Set-up of a Generalized Dataset for Crack-Closure-Mechanisms of Cast Steel

In components, crack propagation is subjected to crack-closure-mechanisms which affect the build-up of the relevant threshold stress intensity factor range during cyclic loading. As structural parts are exposed to service loads incorporating a variety of load ratios, a significant change of the long-crack threshold value occurs, leading to a severe stress ratio dependency of crack-closure-mechanisms. Thus, an extensive number of crack propagation experiments is required to gain statistically proven fracture mechanical parameters describing the build-up of closure effects as crack growth resistance curves.The article presents a generalized dataset to assess the formation of crack-closure-mechanisms of cast steel G21Mn5+N. Numerous crack propagation experiments utilizing single edge notched bending (SENB) sample geometries are conducted, incorporating alternate to tumescent stress ratios. The statistically derived, generalized crack growth resistance curve features the impact of closure effects on the crack propagation rate in a uniform manner. To extend the dataset to arbitrary load ratios, the long-crack threshold approach according to Newman is invoked. The generalized dataset for the cast steel G21Mn5+N is validated by analytical fracture mechanical calculations for the utilized SENB-sample geometries. Incorporating a modified NASGRO equation, a sound correlation of analytical and experimental crack propagation rates is observed. Moreover, the derived master crack propagation resistance curve is implemented as a user-defined script into a numerical crack growth calculation tool and supports a local, node--based numerical crack propagation study as demonstrated for a representative SENB-sample. Concluding, the derived dataset facilitates the calculation of fatigue life of crack-affected cast steel components subjected to arbitrary stress ratios.

Poisoning Effect of CO: How It Changes Hydrogen Electrode Reaction and How to Analyze It Using Differential Polarization Curve

The hydrogen electrode reaction (HER) on Pt electrode in a H2SO4 solution when CO gas was injected/stopped was studied using polarization resistance curve [...]

Quantification of the Complex Crack Geometry Effect On Fracture Resistance Using Strain Based FE Damage Analysis

This paper examines the effect of complex crack geometry on the J-resistance curves obtained by strain-based ductile tearing simulation of complex cracked tension (CC(T)) specimens. The damage model is determined by analyzing the results of a smooth bar tensile test and a C(T) specimen toughness test on an SA508 Gr.1a low-alloy steel at 316 ?. The validity of the damage model and simulation method is checked by comparing the fracture test data for two CC(T) specimen tests. To investigate the effect of the complex crack geometry on the crack growth profiles and J-resistance curves, two geometric parameters (namely, the through-wall crack length and the surface crack depth) are systematically varied. It is found that the J-resistance curves for the CC(T) specimens with various through-wall crack lengths and surface crack depths are consistently lower than the corresponding 1T C(T) J-resistance curves. The effect of the through-wall crack length upon the J-resistance curve is found to be less significant than that of the surface crack depth. Moreover, the J-resistance curve decreases continuously with increasing surface crack depth.

Calculation of the residual resistance of the vessel according to the theoretical drawing

В статье впервые дан метод расчета остаточного сопротивления водоизмещающих судов не по параметрам, а по ординатам теоретического чертежа. Необходимость определения сопротивления воды движению судна возникает на первой же стадии при проектировании корпуса. Достоверную кривую сопротивления получают только путём дорогостоящих буксировочных испытаний, поэтому возможность расчета такой кривой является одной из самых актуальных задач проектирования, решению которой посящены сотни работ. В статье вкратце приводится вековая история поисков метода расчета сопротивления воды движению судна. В статье описаны полученные автором три фундаментальные решения, позволившие, в конце концов, решить эту задачу. Первое решение - это разделение интеграла Мичелла на главную и интерференционную части. Второе – это объяснение гидродинамики создаваемого судном потока и доказательство необходимости учета сдвига подпорными волнами носовой Кельвиновской волновой системы. Третье решение, которому посвящена данная статья, заключается в теоретическом и экспериментальном доказательстве того, что на малых и средних числах Фруда расчет главной части интеграла Мичелла даёт кривую, которая проходит близко к экспериментальной кривой остаточного сопротивления, что позволяет использовать её на практике. В конце статьи приводятся результаты сравнения расчетов с экспериментом для 28-ми моделей. Показано также, что практически нельзя считать интеграл Мичелла по ординатам теоретического чертежа, и приводится метод аппроксимации ватерлиний и шпангоутов с помощью одной кривой,– разработанной для этой цели - «корабельной верзиерой» This article presents the first description of the obtained method for calculating the residual resistance of displacement vessels not by parameters, but by ordinates of a theoretical drawing. The need to determine the resistance of water to the movement of the vessel arises at the very first stage of the hull designing. Usually a reliable resistance curve is obtained only through expensive towing tests, therefore the ability to calculate such a curve is one of the most urgent design problems, the solution of which is devoted to hundreds of works. This article briefly describes the centuries-old history of searching for a method for calculating the resistance of water to the movement of a vessel. The article describes three fundamental solutions obtained by the author, which have allowed to solve this problem. The first solution is the partition of the Michell integral into the main and interference parts. The second is the explanation of the hydrodynamics of the flow created by the vessel, and the proof of the necessity to take into account the shift by the retaining waves of the bow Kelvin wave system. The third solution, to which this article is devoted, consists in the theoretical and experimental proof that, at low and medium Froude numbers, the calculation of the main part of the Michell integral provides the curve which passes so close to the experimental residual resistance curve, that it is possible to use it in practice. At the end of the article, the results of comparing calculations with experiment for 28 models are presented. It is also shown that it is impossible to calculate the Michell integral according to the ordinates of the theoretical drawing, and the method of approximating waterlines and frames with the help of a single curve is presented - a "ship's versier" developed for this purpose.

Influence of Small Volumetric Flaws on the Measurement of Crack Growth and Tearing Resistance in SENT Tests

This study evaluates the influence of volumetric discontinuities on the SENT tearing resistance curve as measured using DCPD and UC techniques. In order to do that, a series of SENT tests was carried out on specimens containing small drilled holes in different locations to simulate the presence of volumetric weld flaws. In addition, porous welds were produced by robotic Gas Metal Arc Welding (GMAW). Welding parameters were fine-tuned in order to obtain specimens with different porosity levels. Afterward, the pores were characterized by means of X-ray Computed Tomography (CT) scans and their position, shape and location were determined. SENT tests were performed in a servo-hydraulic machine using a double clip gauge set up to measure crack opening and DCPD and UC for crack sizing. The results indicated that volumetric discontinuities can influence the accuracy of crack measurement techniques in particular, and the measured resistance curve as a whole.

Effect Range of the Material Constraint in Different Strength Mismatched Laboratory Specimens

Different strength mismatched laboratory specimens that contain the compact tension (CT), single edge-notched tensile (SENT), and central-cracked tension (CCT) specimens with various specimen geometries, loading configurations, and initial cracks were selected to investigate the effect range of the material constraint systematically. The results showed that the effect range of material constraint exists in all the strength mismatched specimens and structures. The numerical value of the effect range is influenced by the geometry constraint. The high geometry constraint reduces the effect range of material constraint. When a material is located outside the effect range of material constraint, the fracture resistance curves and crack propagation paths of the specimens and structures are no longer influenced by the mechanical properties of the material. In addition, an interaction exists between the geometry constraint and material constraint. The high geometry constraint strengthens the effect of material constraint, whereas the fracture resistance curve and crack propagation path are insensitive to the material constraint under the low geometry constraint. The results in this study may provide scientific support for the structure integrity assessment and the design of strength mismatched structures.