Papers by Keyword: Contact Pressure

Abstract: The thickness of the residual limb’s soft tissue plays a crucial role in determining the mechanical behavior and stress distribution at the stump–prosthesis interface. Using finite element analysis (FEA), this study investigates the biomechanical effects of different soft tissue thicknesses (30 mm, 50 mm, and 70 mm) on stress distribution. A patient-specific finite element model of the residual limb was developed to simulate realistic anatomical and mechanical conditions. To replicate physiological loading, a static vertical load of 350 N was applied, and the interface between the residual limb and the prosthetic liner was modeled using appropriate contact mechanics. The results revealed that reducing the soft tissue thickness to 3 cm produced higher Von Mises stress concentrations (0.115 MPa) and contact pressure (0.0697 MPa), which may increase discomfort and the risk of tissue damage. Conversely, increasing the thickness to 70 mm reduced stress values (0.016 MPa) and contact pressure (0.0312 MPa) but led to excessive deformations (6.277 mm) that could compromise prosthetic stability. An optimal soft tissue thickness of 5 cm was identified, where Von Mises stress and contact pressure remained at moderate levels, offering a balance between stress distribution and mechanical stability. These findings provide valuable guidance for optimizing prosthetic socket design, as maintaining appropriate soft tissue thickness can enhance comfort, reduce pressure-related injuries, and improve the overall functionality of lower-limb prostheses.

Abstract: The accurate estimation of thermal contact conductance (TCC) at material contact interfaces is cru cial for determining the temperature distribution in a system, particularly in vacuum conditions such as outer space. Improper estimates of TCC, especially in vacuum environments, may result in under design of thermal management systems resulting in the formation of hot spots, leading to material and system failure. This study introduces two inverse techniques for determining the TCC at the contact interface. The validity of the proposed inverse methods is established by comparing TCC values at the interface with those obtained from experiments performed using the ASTM D5470-17 standard, which is applicable under the assumption of one-dimensional heat transfer. Experiments are meticu lously conducted to ensure the validity of the one-dimensional heat transfer assumption. The variation observed in the TCC estimates obtained from experiments and the inverse methodology is discussed to establish the validity of the proposed inverse techniques. Consequently, these techniques offer ap plicability in scenarios where one-dimensional heat transfer is compromised due to factors such as asperity distribution, vacuum conditions, or low thermal conductivity of the specimen.

Abstract: Due to experimental limitations, sometimes it is challenging to tackle the thorough change in asperity characteristics (contact pressure, real area of contact, asperity radius), which demands a more suitable analytical model for prediction of such characteristics. This work demonstrates an approach for modeling sliding wear that provides an insight into the evolution of surface topography with operational cycles. The wear model is applied on various engineered surfaces to study the change in surface topography with wear cycles. It is concluded that different engineered surfaces nearly with same roughness demonstrate totally different behavior during sliding wear. It is observed that milled surface in comparison to turned, honed and grinding surfaces experiences minimum contact pressure due to very high correlation length. Within the range of wear cycles, maximum increase in the asperity radius is observed for milled surface.

Abstract: In order to restore worn parts during repair work, it is often used to press the repair bushings. While assembling joints, cracks may form in the spanning part (bushing), as it may have surface and structure defects. Therefore, an urgent task is to increase the crack resistance of joints with tension during its assembly. The paper examines the influence of the geometry of the spanning part on the process of cracking. To assess the effect of defects on the crack formation, the method of modeling defects with a surface crack of a semi elliptical shape was used. The crack resistance is estimated using the force criterion of fracture mechanics – the stress intensity coefficient. As a result, it was found that the ratio between the wall thickness of the enclosing sleeve and its outer diameter has a significant effect on the crack resistance of the joint with tension, which allows reducing the origin probability and crack development during its pressing by varying these parameters. While assembling joints, the following methods are often used: mechanical-using a press and thermal with heating of the covering part. When the method of joint with cooling of the covered part, the greatest strength of the joint is achieved, but the probability of cracking increases. This is because when the temperature of the enclosing sleeve decreases in contact with the cooled shaft, the critical stress intensity coefficient (fracture toughness), which is a mechanical characteristic of crack resistance, decreases. To reduce the effect of cooling the sleeve, you can use a combined method of assembling the joint, in which the covered part is cooled and the covering part is heated. It is shown that to assess the fracture resistance at low temperatures, it is optimal to conduct full-scale tests, where the cooling and heating temperatures of the press joint parts are the experimental factors.

Abstract: Total hip replacement is surgical procedure which is widely performed in most of the developed countries due to rapid aging. The extensive application of titanium alloy as hip prosthesis can be seen because of its suitable properties such as good biocompatibility, light weight and high strength. However, coating or bond is required as titanium alloy ineffective to be adhered directly with human bone. Hydroxyapatite (HAp) is common coating material used to bond Ti-6Al-4V hip prosthesis with human bone. HAp-Ti-6Al-4V interface is a possible fretting wear region which is subjected to significant contact pressure. HAp-Ti-6Al-4V interface fretting fatigue delamination leads to contact pressure which can accelerate fretting wear behaviour of HAp coating. Present paper discusses the influence of delamination length and fatigue stress ratio on contact pressure distribution at interface of HAp-Ti-6Al-4V using finite element methodology. A simple two-dimensional finite element contact configuration consisting Ti-6Al-4V substrate, HAp coating and contact pad (representing bone) is employed to examine under static analysis. The finite element predicted results highlighted that contact pressure can be promoted under increased delamination length condition and stress ratio of 0.1 (tension-tension). Contact pressure can accelerate HAp coating fretting wear behaviour.

Abstract: The main motivation in stamping die industry and academia is panel quality and formability issues rather than the weight and cost of the die. A product should be designed according to the loads that it can be faced in service condition. But somehow this rule is not valid for stamping die design since the minimum distance between the ribs is based on the standards and location and pattern of the ribs which are depending primarily on the company experience. In this work, an auto panel drawing die design is investigated numerically whether it is overdesigned or not. The loads on the die surfaces are calculated by numerical methods. When a panel is drawn between upper and lower die, the contact pressure (CP) occurs on the interface surfaces due to this interaction. Since CP is a vital parameter and it is almost impossible to measure it by experimental methods, it is validated by two different numerical codes. The CP values obtained from Autoform^® quasi-static solution are compared with Abaqus^® transient forming analysis solution. Topology optimization is applied on the lower die by using the estimated CP loads. Von-Mises stress, elastic deformation and volume are compared between current and optimized die geometry. Panel thickness variation is also investigated in longitudinal and transverse directions.

Abstract: Based on application the physical constraint equations of state of stress and strain of the metal for the isotropic medium, we get expressions for components of stress tensor. The new theoretical method for calculation of contact pressures and rolling force during rolling of double-T section in a universal beam groove was developed. Reliability of the method is confirmed by the results of experimental verification for conditions of rolling of H-beam No 35B1, 40K2 and 45B2 from steel 15CrSiNiCu on the universal beam mill of "NTMK". The average calculation error is 6.4%. The new method is recommended for calculation pass design and technological modes of H-beam rolling on rail-beam and section mills, equipped with universal stands.

Abstract: During the processing of tubing premium threaded made up, the degree of the thread sealing surface intactness will directly affect the sealing performance of the string. Nevertheless, there are some difficulties to detect the damage of the engaged sealing surface effectively. In the present study the sealing surface damage was judged by the sealing surface contact stress’s relative changes according to the acoustic elasticity theory,. At the same time, the wear defects generated at the tubing sealing surface, during the tubing made up, contrasted with the wear and unworn surface roughness of coupling ultrasonic detected about the sealing surface. The results showed that with the acoustic amplitude evaluated the sealing contact stress was susceptible to the influence of surface roughness of coupling. But the reflection wave with the center frequency on the sealing surface characterization of the contact stress could avoid this problem effectively.

Abstract: A first-order hexahedral (H8)-element-based smoothed finite element method (S-FEM) with a volumetric-deviatoric split for nearly incompressible materials was developed for highly accurate deformation analysis of large-strain problems. In the proposed method, the isovolumetric part of the deformation gradient at the integration point is derived from F based on the beta finite element method (i.e., an S-FEM), whereas the volumetric part of the deformation gradient is derived from F on the basis of the standard FEM with reduced integration elements. This method targets H8 elements that are automatically generated from tetrahedral elements, which makes it quite practical. This is because the FE mesh can be created automatically even if the targeted object has a complex shape. This method eliminates the phenomena of volumetric and shear locking, and reduces pressure oscillations. The proposed method was implemented in the commercial FE software Abaqus and applied to the large-deformation contact problem to verify its effectiveness.

Abstract: As it stands now, rubber has been the main material used in the making of pneumatic vehicle tyres. Speed of the vehicle depends on many factors like steering geometry, inflation pressure, vehicle load, road temperature and environmental conditions. The main aim of this research is to develop a finite element approach and computationally evaluate the performance of a steady-state rolling tyre by changing the tyre tread patterns. The tyre normally composed of rubber and body-ply was investigated with regards to the effect of the inflation pressure. Tyre modeling using six different types of patterns was completed by using Creo parametric 3D modeling software and then the tyre was discretized into small elements through ANSYS R16.2. The rim area of the tyre was fixed and pressure was applied to the inside surface of the rim. Finite element analysis was completed by using ANSYS R16.2 and equivalent stress, contact stress and contact pressure were found out to identify the best tyre pattern. From the final results it was observed that, Pattern-I had good agreement of results as compared to other type of patterns which showed medium frictional stress and contact pressure.