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Wyniki wyszukiwania dla: fracture

Michał Wasilczuk prof. dr hab. inż.
OsobyMichał Wasilczuk, absolwent Wydziału Budowy Maszyn Politechniki Gdańskiej (1986), a obecnie profesor zwyczajny na Wydziale Mechanicznym PG i kierownik Katedry Konstrukcji Maszyn i Pojazdów od początku swojej działalności naukowej zajmuje się hydrodynamicznymi łożyskami wzdłużnymi oraz, szerzej inżynierią łożyskowania, w ramach zespołu naukowego stworzonego przez doc. Olgierda Olszewskiego. Od kilkunastu lat zespół specjalizuje...

Estimation of fracture toughness and shear yield stress of orthotropic materials in cutting with rotating
PublikacjaThe cutting force is an energetic effect of splitting material, and might be considered from a point of view of modern fracture mechanics. Forecasting of the shear plane angle in cutting broaden possibilities for modelling of the cutting process even for thin uncut chips. Such mathematical model has been developed here for description of the orthotropic materials’ cutting on the base of fracture theory, and includes work of separation...

Reliable method of assessing fracture properties of asymmetric bonded joints
PublikacjaTwo methods of assessing fracture properties of adhesive joints were studied. Two wedge tests: with continuous deflection and with force measurements were compared. Asymmetric geometry of the bonded joint was considered, i.e. two different plates of aluminium alloys: AlCu and AlMg, were bonded with epoxy DGEBA adhesive. The analytical model is shown to estimate the values of fracture properties: crack position and critical fracture...

Toughness augmentation by fibrillation and yielding in nanostructured blends with recycled polyurethane as a modifier
PublikacjaIn the present paper, we have carefully investigated the morphology and fracture mechanism of the recycled polyurethane (RPU) /epoxy blend system. The second phase (RPU) added to the epoxy resin has a positive effect on the overall mechanical properties. Interestingly, the recycled polymer has a remarkable effect on the fracture toughness of epoxy resin. The mechanism behind the fracture toughness improvement up on the addition...

Impact of interface heterogeneity on joint fracture
PublikacjaThe effects of heterogeneities (weak zones in particular) inadhesive joints and their importance on overall fracture propertiesare relatively unknown, but doubtlessly they may be crucial inmany applications. Using a model heterogeneous adhesive bond,represented by a given mixture of regions of strong and weakadhesion, we have studied the influence of interface variabilityon overall fracture energy (global energy release rate)....

Sawing Processes as a Way of Determining Fracture Toughness and Shear Yield Stresses of Wood
PublikacjaA new computational model, based on fracture mechanics, was used to determine cutting forces. Unlike traditional computing methods, which depend on many coefficients reflecting the machining of solid wood, the new model uses two main parameters: fracture toughness and shear yield stresses. The aim of this study was to apply this new method to determine these parameters for the tooth cutting edge principal positions and longitudinal...

SAWING PROCESS AS A NEW ALTERNATIVE WAY OF DETERMINING SOME WOOD PROPERTIES
PublikacjaCutting forces (power) could be considered from a point of view of modern fracture mechanics. The developed cutting model, derived from fracture mechanics, includes work of separation (fracture toughness) in addition to plasticity and friction, and also dullness of the cutting edge described by the cutting edge radius. Moreover, forecasting of the shear plane angle for the cutting models, broaden possibilities of energetic effects...

Twodimensional simulations of concrete fracture at aggregate level with cohesive elements based on Xray
PublikacjaThe paper presents results of twodimensional mesoscale simulations of fracture in notched concrete beams subjected to threepoint bending test. Concrete was assumed as a 4phase material composed of aggregate grains placed in the cement matrix, interfacial transitional zones (ITZs) and macrovoids. The particle distribution was taken from real concrete beams on the basis of Xray lCT images. Comprehensive numerical analyses were carried...

AN ALTERNATIVE WAY OF DETERMINING MECHANICAL PROPERTIES OF WOOD BY MEASURING CUTTING FORCES
PublikacjaThe cutting force is an energetic effect of splitting material, and might be therefore considered from a point of view of modern fracture mechanics. The dedicated mathematical model developed for description of the wood cutting has been developed here on the base of fracture theory, and includes work of separation (fracture toughness) in addition to the material plasticity and friction. The effect of the cutting edge dullness is...

Fracture simulations in concrete beam under bending using a mesoscopic model with cohesive elements
PublikacjaThe main aim of this paper was to investigate a complex fracture process in a concrete beam subjected to 3point bending test by means of the 2D mesoscale FEM with 4node cohesive elements embedded in the initial mesh of 3node solid elements. The material heterogeneity was taken into account by considering 3 different phases (aggregate, cement matrix, ITZs) on the basis of randomly generated internal structure of concrete and...

Jakub Kowalski dr inż.
Osoby 
Scientific Mission within COST Action FP1101: development of the infield sensor for estimation of fracture
PublikacjaKnowledge on the fracture properties of materials is essential to assure structural integrity and proper design of mechanical connections in timber constructions. Measurement of this property is, however, a very challenging task. The linear fracture mechanics is usually used for its assessment assisted with experimental data acquired by means of various techniques, usually of destructive nature. The cutting force is an energetic...

MODELLING OF CONCRETE FRACTURE AT AGGREGATE LEVEL USING DEM BASED ON XRAY mu CT IMAGES OF INTERNAL STRUCTURE
PublikacjaThe paper describes twodimensional mesoscale numerical results of fracture in notched concrete beams under quasistatic threepoint bending. Concrete was modelled as a random heterogeneous 4phase material composed of aggregate particles, cement matrix, interfacial transitional zones (ITZs) and air voids. As a numerical approach, the discrete element method (DEM) was used. The concrete microstructure in calculations was directly...

Numerical simulation of asphalt mixtures fracture using continuum models
PublikacjaThe paper considers numerical models of fracture processes of semicircular asphalt mixture specimens subjected to threepoint bending. Parameter calibration of the asphalt mixture constitutive models requires advanced, complex experimental test procedures. The highly nonhomogeneous material is numerically modelled by a quasicontinuum model. The computational parameters are averaged data of the components, i.e. asphalt, aggregate...

Fracture in composite/aluminium joints of variable adhesive properties
PublikacjaA strain gauge technique recently developed with the wedge test, for estimating crack length and, thus, the fracture energy of structural adhesive bonding, has been employed on a system in which one adherend had two types of surface treatment. Simple polishing and polishing with subsequent sandblasting were the treatments used, with a distinct straight line, perpendicular to the sample edges, separating the two. Despite the clearcut...

Metal implants in ostheosynthesis  construction solutions, materials and applications
PublikacjaThe aim of the article is to present two case studies on intramedullary nails. The research included the evaluation of the type of fracture and the analysis of microstructure, chemical composition and hardness of the implant material.

Jacek Chróścielewski prof. dr hab. inż.
Osoby 
Distinctive properties of Scots pine (Pinus sylvestris L.) originating from the Carpathian and Great PolandPomeranian of Nature and Forest Land
PublikacjaIn this paper values of properties of Scots pine, the fracture toughness and of shear yield stress in the shear zone are presented. Samples of Scotch pine (Pinus sylvestris L.) wood of two provenances from Poland were tested. These properties were determined from the values of cutting power obtained experimentally on the saw frame PRW15M. The values of fracture toughness and shear yield stress based on the Atkins model for cutting...

SHEAR YIELD STRESSES AND FRACTURE TOUGHNESS OF SCOTS PINE (PINUS SYLVESTRIS L.)
PublikacjaIn this paper values of the fracture toughness and of shear yield stress in the shear zone of Scots pine are presented. Tests of cutting were carried on samples of Scotch pine (Pinus sylvestris L.) wood of five provenances from Poland. These experimentally cutting tests were carried on the sash gang saw PRW15M and the values of cutting power were obtained. The values of fracture toughness and shear yield stress based on Atkins’s...

ENGINEERING FRACTURE MECHANICS
Czasopisma 
A newlydeveloped model for predicting cutting power during wood sawing with circular saw blades
PublikacjaIn the classical approach, cutting forces and cutting power in sawing processes of orthotropic materials such as wood are generally calculated on the basis of the specific cutting resistance kc (cutting force per unit area of cut). For every type of sawing kinematics (frame saws, band saws and circular sawing machines) different empirical values of specific cutting resistance kc have to be applied. It should be emphasised that...

Investigations on strength and fracture in RC beams scaled along height or length
PublikacjaThe objective of the present paper is to identify experimentally and theoretically differing failure mechanisms in reinforced concrete beams subjected to fourpoint bending for a separate variation of the depth and length at the constant thickness. Experiments were performed on reinforced concrete beams under fourpoint bending. Different failure mechanisms included steel yielding, diagonal tension or shear compression depending...

Meso‐scale analyses of size effect in brittle materials using DEM
PublikacjaThe paper describes numerical mesoscale results of a size effect on strength, brittleness and fracture in brittle materials like concrete. The discrete element method (DEM) was used to simulate the size effect during quasistatic splitting tension with the experimentalbased mesostructure. The twodimensional (2D) calculations were carried out on concrete cylindrical specimens with two diameters wherein two different failure...

The statistical impact of experimental result scatter of asphalt mixtures on their numerical modelling
PublikacjaThe paper presents selected test results of asphalt mixture conducted in low temperatures. The obtained parameters are highly diverse. It concerns ultimate breaking loads, stiffness parameters related to Young's modulus but also the fracture course. Statistical analysis upon the results makes it possible to relevantly estimate the materialdefining parameter values. Such a random approach leads to the mean values of breaking and...

An in situ technique for the assessment of adhesive properties of a joint under load
PublikacjaSlow crack propagation in adhesive bonded joints has been characterised using an asymmetric wedge test. Crack position was evaluated from strain gauge measurements, both in the debonded partof the joint and in the bonded zone. Test temperature was changed during loading, giving insight into bond evolution. The technique allows accurate, and virtually continuous, determination of crack position to be made, and therefore the evaluation...

Fracture Toughness and Shear Yield Strength Determination for Two Selected Species of Central European
PublikacjaWhen offcut of wood is formed by shearing, Atkins’s analyses of sawing processes can be applied. Using this modern approach, it is possible to determine the fracture toughness and shear yield strength of wood. This model is only applicable for the axialperpendicular cutting direction because both of these parameters are suitable for the given direction of cutting edge movement and cannot be considered material constants. Alternatively,...

THE EFFECT OF NOTCH DEPTH ON CTOD VALUES IN FRACTURE TESTS OF STRUCTURAL STEEL ELEMENTS
PublikacjaIn elements of steel structures working at low temperatures, there is a risk of appearance of brittle fracture. This risk is reduced through the use of certified materials having guaranteed strength at a given temperature. A method which is most frequently used to determine brittle fracture toughness is the Charpy impact test, preformed for a given temperature. For offshore structures intended to work in the arctic climat e, the...

Analisys of the failure of fixator used in bone surgery
PublikacjaThe Gamma nail (fixator) made of stainless steel, which has broken in the body, was subjected to examination. The fixator was removed from the patient femur. The fracture occurred in the area of the nail hole after two months' stay in the organism. The research included chemical composition, hardness of the Gamma nail material and the observation and analysis of the type of fracture. The research showed the fatigue failure of the...

Experimental Investigations of Fracture Process Using DIC in Plain and Reinforced Concrete Beams under
PublikacjaThe fracture behaviour of concrete and reinforced concrete beams under quasistatic threepoint bending was comprehensively investigated with experiments at laboratory scale. The eight various concrete mixes were tested. The influence of the shape, volume and size of aggregate particles and reinforcement on concrete fracture under bending was studied. Displacements on the surface of concrete beams were measured by means of the...

Empirical verification in industrial conditions of fracture mechanics models of cutting power prediction
PublikacjaA comparison of experimental results obtained in the industrial conditions at a sawmill located in the Baltic Natural Forest Region (PL) and theoretical cutting power consumption forecasted with the models which include work of separation (fracture toughness) in addition to plasticity and friction has been described. In computations of cutting power consumption during rip sawing of Scots pine wood (Pinus sylvestris L.) values of...

Beam on elastic foundation with anticlastic curvature: Application to analysis of mode I fracture tests
PublikacjaA first order correction is proposed taking into account both interface elasticity and transverse anticlastic curvature of flexible substrate(s) in the DCB (and related tests). Adherends are represented by KirchhoffLove plates, and the interface by Winklertype elastic foundation. Two functions are introduced, representing evolution of beam deflection along the sample midline and anticlastic curvature along the plate. A method...

Fracture mechanics model of cutting power versus widespread regression equations while wood sawing with
PublikacjaA comparison of the theoretical cutting power consumption results forecasted with the model (FM_CM model) which include work of separation (fracture toughness) in addition to plasticity and friction, and two widespread regression equations while wood sawing with circular saw blades has been described. in and cutting power consumption forecasted. In computations of the cutting power consumption during rip sawing of Scots pine wood...

SIMULATIONS OF FRACTURE IN CONCRETE BEAMS UNDER BENDING USING A CONTINUUM AND DISCRETE APPROACH
PublikacjaThe paper describes twodimensional mesoscale results of fracture in notched concrete beams under bending. Concrete was modelled as a random heterogeneous 4phase material composed of aggregate particles, cement matrix, interfacial transitional zones and air voids. Within continuum mechanics, the simulations were carried out with the finite element method based on a isotropic damage constitutive model enhanced by a characteristic...

Accurate and continuous adhesive fracture energy determination using an instrumented wedge test
PublikacjaThe wedge test and the related double cantilever beam test are practical methods of assessing structural adhesive fracture energy. In the former, and to a lesser extent the latter, a recognised problem is the difficulty of following the length of the growing crack, required to calculate fracture energy with any accuracy. We present a novel method of measurement of crack length that has the advantages of being accurate and allowing...

Modelling of cutting by means of fracture mechanics
PublikacjaThe suitability of modern fracture mechanic theory was proved for the estimation of the cutting force and the cutting specific resistance. This paper shows modification of ErnstMerchant theory and its application for determination some other properties of wood sample. This theory is acceptable for evaluation of shear yield stresses and shear plane angle. Sawing by gang saw machine was used as a process similar to the orthogonal...

MODELLING OF CUTTING BY MEANS OF FRACTURE MECHANICS
PublikacjaThe suitability of modern fracture mechanic theory was proved for the estimation of the cutting force and the cutting specific resistance. This paper shows modification of ErnstMerchant theory and its application for determination some other properties of wood sample. This theory is acceptable for evaluation of shear yield stresses and shear plane angle. Sawing by gang saw machine was used as a process similar to the orthogonal...

A threedimensional mesoscale approach with cohesive elements to concrete fracture based on Xray μCT
PublikacjaArtykuł omawia wyniki numeryczne dotyczące pękania betonu uzyskane stosując trójwymiarowy model mezoskopowy z elementami kohezyjnymi. Obliczenia trójwymiarowe zostały wykonane dla zginanej belki betonowej. Beton został opisany jako model 3fazowy. Mikrostruktura betonu odpowiadała zdjęciom tomograficznym. Wyniki numeryczne zostały porównane z wynikami doświadczalnymi. Uzyskano b. dobra zgodność między wynikami numerycznymi i doświadczalnymi.

EXPERIMENTAL AND NUMERICAL INVESTIGATIONS OF CONCRETE BEHAVIOUR AT MESOLEVEL DURING QUASISTATIC SPLITTING TENSION
PublikacjaThe paper describes experimental and numerical results of quasistatic splitting tensile tests on concrete specimens at mesoscale level. The loading strip was made of plywood or steel. Fracture in concrete was detected at the aggregate level by means of three nondestructive methods: 3D xray microcomputed tomography, 2D scanning electron microscope and manual 2D digital microscope. The discrete element method was used to directly...

Methodology for determination of the selected mechanical properties of wood based on cutting tests
PublikacjaFrom kilndried spruce wood (with steam) as well as in natural conditions were randomly selected 8 samples. After determining the average dimensions, moisture content and density of the samples they have been cut on the frame sawing machine PRW15M for measurement of cutting power. Based on those results from a linear relationship of cutting power versus feed per toot mechanical properties of wood such as facture toughness and...

CUTTING POWER FORECASTING WHILE WOOD SAWING: FRACTURE MECHANICS APPROACH AND AXELSSON’S MODEL COMPARISON
PublikacjaIn the classical approach, energetic effects (cutting forces and cutting power) of wood sawing process are generally calculated on the basis of the specific cutting resistance, which is in the case of wood cutting the function of more or less important factors. On the other hand, cutting forces (power) could be considered from a point of view of modern fracture mechanics. Another way is to forecast cutting power consumption on...

Modelling of concrete fracture at aggregate level using FEM and DEM based on Xray uCT images of internal
PublikacjaArtykuł podejmuje problem pękania w zginanych belkach betonowych. Proces pękania był obserwowany przy zastosowaniu mikrotomografii . Zaobserwowany proces był symulowany numerycznie przy zastosowaniu metody elementów skończonych i metody elementów dyskretnych. Beton był opisany jako materiał 4fazowy. Otrzymano dobrą zgodność wyników numerycznych z doświadczalnymi.

Dynamics of cutting power during sawing with circular saw blades as an effect of wood properties changes in the cross section
PublikacjaIn the paper the effect of the method calculation upon the cutting power is presented. In computations were used models in which fracture toughness was incorporated. The comparison concerned models as follows: FMCM – classic model in which the sum of all uncut chip thicknesses of the simultaneously teeth engaged represented the mean uncut chip thickness, FMFDM – full dynamical model in which besides variable uncut chip thickness...

Fracture in Asymmetric Bonded Joints
PublikacjaAdhesion was studied in asymmetric bonded joints using fracture mechanics tests. The asymmetric bonded joints consist of two different type and/or thickness materials bonded by an adhesive. Mentions of asymmetric bonded joint tests employed so far are rare in the literature. They are imperfect and therefore are not standardized. Accordingly three new tests were introduced in this work to study bonded joints. The new metrological...

Effect of adhesive compliance in the assessment of soft adhesives with the wedge test
PublikacjaWedge tests are usually analysed assuming that the free, unbonded members may be treated as encastré cantilever beams. However, if the adhesive layer is sufficiently flexible (e.g., due to low elastic modulus), then significant strain in the bonded region may occur and lead to modification of the behaviour outside this region. Using in conjunction a sensitive strain gauge method on asymmetric wedge tests and a mathematical analysis...

Application of fracture mechanics for energetic effects predictions while wood sawing
PublikacjaIn the classical approach, energetic effects (cutting forces and cutting power) of wood sawing process are generally calculated on the basis of the specific cutting resistance, which is in the case of wood cutting the function of more or less important factors. On the other hand, cutting forces (power) could be considered from a point of view of modern fracture mechanics. Cutting forces may be employed to determine not only toughness...

Mesoscopic simulations of crack propagation in concrete using cohesive elements
PublikacjaThe paper presents results of twoand threedimensional mesoscale simulations of fracture in notched concrete beams subjected to threepoint bending test. Concrete was assumed as a 3phase material composed of aggregate grains placed in the cement matrix with Interfacial Transitional Zones (ITZs) between then. In 2D simulations macrovoids were also taken into account. The particle distribution was taken from real concrete beams...

Antagonist adhesion effects due to variable substrate surface
PublikacjaThe effects of variability of intrinsic adhesion within a joint have been studied using a single cantilever beam (SCB) test. Fracture energy was found not to be a simple function of relative areas of 2 surface pretreatments: a 'weak' zone decreased strength more than expected from simple, additive considerations. By severing the adhesive along the strongweak transition, fracture energy increased.The prior antagonist effect appears...

On the crack front curvature in bonded joints
PublikacjaStandard tests of adhesively bonded specimens are likely to produce heterogeneous stress distribution along the crack front and its vicinity. High separation rate mode I dominated fracture test is performed.Observation of post mortem fractured surfaces with an optical microscope reveals characteristic features of mixed mode I/III fracture near the sides of the specimen but not in the middle. At first, finite elements calculations...

Application of Fracture Mechanics for Energetic Effects Predictions While Wood Sawing
PublikacjaIn the classical approach, energetic effects (cutting forces and cutting power) of wood sawing process are generally calculated on the basis of the specific cutting resistance, which is in the case of wood cutting the function of more or less important factors. On the other hand, cutting forces (or power  more interesting from energetic point of view) could be considered from a point of view of modern fracture mechanics. Cutting...

Simulations of hydrofracking in rock mass at mesoscale using fully coupled DEM/CFD approach
PublikacjaThe paper deals with twodimensional (2D) numerical modelling of hydrofracking (hydraulic fracturing) in rocks at the mesoscale. A numerical model was developed to characterize the properties of fluiddriven fractures in rocks by combining the discrete element method (DEM) with computational fluid dynamics (CFD). The mechanical behaviour of the rock matrix was simulated with DEM and the behaviour of the fracturing fluid flow...