Aspects of structural degradation in old bridge steels by means of fatigue crack propagation

The paper presents conclusions drawn from studies related to old steel structures, especially those erected on the turn of the 19th century. The objects of interest of the authors were Wroclaw Pomorskie Bridges: the Central Pomorski Bridge and the North Pomorski Bridge (1885, 1930 respectively), as well as the Sand Bridge (1861). The material used for their construction was puddled steel or cast steel. In the course of long operation the steels (especially the puddled one) show susceptibility to degradation processes. In this paper the results of metallographic tests (light microscopy, SEM) and mechanical properties tests (hardness measurement, static tensile test) presenting the state of structural degradation have been presented. Also, the initial study results for the puddled steel coming from the Sand Bridge and concerning development of a fatigue crack have been presented. Basic quantities describing the kinetics of fatigue crack growth have been determined.Досліджено сталі мостів біля Вроцлава (Польща): дві пудлингові, експлуатовані з 1861 і 1885 рр., а також ливарну (1930 р.). Сталі, особливо пудлингові, чутливі до деградаційних процесів, що проявилось у зміні структури і механічних властивостей, найвідчутніше – у зниженні опору втомному росту тріщини.Исследованы стали мостов в районе Вроцлава (Польша): две пудлинговые, эксплуатируемые с 1861 и 1885 гг., а также литейную (1930 г.). Стали, особенно пудлинговые, чувствительны к деградационным процессам, что проявилось как в изменении структуры, так и механических свойств, наиболее значительно – в понижении сопротивления усталостному росту трещин

A new method for complexity determination by using fractals and its applications in material surface characteristics

In this article, a new method for complexity determination by using fractals in combination with an artificial intelligent approach is proposed and its application in laser hardening technology is detailed. In particular, nanoindentation tests were applied as a way to investigate the hardness properties of tool steel alloys with respect to both marginal and relevant changes in laser hardening parameters. Specifically, process duration and temperature were considered, together with nanoindentation, later related to surface characteristics by image analysis and Hurst exponent determination. Three different Machine Learning algorithms (Random Forest, Support Vector Machine and k-Nearest Neighbors) were used and predictions compared with measures in terms of mean, variability and linear correlation. Evidences confirmed the general applicability of this method, based on integrating fractals for microstructure analysis and machine learning for their deep understanding, in material science and process engineering

Kinetics of fatigue crack growth and crack paths in the old puddled steel after 100-years operating time

The goal of the authors’ investigations was determination of the fatigue crack growth in fragmentsof steel structures (of the puddled steel) and its cyclic behavior. Tested steel elements coming from the turn ofthe 19th and 20th were gained from still operating ancient steel construction (a main hall of Railway Station,bridges etc.). This work is a part of investigations devoted to the phenomenon of microstructural degradationand its potential influence on their strength properties. The analysis of the obtained results indicated that thoselong operating steels subject to microstructure degradation processes consisting mainly in precipitation ofcarbides and nitrides inside ferrite grains, precipitation of carbides at ferrite grain boundaries and degenerationof pearlite areas [1, 2]. It is worth noticing that resistance of the puddled steel to fatigue crack propagation inthe normalized state was higher. The authors proposed the new kinetic equation of fatigue crack growth rate insuch a steel. Thus the relationship between the kinetics of degradation processes and the fatigue crack growthrate also have been shown. It is also confirmed by the materials research of the viaduct from 1885, which hasnot shown any significant changes in microstructure. The non-classical kinetic fatigue fracture diagrams (KFFD)based on deformation (??) or energy (?W) approach was also considered. In conjunction with the results oflow- and high-cycle fatigue and gradual loss of ductility as a consequence (due to the microstructuraldegradation processes) - it seems to be a promising construction of the new kinetics fatigue fracture diagramswith the energy approach

Fatigue tests of materials with the controlled energy parameter amplitude

Abstract The paper presents a procedure of the determination of the fatigue energy characteristic diagram by using a controlled strain energy parameter which can be an alternative to the well-known stress and strain fatigue curves description of structural materials. The work contains the results of fatigue tests carried out in accordance with the procedure shown in the paper. Obtained test results were presented on diagrams and critically discussed

A matched-pair cluster design study protocol to evaluate implementation of the Canadian C-spine rule in hospital emergency departments: Phase III

BACKGROUND: Physicians in Canadian emergency departments (EDs) annually treat 185,000 alert and stable trauma victims who are at risk for cervical spine (C-spine) injury. However, only 0.9% of these patients have suffered a cervical spine fracture. Current use of radiography is not efficient. The Canadian C-Spine Rule is designed to allow physicians to be more selective and accurate in ordering C-spine radiography, and to rapidly clear the C-spine without the need for radiography in many patients. The goal of this phase III study is to evaluate the effectiveness of an active strategy to implement the Canadian C-Spine Rule into physician practice. Specific objectives are to: 1) determine clinical impact, 2) determine sustainability, 3) evaluate performance, and 4) conduct an economic evaluation. METHODS: We propose a matched-pair cluster design study that compares outcomes during three consecutive 12-months "before," "after," and "decay" periods at six pairs of "intervention" and "control" sites. These 12 hospital ED sites will be stratified as "teaching" or "community" hospitals, matched according to baseline C-spine radiography ordering rates, and then allocated within each pair to either intervention or control groups. During the "after" period at the intervention sites, simple and inexpensive strategies will be employed to actively implement the Canadian C-Spine Rule. The following outcomes will be assessed: 1) measures of clinical impact, 2) performance of the Canadian C-Spine Rule, and 3) economic measures. During the 12-month "decay" period, implementation strategies will continue, allowing us to evaluate the sustainability of the effect. We estimate a sample size of 4,800 patients in each period in order to have adequate power to evaluate the main outcomes. DISCUSSION: Phase I successfully derived the Canadian C-Spine Rule and phase II confirmed the accuracy and safety of the rule, hence, the potential for physicians to improve care. What remains unknown is the actual change in clinical behaviors that can be affected by implementation of the Canadian C-Spine Rule, and whether implementation can be achieved with simple and inexpensive measures. We believe that the Canadian C-Spine Rule has the potential to significantly reduce health care costs and improve the efficiency of patient flow in busy Canadian EDs

Probabilistic Fatigue Crack Initiation and Propagation Fields Using the Strain Energy Density

Recently, Huffman developed a strain energy density based on Walker-like stress life and fatigue crack growth behavior. In this paper, the Huffman model based on local strain energy density is used to predict the fatigue crack initiation and propagation for the P355NL1 pressure vessel steel. This model is combined with the generalized probabilistic fatigue model proposed by Correia aiming the generation of probabilistic fatigue crack initiation and propagation fields. In this study, the local stress and strains at the crack tip were obtained combining linear-elastic and elastoplastic analyses. The probabilistic fatigue crack growth rates fields for several stress R-ratios are estimated considering strain, SWT and equivalent stress amplitude damage parameters. A comparison between the experimental fatigue crack growth (FCG) data and the generated probabilistic FCG fields is made with very satisfactory correlations being found.В настоящее время Хаффман разработал концепцию плотности энергии деформации, основанную на циклической долговечности и развитии усталостной трещины по типу Волкера. Модель Хаффмана, базирующаяся на локальной плотности деформации, используется для прогнозирования инициирования и распространения усталостной трещины в стали P355NL1, применяемой в сосудах высокого давления. Данная модель сочетается с обобщенной вероятностной моделью усталости, ранее предложенной одним из соавторов, суть которой состоит в генерации вероятностных полей инициирования и распространения усталостных трещин. Получены локальные напряжения и деформации в вершине трещины, объединяющие их линейно-упругие и упругопластические составляющие. Для нескольких значений коэффициента асимметрии цикла напряжений R оценены вероятностные поля скоростей роста усталостных трещин с учетом параметров повреждения, параметра Смита–Ватсона–Топпера (SWT) и эквивалентных параметров амплитуды напряжения. Сравнение экспериментальных данных по приращению усталостной трещины с прогнозируемыми вероятностными полями ее роста показывает их тесную корреляцию.На сьогодні Хаффман розробив концепцію густини енергії деформації на основі циклічної довговічності і поширення тріщини від утомленості по типу Волкера. Модель Хаффмана, що базується на локальній густині енергії деформації, використовується для прогнозування ініціювання і поширення тріщини від утомленості в сталі P355NL1, яка використовується для виготовлення посудин високого тиску. Дана модель поєднується з узагальненою імовірнісною моделлю утоми, раніше запропонованою одним із співавторів, суть якої полягає в генерації імовірнісних полів ініціювання і поширення тріщин від утомленості. Отримано локальні напруження і деформації у вершині тріщини, що об’єднують їх лінійно-пружні і пружнопластичні складові. Для декількох значень коефіцієнта асиметрії циклу напружень R оцінено імовірнісні поля швидкостей росту тріщин від утомленості з урахуванням параметрів пошкодження, параметра Сміта–Ватсона–Топпера (SWT) й еквівалентних параметрів амплітуди напруження. Порівняння експериментальних даних щодо приросту тріщини від утомленості з прогнозованими імовірнісними полями її росту свідчить про їх тісну кореляцію

Fatigue crack propagation prediction of a pressure vessel mild steel based on a strain energy density model

Fatigue crack growth (FCG) rates have traditionally been formulated from fracture mechanics, whereas fatigue crack initiation has been empirically described using stress-life or strain-life methods. More recently, there has been efforts towards the use of the local stress-strain and similitude concepts to formulate fatigue crack growth rates. A new model has been developed which derives stress-life, strain-life and fatigue crack growth rates from strain energy density concepts. This new model has the advantage to predict an intrinsic stress ratio effect of the form ?ar=(?amp)?·(?max )(1-?), which is dependent on the cyclic stress-strain behaviour of the material. This new fatigue crack propagation model was proposed by Huffman based on Walkerlike strain-life relation. This model is applied to FCG data available for the P355NL1 pressure vessel steel. A comparison of the experimental results and the Huffman crack propagation model is made

High risk clinical characteristics for subarachnoid haemorrhage in patients with acute headache: prospective cohort study

Objective To identify high risk clinical characteristics for subarachnoid haemorrhage in neurologically intact patients with headache