Effective Stress Distribution Research Articles

The Cold Forming Analysis of Eccentric Parts

In this study, a multi-stage cold forming process for the manufacture of eccentric parts is studied numerically with low carbon steel AISI 1022. The forming processes through five stages and four stages include two-step forward extrusion, eccentric upsetting, and backward extrusion over a moving punch. The numerical simulations of cold forming are conducted using the code of DEFORM-3D. The formability of the workpiece is studied numerically, such as the effect on forging load responses, maximum forging loads, effective stress and effective strain distributions and metal flow pattern. The maximum effective stress of 819 MPa at the third stage is the largest among the stages. The maximum effective stresses of the last stages for the four-stage forming and five-stage forming are almost the same. The effective strain distributions of the last stages for the four-stage forming and five-stage forming are very similar. The flow line distributions of the last stages both for the four-stage forming and five-stage forming are also very similar. For the maximum axial forging force and forming energy, the third stage of eccentric upsetting at the upper end is the largest among the stages. The total maximum axial forging loads from the first to the last stages are 795.8kN for the five-stage forming and 590.4kN for the four-stage forming; and the total forming energies are about 0.751kJ for the five-stage forming and 0.671kJ for the four-stage forming. Although the total maximum axial forging loads and total forming energy of the four-stage forming are smaller than those of the five-stage forming, the maximum lateral forging force in the last stage of the four-stage forming is almost five times that of the last stage of the five-stage forming. Increasing lateral forging force may lead to wear and damage of the punch. Moreover, the inner surfaces of the hexagonal cavity at the upper end are relatively uneven because of simultaneous eccentric upsetting and backward extrusion in the last stage of the four-stage forming.

Analysis of the Effect of Thickness on the Performance of Polymeric Heart Valves

Polymeric heart valves (PHVs) are a promising and more affordable alternative to mechanical heart valves (MHVs) and bioprosthetic heart valves (BHVs). Materials with good durability and biocompatibility used for PHVs have always been the research focus in the field of prosthetic heart valves for many years, and leaflet thickness is a major design parameter for PHVs. The study aims to discuss the relationship between material properties and valve thickness, provided that the basic functions of PHVs are qualified. The fluid−structure interaction (FSI) approach was employed to obtain a more reliable solution of the effective orifice area (EOA), regurgitant fraction (RF), and stress and strain distribution of the valves with different thicknesses under three materials: Carbothane PC−3585A, xSIBS and SIBS−CNTs. This study demonstrates that the smaller elastic modulus of Carbothane PC−3585A allowed for a thicker valve (>0.3 mm) to be produced, while for materials with an elastic modulus higher than that of xSIBS (2.8 MPa), a thickness less than 0.2 mm would be a good attempt to meet the RF standard. What is more, when the elastic modulus is higher than 23.9 MPa, the thickness of the PHV is recommended to be 0.l–0.15 mm. Reducing the RF is one of the directions of PHV optimization in the future. Reducing the thickness and improving other design parameters are reliable means to reduce the RF for materials with high and low elastic modulus, respectively.

Spatial-temporal evolution of reservoir effective stress during marine hydrate depressurization production

In tests of marine hydrate depressurization production in many countries, accidents such as collapse and failure of boreholes have occurred, which caused by the evolution of the effective stress field have motivated further attention. However, in existing effective stress models, the pressure of the fluid in the wellbore is taken as the boundary condition, which did not account for the effects of the wellbore on the effective stress distribution. This paper is aimed at proposing a methodology to research the spatio-temporal evolution of the effective stress during the hydrate depressurization production, in order to provide a theoretical benchmark against which to analyze the borehole stability. We derived a mathematical model of the effective stress by taking into account the interaction between the wellbore and the reservoir on the basis of the theory of elasticity, and coupled with deposited infiltration using fluid-structure interaction theory, a coupled multiple field model considering the kinetic effects of hydrate decomposition was then established. And a solver was developed independently. A case study shows that the wellbore has significant effect on the effective stress within the radius of 0.5 m of the reservoir. At the borehole wall, the radial effective stress is 23.58 MPa, whereas the circumferential effective stress is 7.31 MPa, such nonuniformity of the effective stress lead to the risk of borehole failure. As the production progresses, the effective stress increases rapidly at first and then slowly. The effective stress is slightly affected by the size of the wellbore, it is found that when the outside diameter of the wellbore is increased from 100 mm to 500 mm, the change is less than 3.04%.

The Study of Multi-Stage Cold Forming Process for the Manufacture of Relief Valve Regulating Nuts

Cold forging is widely used in many industries. Multi-stage cold forming is usually utilized in forging fasteners. In this study, numerical simulation and experimental investigations were carried out on a five-stage cold-forming process for the manufacturing of low-carbon steel AISI 1010 relief valve regulating nuts. The forming process through five stages included preparation and centering for backward extrusion, backward extrusion over die pin, upset, backward extrusion over a moving punch, and piercing. The formability of the workpiece was studied, such as the effects on forming force response, maximum forming force, effective stress and effective strain distributions, metal flow patterns, and strength. A comparison of the forming forces obtained in the forming experiment with the numerical simulation results of the five-stage cold forming showed a good agreement with the trend of the forming force growth. For the maximum forming force and forming energy, the fourth stage of backward extrusion over the moving punch at the upper face was the largest among the five stages. The total maximum forming forces from the first to the fifth stages were numerically 440.9 kN and experimentally 449.4 kN, meaning the FE simulation and experimental results were in good agreement. The numerically simulated effective strain distributions were consistent with the experimentally tested hardness distributions. Highly compacted grain flow lines also resulted in higher hardness. The overall hardness of the workpiece formed by five-stage cold forming increased by 31% compared to the initial billet. The hardness of the workpiece increased with the forming stages, and the strain-hardening effect was obvious. The strength of the workpiece was significantly increased by five-stage cold forming.

Hierarchical composite coating for enhancing the tensile behaviour of textile-reinforced mortar (TRM)

We describe a novel class of interface-functionalised textile-reinforced mortar (TRM) composite materials reinforced with basalt and alkali-resistant glass multifilament textiles embedded in a commercially available hybrid lime-cement mortar, usually applied for masonry retrofitting. Spotlight is set on improving the mechanical (tensile) performance of the system through a scalable and easy-to-apply surface treatment for the dry textiles. The treatment consists in soaking the textiles in highly-diluted epoxy resin, to which rice husk ash (RHA) is later added, acting as pozzolanic filler. The resulting functionalised textiles exhibit remarkable adhesion with the matrix owing to the presence of RHA having high specific surface area and rich amorphous content. Three different RHA powders are assessed and their performance is compared to that of plain silica fume. The role of RHA milling is also discussed. The RHA/epoxy coating significantly improves the ultimate tensile strength and energy dissipation capability of the TRMs. In particular, for basalt-textile reinforced composites, the mean tensile strength is three times as large as that of uncoated specimens, whereas the dissipated energy at failure is nearly four times as much. Furthermore, the surface treatment qualitatively changes the cracking pattern of the TRMs, for many diffused small cracks appear during tensile testing, and this provides evidence of effective stress distribution in the matrix as a result of superior interface adhesion.

Stress‐Based and Convolutional Forecasting of Injection‐Induced Seismicity: Application to the Otaniemi Geothermal Reservoir Stimulation

AbstractInduced seismicity observed during Enhanced Geothermal Stimulation at Otaniemi, Finland is modeled using both statistical and physical approaches. The physical model produces simulations closest to the observations when assuming rate‐and‐state friction for shear failure with diffusivity matching the pressure build‐up at the well‐head at onset of injections. Rate‐and‐state friction implies a time‐dependent earthquake nucleation process which is found to be essential in reproducing the spatial pattern of seismicity. This implies that permeability inferred from the expansion of the seismicity triggering front (Shapiro et al., 1997, https://doi.org/10.1111/j.1365-246x.1997.tb01215.x) can be biased. We suggest a heuristic method to account for this bias that is independent of the earthquake magnitude detection threshold. Our modeling suggests that the Omori law decay during injection shut‐ins results mainly from stress relaxation by pore pressure diffusion. During successive stimulations, seismicity should only be induced where the previous maximum of Coulomb stress changes is exceeded. This effect, commonly referred to as the Kaiser effect, is not clearly visible in the data from Otaniemi. The different injection locations at the various stimulation stages may have resulted in sufficiently different effective stress distributions that the effect was muted. We describe a statistical model whereby seismicity rate is estimated from convolution of the injection history with a kernel which approximates earthquake triggering by fluid diffusion. The statistical method has superior computational efficiency to the physical model and fits the observations as well as the physical model. This approach is applicable provided the Kaiser effect is not strong, as was the case in Otaniemi.

Nonlinear Consolidation Analysis of Soft Soils with Vertical Drains Considering Variable Well Resistance with Time and Depth under Multistage Loading

A nonlinear consolidation model of soils with vertical drains was developed by combining the fact that well resistance varies linearly with depth and exponentially with time. In addition, three variation modes related to horizontal permeability in the smear zone were used to improve this model. The degree of consolidation, excess pore pressure, and settlement of soil layers under multistage loading were simulated by the finite-difference method. The proposed solution was verified through a comparison with the literature to demonstrate its validity. Ultimately, the effects of various parameters associated with well resistance, the ratio of compression index to permeability index, external loading, smear effects, and the distribution of initial average effective stress along the depth on consolidation behaviors were investigated in this study.

Preform design with increased materials utilization and processing map analysis for aluminum hot forging process

In this article the conventional aluminum hot crown forging process for mass production of shock absorber assembly is experimentally and numerically studied. The preform design method was proposed to improve the quality of post-forged product, save the material weight, and decrease manufacturing cost for finishing process. Finite element (FE) simulation software was employed to numerically analyze the material flow lines, strain, temperature, and effective stress distribution to reduce time and cost in obtaining the appropriate preform design. Furthermore, the software is used to extract the numerical results of power dissipation efficiency and instability from the processing map analysis of stress-strain rate material data in different temperature and strain conditions, which are useful parameters to analyze formability and microstructures of material. Then, the improved hot forging design was achieved by the combined-analysis of preforming design, material utilization, and processing map. The numerical results have accurately predicted the poor quality and serious underfilling defects in the conventional post-forged product, and finally the improved design have successfully diminished defects, met precision tolerances and satisfied quality requirements. The proposed design saves material weight up to 10.26 %, increases material utilization from 79.01 % to 88.08 % which improves the problem of excessive flash in the conventional case, and reduces the forging load up to 12.40 % which benefit the dies life. Two intriguing areas were microstructurally examined and the results showed that the grain sizes are adequately fine to satisfy the expected mechanical properties.

Steady‐State Effective Normal Stress in Subduction Zones Based on Hydraulic Models and Implications for Shallow Slow Earthquakes

AbstractThe spatial distribution of effective normal stress, , is essential for understanding the fault motion. Although Rice (1992, https://doi.org/10.1016/s0074-6142(08)62835-1) proposed a steady‐state solution for a vertical strike‐slip fault zone with constant fluid properties, models that are based on the concept by Rice (1992, https://doi.org/10.1016/s0074-6142(08)62835-1) and are applicable for other tectonic settings have not yet been developed. Such a model is particularly important in subduction zones because the relationship between low and slow earthquakes is often discussed. To quantitatively examine the causes of a local decrease in on a shallow region of the subduction zone, we performed model calculations that incorporated mechanisms characteristic to subduction zones. Our basic model, which considers the effect of smectite dehydration and the mechanical effect of subduction, yields results that are consistent with those reported by Rice (1992, https://doi.org/10.1016/s0074-6142(08)62835-1): the gradient of remarkably decreases with the increase in depth, whereas the realistic fluid properties rule out nearly constant at depth. We obtained a monotonic increase in with the increase in depth for the physically sound solutions and failed to generate a local decrease in . The presence of a splay fault and fluid leakage though it cannot decrease locally. We found that a local decrease in permeability decreased locally around an impermeable zone and, thus, possibly led to the occurrence of shallow slow earthquakes. The water release caused by the dehydration reaction may not be the dominant factor, although smectite dehydration releases silica and promotes its precipitation.

Numerical investigation of the application of voxel based meshes for stochastic tow based discontinuous composites

Stochastic tow based discontinuous composites (STBDC) are fabricated from compression molding chips of chopped and slit pre-impregnated uni-directional carbon fiber reinforced polymer (CFRP) tape. The discontinuous mesostructure gives the material system increased moldability versus continuous fiber composites; however, this gives the material highly variable effective properties. For applications in finite element analysis, the mesostructural morph ology of STBDCs can be idealized using a non-conforming voxel-based mesh framework. The objective of this study is to investigate the effect of mesh coarsening on the elastic response of STBDC simulations. Furthermore, a method for the homogenization of the voxel based mesostructure is considered, with results compared against detailed simulations of the mesostructure. The results demonstrate that coarse mesostructures provide similar effective properties and internal stress distributions as detailed models. Furthermore, simulations with homogenized properties provide nearly identical results to detailed simulations for a fraction of the simulation time. • Voxel-based representative volume elements can be used to generate finite element models and calculate effective properties. • Chips size influences the magnitude of internal stress concentrations observed in representative volume elements. • Method for homogenization provides a similar elastic response as detailed representative volume elements. • Simulations capture the chip size effects on the effective modulus.

Experimental and Numerical Investigation on Effects of Pin Diameter on Multi-Point Forming

Multi-point forming (MPF) is an advanced and flexible method to form sheet metal workpieces. Although there are studies investigating different aspects of this method, the studies on the effects of pin diameter on sheet and pin contact on MPF are insufficient. In this study, pins with diameters of 10, 12, and 14 mm were used to investigate the damage factor, effective stress distribution, and required forming loads of three forms of aluminum 1100 parts in finite element simulations. In addition, experimental works were conducted for the 12 mm pin and the forming loads and the thinning on the contact points of pin and formed sheet metal parts were compared with the simulations. The 14 mm pin forming provided the highest effective stress distributions and the damage factors of 0.448, 0.770, and 0.329 were obtained for form1, form2, and form3, respectively. The percentage errors between experimental works and simulations using 12 mm pin forming were calculated as 7.4, 5.1, and 2.4% for all forms 1 to 3. In conclusion, pin diameter was shown to have significant effects on the MPF process. Larger diameter pins resulted in higher loads and tearing of sheet metal.

The drained tension capacity of suction buckets in sand under vertical uplift loading

The drained tension capacity of suction buckets under vertical uplift loading is calculated as the sum of friction on the inside and outside bucket wall without considering the submerged self-weight of suction buckets. When using existing methods to predict the drained tension capacity, it may be convenient to assume that the vertical effective stress along bucket walls at ultimate loading keeps the same as the initial static vertical effective stress. However, during uplift loading, the vertical effective stress was found to be reducing due to the gradually mobilized friction. This paper presents the results of finite element analyses on suction buckets in sand. The analyses focus on the distribution of vertical effective stress in the direction of bucket diameter and along the bucket wall. Compared with the initial vertical effective stress, a pronounced decrease in the vertical effective stress along the inside bucket wall is observed, but the vertical effective stress along the outside bucket wall has a minor change. The interface factor (ratio between friction stress and vertical effective stress) increases with the depth rather than a constant. Based on the numerical results, equations to predict the drained tension capacity are proposed for suction buckets in sand.

Fatigue reliability analysis considering corrosion effects and integrating SHM information

Fatigue cracking is a common problem facing steel bridges. S-N curves have been adopted in design specifications to offer guidance on fatigue design of these bridges. Structural health monitoring (SHM) techniques can provide reliable information on stress states at fatigue-prone details using strain sensors, thereby circumventing complex theoretical analyses. When corrosion is present, simply relying on SHM information obtained through the monitoring period may not be sufficient to reliably estimate the damage incurred by corrosion-enhanced fatigue as corrosion is a long-term process and the time-variant effect of corrosion on fatigue needs to be determined. In this paper, time-variant analysis is used to estimate the reliability of fatigue-prone details at the coped region of a transverse diaphragm in a tied-arch bridge. Stress histograms obtained based on SHM information associated with this case study are utilized to establish the distribution of the original effective stress. Finite element analysis is conducted for (a) determining the spatial adjustment factor (SAF) to adjust the stress range obtained at the location of strain sensors, and (b) assessing the effect of corrosion on the effective stress range. The reliability analysis results show that for the fatigue details investigated in this case study, corrosion has a significant effect on the fatigue reliability and, therefore, should be considered in the life-cycle management of fatigue-prone details.

Investigation of mechanical properties of laser welded dual-phase steels at macro and micro levels

The current automotive industry uses new technology in materials processing and lightweight materials to minimize vehicle weight and fuel consumption. As a result, Tailor-Welded Blanks (TWB) are used in regions where additional strength or stiffness is necessary in body-in-white, thus decreasing weight. In this paper, TWB were produced by joining DP600 with 1.8 mm and DP800 with 0.8 mm and 1.5 mm using CO2 laser welding. The effects of laser power and welding speed on the mechanical properties of TWB were investigated. The flow behaviors of the TWB were obtained from tensile tests. The microstructures of the weld zones of the base materials and TWB were revealed, and the numerical analyzes of the microstructures were performed by micromechanical modeling with a 2D representative volume element (RVE). Effective stress and plastic strain distributions in the microstructures and macroscopic flow curves of the base materials and the weld zones were obtained. The uniaxial tensile tests of the samples were modeled, and the flow behaviors of the TWB were obtained with micromechanical modeling. The results showed a significant change in stress distribution and strain localization depending on the grain size of constituents and the thickness ratios of the TWB at micro and macro scales, respectively. The numerical flow curves obtained using the RVE method were in good agreement with those of the experimental.

Enhancement of Accuracy in Multi-Point Stretch Forming: Cushion Stretching

Multi-point stretch forming (MPSF) is one of the flexible manufacturing processes that uses the reconfigurable tools to produce the three-dimensional sheet metal components. An elastic cushion is placed between the tools and sheet surfaces to avoid direct contact and reduce the dimples as well as wrinkles. The cushion is also known to play an important role as it directly affects the component surface characteristics (accuracy and quality) and thickness strain distribution. An attempt made to apply stretching on the cushion resulted in enhancement of accuracy. In the present work, an analytical methodology is proposed to predict the initial thickness of cushion and stretching load necessary to apply on the cushion. FEA of MPSF of the spherical geometry is carried out with and without application of stretching load on the cushion. Results indicate that effective stress and strain distributions are more uniform when the stretching is applied to cushion thickness in certain range. Proposed methodology can be effectively used to determine initial cushion thickness before stretch and stretch load necessary to achieve chosen final cushion thickness to enhance the accuracy of sheet metal components formed using MPSF.

Finite Element Analysis of a Cutting and Hauling Mining Adapter

Abstract A recently completed research focused on the development of a low-volume mining production and transportation prototype machine. By developing this new mining adapter, the number of machines used in the mine can be reduced. Its application in dimensional stone mining can reduce the expenses of mining companies. After the block stone has been cut around, the stone material can be moved with the machine. The cutting forces and power requirements are calculated for the chain speeds used in production. This paper shows the static stress analysis of two kinds of possible structures of the dimension stone mining adapter. Finite element analysis was used to determine the displacements and the effective stress distribution of the adapter.

Additively Manufactured Nested and Non-Nested Cellular Solids for Effective Stress Distribution and Thermal Insulation Applications: An Experimental and Finite Element Analysis Study

In this study, the design, additive manufacturing and experimental as well as simulation investigation of mechanical and thermal properties of cellular solids are addressed. For this, two cellular solids having nested and non-nested structures are designed and additively manufactured via laser powder bed fusion. The primary objective is to design cellular solids which absorb a significant amount of energy upon impact loading without transmitting a high amount of stress into the cellular solids. Therefore, compression testing of the two cellular solids is performed. The nested and non-nested cellular solids show similar energy absorption properties; however, the nested cellular solid transmits a lower amount of stress in the cellular structure compared to the non-nested cellular solid. The experimentally measured strain (by DIC) in the interior region of the nested cellular solid is lower despite a higher value of externally imposed compressive strain. The second objective of this study is to determine the thermal insulation properties of cellular solids. For measuring the thermal insulation properties, the samples are placed on a hot plate; and the surface temperature distribution is measured by an infrared camera. The thermal insulating performance of both cellular types is sufficient for temperatures exceeding 100 °C. However, the thermal insulating performance of a non-nested cellular solid is slightly better than that of the nested cellular solid. Additional thermal simulations predict a relatively higher temperature distribution on the cellular solid surfaces compared to experimental results. The simulated residual stress shows a similar distribution for both types, but the magnitude of residual stress is different for the cellular solids upon cooling from different temperatures of the hot plate.

Transverse liquid composite moulding processes for advanced composites material manufacturing

ABSTRACT The hydrodynamic compaction behaviour in transverse (through-thickness) impregnation variants of Liquid Composite Moulding (LCM) results in a non-homogeneous fibre volume fraction distribution. A fully coupled simulation model of the entire family of transverse resin infusion/compression processes is presented, which simulates the hydrodynamic compaction behaviour and predicts the process time, fluid pressure, effective stress, and fibre volume fraction distribution. The model is applied to the compression of a saturated preform stack, resin injection into a dry preform, and Compression Resin Transfer Moulding. The simulations are verified using analytic solutions and validated against experimental results from the literature. Special forms of the constitutive equations are constructed to lead to a constant diffusion coefficient, and the resulting model is solved semi-analytically. The results are used to verify the full non-linear simulation model. Additionally, it is shown that assumptions of quasi-steady flow and uniform deformation introduce significant errors in processes involving direct piston compaction of the fibre preform.

Quality comparison of Y-shape joints by tube hydroforming with and without counterforce

The design capability, strength, and structural rigidity provided by tube hydroforming (THF) are successfully used in many applications to produce high-strength parts and assemblies with improved mechanical properties, optimized service life, and weight features. In tubular metal forming, output parameters such as branch height, distribution of tube wall material thickness, distribution of damage factor, metal flow, effective stress, and effective strain significantly affect the quality of the product after the forming process. Therefore, this paper aims to evaluate the manufacturing quality of Y-shape joints from AISI304 material steel tube through output parameters of THF process with and without counter punch force on numerical simulation base. The Finite Element Method (FEM) has become an established feature of metal forming technology. The objective of FEM is to replace costly and elaborate experimental testing with fast, low-cost computer simulation. The simulation study uses finite element method-based virtual prototyping techniques to characterize output parameters, gain insight into strain mechanics, and predict mechanical properties of shaped components. The research results are presented clearly and unambiguously through the evaluation of 7 criteria to compare the quality of the specimens hydroformed by two surveyed cases and optimize the crucial input process parameters. And these data can be applied in experiments, more efficient product and process design, calculation, and control of input parameters avoiding costly trial and error in industrial production. The findings can help technologists optimize process parameters in the hydroforming process of products with protrusion from a tubular blank

Evaluation the interface damage influences on mechanical properties of fiber-reinforced composites based on subdomain boundary element theory

In this paper, a novel microscopic method is presented to investigate the effective mechanical properties and local stress distribution of the composites with respect to some specific interfacial cracks. To this end, a subdomain boundary element method (SBEM) is combined with the asymptotic homogenization theory to calculate their effective mechanical properties. In order to accurately capture the stress distribution on the boundary and inside points (Gaussian integral points) of representative volume element (RVE), the parametric sub-cell is firstly constructed to discretize the RVE. On this basis, a node-pair decoupling method is introduced with consideration of unilateral and bilateral damage. The influence on mechanical properties of composites is revealed, which provides a solid foundation for the design and manufacture of the composite interface.