Showing 73 results for Fatigue
Volume 2, Issue 4 (12-2014)
Abstract
Aim: It has been shown that workers who had previously been involved in a work accident had significantly lower situation awareness scores than those who had not had an accident in the workplace. In this study, we examined the role of stress, sleep loss and fatigue in predicting situation awareness among workers.
Methods: The current study was a cross-sectional study. The sample consisting of 180 employees in National Petrochemical Company in 2014 was selected according to the stratified random sampling method. They responded to questionnaires about work situation awareness, work stress, sleep loss and fatigue. The data were analyzed by correlation techniques and stepwise regression.
Findings: The results showed a significant internal correlation among work stress, sleep loss and fatigue, and work situation awareness. Also the results of stepwise regression analysis showed that sleep loss, fatigue and stress predicted, respectively, almost 25%, 23% and 21% of variances of work situation awareness among workers.
Conclusion: The variables of stress, sleep loss and fatigue could predict work situation awareness. Therefore, these variables can be important to promoting the awareness of work situation among workers
Volume 5, Issue 3 (11-2020)
Abstract
SARS-CoV-2 is a coronavirus belonging to the betacoronavirus category that targets the respiratory system and Causes symptoms similar to pneumonia. The patients with-covid 19 do not only suffer from respiratory problems and their clinical symptoms range from no symptoms to severe pneumonia. In fact, they may have a variety of symptoms including fever, shortness of breath, dry cough, nasal congestion, sore throat, nausea, vomiting, myalgia, arthralgia, fatigue (muscular and mental), joint swelling (as reactive arthritis), headache, diarrhea and rarely arthritis. The major musculoskeletal symptoms which might be appeared include arthralgia, myalgia, chronic fatigue, and joint swelling (as reactive arthritis)
Volume 7, Issue 1 (11-2008)
Abstract
In this paper, an experimental investigation of fatigue crack growth behavior and fatigue life of Coach Peel (CP) specimens is reported. In this investigation, the CP specimens with 1 and 1.5 mm thickness and from mild steel are used. Specimens are tested by a 25 kN capacity INSTRON 8802 servo-hydraulic fatigue test machine under constant amplitude but various level loadings. During loading, the crack length and cycle numbers are measured accurately by a 100X light microscope. Initiation and propagation of spot weld specimens are measured by drawing vertical displacement of the specimen’s vs cycle’s curves. Results show that initiation and propagation of cracks often occur in the plate with less thickness. Also in low level loadings, cracks propagate longtitudinaly, but in high level loadings, usually nugget pull out and joints, fail catastrophically. The crack lengths during propagation, are nearly unique in both plates with the same thickness.
Volume 7, Issue 1 (11-2008)
Abstract
In this paper, we report results of stress analysis and fatigue life assessment of a number of spot weld joints. Models are presented for corrugated plates, jointed to an L-shape plate using 7 and 14 spot welds, which are subject to four different types of alternating loading conditions. The analyses are based on the solutions obtained from the ANSYS7 finite element package, using solid elements. In this study, strains and stresses in the weld nugget are evaluated. However, the primary focus is on strain-based fatigue life assessment which considers the 3D state of stress around the weld nugget and the nonlinear effects of the materical and the geometry.
Ehsan Naraghian, Majid Mirzaei,
Volume 8, Issue 1 (10-2008)
Abstract
In this paper, we report results of stress analysis and fatigue life assessment of a number of spot weld joints. Models are presented for corrugated plates, jointed to an L-shape plate using 7 and 14 spot welds, which are subject to four different types of alternating loading conditions. The analyses are based on the solutions obtained from the ANSYS7 finite element package, using solid elements. In this study, strains and stresses in the weld nugget are evaluated. However, the primary focus is on strain-based fatigue life assessment which considers the 3D state of stress around the weld nugget and the nonlinear effects of the materical and the geometry.
Mahmood Shariati,
Volume 8, Issue 1 (10-2008)
Abstract
In this paper, an experimental investigation of fatigue crack growth behavior and fatigue life of Coach Peel (CP) specimens is reported. In this investigation, the CP specimens with 1 and 1.5 mm thickness and from mild steel are used. Specimens are tested by a 25 kN capacity INSTRON 8802 servo-hydraulic fatigue test machine under constant amplitude but various level loadings. During loading, the crack length and cycle numbers are measured accurately by a 100X light microscope. Initiation and propagation of spot weld specimens are measured by drawing vertical displacement of the specimen’s vs cycle’s curves. Results show that initiation and propagation of cracks often occur in the plate with less thickness. Also in low level loadings, cracks propagate longtitudinaly, but in high level loadings, usually nugget pull out and joints, fail catastrophically. The crack lengths during propagation, are nearly unique in both plates with the same thickness.
Volume 11, Issue 1 (1-2023)
Abstract
Aims: Caring for patients during the Covid-19 pandemic exposes nurses to both physical and emotional challenges. This study aimed to investigate the correlation between the professional quality of life and caring behaviors in nurses working during the Covid-19 pandemic.
Instruments & Methods: This cross-sectional and correlational study was conducted in 2022. The study population was all nurses working in selected hospitals of Iran University of Medical Sciences. 124 nurses working during the Covid-19 epidemic by using convenience method were selected. Data collected using the demographic and occupational information form, Stumm's professional quality of life questionnaire, and Wolf's caring behaviors of nurses’ questionnaire. All questionnaires were completed by self-report method. Data were analyzed by Spearman's correlation coefficient, Mann-Whitney U, Kruskal-Wallis, and linear regression tests using SPSS 22 software.
Findings: The overall mean score of caring behaviors was 82.06±7.76, and the overall mean score of professional quality of life was 106.18±18.31. There was a significant and direct correlation between the professional quality of life and caring behaviors of nurses working in the Covid-19 epidemic (r=0.435; p<0.001). The linear regression method also showed a significant and direct linear relationship between the two variables.
Conclusion: The professional quality of life is significantly and directly correlated with caring behaviors in nurses working during the Covid-19 pandemic. Therefore, improving the professional quality of life of employees can be effective in providing better and more quality care.
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Volume 11, Issue 2 (9-2011)
Abstract
The effects of mixed mode fracture and fatigue crack path have been investigated in tensile-shear spot weld specimens having different gaps between their sheets. Non-linear analysis has been performed to obtain the stress distributions along the line perpendicular to the fatigue crack path. The amounts of effective stress and notch strength reduction factors have been obtained using the volumetric method. Fatigue crack growth approach has been applied to obtain stress intensity factors in mode I and mode II of fracture and to estimate fatigue crack propagation of spot welds. The results obtained from numerical predictions such as the volumetric method and the fatigue crack growth approach have been compared with the available fatigue test data. The results obtained from the fatigue crack growth approach show that spot weld specimens with bigger nugget diameter have the smaller values of stress intensity factors compared with those spot welds with smaller nugget diameters. However, with due attention to the fact that fatigue cracks propagate in the mixed mode condition, the ratio of mode I stress intensity factor to the mode II become more important parameter while predicting the fatigue life of specimens.
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Volume 12, Issue 1 (4-2012)
Abstract
In this paper, fatigue lives of tensile-shear multi-spot welded joints with four spot per specimen with different arrangements have been investigated. For this purpose, three types of joints with axial, transverse and almond-shaped have been selected. The prediction of fatigue life of spot welded joints has been carried out based on the available S-N curve of smooth specimens and the values of fatigue strength reduction factors. The experimental results and numerical predictions were compared and it was observed a good agreement between experimental and numerical ones. In addition, the Experimental Modal Analysis (EMA) was applied on the specimens before and after different fatigue loadings. Then percent of the identified natural frequencies decreasing was investigated and its correlation with crack initiation and total fatigue life of spot welded joints was studied.
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Volume 12, Issue 4 (11-2012)
Abstract
The aim of this paper is to show a new geometrical specimen in fatigue to define the behavior of semi elliptical crack growth in thick-walled pressure vessels. This research emphasize on the importance of the behavior of fatigue crack in test specimen and real conditions in vessels .In other word, there must be more adaptations between stress intensity factor in new specimen and real vessel that includes crack along the wall, so, under Fatigue loadings, as a result, more adaptation will be obtained between growth speed and relative crack lifetime according to loading cycles. By introducing this new specimen we compare the results of fatigue loading on propositional new specimen with results of vessel fatigue loading and standard specimen. We estimate the behavior of fatigue crack growth in specimen and pressure vessel with (FEM) and experimental method. In order to comparing of limit component with experimented results, some piece of with new specimen made of steel (ck45) can be used and all of these must be under fatigue testing and results are obtained in these methods.
Volume 13, Issue 1 (1-2025)
Abstract
Aims: This study examined the relationship between innovation practices and occupational fatigue among healthcare professionals in a high-intensity oncology setting.
Instrument & Methods: This cross-sectional study was conducted at the Sultan Qaboos Comprehensive Cancer Center (SQCCC) in Muscat, Oman in 2024, involving 163 clinical staff members. Data were collected using validated self-reported questionnaires that measured innovation practices, occupational fatigue, and demographic characteristics. Descriptive statistics, correlation analyses, and independent samples t-test were performed to identify significant relationships and demographic differences.
Findings: Innovation practices were rated highly across domains, with resource allocation scoring the highest (4.26±0.42). Occupational fatigue levels were relatively low overall (1.73±1.03), with shift-related fatigue being the most prominent (1.92±0.85). A significant negative correlation was identified between occupational fatigue and innovation (r=-0.68, p<0.05). Leadership behaviors (r=-0.62, p<0.05) and organizational climate (r=-0.59, p<0.05) showed the strongest negative associations with fatigue. Participants aged over 40 reported higher fatigue levels compared to younger professionals aged 20-40. Additionally, professionals with over 10 years of experience exhibited significantly higher innovation scores (p=0.032) and lower fatigue levels (p=0.027) than their less experienced counterparts.
Conclusion: Demographic factors, such as age, experience, and education, play significant roles in shaping perceptions of fatigue and innovation.
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Volume 13, Issue 2 (5-2013)
Abstract
The objective of this work was to investigate the effect of nanocaly on fatigue life of air spring. The studies on the air spring fatigue life have shown that the inner layer of the rubber composite bellows of the air spring plays the most important role on its fatigue life. So, as a new idea to improve the life of the air spring, in this research, NR/BR and 0, 3, 5, 7 % of nanoclay were separately melt-blended. X-ray diffraction was employed to characterize the nanocomposite morphology. Then, the curing time of the unvulcanized compound was defined by rheometer test and the final nanocomposites compounds were provided according to their curing characteristics. After that, tensile, heat built-up, tear and fatigue tests were performed on the standard test specimens. It was shown that by increasing the nanoclay percentage, the elasticity modulus, tear strength and heat built-up were increased whereas tensile strength and elongation at break point were decreased. The results also showed that by the addition of 3 % and 5 % of nanocaly to NR/BR, its fatigue life was increased about 33 % and 57 %, respectively, whereas the fatigue life of the compound containing 7 % nanoclay was decreased about 14 %.
Volume 13, Issue 3 (4-2023)
Abstract
Studies show that each person makes an average of 35,000 decisions per day. Although this number is highly exaggerated, it cannot be denied that we make countless decisions on a daily basis. Decision fatigue refers to the fact that making repeated decisions impairs a person's ability to make fully informed and rational subsequent decisions. Therefore, the state of ego depletion, especially as a result of repeated decisions, is called decision fatigue. The lived experience of researchers along with senior managers in different organizations is the origin of this study. The results of this study show that from the set of managers' behavioral strategies, the person acts as a completely rational decision maker. But the evidence shows otherwise. This is true not only for ordinary people, but also for some highly trained professionals. The current study is a qualitative research that was conducted using the narrative research method. The qualitative data in this study is in the form of narratives derived from in-depth interviews with 11 senior managers in the public sector, which were analyzed using thematic analysis. The findings indicate that the causes of decision fatigue are personality traits, interpersonal issues, work difficulty threshold, and organizational factors.
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Volume 13, Issue 6 (9-2013)
Abstract
Thin walled structures are among the main parts for several industrial machines. They usually expose variant stresses; therefore fatigue is their major failure mechanism. However experimental observations of the cross section of failed parts indicate that their fatigue fracture differs from what generally expected as high-cycle fatigue behavior. The mathematical estimations demonstrate that stress concentration due to surface roughness plays greater role compare to other surface metallurgical factors which may be predominant factor in the case of fatigue crack generation for thick walled structures. Generating several experimental data, an attempt is made in this study, to investigate fatigue failure of these particular parts. In addition the practical equation available in machine component design books is modified to implement the effect of manufacturing parameters properly. Application of developed equation makes it possible for designers to communicate with manufactures in a better way by proposing expected surface quality. The manufacturers are supposed to choose suitable fabricating parameters (particularly machining parameters) to achieve required quality. In addition this criterion may be inspected easily by quality control managers even via visual inspection.
, Mohammad Salari,
Volume 13, Issue 6 (9-2013)
Abstract
In this paper, the effect of bandwidth and loading level parameters changes of random load histories on the fatigue crack growth is studied by the central limit theory. In this method, the life probabilistic distribution and probability of failure function and reliability function are derived by the central limit theory. The walker equation is used to account the stress ratio effect in the fatigue crack growth rate equations. Then, the theoretical results are verified by the test results in the three random loading conditions with the various bandwidths and loading levels. A good agreement among the theory and test results was observed. The probability of failure and reliability diagrams via number of cycles is presented too.
, Hamed Mehrabi,
Volume 13, Issue 10 (1-2014)
Abstract
In this paper, experimental analysis of ratchetting-fatigue interaction and ratcheting behavior of Ck45 steel were investigated by uniaxial cyclic loading under stress-controled tests. Stress-controled tests performed in two steps in order to evaluate ratchetting strain influence on fatigue life of specimens. First, pre-ratchetting tests were performed with various loading setups and then, their fatigue life were measured in fatigue test with a constant load for all specimens. In uniaxial cyclic loading for stress-control condition, fatigue life of specimens depends greatly on pre-ratchetting stress amplitude and influence of mean stress on fatigue life is limited to a specific mean stress.
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Volume 13, Issue 11 (1-2014)
Abstract
In order to analyze fatigue life of reinforced cylindrical shells, it is necessary to calculate stress and strain fields of the structure. The cost of three dimensional stress analysis of this structure is very high with respect to its geometric complexity. So the stress analysis of the problem is performed by shell-to-solid sub-modeling technique. For this purpose, the reinforced cylindrical shell is modeled using shell elements at first, which in this case all the bolts, rivets and spot welds are considered as bushing elements. Afterwards the candidate critical zones are modeled using 3D solid elements with the help of shell-to-solid sub-modeling technique and all the connections are also modeled using 3D elements. Then the fatigue life of the problem under multi-axial loading is estimated by Brown-Miller criterion. For this purpose a special script in ABAQUS software has been used.
Mohammad Hossein Gozin, Mehrdad Aghaei,
Volume 14, Issue 4 (7-2014)
Abstract
Experimental and numerical analysis of a single overload on the fatigue life of AISI 4140 CT specimens was studied. Fatigue tests were conducted on base line CT specimen under single overload ratios of 1.5 and 1.75. Numerical analyses were performed on 2D incorporating the stress intensity factor and the J-integral as driving force. Furthermore, ABAQUS commercial software was used to simulate elastic-plastic crack growth and crack closure. Overload-induced retardation effects on the crack growth rate are considered based on the crack closure concept. A novel model for considering pre-overload and post overload effect on the crack growth is introduced. This model is based on the effective stress intensity factor and the effective J value. Overload increases fatigue lives by factors of 1.24 and 1.5 for overload ratios of 1.5 and 1.75, respectively. Two dimensional FEM results are in good agreement with the experiment with a maximum error of 10% using stress the intensity factor based method and -6% using the J integral based method. Comparing present paper method with Harmain model indicates that this model requires fewer experiments and Harmain model requires less calculation.
Soran Hasanifard, Amir Parghazeh,
Volume 14, Issue 8 (11-2014)
Abstract
In this investigation, kinked crack path of friction stir Cu-Al7075-T6 alloy welded joints in four-point bending test conditions has been studied as well as the fatigue lifetime of the welded joints, numerically and experimentally. To do so, four-point bending and fatigue tests of welded specimens have been carried out and the experimental fatigue test data and the kinked crack angles in bending tests have been extracted. Maximum Tangential Stress (MTS) and (KII)min criteria have been used for estimating the kinked crack angles, and Paris law has been applied to predict fatigue crack propagation life of the welded specimens. Functionally graded materials concept has been employed for determining mechanical properties of different regions of welded joints. To do so, the mechanical properties of the weld region such as Young's Modulus and Poisson's ratio have been considered to be linear functions of the positions of the weld region points. It has been shown that, when the original notch is close to the material with the higher fracture toughness (Copper), the kinked crack angle becomes smaller. The results show good agreement between the experimental data and numerical estimations.
Amir Reza Shahani, Iman Shakeri, Hamed Moayeri Kashani,
Volume 14, Issue 13 (3-2015)
Abstract
Bolt joints play an important role in the industries, so the estimation of fatigue life of bolts is an essential task. The aim of present study is estimation of fatigue life of connection bolts of two flanges in reinforced cylindrical shell with cutout. Two groups of data are needed for mentioned bolt: fatigue properties of bolt and value of stress of bolt due to applying load to structure. So, two paths have been gone. First, the fatigue properties of bolt have been measured in laboratory according to ISO 3800 standard. For this purpose a specific fixture was designed and manufactured which provided testing different bolts. By doing fatigue experiments, the fatigue properties of mentioned bolt such as fatigue limit and Basquin’s equation constants (fatigue strength coefficient and fatigue strength exponent) have been measured. Fracture mechanism and fracture surface have been investigated, too. Afterward, in the next step the value of stress in bolt that is subjected to mix loading has been calculated by using of FE modeling. Because of problem complexities, cost of three dimensional analysis of this problem increases, so analysis of the problem has been performed by shell-to-solid sub-modeling technique. At the end, by calculating the nominal stress of bolt from FE modeling and using fatigue properties witch obtained from experiments, life of the mentioned bolt has been estimated.
