Effect Of Fracture Toughness Research Articles

Shape memory polymers structure with different printing direction: Effect of fracture toughness

The direction in which three-dimensional (3D) printing is carried out strongly affects the mechanical properties of the resultant printed part due to differences in interface bonding strengths between layers. In this work, we study the effect of printing direction (e.g., 0°, 30°, 45°, 60° and 90°) on the fracture toughness of the UV-curable specimen fabricated by digital light process (DLP) 3D printing. A compact tension specimen was used to measure the fracture toughness for different print directions. The digital image correlation(DIC) technique was used to characterize the full strain fields of the specimens. The crack pattern and crack surface were investigated using optical and scanning electron microscopy. The obtained results indicate that samples prepared at 0° and 90° exhibited higher crack resistance compared with that of other directions. DIC analysis indicated that the tendency of the crack path was consistent with the actual crack path. The reported fracture test results for computerized tomography of a specimen prepared with different directions provide a means to reveal the fracture mechanism of a DLP 3D printed structure.

Effect of Fracture Toughness on Surface Roughness in ELID Grinding of Silicon Nitride Ceramics for Ball Bearings

Effect of Fracture Toughness on Surface Roughness in ELID Grinding of Silicon Nitride Ceramics for Ball Bearings

Effect of the additive graphene oxide on tribological properties of WC-Co cemented carbide

This article is to devoted to investigate the effect of graphene oxide (GO) on the mechanical and tribological properties on WC-Co cemented carbide. Based on the microstructure and morphology of wear surface, it is found that the addition of GO has little effect on the densification process and the grain size of cemented carbide, thus hardly weakening the hardness, while the fracture toughness has been improved 29.1%. Both friction coefficient and specific wear rate have been significantly decreased due to the added GO. The bridging mechanism caused by GO is considered to be the main reason for the toughening effect in cemented carbide. Increasing fracture toughness by the added GO during sintering is noticed to significantly enhance the anti-wear performance of WC-Co cemented carbide. The effect of fracture toughness on wear resistance should be attributed to the added GO preventing the cobalt binder phase from occurring the combination of plastic deformation and micro-abrasion, and hindering the crack propagation of WC grains during sliding.

An ultrafast time-resolution method based on picosecond pulsed laser for determining rock fracture toughness at multipoint during the crack propagation

An innovative ultrafast time-resolution method based on a picosecond pulsed laser was employed to investigate the mode-I crack propagation characteristics of fractured rock. Its time resolution is as fast as the degree of 45 picoseconds. Then, a series of three-point compressive loading tests with this method were conducted on tuff semi-circular bend (SCB) specimens. Based on this method, we found that the mode-I fracture process of the tuff specimens were composed of repeated crack initiation, arrest, and re-initiation. In addition, the experimental results showed that the fracture rates of the tuff specimens in the initial 10 μs were 636 m/s, 663.9 m/s, and 578 m/s. In comparison, the fracture rates of the specimens were 11.19 m/s, 19.23 m/s, 26.79 m/s during the whole fracture process. As a typical heterogeneous material with primary defects, rock has different fracture toughness at different locations. Therefore, we proposed a new method for determining rock fracture toughness at multipoint during the crack propagation. This new method emphasizes the effect of fracture toughness on crack propagation, which enables to determine the fracture toughness at multipoint and is closer to the original definition of fracture toughness.

An analytical model for micro-cutting considering the cutting tool edge radius effect and material separation

Severe plastic deformation occurs in micro metal cutting process; meanwhile, new surfaces are generated due to the material separation caused by ductile fracture. The energy required for the formation of the new surfaces is of kJ/m2, which should not be neglected in the analysis of micro-cutting. In this work, an analytical model is developed focusing on the analyses of the micro metal cutting process with no stable built-up edge, in which the effects of both edge radius and material separation are taken into account. The cutting tool edge geometry is simplified with the effective rake angle. On the basis of slip-line field theory, the equation of the cutting power is derived. Applying the minimum energy principle, two nonlinear equations are obtained, through which the shear angle and the minimum chip thickness can be estimated simultaneously. The model is examined through the experiments; the investigations show that the calculation results of cutting force and shear angle agreed with the experimental measurements very well. The effects of fracture toughness, shear yield stress, and friction angle to the micro-cutting process are investigated. The numerical results show that the friction angle affects the cutting force and the shear angle greatly.

Evaluation of LBB characteristics of candidate materials for main steam line piping in Korea nuclear power plants

Recently, efforts have been made to apply the leak-before-break (LBB) design concept to the main steam line (MSL) piping in secondary systems of Korea standard nuclear power plants (KSNPs). In this study, the microstructures, mechanical properties, and consequential LBB margins of five candidate materials (SA335 Gr.P11/P22, SA508 Gr.3 Cl.2, SA508 Gr.3 Cl.1, and SA508 Gr.1A steels) were evaluated, and strong/weak points of candidate materials for applying MSL piping were analyzed through the comprehensive analysis including microstructure, mechanical properties, LBB margin, usage history, economics, and so on. SA508 Gr.1A steels, which has been used extensively as a piping material in NPPs and has a low fabrication cost, had a good combination of yield strength and fracture toughness. They had LBB margin of 1.11–1.21. SA508 Gr.3 Cl.1 steel had an excellent combination of yield strength and fracture toughness with an LBB margin of 1.64. SA508 Gr.3 Cl.2 steel had the highest LBB margin (1.84) because it had the highest strength; however, it had low fracture toughness and low upper shelf energy (USE). The effect of yield strength on the LBB margin was considerably higher than the effect of fracture toughness. SA508 Gr.3 Steels have high LBB margin owing to the high yield strength, but they have never been used for piping materials in NPPs before. SA335 Gr.P11 and P22 had the LBB margin of 1.1 and 1.23, respectively. However, the elongation and J-R fracture toughness of SA335 Gr.P11 and P22 decreased significantly at 286 °C owing to dynamic strain aging (DSA).

Study on fracture toughness with different thicknesses CT specimen

The material selected for this study was a WELDOX 900 steel plate. This paper analyzed the size effect of fracture toughness based on experimental results and finite element numerical simulation results. In addition, J-integrals of different thicknesses were investigated and the relational expression between them was acquired in this study. The main conclusions are as follows: Firstly, the formula between the ductile fracture toughness J 0.2 and the specimen thickness was obtained. It proposed a method for predicting the fracture toughness of plane strain state using thin specimens of several thicknesses based on this formula. Secondly, the fracture toughness values of the materials were obtained by finite element numerical simulation. And it was found that the distribution of stress triaxiality near the crack tip could well explain the variation of fracture toughness with thickness.

An Improved Model for Predicting Hydraulic-Fracture-Height Migration

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 173335, “An Improved Equilibrium-Height Model for Predicting Hydraulic- Fracture-Height Migration in Multilayer Formations,” by Songxia Liu, SPE, and Peter P. Valko, SPE, Texas A&M University, prepared for the 2015 SPE Hydraulic Fracturing Technology Conference, The Woodlands, Texas, USA, 3–5 February. The paper has not been peer reviewed. While many factors may influence fracture-height evolution in multilayer formations, the consensus is that the so-called “equilibrium height belonging to a certain treating pressure” provides an upper limit, at least for nonnaturally fractured media. The authors have revisited the “equilibrium-height problem,” and their theoretical and numerical investigations led to a new model that fully characterizes height evolution amid various formation properties. Introduction Solutions for the equilibrium-height problem have been known since the 1970s, and several models have been developed for calculating hydraulic-fracture height. However, because of the complexity of the algebra involved, the equations used in these early models were overly simplified and gave unreliable results. The authors developed an improved, mathematically rigorous model that, for the first time, solves the equilibrium height under various formation-property conditions and fluid properties. The authors started from the definition of fracture toughness, incorporated the effects of hydrostatic pressure, and considered nonsymmetric variations of layered formation properties. The model was applied to the classic three-layer problem and then extended up to six layers. With the new model, the effects of fracture toughness, in-situ stress, fluid density, and their interactive effects on fracture-height growth were investigated. The full height profile with very large top and bottom formation thicknesses showed the ultimate trend of fracture-height migration. Two three-layer pseudo problems were constructed to create an outer and inner height envelope for any multilayer-formation problem, to assess the potential effects of reservoir-parameter uncertainties on height profile. The occurrence of a second solution pair and its analytical solutions were presented, to avoid misleading results in the 3D models.

Fatigue crack growth rate of Ti-6Al-4V considering the effects of fracture toughness and crack closure

Fatigue fracture is one of the main failure modes of Ti-6Al-4V alloy, fracture toughness and crack closure have strong effects on the fatigue crack growth(FCG) rate of Ti-6Al-4V alloy. The FCG rate of Ti-6Al-4V is investigated by using experimental and analytical methods. The effects of stress ratio, crack closure and fracture toughness on the FCG rate are studied and discussed. A modified prediction model of the FCG rate is proposed, and the relationship between the fracture toughness and the stress intensity factor(SIF) range is redefined by introducing a correcting coefficient. Notched plate fatigue tests (including the fracture toughness test and the FCG rate test) are conducted to investigate the influence of affecting factors on the FCG rate. Comparisons between the predicted results of the proposed model, the Paris model, the Walker model, the Sadananda model, and the experimental data show that the proposed model gives the best agreement with the test data particularly in the near-threshold region and the Paris region, and the corresponding calculated fatigue life is also accurate in the same regions. By considering the effects of fracture toughness and crack closure, the novel FCG rate prediction model not only improves the estimating accuracy, but also extends the adaptability of the FCG rate prediction model in engineering.

Fracture Toughness Effects in Geomaterial Solid Particle Erosion

Effects of fracture toughness on the impingement of geomaterials (rocks and cementitious composites) by quartz particles at velocities between 40 and 140 m/s are investigated experimentally and analytically. If schist is excluded, relative erosion (in g/g) reduces according to a reverse power function if fracture toughness increases. The power exponent depends on impingement velocity, and it varies between −0.64 and −1.33. Lateral cracking erosion models, developed for brittle materials, deliver too high values for relative material erosion. This discrepancy is partly attributed to stress rate effects. Effects of R-curve behavior seem to be marginal. An integral approach E R = K 1 · E R P + (1 − K 1) · E R L is introduced, which considers erosion due to plastic deformation and lateral cracking. A transition function \(K_{1} = f\left( {K_{\text{Ic}}^{12/4} /\sigma_{\text{C}}^{23/4} } \right)\) is suggested in order to classify geomaterials according to their response against solid particle impingement.

Experimental Research on Size Effect of Mode II Fracture Toughness of Concrete

Based on specimen size, which is the main reason of the shear fracture toughness of concrete, experimental research was carried out by 5 groups including 40 symmetrically loading specimens with different length and height. Through load and crack tip sliding displacement curve P-CTSD, load and strain curve P-ε and load and time curve P-t, the effects of length and height of specimens to shear fracture toughness were studied. Specimen stability is strengthened with increasing of length and weakened with increasing of height. Size effect of fracture toughness is weakened with increasing of length, is strengthened with the increasing of height. Fracture toughness increases with the increasing of length, decreases with the increasing of height. Research Background The size effect exists in parameters of concrete, such as concrete strength, modulus of elasticity, fracture toughness, fracture energy and so on [1-. In 1961, the theory of fracture mechanics was applied to concrete structure for the first time by Kaplan [. A vast majority of research work about concrete fracture mechanics was carried out by international scholars [6-. As the development of fracture theory of concrete, the size effect of fracture parameters became the focal point in theory study. Karihaloo [ pointed out that the size effect of concrete strength strengthens with the increasing of components size, however, the size effect weakens when crack length decreased relative to the size of specimens. Hu [3, 10, 11] accounted for the size effect by applying the theory of boundary effect and carried out the concept of local fracture energy which changes with width of fracture process zone. Based on the fictitious crack model, an analytical method [12, 13] for predicting the effective fracture toughness of concrete of three-point bending notched beams is proposed and the effects of initial seam height ratio and height on fracture parameters were carried out by Wu and Xu. At present, research on shear fracture toughness of concrete is immature and there are almost no papers about the size effect of shear fracture toughness of concrete. Aiming at the issue, this paper conducts a study on the size effect of shear fracture toughness of concrete by using symmetrically single-edge notched specimen.

Size Effect of Fracture Toughness of High Strength Fiber Concrete

Size Effect of Fracture Toughness of High Strength Fiber Concrete

Effect of fracture toughness on abrasive wear resistance of steels

Various abrasive wear mechanisms were reviewed and an abrasive wear modeling experiment is assessed. Abrasive wear resistance of non-heat treated and heat treated steels has been determined by using a pin-abrasion machine with five abrasive papers, which grinds on a small pin of test materials. The mass loss of test material during abrasive wear was determined gravimetrically. A correlation between abrasive wear resistance and Mode II fracture toughness of materials was established. The effect of fracture toughness on abrasive wear resistance of steels was outlined.

Wear behavior of TiC–MoSi 2 composites

Titanium carbide (TiC) particles have been added to molybdenum disilicide (MoSi 2) to form TiC–MoSi 2 composites. Benefits associated with the addition of the TiC to MoSi 2 include finer microstructure, higher strength, higher fracture toughness and higher hardness. Under the wear condition of this test, the wear resistance of MoSi 2 increases significantly by the addition of TiC particles. The wearing rate of TiC–MoSi 2 composites is as low as tenth of monolithic MoSi 2. The effects of fracture toughness and hardness on wear resistance are discussed.

Solid-particle erosion of hot-pressed silicon carbide and SiC-TiB2 composite

The erosion behaviour of SiC has been studied for hot-pressed materials [1–3]. An anomalous particle size dependence [1], a low velocity exponent of less than 2 [1, 2] and fracture other than by lateral cracking have been reported in the erosion of hotpressed, monolithic SiC [3]. Most of these works were performed on commercial SiC of limited compositions and hot-pressing conditions were not reported. Compared to monolithic SiC, much less information is available on the erosion of composite materials. The erosion behaviour of composites has been reported only for SiC–SiC whiskers [4] and the SiC–Al2O3 system [5]. The objective of the present work is to investigate and compare the erosion behaviour of monolithic SiC and SiC–TiB2 particulate composite, both hot-pressed with 5 vol % Al2O3. These materials are chosen because SiC is toughened by the addition of TiB2 and the erosion rate is greatly affected by the fracture toughness [6, 7]. Two hot-pressed SiC materials were used for this work. One, designated SA, was monolithic SiC containing 5 vol % Al2O3, and the other, designated SBA, was SiC composite containing 5 vol % Al2O3 and 14 vol % TiB2. Specimens were produced from commercial powders of mean particle size of less than 0.9 μm. The combined powders were vibromilled in ethanol using SiC balls with a diameter of 8 mm and hot-pressed in graphite dies lined with graphite foil at 2000 to 2050 8C at 30 to 38 MPa under vaccum. In all cases the density of the hotpressed pieces exceeded 97% of theoretical. After hot pressing, specimens were cut and mechanically ground to dimensions of 20.0 mm by 20.0 mm by 50 mm. Erosion tests were conducted at room temperature using an air blast type apparatus. The erodent used was commercial angular SiC, average particle size of 50, 100 and 150 μm. Erodent velocities were 40, 70 and 100 m sy1 and angles of impact were 30, 60 and 908. The specimens were weighed to an accuracy of 10y5 g, subjected to erosion, cleaned with an air blast and then reweighed. Steady-state erosion rates were determined as the mass lost from the target per mass of impacting particle. Fig. 1 presents the angular dependence of the steady-state erosion rate of the materials SA and SBA for particles 100 μm in diameter eroding at a rate of 40, 70 and 100 m sy1. The shape of the curve is representative of both materials obtained for all particle sizes and velocities. Maximum erosion occurs for α ˆ 608, unlike the previous results on hot-pressed SiC [1–3]. The shift of peak in erosion rate indicates that the erosion of these materials occurs in a more ductile manner [8] compared to materials showing peak erosion for normal incidence. The erosion rate is higher for SA under more test conditions compared to the composite SBA, though the difference in erosion rate is not large under some test conditions. A higher erosion rate is obtained for SA in 13 conditions out of 18 test conditions, as shown in Fig. 1. Thus, a higher erosion rate is obtained for SA, having lower fracture toughness under more test conditions, compared to SBA. The fracture toughnesses of the materials measured by the single-edge pre-cracked beam (SEPB) method are 4.0 and 4.8 MPa m1=2 for SA and SBA, respectively [9]. Toughening observed for SBA is due to crack deflection caused by the interaction of the crack front with a residual stress field that surrounds the TiB2 particles [10]. The origin of this stress field is the difference in thermal expansion and elastic moduli between SiC and TiB2. The effect of fracture toughness on the erosion rate found in this work is roughly consistent with the theoretical predictions

The effect of crystallinity on fracture and yielding of polyethylenes

The effect of the amount of crystallinity on fracture and yielding of polyethylenes as a function of temperature is reviewed. In particular, the effect of fracture toughness, K c, at low temperatures is investigated. Generally, K c increased linearly as density decreased. However, it was found that very low-density polyethylene shows a significant decrease in K c from this general behaviour.

The size effect of fracture toughness and the Irwin βIc adjustment

The size effect of fracture toughness and the Irwin βIc adjustment

An examination of mixed fatigue-tensile surface crack growth in rails

The fracture instability associated with alternating periods of fatigue and tensile growth of surface cracks was investigated in steel rails. Three different steels were tested. The instabilities commenced when the maximum stress intensity factor K exceeded the fracture toughness K IC and resulted in crack jump or total rail failure. The conditions for the establishment of fatigue-tensile crack jump and arrest are described. The load level, residual stresses, crack geometry and fracture toughness effects are analysed. The fatigue surface cracks were penetrated in both stress relieved and stress unrelieved rails. The effective stress intensity factors including the contribution of the applied load and residual stresses were calculated. For both the fatigue-tensile and tensile-fatigue transitions the stress intensity factors were almost the same with the value for the tensile-fatigue transition being slightly lower. Both calculated stress intensity factors were close to the fracture toughness K IC .

Effect of the form and size of a fatigue crack on the fatigue fracture toughness of titanium alloy VT9

At present, one of the most important characteristics of the strength of metal products under fatigue loading, together with the endurance limit, is the fatigue fracture toughness. The introduction of the concept of fatigue fracture toughness [I] was associated with attempts to use the methods of linear fracture mechanics to analyze fatigue fracture. The use of numerical methods of fracture mechanics allowed the authors of [2] to account for the effect of the actual geometry and form of a macroscopic fatigue spot in the fracture of a cylindrical specimen in determining fracture toughness. Obviously, this data is important for engineering calculations and to qualitatively analyze the effect of fracture toughness on endurance if we consider that one of its important terms is the time of propagation Of a fatigue crack to critical size. The data is also important for analyzing the sensitivity of products to stress raisers.