Fracture Curves Research Articles

Research on Interface Critical Fracture of Different Materials Based on Critical Fracture Curve

In order to get the interface fracture curve of different materials under the four-point loading test pieces, firstly the displacement of fracture interface was obtained based on the finite element method. Then the first and second stress intensity factors of two different materials interface cracks in a beam specimen were calculated by the extrapolation method. Comprehensively considered the type of fracture specimen and the relative proportions between first and second section stress intensity, the variables K' , the first and second stress intensity factor were calculated according to the observed values of fracture load when the fissure appeared. By regression analysis of a six-groups of rock-concrete specimens with prefabricated fissure, the interface fracture criterion of different materials was got which was the interface fracture curve of rock-concrete samples. At last the calculated results of this method were compared and verified with the other related research results.

Comparison of different failure criteria for fiber-reinforced plastics in terms of fracture curves for arbitrary stress combinations

Abstract For fiber-reinforced plastics exists a big number of different criteria for the failure prediction. The intention of this paper is to compare the TSAI-HIL-, the LaRC04- and PUCK’s criterion in terms of their fracture curves for a unidirectional glass-fiber reinforced composite layer. Therefore after the implementation of these three criteria, the two-dimensional fracture curves for all possible stress combinations, which can be derived from a general spatial stress tensor, are computed. In this way, the characteristics of the criteria, similarities and differences and possible weak points become obvious.

Derivation and validation of updated QFracture algorithm to predict risk of osteoporotic fracture in primary care in the United Kingdom: prospective open cohort study

Objective To develop and validate an updated version of the QFracture algorithm for estimating the risk of a patient sustaining an osteoporotic fracture or hip fracture in a primary care...

Analysis of Elastic Moduli and Fracture of Concrete with Nature Element Method in Mesoscale

Based on the natural element method (NEM), which is a kind of meshless method, a two-dimensional numerical simulation method is developed and applied to the analysis of overall elastic moduli and fracture of solids. The calculated results are compared with the experimental solutions for overall elastic moduli, fracture and stress-strain curves for two, three and four graded concrete with FEM solutions in plane. The numerical results show the presented method is easy to implement and very accurate, especially for solving the problems of crack propagation.

An Energy-Based Axial Isothermal- Mechanical Fatigue Lifing Procedure

An energy-based fatigue lifing procedure for the determination of full-life and critical-life of in-service structures subjected to axial isothermal-mechanical fatigue (IMF) has been developed. The foundation of this procedure is the energy-based axial room-temperature fatigue model, which states: the total strain energy density accumulated during both a monotonic fracture event and a fatigue process is the same material property. The energy-based axial IMF lifing framework is composed of the following entities: (1) the development of an axial IMF testing capability; (2) the creation of a testing procedure capable of assessing the strain energy accrued during both a monotonic fracture process and a fatigue process at various elevated temperatures; and (3), the incorporation of the effect of temperature into the axial fatigue lifing model. Both an axial IMF capability and a detailed testing procedure were created. The axial IMF capability was employed in conjunction with the monotonic fracture curve testing procedure to produce fifteen fracture curves at four operating temperatures. The strain energy densities for these fracture curves were compared, leading to the assumption of constant monotonic fracture energy at operating temperatures below the creep activation temperature.

Quasi-brittle fracture diagram of structured bodies in the presence of edge cracks

The Neuber-Novozhilov approach is used to obtain necessary and sufficient fracture criteria. Using a modified Leonov-Panasyuk-Dugdale model, simple relations for the critical fracture parameters are derived for opening mode edge cracks for the case where the diameter of the prefracture zone coincides with the diameter of the plasticity zone. These relations are suitable for studying fracture where the crack length is negligibly small. A fracture diagram using critical stresses under both criteria is proposed for a wide range of crack length. At a certain level of loading, three regions are identified, in the first of which the crack is stable, in the second, the crack extends but remains stable, and in the third, the crack is unstable. Experimental data on the fracture of specimens with edge cracks are obtained. It is established that the theoretical critical fracture curves are in good agreement with the obtained critical parameters for flat tensile specimens with two collinear edge cracks.

Typical Upper Bound–Lower Bound Mixed Mode Fracture Resistance Envelopes for Rock Material

Mixed mode fracture experiments were conducted on Harsin marble using two disc-shape samples namely the Brazilian disc (BD) and the semi-circular bend (SCB) specimens. For each specimen, a complete fracture toughness envelope ranging from pure mode I to pure mode II was obtained. The experimental results indicate that the mixed mode fracture toughness depends on the geometry and loading conditions such that for any similar mode mixture, the BD test data were significantly greater than the SCB fracture toughness results. Therefore, the conventional fracture criteria which present a unique mixed mode fracture curve, fail to predict the test results. It is shown that a generalized criterion, which takes into account the effects of geometry and loading conditions, is able to provide individual fracture curves for theses specimens with very good estimates for the test results obtained from both BD and SCB specimens. The BD and SCB specimens can be suggested as appropriate specimens for obtaining typical upper bound and lower bound envelopes for mixed mode fracture toughness of rocks.

Criterion for interlaminar strength of CFRP laminates toughened with carbon nanofiber interlayer

The criterion for the interlaminar strength of unidirectional carbon-fiber-reinforced plastic (CFRP) laminates is discussed. To evaluate the limit curve given by the relation between normal stress and shear stress on the fracture interface, two types of interlaminar strength tests were carried out using short beams of CFRP laminates. The criterion for the interlaminar fracture of the CFRP laminates was investigated in two-dimensional finite element analysis of the CFRP specimens. Interlayers made by carbon nanofiber were inserted between the prepregs of the CFRP laminates. A modified ‘Tsai–Wu’ criterion was employed to evaluate the critical curve of the interlaminar fracture of the CFRP laminates. The effect of the CNF interlayer on the criterion of the interlaminar strength of CFRP laminate is discussed in detail.

Investigation of mixed mode brittle fracture in rounded-tip V-notched components

A criterion is proposed for brittle fracture analysis in rounded-tip V-notched components. This criterion, called RV-MTS, is developed based on the maximum tangential stress (MTS) criterion proposed earlier for investigating mixed mode brittle fracture in sharp cracks. Using the RV-MTS criterion, a set of fracture curves is presented based on the notch stress intensity factors (NSIFs) for predicting mixed mode and also pure mode II fracture toughness of rounded-tip V-notches. The criterion is also able to predict fracture initiation angles under mixed mode loading. The validity of the criterion is evaluated by several fracture tests performed on the rounded-tip V-notched Brazilian disc (RV-BD) specimens made of PMMA. A good agreement is shown to exist between the theoretical predictions and the experimental results for various notch opening angles and different notch radii.

On fracture testing of piezoelectric ceramics

Fracture tests carried out on unpoled and poled PZT-5H four-point bend specimens are presented in this paper. The crack faces were parallel to the poling direction. Both mechanical loads and electric fields were applied to the poled specimens. The experimental results were analyzed by means of the finite element method and a conservative M-integral including the crack face boundary conditions. Fracture tests on four-point bend PIC-151 specimens with the crack faces perpendicular to the poling directions were also analyzed here; the experimental results were taken from the literature. A mixed mode fracture criterion is proposed for piezoelectric ceramics. This criterion is based upon the energy release rate and two phase angles. This criterion was implemented with experimental results from the literature and from this investigation. Excellent agrement was found between the fracture curve and the experimental results of the specimens with the crack faces perpendicular to the poling direction. With some scatter, reasonable agreement was observed between the fracture curve and the experimental results of the specimens with crack faces parallel to the poling direction.

Epidemiological analysis of adult fractures in 5 years. Reports from a Chinese Orthopaedic Hospital over 60,000 fractures cases

Background: The epidemiology of adult fractures is changing quickly. Most of the investigations focus on the osteoporosis and single part of the body, little is known about the epidemiological results of the whole body bone fractures. Methods: An analysis of 59,005 patients and 60,402 fracture sites reviewed in a single orthopaedic trauma centre from 2003 to 2007. We choose to review all the 5 years fractures in our hospital, both outpatient clinicals and inpatient surgery patients. An research team was formed by eight experienced orthopaedic surgeons, they were asked to review all the fracture patients’ image database and do an classification according to the AO/OTA fracture classification systems. An orthopaedic professor and a radiology professor were asked to do a superintendent. Results: The results showed that there are eight different fracture distribution curves into which all fractures can be placed. Only two fracture curves involve predominantly young patients; the other six show an increased incidence of fractures in older patients. It is popularly assumed that osteoporotic fractures are mainly seen in the thoracolumbar spine, proximal femur, proximal humerus and distal radius, but analysis of the data indicates that 11 different fractures should now be considered to be potentially osteoporotic. About 30% of fractures in women, 66% of fractures in man and 70% of inpatient fractures are potentially osteoporotic. Conclusions: It is meaningful to analysis the epidemiology of the adult fractures. Improved social conditions and medical treatment have led to an increasingly aged population with an increasing number of fractures in both men and women. It seems likely that this trend will continue, that there will be further changes in fracture epidemiology and that some of the other fractures will soon have to be regarded as osteoporotic. Keywords: Fracture; Adult; Polytrauma; Epidemiology

Statistical duplex S– N characteristics of high carbon chromium bearing steel in rotating bending in very high cycle regime

Statistical fatigue tests in the very high cycle regime were carried out for the high carbon chromium bearing steel (JIS: SUJ2) in rotating bending as a common research project. Duplex S– N characteristics consisting of different S– N curves for the surface-initiated fracture and the interior-initiated fracture were clearly confirmed. Only the surface-initiated fracture took place at high stress levels, whereas only the interior-initiated fracture occurred at low stress levels. However, at medium levels of the applied stress, both fracture modes were mixed with a certain ratio of each fracture mode depending on the stress level. By applying the concept of the mixed-mode Weibull distribution, the statistical fatigue property was analyzed through the stress dependence of Weibull parameters and the occurrence probability of each fracture mode. It was finally found that the analytical results thus obtained were in good agreement with the statistical aspect of the experimental fatigue data.

A criterion for brittle fracture in U-notched components under mixed mode loading

A failure criterion is proposed for brittle fracture in U-notched components under mixed-mode static loading. The criterion, called UMTS, is developed based on the maximum tangential stress criterion and also a criterion proposed in the past for mode I failure of rounded V-shaped notches [Gomez FJ, Elices M. A fracture criterion for blunted V-notched samples. Int J Fracture 2004;127:239–64]. Using the UMTS criterion, a set of fracture curves are derived in terms of the notch stress intensity factors. These curves can be used to predict the mixed mode fracture toughness and the crack initiation angle at the notch tip. An expression is also obtained from this criterion for predicting fracture toughness of U-notched components in pure mode II loading. It is shown that there is a good agreement between the results of UMTS criterion and the experimental data obtained by other authors from three-point bend specimens.

OS1510 Statistical Analysis of Very High Cycle Fatigue Property of High Carbon Chromium Bearing Steel in Rotating Bending

Statistical fatigue tests in very high cycle regime were carried out for high carbon chromium bearing steel (JIS: SUJ2) in rotating bending as a common research project. Thus duplex S-N characteristics consisting of different S-N curves for surface-induced fracture and interior-induced fracture were confirmed. Fatigue life distribution for each fracture mode was first represented by common Weibull distribution with three parameters and P-S-N curves for each fracture mode were obtained by using common Weibull distribution function. Then fatigue life distribution including both fracture modes was analyzed by applying the concept of mixed modes-Weibull distribution. Thus, it was finally found that the statistical aspect was well explained by the present analytical model.

612 SNCM439鋼低温焼戻し材の回転曲げ荷重下における超高サイクル疲労特性(GS.F-2 疲労)

Fatigue specimens of SNCM439 steel tempered at 160deg.C and 180deg.C were prepared and fatigue tests in gigacycle regime were performed in rotating bending. These steels tempered at both temperatures indicated significant dual S-N characteristics consisting of S-N curves for surface-induced fracture and interior inclusion-induced fracture. In the case of interior inclusion-induced fracture, fish-eye pattern can be observed depending on the depth of the inclusion played a role as the crack starter. Fine granular area(FGA) was found around the inclusion as the crack starter and the SIF range at FGA front was almost constant.

Influence of Three Specimen Fixation Modes on the Micro-tensile Bond Strength of Adhesives to Dentin

The aim of this study was to investigate in how far the way the specimen is fixed to the testing device influences the micro-tensile bond strength of adhesives to dentin. Compared to a flat jig, a notched jig enables the specimen to be aligned easier and more accurately perpendicular to the interface, thereby concentrating better the tensile stress at the actual interface. A notched jig yielded a significantly higher bond strength and the graphs showed more uniform fracture curves. On the other hand, fixation of the specimen at their top and bottom guarantees a perfect perpendicular fixation to the interface, following the specimen's length-axis. The stress-time graphs revealed a completely different stress-distribution pattern. A failure closer to the dentin-composite interface was more often seen and the coefficient of variance was the lowest. Therefore, this completely newly designed top-bottom set-up produced the most reliable bond strength data.

Effect of stress ratio on long life fatigue behavior of high carbon chromium bearing steel under axial loading

Effect of the stress ratio on fatigue properties of a bearing steel (JIS:SUJ2) in the long life regime was experimentally examined under axial loading. As a result, the duplex S– N characteristics given by superposition of S– N curves for surface-induced fracture and interior inclusion-induced fracture were obtained similar to the corresponding results in rotating bending. Fish-eye marks were necessarily observed on the fracture surfaces failed in the latter fracture mode and an inclusion was found at the center of the fish-eye. The fatigue fracture of this steel in the long life regime occurred through three different processes of: (1) formation of the characteristic area of Fine Granular Area (FGA), (2) crack propagation to form the fish-eye and (3)rapid crack propagation to cause the catastrophic fracture. The effect of the stress ratio on the FGA size was confirmed and, this effect was well explained by the stress intensity factor at front of the FGA.

Thermomechanics of brittle fracture

On the basis of the thermodynamics of thermoelastic deformation we propose an energy condition of the Griffith type for brittle fracture of solids under single loading. An analysis is given of the proposed condition under the plane stressed (strained) state for the two known models of an isolated defect. In the first model, stresses on the external (distant) surface of a solid with a defect are prescribed the same as in a similar solid without a defect. In the second model, displacements are prescribed on the external surface of a solid with a defect, which correspond to the load applied to the solid, but before the defect or crack was formed. Stresses on the surface of the defect in both models are equal to zero. It is shown that the first model in the isothermal case of deformation leads to the Griffith condition. The second model meets the energy condition of the Griffith type from which, under additional assumptions concerning the shape of the defect, and from conditions of isotropy and convexity, we obtain a curve of fracture (macroscopic criterion of fracture) in an ellipse form in the space of principal stresses. The orientation of the crack was determined. Coefficients of the curve of fracture obviously depend upon elastic constants, temperature, linear coefficient of thermal expansion and crack dimensions.

Fracture behavior of poled piezoelectric PZT under mechanical and electrical loads

Four point bending samples were poled parallel to the long axis, notched and fractured. During mechanical loading, a constant electric field was applied parallel or antiparallel to the poling direction (perpendicular to the crack surface). Assuming electrical crack boundary conditions of (i) an impermeable or (ii) a completely permeable crack, the stress intensity factors K I and the field intensity factors K IV at failure were determined by linear-piezoelectric finite element calculations. The fracture curve K IC( K IV) for the impermeable crack model does not comply to fracture criteria based on the total energy release rate or on the mechanical energy release rate. Within the completely permeable crack model, it appears generally impossible to describe electric field effects on the fracture resistance. Some theoretical extensions of the crack models are discussed which might contribute to resolve the aforementioned problems.

Analysis of biomass combustion ash behavior at elevated temperatures

Change in tensile strength of a biomass ash powder bed measured by a split-cell type tester at a variety of temperatures up to 900°C was discussed corresponding to the microscopic behavior of ash particles observed by a field emission scanning electron microscope (FE-SEM) with a computer-controlled stage, a heat treatment chamber and an energy dispersive X-ray spectrometer. Tensile strength of a biomass powder bed increased with temperature by two different steps. In temperatures ranging from400 to 700°C, the powder bed had liquid-phase bridging between particles, which caused the relatively large fracture distance in fracture curves. FE-SEM observation showing rounded ash particles after heat treatment at 500°C supported this phenomena. On the other hand, at temperatures higher than 700°C, powder beds showed brittle fracture, which means the absence of any liquid bridge due to evaporation. FE-SEM observation revealed successive evaporation from ash samples in this temperature region.