Normal Contact Stress Research Articles

A novel multi-asperity-based dynamic (MABD) model for piezoelectric actuator: Theory, numerical framework, and experimental validation

Piezoelectric actuators are widely used in precision equipment because of their rapid response, high motion accuracy, and immunity to electromagnetic interference. However, the multi-scale characteristics of contact at the transmission interface between the stator and mover, along with stick-slip motion produce complex nonlinear behaviors in the mover system, resulting in difficulties in solving the dynamic response of the mover. To address this, a multi-asperity line contact mechanics model considering the substrate deformation and roughness is deduced based on the statistical approach to reflect the contact effect between the transmission interface more accurately. Moreover, the contact model is further extended, overcoming the asperity contact limit, to apply to slight and very heavy loads by introducing the Hertz solution. Furthermore, the stick-slip motion considering the tangential stiffness of the interface is solved through the iteration process to determine the stick and slip region. Newmark-β method is used to obtain the dynamic response of the mover when the normal and tangential contact stresses are calculated. Besides, a classical traveling wave piezoelectric actuator is selected for experimental verification of the proposed model. Numerical and experimental results show that the proposed model can effectively calculate the normal contact stress distribution and capture the evolution of stick-slip motion. The predicted torque-velocity curves have good agreement with the experimental values and the accuracy is higher than previous models. In addition, the proposed model can well predict the transient start-up characteristics of the mover. This research provides a theoretical reference for the modelling and dynamic response prediction of piezoelectric actuators, especially for small-size actuators.

Exploring the effects of finite size and indenter shape on the contact behavior of functionally graded thermoelectric materials

The performance enhancement of functionally graded thermoelectric (FGTE) devices is significantly influenced by contact studies of the FGTE materials. It is unclear how the finite thickness and the punch geometry influence the FGTE materials’ contact behaviors. This paper investigates the frictionless contact problem between three types of rigid punches (flat, triangular, and cylindrical) and the FGTE strip with finite thickness. The electric-thermo-elastic parameters of the FGTE strip vary in the thickness direction according to an exponential function. Based on the Fourier integral transform and the transformation matrix method, the problem is transformed into the numerical solution of three sets of singular integral equations. The presence of singular features on either side of the punch demands the adoption of specific collocation strategies. The distribution of the normal current density, the normal energy flux, and the normal contact stress is obtained by adjusting multiple electric-thermo-elastic parameters. The contact stresses in the case of punches with varying shapes can be effectively controlled by modulating the coefficient of thermal expansion and the strip thickness, whereas the effect of the electrical conductivity, the shear modulus, and the thermoelectric load on these stresses depends on whether they are increased or decreased.

Research on the distribution structure of 2D piston electro-hydraulic pump based on fluid-structure interaction

To address the drawbacks of traditional hydraulic power units, we embedded a 2D piston pump inside the motor rotor, proposing a 2D piston electro-hydraulic pump. The space cam mechanism serves as the primary force-bearing structure during its operation. Excessive wear occurs at the highest point of the space cam when subjected to significant axial forces, which leads to deviations between the motion law of the 2D piston and the theoretical design. Aiming this problem, we conduct research from two perspectives: theoretical analysis and fluid-structure interaction. Firstly, the operational principle of the electro-hydraulic pump is introduced. Then, the contact normal stress of the space cam mechanism is studied, and backflow and chamber pressure overshooting are discussed. Finally, the fluid-structure interaction model of the electro-hydraulic pump is established. Based on the fluid-structure interaction model, the effects of the width and depth angles of the triangular damping groove on the backflow and chamber pressure overshooting are analyzed. The simulation results demonstrate that adding triangular damping grooves can improve the flow field characteristics. With the increase in the width and depth angles, the peak flow of the backflow and chamber pressure overshooting increase, with the depth angle exerting a more pronounced effect.

Wheel-rail wear characteristics of a modern tram passing curves with small radius

The wheel-rail wear was predicted for modern trams with independently rotating wheelset running on a groove-shaped rail. The tram vehicle-track coupled dynamics model, considering the wheel-rail multi-point contact, was developed using software UM to evaluate the dynamic responses of the vehicle and track. Hertz contact theory, the FastSim algorithm, and Archard material wear model were used to solve the normal contact stress, tangential contact stress, and wheel-ail wear, respectively. The wheel and rail profiles were updated when the wear depth reached to 0.1 mm. In calculation, the wheel and rail wear was calculated and analyzed separately. The results of groove rail and independently rotating wheelset wear predicted by this model coincided with relevant literature, which proved the effectiveness of this model. The wheel and rail wear characteristics of modern trams passing through curved tracks with small radii and the influence of wheel-rail friction coefficient on wheel and rail wear were calculated and analyzed using this model. The results show that the wheel and rail wear on the circular curve and the rear transition curve is more intense. The wheel wear is the most intense on circular curve while the rail wear is on the rear transition curve. The wear of inner and outer rails and wheels of wheelset one increases with the increase of wheel-rail friction coefficient while the wear of inner and outer wheels of wheelset three have no obvious change. The wear of the inner and outer rails is the most intense at the gauge corner position while is the lightest at the guard rail. The wear of wheelset one is more intense than that of wheelset three and the inner wheel wear is more intense than that of the outer wheel. The present analysis contributes to improve the life of tram wheel and rail and reduce the frequency of wheel-rail maintenance during operation.

Vibration Friction Investigation on the NCS of Joints of the CNC Machine Tools Considering Friction Factor

Machine tool vibrations play a significant role in hindering productivity during machining. The growing vibrations accelerate tool wear and chipping, cause a poor wave surface finish, and may damage the spindle bearing. Some research showed that tribological properties such as friction factors can have obvious influences on the topography of rough surfaces and the nonlinear dynamic characteristics of machine tool systems. Therefore, studying the vibration friction dynamic characteristics on the normal contact stiffness (NCS) of joints of CNC machine tools is absolutely necessary for improving the machining accuracy and precision of the whole system. The study results of NCS of joints of the CNC and the friction coefficient are discussed in this paper. The model of NCS based on fractal parameters was obtained. The models of deformations of the rough surfaces and contact surfaces were deduced. The results showed that the NCS based on the calculation method considering the elastic–plastic deformation of the asperity is much higher in precision than the methods considering only elastic or plastic deformation separately. The observations this paper described suggest that in the CNC machine tools system, higher D and G and higher friction coefficients lead to higher normal contact stresses (NCSs).

Machine Learning Algorithms for Prediction and Characterization of Cohesive Zone Parameters for Mixed-Mode Fracture

Fatigue and fracture prediction in composite materials using cohesive zone models depends on accurately characterizing the core and facesheet interface in advanced composite sandwich structures. This study investigates the use of machine learning algorithms to identify cohesive zone parameters used in the fracture analysis of advanced composite sandwich structures. Experimental results often yield non-unique solutions, complicating the determination of cohesive parameters. Numerical determination can be time-consuming due to fine mesh requirements near the crack tip. This research evaluates the performance of Support Vector Regression (SVR), Random Forest (RF), and Artificial Neural Network (ANN) machine learning methods. The study uses features extracted from load–displacement responses during the fracture of the Asymmetric Double-Cantilever Beam (ADCB) specimen. The inputs include the displacement at the maximum load (δ*), the maximum load (Pmax), the total area under the load–displacement curve (At), and the initial slope of the linear region of the load–displacement curve (m). There are two objectives in this research: the first is to investigate which method performs best in identifying the interfacial cohesive parameters between the honeycomb core and carbon-epoxy facesheets, while the second objective is to reduce the dimensionality of the dataset by reducing the number of input features. Reducing the number of inputs can simplify the models and potentially improve the performance and interpretability. The results show that the ANN method produced the best results, with a mean absolute percentage error (MAPE) of 0.9578% and an R-squared (R²) value of 0.7932. These values indicate a high level of accuracy in predicting the four cohesive zone parameters: maximum normal contact stress (σI), critical fracture energy for normal separation (GI), maximum equivalent tangential contact stress (σII), and critical fracture energy for tangential slip (GII).

Computational Modeling of Tool-Rock Frictional Contact With Anisotropic Damage

The mechanism of frictional contact is investigated between a blunt tool and quasi-brittle rocks with anisotropic damage. A recently developed anisotropic elasto-plastic-damage model is further validated using experimental results under monotonic and cyclic loadings for rocks and concrete. A finite element model of tool-rock frictional contact is validated by analytical results in the two asymptotic regimes of an elastoplastic rock. The mesh sensitivity is reduced using a fracture energy-based method for anisotropic damage. The tool-rock frictional contact is predominantly controlled by three dimensionless parameters: η\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta$$\\end{document}, ξ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\xi$$\\end{document}, and ζ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\zeta$$\\end{document}, which characterize elastoplasticity, brittleness, and anisotropic damage, respectively. The newly introduced damage coefficient ζ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\zeta$$\\end{document} controls the ratio of damage in different directions. As the elastoplastic parameter η\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\eta$$\\end{document} increases with more plastic deformation, the dimensionless average contact stress Π~\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\widetilde{\\Pi }}$$\\end{document} increases and then slightly varies before stabilizing. As the brittleness number ξ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\xi$$\\end{document} increases in a more brittle mode, the contact stress Π~\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\widetilde{\\Pi }}$$\\end{document} generally decreases. When the damage coefficient ζ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\zeta$$\\end{document} decreases from isotropic to anisotropic damage, the contact stress Π~\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$${\\widetilde{\\Pi }}$$\\end{document} generally increases. The magnitudes of the average contact stress in numerical modeling are closer to experimental results when considering anisotropic damage.

Topology optimization of forming tools: pressure die in rotary draw bending process

AbstractThe forming tools are conventionally manufactured from alloy steels. These tools can be designed to be light weight and cost effective without compromising performance characteristics. In this research, a fundamental forming tool (pressure die) of ‘rotary draw bending processes’ is topology optimized and 3D printed by using polymeric material. An accurate FE-simulation model of a rotary draw bending process is developed and topology optimization of the pressure die is carried out on the basis of contact stresses provided by FE-simulation results. The topology optimized pressure die is compared with its conventional metal made counter-part in terms of contact forces, contact normal stresses, effective area in-contact and cost performance index. This manuscript demonstrates that topology optimized lightweight 3D printed polymeric forming tools are a cost effective alternative to comparatively heavy alloy steels. This research contributes to widen the avenue of cost effective manufacturing by incorporating topology optimization regimes into existing production setups.

Mechanical behavior and waterproof performance of longitudinal section of tunnel segment joint gasket

In the construction stage, due to construction errors and longitudinal differential settlement during tunnel operation, the amount of dislocation and opening at the segment joint increases, increasing the likelihood of water leakage. Therefore, it is necessary to conduct an in-depth study on the influence of the amount of dislocation and opening at the segment joints on the contact stress of the longitudinal section. Firstly, through theoretical analysis, this paper deduces that the waterproof performance of the gasket depends not only on its own contact area, linear compression stiffness, and Poisson’s ratio but also on the height of the segment joint specimen and the amount of joint opening caused by the sinking offset angle. Then, the effects of different openings and dislocations at the segment joints on the contact stress of the segment gasket section were compared using numerical simulation and model experiments. Through numerical simulation, it is found that the dislocation has a greater influence on the longitudinal left section. The average contact stress at 16 mm is 28.3% lower than that at 4 mm, and the influence of the opening amount on the sealing gasket section is greater than that of the dislocation. Combined with the test results, it is also shown that the influence of the opening amount of the waterproof performance at the segment joint is greater than that of the dislocation, and the waterproof rate of the segment gasket section joint is greater than 40% under the modified working condition.

Detection method for contact stress distribution of tapered roller bearings

The axle box of high-speed train adopts double row tapered roller bearings as transmission parts, and the reliability of bearings directly affects the safety of train operation. Tapered roller bearings can withstand axial and radial loads, their service life being closely related to the distribution of contact stress. The test object is the axle box bearing of high-speed train. According to bearing’s structural characteristics, based on the digital speckle correlation method (DSCM) and machine vision, the contact stress distribution detection devices for rollers and complete sets of bearings are developed respectively and an effective detection method is proposed. The contact stress data of the bearing which has reached the service life and the new bearing under the condition of no lubrication and grease lubrication are collected and normalized. Through the geometric relationship, based on the measured data of the selected detection points, the normal and tangential contact stress distribution of the roller and raceway under different contact conditions is obtained by data fitting. The test can be used as an evaluation basis for the effectiveness of bearing modification and provide reference for bearing design.

Comparison of the reliability of strength limit calculation methods for prismatic samples with different spreading of normal contact stresses in their wedge failure shape

This article explores methods for calculating the strength limits of solid objects subjected to compression. Traditionally, two stress distribution patterns are used: the exponential pattern by E.P. Unksov and the linear pattern by L. Prandtl. The authors introduce an enhanced stress distribution method. They compare the accuracy of these methods in calculating strength limits and constructing “normal stress - longitudinal strain” diagrams for wedge-shaped failures in rock samples. Four properties are considered: shear strength, coefficients of internal and external friction, and elasticity modulus. The results show that, with an external friction coefficient up to 0.3, all methods yield similar accuracy in strength limit calculations and ultimate stress-strain curves. Some curves exhibit stress drops, explained by a transition from convex to concave slip lines during failure. Additionally, there are hardening curves in the ultimate curves without theoretical justification. The comparison of calculated strength limits with experimental data confirms the method’s accuracy: 13.7% error for the exponential method, 11.4% for the linear method, and 8.1% for the enhanced distribution, especially for low contact friction values (up to f c=0.3).

Finite element investigations for chip scraping during orthogonal cutting process with micro-textured tools

Compared with the conventional tool (CT), the micro-textured tool (MTT) has the advantages of reducing cutting forces, lowering cutting temperatures and inhibiting tool wear. However, the chip scraping phenomenon generated in the cutting process has negative effects and degrades cutting performance when using the MTT with grooves perpendicular to the cutting edge. Due to the difficulty in observing and characterizing chip scraping in situ by experiments, its mechanism and influence on specific cutting forces and tool wear are not fully understood. To this end, finite element (FE) method is employed for simulating the cutting process with MTT. The simulation model is validated by comparing the predicted and measured specific cutting forces. The average prediction error of specific cutting and feed forces is 12.4 % and 18.8 %, respectively. The simulation results indicate that chip scraping mainly results from the discontinuity, non-uniformity and high contact stress state of the tool-chip interface. The minimum specific cutting force is achieved when the advantages of micro-texture and the chip scraping effects are balanced. The MTT rake face wear is subdivided into a severe and a sliding wear zone. This partition characteristic is closely associated with normal contact stress and temperature distributions. The work in this paper contributes to improving the understanding of chip scraping, optimizing micro-texture and cutting parameters, and promoting MTT applications in the manufacturing industry.

Biomechanical Effects of Hindfoot Alignment in Supination External Rotation Malleolar Fractures: A Human Cadaveric Model.

Pressure distribution in the ankle joint is known to be dependent on various factors, including hindfoot alignment. We seek to evaluate how hindfoot alignment affects contact pressures in the ankle joint in the setting of supination external rotation (SER) type ankle fractures. SER fractures were created in 10 human cadaver lower extremity specimens, simulating progressive stages of injury: without fracture (step 0), SER fracture and intact deltoid ligament (step 1), superficial deltoid ligament disruption (step 2), and deep deltoid ligament disruption (step 3). At each step, varus and valgus alignment was simulated by displacing the calcaneal tuberosity 7 mm medial or lateral. Each limb was axially loaded following each osteotomy at a static load of 350 N. The center of force (COF), contact area (CA), and peak contact pressure (PP) under load were measured, and radiographs of the ankle mortise were taken to analyze the medial clear space (MCS) and talar tilt (TT). The COF (5.3 mm, P = .030) and the CA (-188.4 mm2, P = .015) changed in step 3 in the valgus hindfoot alignment compared to baseline parameters, indicating the importance of deep deltoid ligament integrity in maintaining normal ankle joint contact stress in the valgus hindfoot. These changes were not seen in the setting of varus alignment (COF: 2.3 mm, P = .059; CA -121 mm2, P = .133). PP were found to not change significantly in either varus or valgus (varus: -4.9 N, P = .132; valgus: -4 N, P = .464).The MCS demonstrated widening in step 3 compared to step 2 (0.7 mm, P = .020) in both varus and valgus hindfoot. The TT increased significantly in step 3 in the valgus hindfoot (2.8 degrees, P = .020) compared to step 0. SER-IV fractures with valgus hindfoot alignment showed significant changes in pressure distribution and radiographic parameters when compared to SER-IV fractures with varus hindfoot alignment. Based on this cadaver modeling study, patients with SERIV fracture with varus hindfoot alignment and complete deltoid ligament lesion may not need fracture fixation, whereas those with valgus hindfoot alignment likely need fracture fixation.

A laboratory investigation into tyre-pavement contact behaviour of passenger car

ABSTRACT Understanding tyre-pavement contact behaviour helps to address pavement skid resistance which is highly related to traffic safety. In this study, a pressure distribution measurement system was employed to investigate the tyre-pavement contact behaviour of a passenger car in laboratory. The pavement macrotexture was characterised by a 3D scanner and the sand patch method. It was shown that the asphalt pavement gradation, the vertical force, the tyre inclination angle and the tyre pressure significantly have effects on tyre-pavement contact behaviour. The cumulative frequency curve of tyre-pavement contact stress can be well fitted by the Boltzmann model. Under the vertical force of 4 kN, the average contact stress increases significantly when the inclination angle exceeds 3.2°, while an inclination angle within 3.2° has almost no effect. The force on the rib on the side that the tyre leans to changes the most with the inclination angle. As the tyre pressure increases, the average contact stress increases linearly and the contact area decreases linearly. With the increase of tyre pressure, the contact region gradually shrinks towards the middle and the contact force slightly increases in the middle and decreases at the edges.

Hydro‐mechanically coupled CEL analyses with effective contact stresses

AbstractThe coupled Eulerian–Lagrangian (CEL) method implemented in Abaqus is an established tool for modelling large deformations in numerical geomechanics. As shown in previous work, it can be extended to a hydro‐mechanically coupled scheme by exploiting the similarity of the heat balance equation to the mass balance equation of fluids. However, the distinction between effective and total contact stresses has not been possible in this approach, which hinders its application to problems with interface friction as frictional stresses are calculated based on total normal contact stress. An approach to circumvent this problem is presented in this work. Its relevance is demonstrated by the simulation of vibratory pile driving model tests in water‐saturated sand. The implementation by means of user‐subroutines is available and works for any total‐stress analysis.

Numerical analysis of the dependence of damage on friction during deep drawing of asymmetric geometries

The manufacturing of three-dimensional sheet metal components, such as car body parts, heavily relies on deep drawing. With the increasing demand for lightweight measures in the automotive industry due to CO2 limitation requirements, various methods are currently employed to reduce the weight of deep drawn components. However, these methods often overlook the potential for influencing the stress-strain dependent damage state within the component, even though it can greatly affect its performance in subsequent applications, and thus offers lightweight potentials. Friction between the deep drawing tools and the sheet metal is a key factor influencing the stress-strain state, and hence, represents a lever that can be utilized to manipulate the damage state in the component. This paper focuses on the numerical analysis of the dependence of damage on friction during deep drawing. Therefore, a rectangular geometry with an asymmetrical material flow is numerically investigated. A friction ratio is introduced with different constant friction coefficients for the corner of the tools and the straight sides. The established load paths at a chosen reference point are then considered in the form of selected stress and strain characteristics and the numerically predicted damage state is compared. The results are used to derive a recommended friction ratio that leads to less damage in the corner of the geometry. Afterwards strip drawing tool surfaces are modified to manipulate their friction properties using machine hammer peening. Subsequently, the influence of the structures of the strip drawing tool surfaces is quantified using strip drawing tests. The identified contact normal stress dependent friction coefficients are then implemented in the numerical simulation and the established numerical predicted damage state is examined to gain a more comprehensive understanding of how the friction ratio and the structure of the tool surfaces influence the damage state.

Prediction of contact pressure during cold rolling of thin strips with predominance of front tension

The results of theoretical studies of the average relative contact stress during cold rolling of thin steel strips with a predominance of front tension are presented. The transition from symmetric to the asymmetric tension mode helps to reduce the contact stress by 6.4...13.5 %. This makes it possible to increase the service life of rolling rolls. A regression equation is obtained for predicting of the average relative contact stress for the studied range of change in the main technological parameters.

Piezoelectric sensing method for segmental joint contact stress during shield tunnel construction

The emergence of curved shield tunnels poses a significant construction challenge. If the quality of the segment assembly is not guaranteed, many segment cracks and damage will result from the stress concentration. Sensing the contact stresses between segmental joints is necessary to improve the quality of segments assembled for shield tunnel construction. Polyvinylidene difluoride (PVDF) piezoelectric material was chosen for the sensor because it can convert contact stresses into electrical signals, allowing the state of the segmental joints to be effectively sensed. It matches the working environment between the segmental joints of the shield tunnel, where flexible structures such as rubber gaskets and force transfer pads are present. This study proposes a piezoelectric sensing method for segmental joints in shield tunnels and conducts laboratory tests, numerical analyses, and field tests to validate the feasibility of the method. The results indicate that the PVDF film sensor can effectively sense the entire compression process of the gasket with different amounts of compression. The piezoelectric cable sensor can effectively sense the joint offset direction of the gasket. For differently shaped sections, the variation in the force sensed by the piezoelectric cable sensors was different, as verified by numerical simulation. Through the field test, it was found that the average contact stress between the segmental joints was in the range of 1.2–1.8 MPa during construction of the curved shield tunnels. The location of the segmental joints and the type of segment affect the contact stress value. The field monitoring results show that piezoelectric sensing technology can be successfully applied during assembly of the segments for effective sensing of the contact stress.

Study of a Methodology for Calculating Contact Stresses during Blade Processing of Structural Steel

The article presents data about the distribution of contact stresses on the rake surface of the cutter when turning steel (Fe-0.4 C-1Cr), which were obtained by the split cutter method. The article also provides graphs of the effect of the uncut chip thickness a and the rake angle γ on the main parameters of the plots of shear τ and normal σ contact stresses. For this case, The initial data were obtained by longitudinal turning of a steel workpiece with the measurement of the technological components of the cutting force by a three-component Kistler dynamometer, followed by the calculation of the physical components of the cutting force. The rake angle varied widely, from +35 to −10°, and the uncut chip thickness a varied from 0.05 to 0.37 mm. A decrease in the rake angle from +35 to −10° leads to a significant increase in the maximum normal contact stress at the cutting edge σmax: from 400 to 1400 MPa with the uncut chip thickness a = 0.37 mm. In the area of small uncut chip thickness, a (less than 0.1 mm), the paradoxical increase in the magnitude of the greatest normal contact stress with a large positive rake angle (more than +15°) is explained by the indentation (pressing) of the being machined material under the rounded cutting edge of the cutter in the chip formation zone, and their paradoxical decrease with a negative rake angle is due to the presence of a sag (deflection) of the transient surface. According to the magnitude of the reference points obtained on the basis of experimental data, it is possible to plot the contact stresses epures on the rake surface of the cutting tools when machining steel.

Finite element analysis and experimental validation of polymer–metal contacts in block-on-ring configuration

The wear profile analysis, obtained by different tribometers, is essential to characterise the wear mechanisms. However, most of the available methods did not take the stress distribution over the wear profile in consideration, which causes inaccurate analysis. In this study, the wear profile of polymer–metal contact, obtained by block-on-ring configuration under dry sliding conditions, was analysed using finite element modelling (FEM) and experimental investigation. Archard’s wear equation was integrated into a developed FORTRAN–UMESHMOTION code linked with Abaqus software. A varying wear coefficient (k) values covering both running-in and steady state regions, and a range of applied loads involving both mild and severe wear regions were measured and implemented in the FEM. The FEM was in good agreement with the experiments. The model reproduced the stress distribution profiles under variable testing conditions, while their values were affected by the sliding direction and maximum wear depth (hmax). The largest area of the wear profile, exposed to the average contact stresses, is defined as the normal zone. Whereas the critical zones were characterized by high stress concentrations reaching up to 10 times of that at the normal zone. The wear profile was mapped to identify the critical zone where the stress concentration is the key point in this definition. The surface features were examined in different regions using scanning electron microscope (SEM). Ultimately, SEM analysis showed severer damage features in the critical zone than that in the normal zone as proven by FEM. However, the literature data presented and considered the wear features the same at any point of the wear profile. In this study, the normal zone was determined at a stress value of about 0.5 MPa, whereas the critical zone was at about 5.5 MPa. The wear behaviour of these two zones showed totally different features from one another.