Fatigue life prediction model of WC-Co cold forging dies based on experimental and numerical studies

This study presents experimental and numerical studies to predict fatigue life of WC-Co 20% cold forging die. In order to determine the fatigue behavior of the material, three-point bending fatigue tests were performed and Morrow-Haigh diagrams were constructed. The analytical formulation was established by means of Basquin correlation obtained from the experimental results and die life was estimated according to the stress amplitude and mean stress values obtained from the finite element analysis. Verification of the analytical formulation was also carried out by obtaining the fatigue life cycle of the die from production line. The findings obtained showed that the life estimation method made the correct prediction with a deviation of 5.6%

Fatigue and Fracture of Materials and Structures, Stractural Integrity

Threaded fasteners are one of the most preferred joining methods today. Although there are many studies in this field, the number of researches on fatigue life as a result of the loosening behavior of fasteners is very limited. Within the scope of the study, the effects of preload loss due to transversal displacement for re-tightened bolted joints to their fatigue behaviors were investigated. The study was conducted by using M8 × 1.25 10.9 DIN 933 bolts and DIN 934 nuts with various preloads. Tightened bolts were subjected to repeated transversal displacement, and clamp load values were monitored and recorded for each cycle. Bolts subjected to preload loss were re-tightened to their desired clamp load values, and Junker vibration test was restarted. Increase on the tightening torque values after each usage was observed. This situation is caused by the friction coefficient change after reusing fasteners. Due to the increase in the friction coefficient, tightening torque values were increased as expected. Fastener subjected to repeated tightening failed during Junker vibration test due to fatigue. This phenomenon was mainly caused by high friction coefficient which prevents loosening and lead fasteners to take higher shear loads. A critical tightening-preload loss factor has been found for predicting early fatigue failure caused by loosening for re-tightened bolted joints.</p

Determination of the critical socket depths of 10.9 and 8.8 grade M8 bolts with hexagonal socket form

In this work, the effect of various socket depths of fasteners was investigated for the sake of weight reduction. M8x1.25 x 50 Full Thread (FT) bolts with 10.9 and 8.8 grade were examined in detail. The finite element simulations were performed by using SIMUFACT Forming Software. Empirical studies including fatigue and torque-tension experiments were conducted with the bolts having various socket depths. In addition, the effect of washer as used in most assembly conditions was investigated. One of the analytical methods used in the literature was also employed to compare the results obtained by the numerical and experimental methods. Based on the results obtained in this study, critical socket depths leading to the shift of failures from the thread region to head region were obtained for the investigated M8x1.25 x 50 FT bolts with 10.9 and 8.8 grades. The experimental results were compared with the analytical model and found that the analytical model underestimated the critical socket depths for both 10.9 and 8.8 grade bolts

A new analytical model to estimate maximum internal socket depth of non-reduced strength bolts

In this study, an analytical model for calculation of the maximum socket depth of bolts having shaft diameter smaller than socket diameter was introduced. A representative bolt was chosen and maximum socket depth satisfying the minimum ultimate tensile strength was calculated by the developed analytical model. The analytical findings were also compared with numerical simulations for validation. Numerical studies were carried out by using Simufact.forming finite element software. The maximum socket depth estimated by using the developed analytical model was in good agreement with the numerical results. The obtained critical socket depth through the analytical model was 1.4% safer compared to numerical simulation results. Therefore, it was concluded that the developed analytical model could be used to estimate the critical socket depths of bolts having shaft diameter smaller than socket diameter. (C) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExC

Effect of socket depth on failure type of fasteners

In this study, the effect of socket depth on failure types of fasteners were investigated in detail. Socket depth plays a vital role in structural integrity of fasteners particularly in weight reduction studies. Therefore, experimental studies were carried out by cold forged bolts having various socket depths. Fatigue and torque-tension tests were conducted to examine the critical socket depths under different loading types. Finite element analysis were also performed using SIMUFACT FORMING software. According to experimental and numerical investigations, it was shown that the socket depth has significant influence on failure mechanism of fasteners. Depending on the depth of sockets, the locations of the failures were shifted from the threads to the head of fasteners. The main reason for this type of shift was associated with the higher stress levels due to decrease in cross-sectional area of fastener heads. Consequently, it was shown that the critical socket depth is very important parameter in terms of structural integrity of fasteners and it has to be taken into account in the design stage of the every fasteners. (C) 2018 The Authors. Published by Elsevier B.V

Loosening Behavior of Ripped Nuts Based on the Fastener Tightening Strategy and Plate Hardness

Within the scope of this study, loosening behavior under vibration was investigated depending on the plate hardness, clamp length and tightening strategy of M8x1.25 10.9 quality nuts with rip form under flange. Two different plate hardness were used and two different types of tightening strategy, i.e. application of torque to either from bolt head or nut, were carried out by using bolts with 29 mm and 40 mm clamp length. During tightening, the effects created by rips on the plate were examined. A parametric study was also carried out to understand loosening behavior of fasteners depending on the plate hardness. Based on the experimental study, it was shown that plate hardness, clamp length and tightening strategy played a key role on the loosening behavior of fasteners. To decrease the loosening rate of the assembly on softer plate, nut with rip form should be tightened from the bolt element. However, for harder plates the selection of tightening strategy was less significant compared to that of softer plate. (C) 2020 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (https://creativecommons.org/licenses/by-nc-nd/4.0) Peer-review under responsibility of the European Structural Integrity Society (ESIS) ExC

Effect of socket depth on failure type of fasteners

In this study, the effect of socket depth on failure types of fasteners were investigated in detail. Socket depth plays a vital role in structural integrity of fasteners particularly in weight reduction studies. Therefore, experimental studies were carried out by cold forged bolts having various socket depths. Fatigue and torque-tension tests were conducted to examine the critical socket depths under different loading types. Finite element analysis were also performed using SIMUFACT FORMING software. According to experimental and numerical investigations, it was shown that the socket depth has significant influence on failure mechanism of fasteners. Depending on the depth of sockets, the locations of the failures were shifted from the threads to the head of fasteners. The main reason for this type of shift was associated with the higher stress levels due to decrease in cross-sectional area of fastener heads. Consequently, it was shown that the critical socket depth is very important parameter in terms of structural integrity of fasteners and it has to be taken into account in the design stage of the every fasteners. (C) 2018 The Authors. Published by Elsevier B.V

Clinical features of generalized lipodystrophy in Turkey: A cohort analysis

Aim: To describe the Turkish generalized lipodystrophy (GL) cohort with the frequency of each complication and the death rate during the period of the follow-up. Methods: This study reports on 72 patients with GL (47 families) registered at different centres in Turkey that cover all regions of the country. The mean ± SD follow-up was 86 ± 78 months. Results: The Kaplan–Meier estimate of the median time to diagnosis of diabetes and/or prediabetes was 16 years. Hyperglycaemia was not controlled in 37 of 45 patients (82.2%) with diabetes. Hypertriglyceridaemia developed in 65 patients (90.3%). The Kaplan–Meier estimate of the median time to diagnosis of hypertriglyceridaemia was 14 years. Hypertriglyceridaemia was severe (≥ 500 mg/dl) in 38 patients (52.8%). Seven (9.7%) patients suffered from pancreatitis. The Kaplan–Meier estimate of the median time to diagnosis of hepatic steatosis was 15 years. Liver disease progressed to cirrhosis in nine patients (12.5%). Liver disease was more severe in congenital lipodystrophy type 2 (CGL2). Proteinuric chronic kidney disease (CKD) developed in 32 patients (44.4%) and cardiac disease in 23 patients (31.9%). Kaplan–Meier estimates of the median time to diagnosis of CKD and cardiac disease were 25 and 45 years, respectively. Females appeared to have a more severe metabolic disease, with an earlier onset of metabolic abnormalities. Ten patients died during the follow-up period. Causes of death were end-stage renal disease, sepsis (because of recurrent intestinal perforations, coronavirus disease, diabetic foot infection and following coronary artery bypass graft surgery), myocardial infarction, heart failure because of dilated cardiomyopathy, stroke, liver complications and angiosarcoma. Conclusions: Standard treatment approaches have only a limited impact and do not prevent the development of severe metabolic abnormalities and early onset of organ complications in GL