to years of operations and abandonment, these wells can have cracks in the cement, cement-casing interface, and/or cement-formation interface. During CO2 injection, changes in temperature may result in stress variations that can further damage the well, threatening its integrity. The temperature difference between the cold injected CO2 and warm reservoir, and different thermal properties for the wellbore casing, cement, and the lithology, will stress the near wellbore environment, potentially extending pre-existing defects creating leakage pathways from the storage reservoir to the overlying strata. We have conducted a systematic numerical study to explore the role of CO2 injection temperature, downhole effective in-situ horizontal stress, and the thermo-mechanical properties by coupling a linear elastic stress model with heat conduction. We consider conditions in non-perforated casing above the injection zone where conductive heating is dominant. The injection temperatures considered covers current industrial practice as well as sub-zero temperatures. The latter represents direct injection following ship transport, without pre-heating.In this study, we consider the connection between damage risk and the temperature difference between the injected CO2 and the formation and downhole effective in-situ horizontal stress. The study found that the negative impacts of thermal stress in the wellbore environment are mitigated by the presence of effective in-situ horizontal stresses. Stresses normal to the well have the potential to reduce the tensile stress and stress intensity factor. In the absence of sufficient effective in-situ horizontal stress, thermal stress may cause the fracture to propagate due to high stress concentration near the fracture edges. In general, formations with large effective in-situ horizontal stress can prevent leakage paths from growing even when large temperature difference exists between the formation and the injected CO2. Our simulations suggest that CO2 can be injected at sub-zero temperatures, suitable for ship transport, when the downhole effective in-situ horizontal stress is greater than 10 or 12 MPa, depending on the location of the pre-existing cracks. For onshore transportation, injection of liquid CO2 results in minimal damage, provided there is ample in-situ horizontal stress.

Failure Study of Compression Glass-Metal Joint for Parabolic Trough Receiver Tube application

The concentrated solar power plant technology has been proven to be a latest source for generation of renewable energy. Its performance depends on efficiency of the parabolic trough receiver tube or heat collecting element (HTC). In this paper, experimental study on fabrication of glass metal joint has been elaborated for parabolic trough receiver tube. Borosilicate glass tube was joined with austenitic stainless steel (SS304) metal ring using compression glass-metal type assembly with the help of induction heating and using 40SiO2-54B2O3-4Na2O-2Al2O3 material as the glass sealant. The process parameters for joining were selected on the basis of wettablity, pre-oxidation and microstructure studies. The generated residual stresses in glass tube after fabrication process was measured experimentally with the help of photo elastic technique using polariscope ‘PS-100-BS’. From the experimental results, it was observed that, the intensity of residual tensile stress in glass tube increases as thickness of metal ring increases. The cracking of glass just 1mm above the interface was also observed corresponding to maximum metal thickness ring.

Mechanical Properties of Unsaturated Polyester Resin (UPR)-Mortar and its Potential Application to Restore the Strength and Serviceability of Patched Reinforced Concrete Slab

Degradation of reinforced concrete could occur in various forms including spalling of concrete cover as a result of reinforcement corrosion. The degradation would shorthen the service life of the reinforced concrete structure. Patch repair method may be employed to recover this type of degradation using a suitable patch repair material. The authors have developed a patch repair material made from unsaturated polyester resin (UPR)-mortar. In this paper, the mechanical properties of this material which includes compressive strength, elastic modulus, flexural strength and bond strength are highlighted. Comparisons are also made with the normal mortar to emphasize the superior properties of UPR-mortar. Based on these properties, the potential application of UPR-mortar for repairing damaged reinforced concrete slab is examined through finite element simulation. It is pointed out that the tensile stress intensity in the UPR-layer is reduced with a consequence of reducing a risk of cracking in the repair zone. In addition, the patching of damaged zone with UPR-mortar could minimize the deflection.

КОНЕЧНО-ЭЛЕМЕНТНОЕ МОДЕЛИРОВАНИЕ РАЗВИТИЯ ТРЕЩИНЫ В ОБРАЗЦЕ С КОНЦЕНТРАТОРОМ В УСЛОВИЯХ ВЫСОКОТЕМПЕРАТУРНОЙ ПОЛЗУЧЕСТИ

A numerical methodology for analyzing failure processes in structures in the framework of relations of damaged medium mechanics is considered; the methodology makes it possible to analyze the behavior of structures, accounting for characteristic failure processes at both the initial stage of nucleation and the final stage of crack propagation. The results of numerically studying laws of nucleation and propagation of cracks in a cylindrical specimen with a concentrator, loaded in axial tension under high-temperature creep in the assumption of a viscous character of failure of the specimen, are given, as obtained using the present methodology. The results of the analyses are shown to depend on the parameters of the FE-discretization of the specimen in the region of the crack propagation trajectory. Nucleation time, stable propagation time and crack propagation rate are correlated with the value of the stress concentration coefficient in the notch and the intensity of tensile stresses. Keywords: creep, stress concentrator, damage accumulation, fracture, crack, finite element method.

Insight into Vent Opening Probability in Volcanic Calderas in the Light of a Sill Intrusion Model

The aim of this paper is to discuss a novel approach to provide insights on the probability of vent opening in calderas, using a dynamic model of sill intrusion. The evolution of the stress field is the main factor that controls the vent opening processes in volcanic calderas. On the basis of previous studies, we think that the intrusion of sills is one of the most common mechanism governing caldera unrest. Therefore, we have investigated the spatial and temporal evolution of the stress field due to the emplacement of a sill at shallow depth to provide insight on vent opening probability. We carried out several numerical experiments by using a physical model, to assess the role of the magma properties (viscosity), host rock characteristics (Young’s modulus and thickness), and dynamics of the intrusion process (mass flow rate) in controlling the stress field. Our experiments highlight that high magma viscosity produces larger stress values, while low magma viscosity leads to lower stresses and favors the radial spreading of the sill. Also high-rock Young’s modulus gives high stress intensity, whereas low values of Young’s modulus produce a dramatic reduction of the stress associated with the intrusive process. The maximum intensity of tensile stress is concentrated at the front of the sill and propagates radially with it, over time. In our simulations, we find that maximum values of tensile stress occur in ring-shaped areas with radius ranging between 350 m and 2500 m from the injection point, depending on the model parameters. The probability of vent opening is higher in these areas.

Comparative Analysis of Overburden Strata Movement in Fully Mechanized Top Coal Caving Mining in Entire (Sub) Layer of Ultra Thick Seam

Reasonable determination of entire layer or sublayer mining method is the key factor of safe and efficient mechanized caving mining of 14.0～28.0m ultra thick seam , numerical simulation on the entire (sub) layer coal caving mining by the FLAC3D , studying the stress and displacement variation of overburden strata , combining the underground pressure theory , comparative analysis on the calculation results . The results show that entire (sub) layer mining roof stress , movement contours are presented in a semi-elliptical arch morphology , indicating the existence of a high arch structure overburden formations , mining process appears roof tensile destruction , but the entire layer caving tensile stress intensity is lower than sublayer caving . When advancing the same distance , entire layer caving puts a greater impact on the overburden strata than the sublayer caving , has some features such as big range of influence and extent , small roof pressure , lead abutment pressure forward from grand , short time of achieving full extraction , etc.

Thermal shock resistance of solids associated with hyperbolic heat conduction theory

The thermal shock resistance of solids is analysed for a plate subjected to a sudden temperature change under the framework of hyperbolic, non-Fourier heat conduction. The closed form solution for the temperature field and the associated thermal stress are obtained for the plate without cracking. The transient thermal stress intensity factors are obtained through a weight function method. The maximum thermal shock temperature that the plate can sustain without catastrophic failure is obtained according to the two distinct criteria: (i) maximum local tensile stress criterion and (ii) maximum stress intensity factor criterion. The difference between the non-Fourier solutions and the classical Fourier solution is discussed. The traditional Fourier heat conduction considerably overestimates the thermal shock resistance of the solid. This confirms the fact that introduction of the non-Fourier heat conduction model is essential in the evaluation of thermal shock resistance of solids.

Fracture mechanics analysis of asperity cracking due to adhesive normal contact

A two-dimensional linear-elastic fracture mechanics analysis of asperity cracking induced by adhesive normal contact was performed with the finite element method. Normal contact between two elastic asperities was analyzed with the equivalent contact system of an elastic asperity with equivalent radius of curvature and effective elastic modulus compressed by a rigid plane. Surface adhesion was modeled by nonlinear springs obeying a constitutive force-distance law derived from the Lennard–Jones potential. The maximum ranges of the tensile and shear stress intensity factors were used to determine the crack-growth direction and the dominant mode of asperity fracture in terms of the Maugis parameter (a function of the equivalent radius of curvature, work of adhesion, effective elastic modulus, and intermolecular equilibrium distance), friction coefficient at the crack interface, maximum surface interference, and crack position. Finite element simulation results indicate that the direction and the rate of crack growth are mostly affected by the Maugis parameter and the maximum surface interference. A transition from shear to tensile dominant mode of crack growth is encountered with the increase of the Maugis parameter and/or the decrease of the maximum surface interference. Opening, slip, and stick between the crack faces during loading and unloading are discussed in the context of crack mechanism maps.

Long term performance of warm mix asphalt versus hot mix asphalt

The fatigue behavior, indirect tensile strength (ITS) and resilient modulus test results for warm mix asphalt (WMA) as well as hot mix asphalt (HMA) at different ageing levels were evaluated. Laboratory-prepared samples were aged artificially in the oven to simulate short-term and long term ageing in accordance with AASHTO R30 and then compared with unaged specimens. Beam fatigue testing was performed using beam specimens at 25 °C based on AASHTO T321 standard. Fatigue life, bending stiffness and dissipated energy for both unaged and aged mixtures were calculated using four-point beam fatigue test results. Three-point bending tests were performed using semi-circular bend (SCB) specimens at −10 °C and the critical mode I stress intensity factor KI was then calculated using the peak load obtained from the load-displacement curve. It is observed that Sasobit and Rheofalt warm mix asphalt additives have a significant effect on indirect tensile strength, resilient modulus, fatigue behavior and stress intensity factor of aged and unaged mixtures.