Internal Stress Distribution Research Articles

Thermal stresses in growing thermoviscoelastic cylinder and their evolution in the course of selective laser melting processing

AbstractThe evolution in time of stresses and strains in a solid during its manufacturing through selective laser melting (SLM) process is studied. The technological technique, which allows to reduce the intensity of internal and residual stresses is proposed and theoretically grounded. The basic concept of the technique is that the additional in‐homogeneous inductive heating in the vicinity of the growing boundary is applied in the processing. The term “growing boundary” refers to the part of the boundary, on which the additional melted material is added. The evolutionary problem for a growing thermoelastic body is considered in approach of thermal stresses (for slow additive processes) and in the approach of full coupled thermoelasticity (for fast processing). The time depend distribution of internal stresses and their residual counterparts has been evaluated in analytical form in the case of model cylindrical problem. The analysis of the influence of frequency and amplitude of electromagnetic induction as well as viscoelastic properties of heated material being added has been carried out. The results are analyzed numerically for Titanium and Copper materials.

Quasi-honeycomb grain morphologies strengthen passivating layers in Inconel-718 superalloy: Lessons learned from Additive Manufacturing

Despite intensive studies on the effect of grain morphology, that results from Selective Laser Melting (SLM) fabrication, on the mechanical properties of Inconel-718 (IN718), there is a lack of insight into its effect on the alloy’s oxidation behavior. This work compared the oxidation of IN718 alloy manufactured by SLM (SLM-IN718) with that of a cast-rolled commercially available sample (Comm-IN718) when heating to 900 °C. Our results showed that the passivating chromia layer that forms on Comm-IN718 was resistant to rupture because it is a thin oxide layer with a favorable distribution of internal stress due to the alloy’s well-defined quasi-honeycomb primary grain morphology. In comparison, SLM-IN718 had a poorly defined grain morphology, with two distinct length-scales best described as dendritic structures. This morphology resulted in the formation of a thicker oxide scale without favorable distribution of the stress into the alloy grain boundaries. This led to the rupture of the passivation layer. These findings give us a new insight into how the primary microstructure of Inconel alloys can affect their oxidation behavior by affecting the stress distribution within surface oxide films. We are the first to show that morphology characteristic control plays a key role in improving Inconel oxidation.

Theoretical modelling of the effect of thermal delamination of an asphalt concrete pavement from a rigid foundation of a road or bridge

In the practice of road construction, one of the most common phenomena accompanied by delamination, subsequent cracking and destruction of the asphalt concrete pavement on a rigid (cement concrete or metal) base of a road or bridge is the effect of concentration of shear thermal stresses between the pavement and the base in the edge zones of the structure. They are caused by the fact that, as a rule, the coefficients of linear thermal expansion of the phases of the system have different values, which contributes to the occurrence of incompatible shrinkages and expansions in them. Under conditions of frequent temperature changes in heterogeneous asphalt concrete structures with thermomechanical incompatibility of their components, these effects can contribute to their accelerated aging. At the same time, with the thermomechanical compatibility of materials, a more favorable distribution of internal stresses of thermal and mechanical origin is achieved, which excludes premature degradation of the strength of the contacting phases and the entire system as a whole. Using the methods of strengthof materials and the finite element method, it has been established that under the conditions of a change in the temperature of the system during its seasonal and daily fluctuations, shear stresses are subjected to the highest concentration. They are localized in the edge zone of the plane of contact between the layers and increase with an increase in the thickness and modulus of elasticity of the upper layer. These stresses are the main reason for the occurrence of plastic deformations in these zones and subsequent delamination of the structure in them. It is proposed to reduce the concentration and level of generated high-gradient shear stresses by reducing the thickness of the asphalt concrete layer in these areas.

Photodimerization induced hierarchical and asymmetric iontronic micropatterns

Micropatterning various ion-based modality materials offers compelling advantages for functionality enhancement in iontronic pressure sensing, piezoionic mechanoreception, and skin-interfaced electrode adhesion. However, most existing patterning techniques for iontronic materials suffer from low flexibility and limited modulation capability. Herein, we propose a facile and robust method to fabricate hierarchical and asymmetrical iontronic micropatterns (denoted as HAIMs) through programmed regulation of the internal stress distribution and the local ionic migration among an iontronic host. The resultant HAIMs with arbitrarily regulated morphologies and region-dependent ionic electrical performance can be readily made via localized photodimerization of an anthracene-functionalized ionic liquid copolymer (denoted as An-PIL) and subsequent vapor oxidative polymerization of 3,4-ethylenedioxythiophene (EDOT). Based on the piezoionic effect within the resultant distinct doped PEDOT, HAIMs can serve as a scalable iontronic potential generator. Successful syntheses of these fascinating micropatterns may accelerate the development of patterned iontronic materials in a flexible, programmable, and functionally adaptive form.

The Influence of Internal Stress on the Nanocrystal Formation of Amorphous Fe73.8Si13B9.1Cu1Nb3.1 Microwires and Ribbons

The early stages of nanocrystallization in amorphous Fe73.8Si13B9.1Cu1Nb3.1 ribbons and microwires were compared in terms of their internal stress effects. The microstructure was investigated by the X-ray diffraction method. Classical expressions of crystal nucleation and growth were modified for microwires while accounting for the internal stress distribution, in order to justify the XRD data. It was assumed that, due to the strong compressive stresses on the surface part and tensile stresses on the central part, crystallization on the surface part of the microwire proceeded faster than in the central part. The results revealed more rapid nanocrystallization in microwires compared to that in ribbons. During the initial period of annealing, the compressive surface stress of a microwire caused the formation of a predominantly crystallized surface layer. The results obtained open up new possibilities for varying the high-frequency properties of microwires and their application in modern sensorics.

Research on an Ultrasonic Longitudinal Critically Refracted Wave Detection Method for the Depth Distribution of Stress

Aluminum alloy components typically have structural characteristics such as large size and complex shape, making the in situ non-destructive detection of internal residual stress in these structures a challenge that the manufacturing sector has tried to solve. Ultrasonic longitudinal critically refracted (LCR) waves have shown good sensitivity to normal stress in the horizontal direction and could be used to detect the distribution of internal residual stress in components, offering an advantage not shared by other detection methods. In this study, we investigated the propagation mode of LCR waves in a 2A14 aluminum alloy component and established the characterization model of the average normal stress of LCR waves in different depth ranges. The blocking effect of LCR waves by a groove with a depth equal to twice the wavelength was analyzed and experimentally verified using a machined aluminum alloy test specimen. Then, the propagation depths of LCR waves in the aluminum alloy at different frequencies were determined. A load test on a cantilever beam based on the stress depth distribution model was designed, and the stress characterization model and LCR waves’ propagation depth were further verified by the self-developed LCR wave stress detection system. The test results showed that the LCR wave could accurately detect the depth distribution of stress and could serve as a useful tool for evaluating the depth distribution of normal stress inside aluminum alloy components.

Numerical analysis of deformation and failure mechanism of metal truss structure of spacecraft under re-entry aerothermodynamic environment

A coupled aerodynamic-thermoelastic analysis framework is presented to simulate the deformation and failure mechanism of metal truss structure for spacecraft under re-entry aerothermodynamic environment. The three-dimensional dynamic thermo-mechanical coupling finite element algorithm is developed by computable modeling of thermoelasticity and heat conduction equations to solve the thermo-mechanical coupling response of spacecraft structure. The aerodynamic boundary conditions such as temperature, heat flux and pressure distribution are computed and provided by the gas-kinetic unified algorithm (GKUA) based on the Boltzmann model equation. The linear interpolation method is designed and employed to couple the boundary conditions between the external aerodynamic flow field and the solid structure interface. The present thermo-mechanical coupling algorithm is verified on one-dimensional and two-dimensional transient heat flow problems with analytical solutions, and good consistency is achieved. The reliability of the GKUA for solving the boundary conditions of the external flow field and the dynamic thermo-mechanical coupling algorithm for the thermal response behavior of the internal structure material is verified by the consistency calculation of the internal and external temperature distribution. Then, the aerodynamic-thermoelastic analysis framework is further applied to study the deformation behavior of structural thermo-mechanical responses and failure mechanism of a hollow sphere under re-entry aerothermodynamic environment with emphasis placed on the influence of flight speeds, rarefied effects, algorithm schemes and damping effects. The numerical results obtained by the presented algorithm including the internal temperature, thermal stress and deformation distribution law are compared and analyzed. Finally, the deformation and failure mechanism of spacecraft structure during re-entry process are solved and analyzed by the present algorithm framework. The displacement, temperature and stress distribution contours of the structure are presented to make a preliminary understanding and evaluation on the process of spacecraft deformation and failure disintegration. It is indicated that the present coupled aerodynamic-thermoelastic analysis framework can provide a reliable, applicable and efficient platform for the thermo-mechanical coupling responses and failure mechanism of re-entry spacecraft in the end of life.

Time-resolved in-situ dislocation density evolution during martensitic transformation by high-energy-XRD experiments: A study of C content and cooling rate effects

Recent studies on the mechanical behavior of martensitic steels show the importance of considering lath martensite as a “polycrystalline aggregate” with a large distribution of the local yield strength. The latter depends on local microstructural features, such as lath sizes, carbon distribution (in solid solution, segregated to defects, in carbides) and density of defects Internal stresses have to be considered as an additional contribution to the yield strength participating to enlarge the distribution of the local flow stresses at the microstructure scale.This study focuses on one of these microstructural features, the dislocation density. Its evolution is followed in situ upon martensitic transformation by High Energy X-Ray Diffraction experiments on a synchrotron beamline. A previously introduced method, based on modified Williamson-Hall (mWH) analysis, is improved in order to take account of the martensite lattice tetragonality when applying the mWH method.The influence of the steel carbon content (0.11, 0.21 and 0.31 wt.% C steels) and of the cooling rate (-10, -50, -100 °C/s and water-quench) on the dislocation density evolution in martensite during the martensitic transformation is established. The effect of the cooling rate on the dislocation density is low between -10 and -100 °C/s, but becomes visible after the water-quench. The higher the C content, the higher the dislocation densities at the end of the transformation. The steels with higher C content also show a wider distribution of the local dislocation density and, therefore, of the local yield strength.

Methodology for Mapping the Residual Stress Field in Serviced Rails Using LCR Waves.

Non-destructive stress measurement by ultrasonic testing is based on calculating the acoustoelastic modulus obtained from the relationship between material stress and sound wave velocity. A critically refracted longitudinal (LCR) wave, which is a bulk longitudinal wave penetrating below and parallel to the surface below an effective depth, is most suitable for ultrasonic stress measurement tests because it exhibits a relatively large change in travel time in response to a change in stress. In particular, the residual stress distribution through the thickness of the subject can be calculated if transducers of different frequencies are applied because of the characteristic of propagation to different depths of penetration depending on the frequency. The main purpose of this study was to visualize the internal or residual stress distribution through the thickness of rails using LCR waves. To this end, LCR probes with different center frequencies were designed and manufactured, and the residual stress values ​​of an unused railroad rail and two used railroad rails operated under different conditions were calculated. This was done using the ultrasonic signals received from each probe, of which the distributions were mapped. Through these mapping results, different residual stress values could be calculated according to the depth. The differences in residual stress generation and distribution according to the conditions surrounding the contact between train wheels and rails, and their characteristics, were visualized and analyzed. As a result, it could be concluded that the non-destructive evaluation technique using LCR waves could detect differences in the residual stress of a rail, and thus can be used to measure the residual stress of the rail accurately.

Application of a New Alloy and Post Processing Procedures for Laser Cladding Repairs on Hypereutectoid Rail Components.

The development of a laser cladding repair strategy is critical for the continued growth of heavy-haul railway networks. Premium hypereutectoid rails have undergone laser cladding using a new martensitic stainless-steel alloy, 415SS, developed for high carbon rails after standard cladding metals were found to be incompatible. Non-destructive neutron diffraction techniques were used to measure the residual stress in different layers generated across a dissimilar metal joint during laser cladding. The internal stress distribution across the cladding, heat-affected zone (HAZ), and substrate was measured in the untempered rail, after 350 °C and 540 °C heat treatment procedures and two surface grinding operations. The martensitic 415SS depositions produce compressive stress in the cladding, regardless of tempering procedures, which may inhibit fatigue crack propagation whilst grinding operations locally relive surface stress. Balancing tensile stresses were recorded below the fusion boundary in the HAZ due to thermal gradients altering the microstructure. The combination of 540 °C tempering and 0.5 mm surface layer removal produced a desirable combination of compression in the cladding deposition with significantly reduced tensile stresses in the HAZ. A comparison with the current literature shows that this alloy achieves a unique combination of desirable hardness, low tensile stress, and compression in the cladding layer. Data obtained during strain scanning has been used to determine the location of microstructural changes at the fusion boundary and HAZ through correlation of the stress, strain, full width at half maximum (FWHM), and intensity profiles. Therefore, neutron diffraction can be used for both the accurate measurement of internal residual stress and to obtain microstructural information of a metallurgical join non-destructively.

Numerical Analysis of Microcrack Propagation Characteristics and Influencing Factors of Serrated Structural Plane.

The serrated structural plane is the basic unit of structural plane morphology. However, the understanding of its internal stress distribution, failure mode and crack evolution law was not clear enough in previous studies. In this paper, the shear mechanical properties of the serrated structural planes were studied by numerical simulation, and the crack evolution law of the serrated structural planes and the effects of four microscopic parameters on the shear properties were analyzed. The results show that: (1) the number of microcracks increases with the increase in normal stress; the crack expansion rate is slow before the shear stress reaches the peak. After the shear stress reaches the peak, the crack expansion rate continues to increase, and the microcracks keep sprouting and expanding, and the number of microcracks tends to stabilize when the shear stress reaches the residual shear strength. (2) The particle contact stiffness ratio and parallel bond stiffness ratio were negatively correlated with the shear strength; and the particle contact modulus and parallel bond modulus were positively correlated with the shear strength. As the particle contact modulus and parallel bond modulus increase, the peak shear displacement gradually decreases. The parallel bond stiffness ratio has a negative correlation with the peak shear displacement. This study is expected to provide theoretical guidance for the microscopic parameter calibration and shear mechanical analysis of serrated structural planes. (3) Several XGBoost, WOA-XGBoost, and PSO-XGBoost algorithms are introduced to construct the quantitative prediction model, and the comparative analysis found that WOA-XGBoost has the best fitting effect and can be used for the prediction of shear strength. When using this model to calculate the weight shares of micro-parameters, it was found that has the greatest influence on shear strength, followed by ; and had the least influence.

Finite Element Analysis of Proximal Femur Bionic Nail (PFBN) Compared with Proximal Femoral Nail Antirotation and InterTan in Treatment of Intertrochanteric Fractures.

ObjectiveTo compare the biomechanical properties of proximal femur bionic nail (PFBN), proximal femoral nail antirotation (PFNA) and InterTan in the treatment of elderly intertrochanteric fractures AO/OTA 31‐A1.3 by finite element analysis.MethodsWe used Mimics, Unigraphics and other software to establish normal femur and AO/OTA 31‐A1.3 fracture models, and reconstructed PFBN, PFNA and InterTan intramedullary nail models, and assembled them on the fracture model. The ANSYS software was used to compare the femoral von Mises stress distribution, deformation distribution, and internal fixation stress distribution of each group under a load of 2100 N.ResultsIt could be seen that the femoral maximum stress, femoral maximum displacement, and maximum stress of internal fixation of the PFBN group were lower than those in the PFNA group and the InterTan group. The maximum femoral stress of the PFBN was 190.25 MPa, while the maximum stress of the femur of the PFNA and InterTan groups were 238.41 Mpa and 226.97 Mpa. The maximum femoral displacement of each group were located at the top of the femoral head, and the maximum displacement of the PFBN group was 14.373 mm, and the maximum displacement values of the PFNA and InterTan groups were 19.49 and 15.225 mm. For the stress distribution of intramedullary nail, the maximum stress of the three kinds of internal fixation was located on the main nail. The maximum stress of PFBN was 1191.8 MPa, compared with 2142.8 MPa for PFNA and 1702.3 MPa for InterTan. And the maximum stress on the PFBN pressure nail was 345.35 MPa, compared with 868.6 MPa for the PFNA spiral blade and 545.5 MPa for InterTan interlocking twin nails.ConclusionCompared with PFNA and InterTan, PFBN has better mechanical properties. The biomechanical characteristics of PFBN are more advantageous than PFNA and InterTan internal fixation system in the treatment of femoral intertrochanteric fractures.

An investigation of the ankle contact forces in a foot with hammer toe deformity. A comparison of patient-specific approaches using finite element modeling and musculoskeletal simulation.

The internal forces and stresses in the tissue are important as they are linked to the risk of mechanical trauma and injuries. Despite their value, the internal stresses and forces cannot be directly measured in-vivo. A previously validated 3D finite element model (FEM) was constructed using Magnetic Resonance Imaging (MRI) of a person with diabetes and hammer toe deformity. The foot model simulated at five different instances during the stance phase of gait. The internal stress distribution on the talus that was obtained using the FEM simulation, was used to calculate the joint reaction force at the ankle joint. In addition, the musculoskeletal model (MSM) of the participant with hammer toe foot was developed based on the gait analysis and was used to determine the muscle forces and joint reactions. The result showed that the vertical reaction forces obtained from the FEM and MSM follow a similar trend through the stance phase of gait cycle and are significantly correlated ( R=0.99). The joint reaction forces obtained through the two methods do not differ for the first 25% of the gait cycle, while the maximum difference was ∼0.7 Body weight that was observed at 50% of the stance phase. Clinical Relevance: Finite element modeling and musculoskeletal simulation can shed light on the internal forces at the ankle in pathological conditions such as hammer toe. The similarities and differences observed in the joint reaction forces calculated from the two methods can have implications in assessing the effect of clinical interventions.

Atomistic simulations of plasticity heterogeneity in gradient nano-grained FCC metals

Gradient nano-grained (GNG) metals are an emerging class of heterogeneous structured materials with extraordinary mechanistic performances and unnatural plasticity mechanisms, which are unachievable in traditional homogeneous nanocrystalline metals. Here, the metal-type dependence of plasticity heterogeneity in three different GNG structured face-centered cubic metals (Cu, Al, and Ni) was studied by large-scale molecular dynamic simulation, from the plasticity perspectives of dislocation, deformation twinning, and grain boundary. The dislocation and deformation twinning-based plasticity show clear metal-type dependence in GNG structure of different selected metals. For grain boundary activities, GNG Cu, Al, and Ni are equivalent in the overall grain boundary sliding and micro-cracking process, but GNG Ni shows markedly higher grain boundary-free volume and stress due to the grain size gradient-induced twinning process. We find that GNG Al shows the weakest plasticity-induced strengthening due to its weak strain hardening and ununiform plasticity distribution, while GNG Ni exhibits prominent plasticity-induced strengthening because of the obvious extra strain hardening process. Besides, we further discuss the reasonable gradient grain size design of GNG structure, considering the critical grain size of the Hall-Petch and inverse Hall-Petch relationship, which will demonstrate a more rational plasticity heterogeneity and internal atomic stress distribution.

Investigation of mechanical force acting on the surface modified-substrate layer area during the chemical-mechanical micro-grinding of monocrystalline silicon

The application and demand of monocrystalline silicon components are becoming more and more urgent for many advanced applications like solar cells. Chemical-mechanical micro-grinding is one of the effective methods for processing such components. However, the theory of chemical-mechanical micro-grinding of monocrystalline silicon has not been fully established, and the mechanism of material removal is still unclear. In this paper, the monocrystalline surface is modified by catalytic modification, resulting in a modified-substrate layer region. A model is proposed to study and analyze force conditions based on Green's function for modified-substrate layer region under the action of normal force and tangential force. The nanoindentation, XPS, and Raman spectroscopy have been done to verify the theoretical model and explore the phase change process of monocrystalline silicon. The results showed that the established mechanical model can predict the stress distribution at the interface between the surface modification layer of the monocrystalline silicon material and the substrate layer. Furthermore, the internal stress distribution of the surface of the monocrystalline silicon material that has undergone surface chemical modification under load can be obtained. Therefore, the recent paper provides a theoretical basis for the optimization of the process of chemical-mechanical micro-grinding of monocrystalline silicon.

Structural design of responsive under-deck cable-stayed footbridges

The use of prestressing through external tendons has been extensively adopted in bridges to optimize the internal stress distribution. The contribution in withstanding permanent and live loads depends on the initial stressing and the relative stiffness between the deck and the tendons. However, these configurations only allow an optimal structural behaviour for a specific load distribution. This paper proposes to extend this ideal behaviour for any loading condition, using a responsive system which gradually modifies the tension in the cables as the live load increases. The responsive system is applied to a footbridge, where the adaptive behavior is materialized through a linear actuator located between the deck and the under-deck cable-stayed system.This study presents analytical and numerical analyses to shed light on the structural design of these systems. Considering a variable degree of responsiveness, it is possible to quantify the benefits of the responsive system. Furthermore, several parametric analyses are carried out to identify the optimal solution in terms of material savings. In addition, it is verified that fatigue in cables, vibrations and the eventual shutdown of the actuator do not compromise the structural performance of the system.Results show that a relevant material reduction can be achieved using partially responsive systems. Specifically, the slenderness of the structure can almost be doubled if compared to the same system without any responsive behaviour.

Numerical and experimental investigation of reduced temperature effect on asphalt concrete waterproofing layer in high-speed railway

ABSTRACT The thermal fatigue cracking of asphalt concrete waterproofing layer (ACWL) in high-speed railway is mainly caused by the daily reduced temperature effect. In this study, numerical and experimental investigations on this effect were respectively conducted through the determination of surface temperature field, finite element modelling (FEM), and experiments using the customized overlay test (OT). The results indicated the thermal condition in Northern China was more severe for ACWL compared with that of other regions. The stress concentration effect on ACWL surface was mainly attributed to the temperature variation, average temperature, and viscoelastic behaviour of asphalt concrete. In addition, the OT results indicated the internal damage might happen in ACWL without obvious surface feature. Finally, the OT was in consistent with FEM analysis regarding internal stress distribution and fatigue characteristics, and thus could be used as a feasible test method to evaluate the thermal fatigue of ACWL.

2D Stress Analysis of an Infinite Plate with Orthotropic Inclusions by Embedding Continuous Force Doublet

The body force method is an elastic stress analysis method based on the principle of superposition, where the concentrated force is distributed to satisfy the boundary conditions to obtain a highly accurate elastic solution. In the problem of orthotropic inclusions, the strain difference caused by orthotropic inclusions is expressed as a pair of concentrated forces called a force doublet. For this purpose, the interior of the orthotropic inclusion is discretized by triangular elements, and the fundamental solution of the force doublet is calculated by surface integrating inside the elements. The singularity of concentrated force doublet can be easily eliminated by Green’s theorem when distributing force doublet of uniform magnitude inside a triangular element. However, since the stress distribution inside the orthotropic inclusion is represented by a discontinuous function and the magnitude of the force doublet, the stress inside the inclusion cannot be analyzed accurately. By approximating the magnitude of the force doublet in a triangular element with a linear function, it is possible to obtain the internal stress distribution continuously. The method used to analyze the crack problem is applied to deal with the singularity of the concentrated force doublet. The above method was validated by solving the problem of orthotropic inclusions in the vicinity of the stress concentration.

Finite Element Analysis of Bi-directional Shear Panel Damper with Square Hollow Section under Monotonic Loading

This study aims to determine the finite element analysis of a BSPD-SHS (bi-directional shear panel damper with a square hollow section) device, to dissipate the seismic excitation energy through the lateral relative displacement between the pier and girder of the simple support bridge. The configuration of the square hollow section is also performed for a double role, such as web panel and flange, indicating the expectations to reduce the seismic force within the lateral and longitudinal directions. In the preliminary development phase, the finite element analysis was conducted under monotonic loading, to examine the skeleton curve characteristics and internal stress action on resisting seismic force. The characteristics of this curve include elastic stiffness, shear strength, post-yield behavior, and internal stress distributions. Based on the evaluation of the BSPD-SHS slenderness effect, the variation of depth-thickness ratio was considered between 25 to 67. To investigate the fitness of the theoretical shear strength formulation, two different hardening roles of the metal plasticity model were subsequently compared in this study, including the elastic-perfectly plastic and isotropic/kinematic techniques. Furthermore, the effect of the restrained degree of freedom idealization on the top base plate was captured. This indicated that all specimens model with the restrained top base plate achieved stable post-yield stiffness. In implementing the unrestrained top base plate, this stiffness was achieved when the web slenderness ratio equaled 25. The differences observed between the hardening roles also generated a slight yield shear strength discrepancy. However, significant differences occurred in the post-yield shear strength. The shear resistance proportion of the stress components was also accurately quantified with an analytical stress integration. Based on the restrained top base plate, the flange tension field generated a significant contribution to the post-yield shear resistance.

A New Finite Element Analysis Model to Estimate Contact Stress in Ball Screw

A ball screw is a mechanical part that converts rotational motion into translational motion, but when it receives an excessive axial load, permanent deformation occurs inside. As ball screws are mostly used for precise driving, permanent deformation has a fatal effect on the operation of the system. As this permanent deformation mostly occurs on the contact surface between the ball and other parts, it is necessary to observe the change of internal stress caused by the contact of the parts in order to determine whether permanent deformation occurs. Theoretical calculations or finite element analysis (FEA) are mainly used for the analysis of rotating parts, but existing methods have difficulty in observing stress changes occurring on the narrow contact surface of ball screws. In this paper, a new FEA model that can efficiently estimate the stress caused by internal contact inside the ball screw is presented. This model is a synthetic model that applies theoretical calculation results to a 3D FEA model. Factors derived by theoretical calculation include the shape of the contact surface where the ball and other parts meet and the contact pressure at the contact surface, which were derived by a method based on Hertz contact theory. As a result of observing the internal stress distribution of the ball screw estimated by the model, it was confirmed that the shape was similar to that of the actual stress distribution and, compared with the analysis results of other conventional methods conducted with the same mesh shape, the results of the model presented in this paper were more valid.