Papers by Keyword: Stress

Abstract: This work is part of the European project MOTION (Interreg 2 Seas Mers Zeeën), which aims to develop an exoskeleton for children with cerebral palsy (CP). The developed exoskeleton is equipped with a smart garment in order to detect the stress (e.g. physical, physiological) during the rehabilitation. Five different sensors, i.e. electrocardiogram (ECG), respiratory rate (RR), pressure, galvanic skin response (GSR) and textile heat fluxmeter (THF), are integrated into this smart garment for stress detection. This paper focuses on the development of the textile heat fluxmeter. Several researchers used heat fluxmeters in physiological studies to measure the body heat exchanges with the environment. However, the non-permeability of such fluxmeter gives inaccurate measurements in wet condition. Innovative flexible textile heat fluxmeter may detect, analyze, and monitor the heat and mass transfers with minimum disturbance due to its porosity. Moreover, it is desirable to have flexible sensors when they need to be in contact with the human body, in which the flexibility and non-irritability requirements are of utmost importance.

Abstract: In this work, we investigate, by μ-Raman spectroscopy the distribution of stress field on a micro-machined structures. They were realized on a 3C-SiC substrate, grown on a Silicon On Insulator (SOI) wafer, after lithography and etching processes. Various structures, such as strain gauge, single and double clamped beams, were analyzed, showing different stress distributions. All the structures show an intense variation of stress close to the undercut region.

Abstract: Pipelines are widely used in industry for transporting oil and gas. Dents are one of the most common mechanical damage to pipelines due to external factors and significantly affect the performance of the pipelines. A dent is a permanent deformation of the circular cross-section of the pipelines. In this paper, numerical simulation using finite element analysis on API 5L X52 pipelines subjected to denting by a spherical indenter was carried out to determine the distribution of Von-Mises stress and permanent deformation. The given load was between the yield strength and ultimate strength of API 5L X52. The effect of indenter diameter and indenter displacement was studied. The results show that the indenter diameter and indenter displacement affect the value and area distribution of Von-Mises stress and permanent deformation.

Abstract: The paper presents the results of metallographic and electrophysical studies of the structure of 12X18H10T steel after plastic deformation. Studies allow us to determine the optimal modes of plastic deformation of corrosion-resistant steels.

Abstract: A mathematical approach to studying the process of establishing the effect of degree of significance of multilayer shell mold material physical properties and macrostructure on the mold stress-strain state is proposed. It is not possible to solve this problem analytically; therefore, a numerical approach was applied, namely, a proven numerical method and a set of author-developed programs. Knowledge of how the basic physical properties of the shell mold materials and shell mold macrostructure affect the shell resistance to cracking allows, even at the design stage of the pilot shell mold structures, virtual modeling of the thermal and deformation processes occurring therein, i.e. prediction the operability of the designed shell mold. Based on the results of modeling the processes of predicting possible shell mold destruction conditions, the most important parameters and factors of crack formation are established and approach to study of new shell mold fabrication processes is defined.

Abstract: This study aims to analyze the stress that occurred on the automotive coil spring made of SAE 5160 carbon steel due to various types of road surfaces. The 60-second strain signals measured on a coil spring of a car being driven on a flat, uphill, and downhill road surface were used as the loads in these dynamic analyses. The analysis results showed that the maximum stress occurred on the inside of the spring in the second coil from the top. The results of this dynamic analysis also showed that the three types of road surfaces provided almost the same stress. The downhill road surface gave the highest stress, which was 0.622 GPa, followed by flat road (0.621 GPa) and uphill road (0.62 GPa). The reasons for this are the shifting of the vehicle load to the front wheels together with the braking effect when driving downhill.

Abstract: The paper presents the results of numerical experimental studies of cutting titanium blanks using mathematical modeling programs, which make it possible to completely repeat technological processes in a computer (digital twin). The LS-DYNA product was used as a program to simulate the process of stock removal from titanium blank. It has been established that the use of this method adequately describes the cutting processes, including with the introduction of the energy of an ultrasonic field into the processing zone, can significantly reduce the duration of experimental research and evaluate the influence of the elements of the cutting mode and design parameters of the tool on the thermal power aspects of the formation of new surfaces of machine parts.

Abstract: Information on the stress state of protective and decorative coatings during the curing process, in particular on the cohesive state of destruction, is given. The influence of the type of substrate on the change in internal stresses in the coating is considered. It was revealed that the greatest value of shear stresses is observed in coatings on a heavyweight concrete substrate. The subsequent increase in temperature after curing to 50°C leads to an increase in the value of the normal stresses. The probability of cracking of coatings during thermal aging is estimated. It was revealed that during aging there is an exponential decrease in the cohesive strength of coatings and an increase in internal stresses. Aging tends to increase the likelihood of cracking of coatings. The change in stresses in coatings as a result of seasonal fluctuations in air temperature is considered.

Abstract: The article presents the developed method of channel angular pressing of the annular billets and gives the examples of hardening annular aluminum billet by channel angular pressing. The channel angular pressing is shown to result in aluminum hardening by 1.4 to 1.5 times. This increases the diameter of the annular billet.

Abstract: The study of the deformation characteristics of thin polymer films has established 2 stages of increasing strain with increasing stress: the first stage in the elastic region is slow linear; the second stage is sharply exponential. The dependence of deformation (ε) on stress (σ) in polytetrafluoroethylene at various exposure doses has been experimentally investigated. Irradiation of the fluoroplastic films under study with electrons doses of 1, 3, 5, 7, and 10 kGy leads to significant changes in their mechanical properties, while the samples lose their plasticity and begin to break at a lower strain, which is associated with the formation of nanodefects in the structure of the material. A significant decrease in elongation is observed compared with unirradiated material. The reason for this is the degradation of the main chains of the fluoroplastic. With an increase in the absorbed dose, the Young's modulus increases exponentially, which is associated with a decrease in the distance between atoms in the structure of the sample. The resulting effect can be used in industry. The curves obtained for both non-irradiated and irradiated material are satisfactorily described in the exponential model.