Environmental fatigue behavior of non‐crimp,E‐glass fiber reinforced polyester composites for marine applications

This study is aimed to find the fatigue behavior of Glass Reinforced Plastics, a material which is a widely preferred material for small marine crafts, as well as several other applications. The type of composite tested is hand‐laid E‐glass non‐crimp reinforcements with an polyester resin matrix. The specimens were produced in two standard thicknesses and with these material directions and were tested both under atmospheric and simulated seawater environments for fatigue. It was seen that the results of fatigue lifetime obtained by testing the material in seawater is much lower than the results obtained from testing similar specimens under atmospheric conditions. However, the stress curves indicate the same slope, suggesting that the fatigue failure mechanism of both testing conditions is the same and the fiber‐related factors dominate. It was found that the thickness and material direction did not have a significant effect on the fatigue behavior of the material.     

Untersuchungen zur Dauerfestigkeit carbonitrierter Proben aus den Einsatzstählen 18CrNiMo7‐6und 20MnCr5

The endurance limit of carbonitrided specimens of 18CrNiMo7‐6 and 20MnCr5 case hardening steels were examined under bending conditions. Four variants were manufactured differing in heat treatment and surface conditions. Besides conventional gas carburised variants, carbonitrided specimens with a low and a raised nitrogen content of 0.2 and 0.45% at the surface as well as a carbonitrided and ground variant were examined. The specimens were tested with stress ratios R = –1 and 0. Depending on the nitrogen content cyclic loading evokes compressive residual stresses at the specimens' surfaces, caused by elastic‐plastic deformation. Specimens of the ground variant show additionally a decrease of the residual austenite content when cycled. The induced compressive residual stresses are substantially responsible for high endurance limits at both stress ratios and are the key for understanding the beneficial effect of carbonitriding in this regard.     

Investigations of hypocycloidal shaft and hub connections

This paper presents current research results for polygonal connections with hypocycloidal profiles (H‐profiles). It proposes a design concept including permissible stress with respect to limits of plasticity. Moreover, notch effect figures are specified for use in the nominal stress concept. A comparison with conventional shaft‐hub connections reveals the benefits of new polygonal connections.     

Ermüdungsverhalten von Schraubendruckfedern bei konstanten und variablen Beanspruchungsamplituden bei sehr hohen Schwingspielzahlen

A test rig for simultaneous testing of up to 88 compression springs under constant as well as variable amplitude loading is presented in this paper. The test rig utilizes a servo‐hydraulic testing machine. The results of long‐term fatigue tests of compression springs under constant and variable amplitude loading up to 5 ? 10⁸ and 1.4 ? 10⁷ cycles are presented. Experimental Woehler‐ and Gassner‐curves are obtained using the maximum likelihood method. Theoretical Gassner‐curves are generated using Miner's rule and experimental Woehler‐curves. The theoretical Gassner‐curves are compared to the experimental ones. The results of the constant amplitude loading tests are compared to literature data. The possibility to increase the testing frequency in variable amplitude loading tests is discussed. Thereto, the comparability of results from fatigue tests of material specimens using torsional ultrasonic fatigue testing equipment to results from fatigue tests on compression springs is addressed.     

Anwendung des Örtlichen Konzepts in der Turbinenschaufelauslegung

Die Anforderungen an große Kraftwerksturbinen (Gas‐ und Dampfturbinen) sind im Zusammenhang mit der Energiewende in den letzten Jahren signifikant gestiegen. Durch die wachsende Einspeisung von Strom aus erneuerbaren Energien wie Wind und Sonne gewinnt die Erhöhung der Flexibilität im Kraftwerksbetrieb immer mehr an Bedeutung. Dafür müssen zuverlässige und robuste Turbinen entwickelt werden. Turbinenschaufeln sind eine der Schlüsselkomponenten einer Turbine und ein entscheidender Erfolgsfaktor, um die aktuellen und zukünftigen Markt‐ und Kundenanforderungen zu erfüllen und die damit verbundenen Herausforderungen zu meistern. Die Auslegung von Turbinenschaufeln ist komplex. Turbinenschaufeln sind im Betrieb häufig extremen, hohen sowie komplexen mechanischen und thermischen Belastungen ausgesetzt. Diese mechanischen und thermischen Betriebsbelastungen führen zu hohen Bauteilbeanspruchungen und häufig zu einem Ermüdungs‐ und/oder Kriechlebensdauerverbrauch. Hersteller großer Kraftwerksturbinen können ihre Turbinen und deren Komponenten in den allermeisten Fällen nicht im Vorfeld auf Prüfständen testen. Außerdem können Fehler in der Auslegung der Komponenten zu deren Versagen im Betrieb und damit zumindest zu erheblichen wirtschaftlichen Schäden führen. Aus diesen Gründen und vor dem Hintergrund der zunehmend flexibleren Fahrweise von Kraftwerken und der damit verbundenen höheren Anzahl an Lastwechseln sind für die Entwicklung und Auslegung von Turbinenschaufeln sowie deren Lebensdauervorhersage geeignete, zuverlässige und abgesicherte Berechnungs‐ und Bewertungskonzepte sowie Regeln unerlässlich, um den sicheren Betrieb der Turbinenschaufeln zu ermöglichen. Dies gilt insbesondere für die genaue Beschreibung des Ermüdungsverhaltens unter Betriebsbelastung. Der vorliegende Artikel beschäftigt sich mit den hier verwendeten Konzepten zur Lebensdauervorhersage und zum Betriebsfestigkeitsnachweis von Gas‐ und Dampfturbinenschaufeln.     

Durability‐based design for endurance strength of hydroforming tools

Hydroforming tools must be designed fatigue resistant because in case of tool rupture high costs for repair and production downtime occur. Available guidelines for lifetime estimation of cyclically loaded parts usually are of general nature. In order to examine their applicability to the special concerns of hydroforming tools, stress states occuring during operation were investigated by means of numerical simulation. Basing on the results, specimen geometries were developed, representing a typical stress state. The estimated durability was calculated using the “FKM‐guideline”. The real durability was determined experimentally in form of Wöhler‐graphs. Eventually calculation and experiments were compared. Hence, the qualtity of the lifetime prediction was evaluated and correction factors were proposed.     

Study on performance and continuous durability test of single input multi output power take-off (PTO) gear box

The power take-off (PTO) gearbox is widely used for special vehicles, large construction machinery, industrial machinery and ships, to distribute the power of a single input shaft from an engine or a motor to several shafts or to collect several shafts by single shaft power (Torque × rotation speed). The super large hydraulic excavator is equipped with a power take-off (PTO) gearbox between the main engine and a number of pumps for the purpose of improving the fuel efficiency and improving the system efficiency. The power take-off (PTO) gearbox of a large hydraulic excavator with a body weight of 100 ton ( = 10⁵ kg) is connected with two large hydraulic pumps and one small hydraulic pump on three output shafts and different axial loads are generated depending on the working characteristics of the excavator. In this paper, we evaluated the performance and durability of a power take-off (PTO) gearbox of a large hydraulic excavator with a 100-ton body weight. The test evaluation criteria for non-fault life time calculation, performance and accelerated life test were established, and the types and characteristics of acceleration test equipment were analyzed. The torque distribution with the use of the gear phase difference to maintain the gearbox output condition was investigated, and energy was saved by circulating experimental power while controlling speed and load with two electric dynamometers. We analyzed the life of the gearbox by analyzing the metal particles generated in the lubricating oil of the gearbox.     

Vorhersage der Lebensdauer und Dauerfestigkeit von hochfesten,durchhärtenden Stählen

Fatigue Lifetime and Endurance Limit Prediction for High‐Strength Steels Smooth and notched specimens of the bearing steel 100Cr6 (SAE 52100) in a bainitic condition were used to determine the S‐N curves under tensile, torsional and combined in‐ and out‐of‐phase loading. In the area of high‐cycle fatigue, crack initiation was most likely caused by inclusions like Titanium Carbonnitrides or Aluminium Oxides. A micro mechanical model for the crack initiation by inclusions was developed. Another model was developed to describe the influence of these inclusions on the lifetime. A weakest‐link model, using the statistical distribution of inclusions and surface flaws, was used to describe the endurance limit.