The critical influence of some “tiny” geometrical details on the stress field in a Brazilian Disc with a central notch of finite width and length

The role of some geometrical characteristics of the notches ma­chined in circular discs, in order to determine the mode-I fracture tough­ness of brittle materials, is discussed. The study is implemented both analyti­cally and numerically. For the analytic study advantage is taken of a recently intro­duced solution for the stress- and displacement-fields developed in a finite disc with a central notch of finite width and length and rounded corners. The vari­ation of the stresses along strategic loci and the deformation of the peri­me­ter of the notch obtained analytically are used for the calibration/validation of a flexible nu­mer­ical model, which is then used for a parametric investiga­tion of the role of geometrical features of the notched disc (thickness of the disc, length and width of the notch, radius of the rounded corners of the notch). It is con­cluded that the role of the width of the notch is of critical im­port­ance. Both the ana­lytic and the numerical studies indicate definitely that ignoring the ac­curate geo­metric shape of the notch leads to erroneous results concerning the actual stress field around the crown of the notch. Therefore, it is possible that misleading values of the fracture toughness of the material of the disc may be obtained.

Theoretical studies of the stress-strain state of the elements of joints on glued washers

In order to study the stress-strain state of the elements of joints on glued washers, a computational model of a multi-row joint on glued steel washers has been developed. The picture and character of the actual stress-strain state of a wooden element with glued washers are obtained. By analyzing the stress-strain state of the wooden element, the optimal step of the arrangement of washers in a multi-row connection is determined.

Self-Excited Acoustical Measurement System for Rock Mass Stress Mapping

This paper presents the results of a preliminary study of a self-excited acoustical system (SAS) for nondestructive testing (NDT). The SAS system was used for mine excavation stresses examination. The principle of operation of the SAS system based on the elastoacoustical effect is presented. A numerical analysis of the excavation was carried out considering the stress factor. An equivalent model based on a two-degree-of-freedom system with a delay has been developed. This model allowed to determine the relation which relates the frequency of the self-excited system to the stress level in the studied ceiling section. This relationship is defined by the elastoacoustic coefficient. The test details for anchorages in laboratory conditions and Wieliczka Salt Mine were presented. This research details of a method for creating actual stress maps in the ceiling of a mine excavation. The results confirmed the possibility of using the new measurement system to monitor the state of stresses in the rock mass.

Determination of the Actual Stress–Strain Diagram for Undermatching Welded Joint Using DIC and FEM

This paper presents new methodology for determining the actual stress–strain diagram based on analytical equations, in combination with numerical and experimental data. The first step was to use the 3D digital image correlation (DIC) to estimate true stress–strain diagram by replacing common analytical expression for contraction with measured values. Next step was to estimate the stress concentration by using a new methodology, based on recently introduced analytical expressions and numerical verification by the finite element method (FEM), to obtain actual stress–strain diagrams, as named in this paper. The essence of new methodology is to introduce stress concentration factor into the procedure of actual stress evaluation. New methodology is then applied to determine actual stress–strain diagrams for two undermatched welded joints with different rectangular cross-section and groove shapes, made of martensitic steels X10 CrMoVNb 9-1 and Armox 500T. Results indicated that new methodology is a general one, since it is not dependent on welded joint material and geometry.

Alternating optimization of design and stress for stress-constrained topology optimization

Handling stress constraints is an important topic in topology optimization. In this paper, we introduce an interpretation of stresses as optimization variables, leading to an augmented Lagrangian formulation. This formulation takes two sets of optimization variables, i.e., an auxiliary stress variable per element, in addition to a density variable as in conventional density-based approaches. The auxiliary stress is related to the actual stress (i.e., computed by its definition) by an equality constraint. When the equality constraint is strictly satisfied, an upper bound imposed on the auxiliary stress design variable equivalently applies to the actual stress. The equality constraint is incorporated into the objective function as linear and quadratic terms using an augmented Lagrangian form. We further show that this formulation is separable regarding its two sets of variables. This gives rise to an efficient augmented Lagrangian solver known as the alternating direction method of multipliers (ADMM). In each iteration, the density variables, auxiliary stress variables, and Lagrange multipliers are alternatingly updated. The introduction of auxiliary stress variables enlarges the search space. We demonstrate the effectiveness and efficiency of the proposed formulation and solution strategy using simple truss examples and a dozen of continuum structure optimization settings.

Stress for Success: Potential Benefits of Perceived and Actual Stress While Cruising

Understanding the effects of travel on the health of travelers could have profound effects on the tourism industry and behaviors of tourists. While psychometric analyses have suggested travel has the ability to relieve stress and improve one’s overall well-being, scant research has utilized physiological data to examine the effects of travel on health. The current study, guided by the cognitive activation theory of stress (CATS), compared self-reported diaries and physiological data (using heart rate monitors) to examine the effects cruising has on both perceived and actual stress. Results empirically validate the use of CATS as a theoretical framework for understanding travelers’ perceived and actual stress. Findings also inform specific guidance to both cruise management, on how to engineer cruise experiences based on stress, and individuals, on how to experience positive stress while traveling.

Gender differences in perceived stress level among undergraduate students in Armenia

Background Stress is an important issue in academic institutions and can have a negative impact on overall academic performance. This study was conducted as a research assignment during the Basics of Healthy Lifestyle course and aimed to investigate the stress level among undergraduate students at the American University of Armenia (AUA). Methods A cross-sectional survey was conducted among undergraduate students recruited by non-random convenience sampling. The study utilized a structured questionnaire to conduct face to face interviews. The questionnaire contained 40 close-ended questions on students' perceived stress level, the Student Stress Scale (SSS) (sum of scores of 31 questions) to measure actual stress, and socio-demographic characteristics. Data entry, descriptive and comparative statistics were performed using SPSS software. Secondary data analysis was conducted to explore gender differences in stress level. Results Overall, 111 AUA students participated and slightly over half of participants (59.5%) were female. The SSS revealed that 46.0% of students experience medium stress levels (self-perceived mean stress score =-5.8). Only 21.6% perceived themselves as having high stress levels; however, SSS showed that about one third had high stress. Female participants' perception of being highly stressed and having high stress level based on SSS were similar (28.8% and 27.3%, respectively). In contrast, less males perceived being highly stressed (13.3%), though, SSS showed that 40.0% of males experienced high stress levels. Conclusions The majority of AUA undergraduate students experienced medium or low stress levels. Male students experience higher stress levels, but their perceived stress level was much lower than in among females. Research is needed to explore the gender differences in stress levels and coping mechanisms among students. These findings may be useful for university administration for developing stress-reduction and stress-management strategies. Key messages There are disparities in perceived stress and actual stress levels between male and female students that warrant further exploration. Gender differences in stress level of the students should be considered for stress-reduction and stress-management strategies.

Research and Implementation of Axial 3D Printing Method for PLA Pipes

Additive manufacturing has been applied in many fields, but its layer-by-layer fabrication process leads to a weak inter-layer bond strength of printed parts, so it cannot meet the higher requirements for mechanical properties of the industry. At present, many researchers are studying the printing path planning method to improve the mechanical properties of printed parts. This paper proposes a method to plan the printing path according to the actual stress of pipe parts, and introduces the realization process of an algorithm in detail, and obtains the printing control G-code. Additionally, a 5-axis material extrusion platform was built to realize the printing of polylactic acid pipes with plane and space skeleton curves, respectively, which verified the feasibility and applicability of the method and the correctness of the planning path with standard material extrusion filaments. Finally, the tensile and bending experiments prove that axial printing enhances the mechanical properties of pipe parts.

Load Capacity of Eccentric Roller Bearings

Eccentric roller bearings are commonly used in engineering and serve as actuating links in mechanical drives of various machines. Load capacity is one of the main parameters of such bearings. This paper presents possible kinematic schemes of an eccentric roller bearing and the specifics of the actual radial load distribution when it is applied to the driving ring between the rolling bodies. It is established that the load capacity of the eccentric roller bearing depends on the actual stress occurring when the rolling body of the minimal radius and the inner ring raceway are in contact. Equations are obtained for calculating the permissible radial load that the rolling body of the minimal radius with a raceway can bear. The limiting load is determined that satisfies the conditions of contact strength of the bearing’s assembly units and ensures performance of the bearing in a mechanical drive of a machine. The results of determining the limiting load of the eccentric roller bearing and the results’ analysis are presented using a specific example. To ensure the performance of the bearing, the optimal ratio of the inner ring radius to the minimum rolling body radius is determined.