Staff

Abstract:
The aim of this research was to compare the effect of 80 000 h exploitation time in high temperature on mechanical properties and microstructure of X10CrMoVNb9-1 (P91) power engineering steel for pipes. The specimens obtained from two pipes: new, as-received and after exploitation were subjected to fatigue loadings to compare their mechanical responses. Additionally, the uniaxial tensile tests on both types of P91 steel were performed. The microstructure evolution before and after deformation was monitored using optical and scanning electron microscopy. The time intensive, high temperature exposure of P91 power engineering steel led to significant phase transformation and subsequent deterioration of mechanical properties and was further described as a function of the fatigue damage measure, φ, and the fatigue damage parameter D. Further proposed methodology of power exponent approximation of the fatigue damage measure, φ, and fatigue damage parameter D, allowed to successfully determine the fatigue life of P91 steel.

Keywords:
fatigue development, damage, P91 steel, microstructure

Abstract:
The aim of this study was to investigate the effect of plasterboards' humidity absorption on their performance. Specimens' hydration procedure consisted of consecutive immersing in water and subsequent drying at room temperature. Such a procedure was performed to increase the content of moisture within the material volume. The microstructural observations of five different plasterboard types were performed through optical and scanning electron microscopy. The deterioration of their properties was evaluated by using a three-point bending test and a subsequent ultrasonic (ultrasound testing (UT)) longitudinal wave velocity measurement. Depending on the material porosity, a loss of UT wave velocity from 6% to 35% and a considerable decrease in material strength from 70% to 80% were observed. Four types of approximated formulae were proposed to describe the dependence of UT wave velocity on board moisture content. It was found that the proposed UT method could be successfully used for the on-site monitoring of plasterboards' hydration processes.

Keywords:
plasterboards, moisture content, hydration processes, mechanical properties, ultrasound measurements

Abstract:
Two types of composites, consisting of pure magnesium matrix reinforced with two commercially used carbon fibers, were systematically studied in this paper. The composites fabricated by the pressure infiltration method, were subjected to quasistatic and dynamic compression tests. Morphology of fiber strands was observed using scanning electron microscope (SEM). The application of carbon fibre reinforcement led to the stiffening of tested materials, resulting in the limitation of the possible compression to approx. 2.5%. The performed tests revealed the remarkable difference in compression strength of investigated compositions. The cause of that effect was that GRANOC fiber reinforced composite exhibited insufficient bond quality between the brittle fibers and the ductile matrix. T300 reinforced composite presented good connection between reinforcement and matrix resulting in increased mechanical properties. Investigated composites demonstrated higher mechanical strength during deformation at high strain rates. Microscopic observations also proved that the latter fibers with regular shape and dense packaging within the filaments are proper reinforcement when designing the lightweight composite material.

Keywords:
Mg matrix composite, compressive properties, carbon fiber, Split-Hopkinson pressure bar

Abstract:
W pracy omówiono przyczyny występowania uszkodzeń i ich rodzaje. Zawarto cechy charakterystyczne przełomów zmęczeniowych w odniesieniu do wskazania przyczyn ich występowania. Zaprezentowano wybrane stanowiska badawcze do testowania podzespołów motoryzacyjnych i ich wersje modułowe – wyposażane w specjalistyczne komory oraz rekonfigurowalne – zawierające gabarytową płytę montażową. Przedstawiono szczegóły testów stanowiskowych komponentów pojazdów specjalnych, jak ramy wychylne oraz stałe, w tym wykonane ze stali wysokowytrzymałej S700MC. Zaprezentowano charakterystyki naprężenie-odkształcenie, parametry mechaniczne oraz krzywe Wöhlera wymienionego rodzaju materiału w stanie dostawy i po spawaniu.

Abstract:
The paper presents experimental results from test on tow truck frame made of the high strength steel S700MC subjected to fatigue loading. The mounting manner of the frame with anti-vibration platform and connection with a coupling ball to apply the loading are presented. Cracks features captured by means of macrophotography and microscopic observations are illustrated. Reasons for the crack occurrence are discussed by the use of fractography, hardness tests, microstructural analysis of the parent material, Heat Affected Zone and weld.

Keywords:
cyclic loading, fatigue, fracture, crack, higth strength steel, hardness, microstructure, welding, HAZ

Abstract:
The paper presents an attempt of application of the acoustic birefringence coefficient for early stage degradation assessment of Inconel 718 nickel superalloy after short-term creep. It is shown that it can serve as a good damage sensitive parameter and, moreover, it can be well correlated with hardness variation.

Keywords:
creep, nickel superalloy, microstructure, pre-deformation, hardness, acoustic birefringence

Abstract:
The paper reports the results of tests carried out for kinematic properties determination of components under cyclic loading. DIC system called 5M PONTOS was employed to follow variations of displacement versus time. It was conducted by the use of markers stuck on selected sections of components tested. The results are presented in 2D and 3D coordinate systems expressing behaviour of such elements as: mechanical coupling device, boat frame and car engine. These data enabled to capture weak and strong sections of the component examined at various loading conditions.

Keywords:
Digital Image Correlation System, Cyclic Loading, PONTOS, Motion, Displacement, 3D Coordinate System

Abstract:
W pracy zaprezentowano wyniki badań trwałościowych końcówki drążka kierowniczego pojazdu o dmc powyżej 3.5 tony. W badaniach wykorzystywano wielkogabarytową platformę wibroizolowaną, serwohydrauliczny siłownik mobilny oraz cyfrowy kontroler sygnałów IST Instron. Próby prowadzono w warunkach działania obciążenia zmiennego cyklicznie do uzyskania 2×106 cykli. Ze względu na kompleksową ocenę zachowania końcówki drążka kierowniczego testy przerywano, by wykonywać oględziny obiektu badań. Wyznaczono zmiany kąta wychylenia oraz momentu siły w funkcji liczby cykli oraz przedstawiono ich prognozę. Omówiono procedurę badawczą służącą ocenie trwałości przegubu kulistego.

Keywords:
przegub, zmęczenie, obciążenie zmienne cyklicznie, liczba cykli, trwałość, pęknięcie

Abstract:
W pracy omówiono technike cyfrowej korelacji obrazu (DIC) przeznaczona do bezkontaktowego okreslania rozkładów składowych przemieszczenia i na ich podstawie obliczania składowych odkształcenia oraz naprezenia. Umozliwia ona równiez wyznaczanie parametrów kinematycznych obiektów inzynierskich w postaci predkosci i przyspieszenia, które okreslane sa metoda rózniczkowania po czasie zarejestrowanych wartosci składowych przemieszczenia. Zaprezentowano polowe zmiany rozkładów odkształcenia wzdłuznego oraz rozkładów składowych głównych odkształcenia podczas rozciagania stali konstrukcyjnej, które monitorowano az do chwili zniszczenia materiału. Przedstawiono wyniki próby porównawczej, w której jednoczesnie stosowano ekstensometr oraz system DIC. Dodatkowo zaprezentowano rezultaty prób stanowiskowych mechanicznego elementu sprzegajacego przeprowadzonych przy uzyciu systemu pomiarów cyfrowych w warunkach oddziaływania cyklicznie zmiennego obciazenia.

Abstract:
The paper reports experimental results from tests carried out at room temperature on servo-hydraulic system dedicated for examination of the exploitation properties of rocker arms. The ball joint of this element was modified by an application of composite coating such as the tungsten carbide (WC). To apply cyclic loading to rocker arms the griping system was designed and elaborated. Results from tests performed on the composite coated ball joints were compared with data obtained for typical elements. Variations of the following parameters versus time i.e. force, temperature and surface topography of balls were analysed with respect to exploitation properties of the modified ball joints. An increase of the wear coefficient was achieved for sliding joints of the steel ball-steel cups coated by the WC.

Keywords:
Ball Joint, Composite, Cyclic Loading, Surface Topography, Tungsten Carbide, Wear

Abstract:
The analysis involved subjecting DP 500 steel to pre-fatigue loads, and then tension at high strain rates using Hopkinson bar. Digital image correlation method was used to investigate how the pre-fatigue loads change the strains’ distribution on the surface of the sample subjected to tension. The analysis involved both films recorded at low rates of deformation (1.0 × 10−2 s−1) using ARAMIS system and the images captured with a high-speed camera during dynamic deformations with a Hopkinson bar (6.0 × 102 s−1). It was noted, based on the micro-structural analysis, that pre-fatigue loads cause the formation of micro-damages in the examined material. Thus, macroscopically observed stress–strain characteristic as well as Huber–Mises substitute strains’ distribution determined locally by the image correlation method is also subject to changes. The observed effects include the following: reduction of deformation corresponding to the tensile strength, decrease in elongation at break, and increase in yield limit and tensile strength. The observed effects are intensified with an increased stress value and pre-fatigue cycles’ number. Furthermore, these phenomena are more intensive in the conditions of dynamic deformation.

Keywords:
Hopkinson bar, fatigue, viscoplastic response, damage, stress–strain, tensile, high strain rate

Abstract:
The paper concerns numerical and experimental investigations carried out for determination of an influence of holes on material behaviour under monotonic tension. The 40Cr steel commonly applied in automotive and power plant branches of industry was tested. The analysis was performed by the use of analytical and Finite Element Method calculations. It enabled identification of stress concentration/maximum stress versus hole diameter relationships, and the HMH stress distribution. Full-field contactless Digital Image Correlation (DIC) system was used for capturing the effective strain variations from the beginning of test up to specimen fracture. It enabled us to indicate the most important stress concentrator, and moreover, distribution of the HMH effective strain in 2D coordinate system. A comparison of tensile characteristic obtained by means of smooth and perforated specimens showed 70% reduction of yield point and 50% lowering of elongation as an effect of the artificial defects introduced.

Keywords:
Monotonic tension, holes, steel, stress concentration factor, maximum stress, yield point, ductility, FEM, DIC

Keywords:
structural components, static loading, markers, displacement, deflection, DIC

Keywords:
mini-specimen CT, fracture toughness, CTOD, fatigue pre-cracking, notch, fracture, parent material, weld, HAZ

Keywords:
cyclic loading, damage evolution, laminate composites

Keywords:
mini-próbka, parametry mechaniczne, rozciąganie, skręcanie, pękanie

Abstract:
The paper reports results of tests focused on determination of kinematic properties of components under cyclic loading. DIC system called 5M PONTOS was employed to follow variations of displacement and velocity versus time. It was conducted by a use of markers stuck on selected sections of components tested. Results are presented in 2D and 3D coordinate systems expressing behaviour of elements such as: car engine, boat frame and mechanical coupling device. These data enable to capture weak and strong sections of the component tested at various loading conditions.

Keywords:
digital image correlation system, cyclic loading, PONTOS, motion, displacement, 3D coordinate system

Abstract:
The paper shows how modern contactless Digital Image Correlation (DIC) method can be implemented for examination of material behaviour under various types of loading. DIC method was used to evaluate material straining under monotonic tension conducted by the use of flat specimens having artificial defects in the form of U and V notches. This technique was also examined during capturing of strain distribution in dynamic tests on Split Hopkinson Pressure Bar. On the basis of DIC results the strain maps at various stages of material deformation were elaborated in order to indicate characteristic features of a material behaviour. It enabled an analysis of damage zone evolution up to specimen fracture.

Keywords:
Digital Image Correlation, specimen, monotonic tension, Split Hopkinson Pressure Bar, strain maps

Abstract:
The paper presents results of numerical and experimental investigations conducted in order to determine an influence of notch type on material behaviour under monotonic tension. Two kinds of specimens having U and V notches were applied. Digital image correlation system was used to detect variations of strain/stress state components from beginning of the test up to fracture of the material in question. Assessments of the results enabled identification of stress concentrations in tips of notches. A comparison of tensile characteristics of unnotched and notched specimens exhibited a great reduction of the yield point independently of the geometrical discontinuities applied. In the case of V-notched specimen 50% lowering of elongation was observed.

Keywords:
stress concentration, stress distribution, notches, tensile curve, digital image correlation