Estimation of the residual strength resource of machines

2019 ◽  
Author(s):  
Kh.B. Kishtykov
Keyword(s):  
Endurance Limit ◽  
Statistical Tests ◽  
Engineering Practice ◽  
Endurance Limits ◽  
Single Overload ◽  
Fatigue Characteristics ◽  
Number Of Cycles ◽  
High Level ◽  
Anomalous Nature ◽  
Irregular Loading

For objective reasons, machines experience short-term overload, which can lead to damage or destruction of the structure. Under these conditions, it is important to estimate the residual resource of machine fatigue characteristics. For this purpose in engineering practice the method of single overloads (from a high level to low) is widely used. The method allows simulating a mode of adverse irregular loading. Single overload at a level exceeding the initial endurance limit for a certain number of cycles reduces the endurance limit and the residual resource of the structure durability. The empirical dependences proposed in the literature for estimating the relative decrease in endurance limits from the overload coefficient and the cyclic ratio give a complete decrease in the secondary endurance limit at a cyclic ratio equal to one. This is inconsistent with experimental results indicating the existence of a marginal reduction in secondary endurance limits. The formula allowing to correct slightly these dependences and to describe marginal decrease of secondary endurance limits, also under some conditions gives full decrease of secondary endurance limits or loses physical sense. Although the dependence proposed for titanium alloys gives a marginal reduction in the secondary endurance limits other than zero, it determines the anomalous nature of the asymptotic curve which does not correspond to numerous experimental data and mathematical models of damage. Earlier, the author has developed a mathematical model of single overloads and on its basis he has performed an estimation of the residual resource of machine durability based on the results of statistical tests of laboratory samples. In this paper, this model is used to estimate the residual structural strength of machines. The calculated dependences are proposed that satisfactorily describe the experiment and are free from the above shortcomings. These relations can be recommended for implementation in the practice of engineering calculations.

scholarly journals Effects of Knit Stretching and Matrix Crystallinity on the Fatigue Behaviour of Knitted Fabric-Reinforced Gf/Pet Composites

1997 ◽  
Vol 6 (3) ◽  
pp. 096369359700600 ◽  
Author(s):  
E. Moos ◽  
J. Karger-Kocsis
Keyword(s):  
Endurance Limit ◽  
Damage Zone ◽  
Stress Transfer ◽  
Fatigue Behaviour ◽  
Knitted Fabric ◽  
The Matrix ◽  
Static Tensile ◽  
Matrix Morphology ◽  
Number Of Cycles ◽  
Fatigue Endurance

In this study the tension-tension fatigue behaviour of weft-knitted glass fibre fabric-reinforced polyethylene terephthalate (GF/PET) composites was studied as a function of the stretching ratio of the knit The knits were stretched prior to consolidation in wale direction in 0, 25, 50 and 73%, respectively, in order to increase the anisotropy and to alter the mechanical properties of the composites. The influence of the matrix morphology (crystalline, amorphous) on the fatigue response was also investigated by using a composite with unstretched knit reinforcement. The results, displayed in normalized maximum fatigue stress Ms number of cycles (S-N) diagrams showed that the fatigue endurance limit of the GF/PET composites did not depend either on the knit stretching or the matrix crystallinity. The fatigue endurance limit, normalized to the static tensile strength, was found at ≍27 and ≍50 % for the knitted fabric-reinforced composite sheets tested in wale (W) and course (C) direction, respectively. The damage zone seemed to be localized for 1 and 2 rows of loops in C-and W-directions, respectively. This failure mode reflects the stress transfer and redistribution capability of the plain weft-knit reinforcement

scholarly journals Designing Two Secure Keyed Hash Functions Based on Sponge Construction and the Chaotic Neural Network

Entropy ◽  
2020 ◽  
Vol 22 (9) ◽  
pp. 1012 ◽  
Author(s):  
Nabil Abdoun ◽  
Safwan El Assad ◽  
Thang Manh Hoang ◽  
Olivier Deforges ◽  
Rima Assaf ◽  
...  
Keyword(s):  
Neural Network ◽  
Statistical Tests ◽  
Hash Functions ◽  
Message Authentication ◽  
Security Measures ◽  
Chaotic Neural Network ◽  
Chaotic Neural Networks ◽  
Classical Chaos ◽  
Neural Network System ◽  
Number Of Cycles

In this paper, we propose, implement, and analyze the structures of two keyed hash functions using the Chaotic Neural Network (CNN). These structures are based on Sponge construction, and they produce two variants of hash value lengths, i.e., 256 and 512 bits. The first structure is composed of two-layered CNN, while the second one is formed by one-layered CNN and a combination of nonlinear functions. Indeed, the proposed structures employ two strong nonlinear systems, precisely a chaotic system and a neural network system. In addition, the proposed study is a new methodology of combining chaotic neural networks and Sponge construction that is proved secure against known attacks. The performance of the two proposed structures is analyzed in terms of security and speed. For the security measures, the number of hits of the two proposed structures doesn’t exceed 2 for 256-bit hash values and does not exceed 3 for 512-bit hash values. In terms of speed, the average number of cycles to hash one data byte (NCpB) is equal to 50.30 for Structure 1, and 21.21 and 24.56 for Structure 2 with 8 and 24 rounds, respectively. In addition, the performance of the two proposed structures is compared with that of the standard hash functions SHA-3, SHA-2, and with other classical chaos-based hash functions in the literature. The results of cryptanalytic analysis and the statistical tests highlight the robustness of the proposed keyed hash functions. It also shows the suitability of the proposed hash functions for the application such as Message Authentication, Data Integrity, Digital Signature, and Authenticated Encryption with Associated Data.

scholarly journals Healthworker Preparedness for COVID-19 Management and Implementation Experiences: A Mixed Methods Study in Uganda’s Refugee-Hosting Districts

2021 ◽  
Author(s):  
Gloria Seruwagi ◽  
Catherine Nakidde ◽  
Felix Otieno ◽  
Joshua Kayiwa ◽  
Brian Luswata ◽  
...  
Keyword(s):  
Health System ◽  
Work Environment ◽  
Negative Impact ◽  
Statistical Tests ◽  
Statistical Significance ◽  
Total Sample ◽  
P Value ◽  
Cross Sectional ◽  
Validated Questionnaire ◽  
High Level

Abstract Background : The negative impact of COVID-19 on population health outcomes raises critical questions on health system preparedness and resilience, especially in resource-limited settings. This study examined healthworker preparedness for COVID-19 management and implementation experiences in Uganda’s refugee-hosting districts.Methods : A cross sectional, mixed-method descriptive study in 17 health facilities in 7 districts from 4 major regions. Total sample size was 485 including >370 health care workers (HCWs). HCW knowledge, attitude and practices (KAP) was assessed by using a pre-validated questionnaire. The quantitative data was processed and analysed using SPSS 26, and statistical significance assumed at p<0.05 for all statistical tests. Bloom's cutoff of 80% was used to determine threshold for sufficient knowledge level and practices with scores classified as high (80.0%–100.0%), average (60.0%–79.0%) and low (≤59.0%). HCW implementation experiences and key stakeholder opinions were further explored qualitatively using interviews which were audio-recorded, coded and thematically analysed.Results: On average 71% of HCWs were knowledgeable on the various aspects of COVID-19, although there is a wide variation in knowledge. Awareness of symptoms ranked highest among 95% (p value < 0.0001) of HCWs while awareness of the criteria for intubation for COVID-19 patients ranked lowest with only 35% (p value < 0.0001). Variations were noted on falsehoods about COVID-19 causes, prevention and treatment across Central (p value < 0.0356) and West Nile (p value < 0.0161) regions. Protective practices include adequate ventilation, virtual meetings and HCW training. Deficient practices were around psychosocial and lifestyle support, remote working and contingency plans for HCWs safety. The work environment has immensely changed with increased demands on the amount of work, skills and variation in nature of work. HCWs also reported moderate control over their work environment, high level of support from supervisors (88%) and colleagues (93%). Conclusions: HCWs preparedness is inadequate in some aspects. Implementation of healthcare interventions is constrained by the complexity of Uganda’s health system design, top-down approach of the national response to COVID-19 and longstanding health system bottlenecks. We recommend continuous information sharing on COVID-19, a design review with capacity strengthening at all health facility levels and investing in community-facing strategies.

scholarly journals Healthworker preparedness for COVID-19 management and implementation experiences: a mixed methods study in Uganda’s refugee-hosting districts

2021 ◽  
Vol 15 (1) ◽  
Author(s):  
Gloria Seruwagi ◽  
Catherine Nakidde ◽  
Felix Otieno ◽  
Joshua Kayiwa ◽  
Brian Luswata ◽  
...  
Keyword(s):  
Health System ◽  
Work Environment ◽  
Negative Impact ◽  
Statistical Tests ◽  
Statistical Significance ◽  
Total Sample ◽  
Cross Sectional ◽  
Resource Limited ◽  
Validated Questionnaire ◽  
High Level

Abstract Background The negative impact of COVID-19 on population health outcomes raises critical questions on health system preparedness and resilience, especially in resource-limited settings. This study examined healthworker preparedness for COVID-19 management and implementation experiences in Uganda’s refugee-hosting districts. Methods A cross sectional, mixed-method descriptive study in 17 health facilities in 7 districts from 4 major regions. Total sample size was 485 including > 370 health care workers (HCWs). HCW knowledge, attitude and practices (KAP) was assessed by using a pre-validated questionnaire. The quantitative data was processed and analysed using SPSS 26, and statistical significance assumed at p < 0.05 for all statistical tests. Bloom's cutoff of 80% was used to determine threshold for sufficient knowledge level and practices with scores classified as high (80.0–100.0%), average (60.0–79.0%) and low (≤ 59.0%). HCW implementation experiences and key stakeholder opinions were further explored qualitatively using interviews which were audio-recorded, coded and thematically analysed. Results On average 71% of HCWs were knowledgeable on the various aspects of COVID-19, although there is a wide variation in knowledge. Awareness of symptoms ranked highest among 95% (p value < 0.0001) of HCWs while awareness of the criteria for intubation for COVID-19 patients ranked lowest with only 35% (p value < 0.0001). Variations were noted on falsehoods about COVID-19 causes, prevention and treatment across Central (p value < 0.0356) and West Nile (p value < 0.0161) regions. Protective practices include adequate ventilation, virtual meetings and HCW training. Deficient practices were around psychosocial and lifestyle support, remote working and contingency plans for HCW safety. The work environment has immensely changed with increased demands on the amount of work, skills and variation in nature of work. HCWs reported moderate control over their work environment but with a high level of support from supervisors (88%) and colleagues (93%). Conclusions HCWs preparedness is inadequate in some aspects. Implementation of healthcare interventions is constrained by the complexity of Uganda’s health system design, top-down approach of the national response to COVID-19 and longstanding health system bottlenecks. We recommend continuous information sharing on COVID-19, a design review with capacity strengthening at all health facility levels and investing in community-facing strategies.

scholarly journals USING THE LINEAR DAMAGE SUMMATION HYPOTHESIS IN THE FATIGUE TESTS ANALYSIS OF TITANIUM ALLOY PIECES

2021 ◽  
pp. 1-6
Author(s):  
Evgeniya Gnatyuk ◽  
Arkadiy Skvortsov ◽  
Svetlana Kuleshova
Keyword(s):  
Titanium Alloy ◽  
Endurance Limit ◽  
Linear Regression Analysis ◽  
High Strength ◽  
Fatigue Tests ◽  
Test Pieces ◽  
Operational Testing ◽  
Strength Material ◽  
Number Of Cycles ◽  
Damage Summation

This paper presents the results of fatigue tests of titanium alloy, and also describes the use of the hypothesis of linear damage summation when processing the results of fatigue tests. On the basis of the experiments, the endurance limit of the titanium alloy was determined, which lies in the range from 460 to 480 MPa with the number of cycles from 105 to 108. The purpose of the experiment was to determine the endurance limit of high strength material, as well as a mathematical measurement of the expected destruction. In this study, empirical methods were used such as indirect observation of the object under study, description and measurement of technical influences exerted on it by an artificial means, as well as linear regression analysis to establish the relationship between stress and durability. As a result of the experiment, fatigue curves were obtained for various probabilities, which give grounds to conclude that the use of the linear damage summation hypothesis in processing the results of fatigue tests entails a satisfactory practical accuracy of the calculation of endurance limit. This experiment is aimed at improving metal production by studying the quality of titanium alloy test pieces and performing mathematical analysis of possible problems arising in the process of its operational testing.

scholarly journals The Influence of Respiratory Component on Satisfaction with Physical Therapy after Cardiosurgical Interventions

2021 ◽  
Vol 6 (4) ◽  
pp. 142-148
Author(s):  
V. V. Vitomskyi ◽  
◽  
Keyword(s):  
Physical Therapy ◽  
Physical Therapist ◽  
Control Group ◽  
Surgical Interventions ◽  
Level Of Satisfaction ◽  
Number Of Cycles ◽  
High Level ◽  
Previous Group ◽  
Incentive Spirometry ◽  
Positive Expiratory Pressure

The purpose of the study was to investigate the effect of additional respiratory physical therapy on the level of satisfaction with physical therapy among patients after cardiac surgery. Materials and methods. The study involved 150 patients. The patients were randomly divided into three groups: control (respiratory physical therapy was limited to cough), group of incentive spirometry (in classes with a physical therapist patients performed additional 3 approaches of 10 breaths through the simulator; they received recommendations for hourly performance of a similar number of cycles of exercise), a group of patients who received additional respiratory physical therapy with positive expiratory pressure in the form of exhalation into a bottle of water through a tube (number of repetitions and recommendations are similar to those received by the previous group). All groups underwent the same protocol of mobilization and use of therapeutic physical exercises in the procedure of therapeutic gymnastics. Performing exercises with breathing simulators began on the first postoperative day. Results and discussion. A questionnaire (17 questions) was used to assess the satisfaction with physical therapy. The survey was conducted on the seventh postoperative day. The answers were distributed on a 5-point Likert scale from 1 point to 5 points. The key preoperative indicators and time indicators of surgical interventions of the examined groups did not differ significantly. Analysis of satisfaction with physical therapy revealed a high level in all items of the questionnaire. Statistical differences between the groups were found in only three items of the questionnaire, but they were not related to either the use of equipment or diligence in treatment or the content of physical therapy. The overall score of the questionnaire did not differ in groups according to the Kraskel-Wallis criterion, and Me indicators (25%; 75%) were in the control group – 81 (77; 85) points, in the group of stimulating spirometry – 81 (72; 85) points in the group with positive expiratory pressure – 79 (73; 84) points (χ2 = 4.560; p = 0.102). Conclusion. Additional respiratory physical therapy did not affect the overall satisfaction rate and results of most items of the questionnaire. The differences found in the three items did not indicate any effect of the use of respiratory physical therapy on the level of satisfaction, as higher scores in these items were in the control group. All items in the questionnaire received high scores

A Nonlinear Least Squares Logistic Fit Approach to Quantifying Uncertainty in Fatigue Stress-Life Models and an Application to Plain Concrete

2018 ◽  
Author(s):  
Jeffrey T. Fong ◽  
N. Alan Heckert ◽  
James J. Filliben ◽  
Paul H. Ziehl
Keyword(s):  
Least Squares ◽  
Endurance Limit ◽  
Stress Amplitude ◽  
Plain Concrete ◽  
Cyclic Stress ◽  
Logistic Function ◽  
Fatigue Stress ◽  
Least Squares Fit ◽  
Horizontal Asymptote ◽  
Number Of Cycles

A large number of fatigue life models for engineering materials such as concrete and steel are simply a linear or nonlinear relationship between the cyclic stress amplitude, σa, and the log of the number of cycles to failure, Nf. In the linear case, the relationship is a power-law relation between σa and Nf, with two constants determined by a linear least squares fit algorithm. The disadvantage of this simple linear fit of fatigue test data is that it fails to predict the existence of an endurance limit, which is defined as the cyclic stress amplitude at which the number of cycles is infinity. In this paper, we introduce a nonlinear least square fit based on a 4-parameter logistic function, where the curve of the y vs. x plot will have two horizontal asymptotes, namely, y0, at the left infinity, and y1, at the right infinity with y1 < y0 to simulate a fatigue model with a decreasing y for an increasing x. In addition, we need a third parameter, k, to denote the slope of the curve as it traverses from the left horizontal asymptote to the lower right horizontal asymptote, and a fourth parameter, x0, to denote the center of the curve where it crosses a horizontal line half-way between y0 and y1. In this paper, the 4-parameter logistic function is simplified to a 3-parameter function as we apply it to model a fatigue sress-life relationship, because in a stress-log (life) plot, the left upper horizontal asymptote, y0, can be assumed as a constant equal to the static ultimate strength of the material, U0. This simplification reduces the logistic function to the following form: y = U0 − (U0 − y1) / (1 + exp(−k (x − x0)), where y = σa, and x = log(Nf). The fit algorithm allows us to quantify the uncertainty of the model and the estimation of an endurance limit, which is the parameter, y1. An application of this nonlinear modeling technique is applied to fatigue data of plain concrete in the literature with excellent results. Significance and limitations of this new fit algorithm to the interpretation of fatigue stress-life data are presented and discussed.

scholarly journals Reform and Practice of the Course “Application of Computer in Materials Science”

2020 ◽  
Vol 3 (3) ◽  
pp. 63
Author(s):  
Li Li
Keyword(s):  
Curriculum Reform ◽  
Materials Science ◽  
Engineering Practice ◽  
Teaching Characteristics ◽  
Teaching Content ◽  
Innovation Ability ◽  
Materials Science And Engineering ◽  
The Subject ◽  
High Level ◽  
Basic Course

<p>The application of computer in materials science, as a professional basic course for undergraduates majoring in materials science and engineering, is both theoretical and operational. At the same time, the practicality and applicability of this course are also obvious. Therefore, there are great challenges for teachers’ teaching and students’ learning. Based on this, combined with the teaching characteristics of the subject, this article explores the teaching reform and practice in terms of teaching content, teaching means and teaching methods, in order to improve the training of high-level applied talents in colleges and universities. The curriculum reform has changed the traditional one-way knowledge transmission teaching mode, which is of great benefit to cultivating students’ engineering literacy, engineering practice ability and innovation ability.</p>

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