Fracture Energy Values Research Articles

Modeling of the fracture energy on the finite element simulation in Ti6Al4V alloy machining

One of the main problems that exists when working with Finite Element Methods (FEM) applied to machining processes is the lack of adequate experimental data for simulating the material properties. Moreover, for damage models based on fracture energy, the correct selection of the energy value is critical for the chip formation process. It is usually difficult to obtain the fracture energy values and requires complex tests. In this work, an analysis of the influence of this fracture energy on the cutting force and the chip generation process has been carried out for different sets of cutting parameters. The aim is to present an empirical relationship, that allows selecting the fracture energy based on the cutting force and cutting parameters. The work is based on a FEM model of an orthogonal turning process for Ti6Al4V alloy using Abaqus/Explicit and the fracture energy empirical relation. This work shows that it is necessary to adjust the fracture energy for each combination of cutting conditions, to be able to fit the experimental results. The cutting force and the chip geometry are analyzed, showing how the developed model adapts to the experimental results. It shows that as the cutting speed and the feed increase, the fracture energy value that best adapts to the model decreases. The evolution shows a more pronounced decrease related to the feed increment and high cutting speed.

Mode II fracture tests on asphalt concrete at different temperatures using semi-circular bend specimen loaded by various types of supports

In this paper, the influence of support type on mode II fracture experiments of asphalt concrete is investigated. The experiments were performed using three various types of supports i.e. roller, roller-in-groove and fixed supports, employed in semi-circular bend (SCB) testing fixture, under pure mode II fracture loading. These experiments were conducted at five different temperatures including −20, −10, 0, 10 and 20 °C. Based on the results, the fixed and roller types of supports exhibited the highest and lowest values of mode II fracture toughness and mode II fracture energy, respectively at all the test temperatures. While, the values of fracture toughness and fracture energy for the roller-in-groove type of supports were in between. Furthermore, friction coefficients at the contact regions between the supports and specimen were computed using the finite element analyses. A relation was finally proposed to calculate the value of mode II geometry factor for any value of the friction coefficient. Indeed, this relation can be used to calculate the mode II fracture toughness of asphalt concrete for various types of supports.

Fracture Resistance of AAAS Composites with Ceramic Precursor

The paper deals with selected alkali-activated aluminosilicate (AAAS) composites based on ceramic precursors in terms of their characterization by mechanical fracture parameters. Composites made of brick dust as a precursor and an alkaline activator with a silicate modulus of Ms = 0.8, 1.0, 1.2, 1.4 and 1.6 were investigated. The filler employed with one set of composites was quartz sand, while for the other set it was crushed brick. The test specimens had nominal dimensions of 40 × 40 × 160 mm and were provided with notches at midspan of up to 1/3 of the height of the specimens after 28 days. 6 samples from each composite were tested. The specimens were subjected to three-point bending tests in which force vs. displacement (deflection at midspan) diagrams (F–d diagrams) and force vs. crack mouth opening (F–CMOD) diagrams were recorded. After the correction of these diagrams, static modulus of elasticity, effective fracture toughness, effective toughness and specific fracture energy values were determined using the Effective Crack Model and the Work-of-Fracture method. After the fracture experiments, informative compressive strength values were determined from one of the parts. All of the evaluations included the determination of arithmetic means and standard deviations. The silicate modulus values and type of filler of the AAAS composites significantly influenced their mechanical fracture parameters.

Prediction of load-CMOD curves for HMA mixtures at intermediate temperatures subjected to mixed mode loading

This paper discusses the effects of mixed mode loading on cohesive zone parameters obtained from load-crack mouth opening displacement (CMOD) curves in asphalt mixtures at intermediate temperature. To this end, a coupled viscoelastic numerical-experimental approach has been used to capture the cohesive strength and fracture energy in the fracture process zone utilizing asymmetric semi-circular bending test. Three mode mixities (i) pure mode I (ii) mixed mode I/II with higher fraction of tensile deformation and (iii) mixed mode I/II with higher fraction of shear mode were tested and simulated. The load-CMOD curves for the investigated mode mixities and for different asphalt mixtures were predicted successfully using the aforementioned computational framework. The results showed that the binder type and loading mode have significant effect on both cohesive strength and cohesive fracture energy values of asphalt mixtures. Aggregate gradation was only effective on the cohesive strength values. Considering the interactions of the mixtures’ constituents and loading, the binder- loading mode and binder-aggregate gradation were significantly effective only on cohesive fracture energy. The stiffer an asphalt binder, the more cohesive strength and fracture energy values were observed. Decreasing the distance between the supports which is equivalent to higher fraction of the shear mode in the ASCB test contributes to greater cohesive fracture energy.

Effect of support type on the fracture toughness and energy of asphalt concrete at different temperature conditions

This research deals with the effect of support type on the fracture toughness and fracture energy of asphalt concrete at various temperatures of −20, −10, 0, 10 and 20 °C. Fracture experiments were conducted on the SCB specimens using three different types of support including roller, roller-in-groove and fixed supports. Both the fracture toughness and the fracture energy of asphalt concrete reduced as the temperature enhanced. The results of fracture toughness and fracture energy showed that their values were highly dependent on the type of supports due to existing friction forces at the support boundary conditions. The fixed support type provided the highest values of fracture toughness and energy, and those for the roller-in-groove and roller support types were in the next ranks. From finite element modeling, the friction coefficients of 0.03 and 0.1 were finally found to be suitable to take account of friction effects in the roller-in-groove and fixed support cases. The results also revealed that the fixed support type was not suitable for measuring the fracture parameters of asphalt concrete particularly at the temperatures over 0 °C.

Investigation of the fracture energy of hot mixtures asphalt incorporating metallic wastes via semi-circular bending test

In the study, metallic wastes were evaluated in order to reduce environmental impacts and to contribute fracture energy of HMA mixtures. In this context, aluminum chips and iron powders were included in the mixtures at 0.50%, 1.00%, and 1.50% (by weight of mixtures), and the effect of HMA mixtures on fracture energy was investigated by Semi-Circular Bending (SCB) test. Experiments were performed on a total of 28 SCB test specimens from 7 different series including reference, Al-0.50, Al-1.00, Al-1.50, Fe-0.50, Fe-1.00, Fe-1.50. Basic physical properties, dissipated energy (DE), fracture energy (Gf), flexibility index (FI), and crack resistance index (CRI) values of HMA specimens were measured and compared. Based on test results, carrying load capacity and Gf values of the mixtures were increased in the use of waste iron powders. A decrease in Gf and peak load values were obtained while increasing the aluminum chips ratios. However, with the use of 0.5% waste aluminum chips were contributed Gf, peak load, CRI, and FI values compared by the reference sample. It is concluded that both aluminum chips and iron powders contributed to fracture energy of HMA mixtures.

The influence of the hygrothermal aging on the strength and stiffness of adhesives used for civil engineering applications with pultruded profiles: an experimental and numerical investigation

ABSTRACT The use of the composite pultruded materials is increasing due to the particular characteristics of lightness, ease of installation, high corrosion resistance and, finally, lower maintenance costs. Even if the bolting technique is the most widely used, especially in the field of civil engineering re-adapting the rules valid for steel structures, thanks to several studies on adhesives, there is reason to believe that the best connection technique for pultruded profiles is gluing (the continuity of the fibers is guaranteed). Current applications involving such materials, strictly related to the field of civil engineering, include bridges, pedestrian and the motorway bridges, roof structures, helipads, solar charging stations, offshore structures, cooling towers and lockgates. In some of these structures, the system (composite material and resin) is in contact with water. Even if there are several studies on the durability of composite pultruded material, current literature referring to adhesives between pultruded adherents needs further investigation. Within this framework, the paper aims to investigate, from an experimental and numerical point of view, the effect of the hygrothermal ageing on both the fracture energy in mode II as well as the strength and stiffness of two commercial epoxy resins taking into account the further effect of the desorption. Finally, in view of a safe design of a bonded joint, limiting its behaviour to the elastic field only, a lower fracture energy value is presented in relation to the classical one.

Bond behavior of CFRP-concrete bonding interface considering degradation of epoxy primer under wet-dry cycles

The excellent performance of the CFRP-concrete bonding interface is a key to ensure the reliability and effectiveness of the rehabilitation in concrete structures with external fiber reinforced polymer (FRP). Meanwhile, the epoxy primer, which bonded the FRP plate and the concrete substrate, is significantly affected by the aggressive environment. In this paper, two kinds of experiments which associated with the CFRP-concrete specimens and the epoxy primer after corroding in a wet-dry cycles environment were conducted. It shows that the immersion area of the epoxy primer has a significant influence on the properties of the moisture absorption, and that would lead to a degradation in the mechanical properties of the CFRP-concrete interface. Simultaneously, the failure modes of the CFRP-concrete interface presented a transformation from the epoxy/concrete interaction layer to the epoxy primer layer along with the increase of aging duration. To further depict the degraded bond behavior, a time-dependent bond-slip model considering the degradation of epoxy primer was proposed, and the interface fracture energy was utilized to quantify the degree of the deterioration. By comparing with the value of interface fracture energy, it was figured out that the normal bond-slip model (Popovics model) is not enough for the safety of the concrete structures rehabilitated with external CFRP, and the proposed time-dependent bond-slip model is more accurate in evaluating the time-dependent mechanical properties of concrete structures suffering in an aggressive environment.

Basal Plane Delamination Energy Measurement in a Ti3SiC2 MAX Phase

The {0001} basal plane delamination dominating the crack-wake bridging in MAX phases at a bulk scale has been investigated by studying the small-scale fracture of a Ti3SiC2. In situ micro-double cantilever beam (DCB) tests in a scanning electron microscope were used to grow a stable crack along the basal plane, measure the fracture energy, and study the crack propagation mechanism at the nanoscale. The results show that the fracture energy (10–50 J/m2) depends on small misorientations angles (e.g., 5°) of the basal plane to the stress field. This induces permanent deformation which can be observed once the DCB has been unloaded. The nanoscale study of the crack shows that the plasticity at the crack tip is small, but a number of pairs of dislocations are forming at each side of the crack. Hence, this study helps to explain the enhanced fracture energy values and possible sources of energy dissipation in basal plane delamination, which is the one of the main toughening mechanisms in the bulk fracture of MAX phases.

FRACTURE ENERGY OF ILLITIC RAMMED EARTH WITH HIGH WATER-CLAY RATIO

The article is focused on design of mixture of rammed earth, producing, testing and determination of fracture energy of unfired rammed earth and its stress-strain curve in tensile bending test. Three different mixtures of rammed earth were designed and tested. The amount of water and binder is one of the key properties of the rammed earth, the amount of the water is expressed by the water-clay ratio. Mechanical properties of the earth material highly depend on the composition of sand, clay and water. The prescription AGL III with 80 % of sand, 20 % of clay and 0.400 water-clay ratio reached the maximum value of fracture energy 4.858±0.002 J/m2 and set AGL V had the minimum value 1.934±0.310 J/m2.

Mechanical and curing behavior of epoxy composites reinforced with polystyrene-graphene oxide (PS-GO) core-shell particles

Epoxy is a high performance yet brittle thermosetting resin. To deem epoxy fit for aircraft applications, its mechanical properties, especially fracture toughness, must be improved. In this work, epoxy resin was reinforced with 0.1, 0.5 and 1.0 wt.% polystyrene-graphene oxide (PS-GO) core-shell nano-particles to enhance its fracture toughness. Styrene monomer (oil phase) was polymerized in situ using aqueous GO dispersion (water phase) to obtain PS-GO core-shell nano-particles, which appeared as wrinkled spheres under the electron microscope, confirming that the PS particles were wrapped by the GO sheets. The effect of PS-GO and GO on the curing of epoxy resin was studied and compared. The fracture tests of the cured composites revealed 28% and 26% improvements in the fracture toughness (KIC) and fracture energy (GIC) values for the 1.0 wt.% PS-GO epoxy composite, respectively. Toughening in the composites majorly occurred due to filler debonding accompanied by void formation, crack deflection and blunting and strong filler matrix interaction. The compressive strength and strain at failure improved by 25% and 52% for the 0.1 wt.% PS-GO epoxy composite, respectively. Dynamic mechanical analysis (DMA) revealed that epoxy's stiffness improved slightly after PS-GO addition while the Tg remained almost constant. Finally, the FTIR analysis of cured epoxy composites in agreement with the curing studies ascertained that, irrespective of the filler loading, the amount of hardener used was adequate to achieve complete curing of the epoxy.

FEM Simulation of High Speed Impact Behaviour of Additively Manufactured AlSi10Mg Alloy

The present work investigates impact behaviour of additively manufactured AlSi10Mg alloy and ballistic limit of projectiles using FEM simulations. Tensile tests, dynamic tests and elevated temperature tensile tests simulations were performed on smooth and notched specimens to calculate Johnson–Cook material and damage model parameters, which are subsequenty given as inputs for impact simulation. The relationship between residual velocity versus initial projectile velocity is expressed using Jonas–Lambert’s model for calculating ballistic limit. The effects of projectile velocity, its shape, thickness and material property of AlSi10Mg on ballistic limit were thoroughly investigated. C3D8R elements are used to discretize the target plate and mesh transition zone was created in impact region. Johnson–Cook elasto-viscoplastic model was employed to study the ballistic resistance behaviour of AlSi10Mg alloy. Fracture energy value of 43.6 kN/m for AlSi10Mg alloy is used to initiate the damage in target plate. All FE simulations were performed by using ABAQUS/Explicit. It is observed that ballistic impact on 3D printed AlSi10Mg has shown plugging and petaling failure when hemispherical projectile was used while plugging failure in the case of blunt projectiles. The ballistic limit of hemispherical projectiles is found to be higher (311 m/s, 400 m/s) compared to the blunt projectiles (216.5 m/s, 245 m/s). The impact velocity to completely penerate 6 mm thick target plate is relatively higher as compared to 3 mm thick target plate for both projectiles.

Fracture energy comparison of aluminum and boron composites for fuel cell end plates

Fuel cells have become an attractive choice because they do not cause environmental and noise pollution. Additionally, they do not contain any moving parts and have higher efficiency than fossil fuels. Therefore, improving the capability of fuel cells helps to provide clean energy. Among fuel cells, the proton exchange membrane fuel cell (PEMFC) includes five main parts that are end plate, membrane, gas diffusion layer (GDL), catalyst layer (CL), bipolar flow plate (BFP). End plates hold PEMFC parts together securely. They should have high mechanical strength and low density properties. Therefore, the choice of materials for the PEMFC endplate is important. The calculated values of fracture energy show quantitatively how much energy must be placed in the sample to create the fracture surface. In this study, a finite element study was performed to understand the fracture behavior of cracks in the selected materials under different loading angles. The results revealed that the total fracture energy of aluminum was higher than boron-aluminum 50 and boron-aluminum 65 composites.

The effects of gilsonite and crumb rubber on moisture damage resistance of stone matrix asphalt mixtures

The current study was performed to investigate the influence of gilsonite on properties of binder and moisture resistance of SMA mixtures modified by Crumb Rubber (CR) additive. For this purpose, softening point, penetration, and Dynamic Shear Rheometer tests were implemented to investigate the performance of different binders. To evaluate the water sensitivity of modified mixtures, four different methods were performed, including Resilient Modulus Ratio (RMR), Fracture Energy Ratio (FER), Tensile Strength Ratio (TSR) and Texas boiling. To analyze the data, two-factor analysis of variance (ANOVA) was carried out. Based on the results, utilization of Gilsonite additive enhances the Resilient Modulus (Mr), Indirect Tensile Strength (ITS), and Fracture Energy (FE) of asphalt mixtures. The results also revealed that by utilization of CR, ITS and FE values increase. While, the MR values increase by addition of 10% CR, and by addition of higher percentages of CR (15 and 20%), the MR values decrease. Among different specimens fabricated, mixtures containing 30% Gilsonite and 20% CR have the highest ITS and FE values. Also, according to the results, 30% Gilsonite mixture modified by 20% CR has the highest TSR, and FER value, which indicates that the mentioned specimens have better resistance to water susceptibility.

Direction-dependent fracture in solids: Atomistically calibrated phase-field and cohesive zone model

We propose a new phase-field damage formulation which takes into account anisotropic damage evolution in solids. Such anisotropy projects itself in fracture energy values which depend on the direction of the crack surface. Therefore, instead of one constant scalar parameter for the fracture energy value, we use a direction-dependent fracture energy function. By incorporating a direction-dependent fracture energy function, only a single damage variable as well as a first order damage gradient need to be used within the standard phase-field damage model. This is in contrast to other available anisotropic phase-field models which typically use multiple variables or higher order gradient terms. To obtain values for the fracture energy function, atomistic calculations are performed. Here, molecular static simulations are utilized to calculate the energy of free surfaces within an Aluminum crystal. As a result, we report the fracture energy value as a function of the surface orientation. The obtained fracture energy function is passed directly to the phase-field damage formulation to investigate transgranular fracture within a single crystalline. Moreover, the grain boundary is represented via a cohesive zone model to take into account intergranular fracture in a bi-crystalline structure. The predicted crack path is in good agreement with obtained results from molecular dynamics simulations. Finally, by calibrating the length scale parameter in the phase-field damage model, it is possible to compare the reaction forces from finite element calculations with atomistic ones.

Development of a Weight-Drop Impact Testing Method for Dental Applications.

For evaluating the impact strength of dental materials, the Izod test or Charpy test has been used, but specimen preparation for these tests is difficult due to the adjustment of a notch on them. By contrast, a weight-drop impact test does not require notched specimens. Therefore, it might be possible to measure the impact strength more accurately than conventional methods. This study aimed to establish appropriate conditions for applying the weight-drop impact test on small specimens of acrylic resin. To determine the most reliable impact fracture energy of acrylic resins, different diameters and thicknesses of PMMA resin specimens, diameters and weights of the striker, and diameters of the supporting jig were compared. For all specimen thicknesses, when the striker diameter was 6–10 mm, the impact fracture energy was constant when the inner diameter of the specimen-supporting jig was 8–10 mm. In addition, the measured E50% value was mostly equal to the median value of the impact fracture energy. Thus, for the weight-drop impact test, this method was effective for material testing of small specimens, by clearly specifying the test conditions, such as the thickness of disc-shaped specimens, the diameter of the striker, and the inner diameter of the specimen-supporting jig.

Phase-Field Fracture Modelling of Thin Monolithic and Laminated Glass Plates under Quasi-Static Bending

A phase-field description of brittle fracture is employed in the reported four-point bending analyses of monolithic and laminated glass plates. Our aims are: (i) to compare different phase-field fracture formulations applied to thin glass plates, (ii) to assess the consequences of the dimensional reduction of the problem and mesh density and refinement, and (iii) to validate for quasi-static loading the time-/temperature-dependent material properties we derived recently for two commonly used polymer foils made of polyvinyl butyral or ethylene-vinyl acetate. As the nonlinear response prior to fracture, typical of the widely used Bourdin–Francfort–Marigo model, can lead to a significant overestimation of the response of thin plates under bending, the numerical study investigates two additional phase-field fracture models providing the linear elastic phase of the stress-strain diagram. The typical values of the critical fracture energy and tensile strength of glass lead to a phase-field length-scale parameter that is challenging to resolve in the numerical simulations. Therefore, we show how to determine the fracture energy concerning the applied dimensional reduction and the value of the length-scale parameter relative to the thickness of the plate. The comparison shows that the phase-field models provide very good agreement with the measured stresses and resistance of laminated glass, despite the fact that only one/two cracks are localised using the quasi-static analysis, whereas multiple cracks evolve during the experiment. It was also observed that the stiffness and resistance of the partially fractured laminated glass can be well approximated using a 2D plane-stress model with initially predefined cracks, which provides a better estimation than the one-glass-layer limit.

The electrical and mechanical properties of Cadmium chloride reinforced PVA:PVP blend films

In this study, pure polymer blend (PVA:PVP) film and salt (CdCl2·H2O) reinforced polymer blend films were prepared at different weight ratios (10 wt%, 20 wt%, 40 wt%) using the casting method. The effect of the salt weight ratio on the dielectric properties of the polymer blend films reinforced by CdCl2·H2O salt were investigated, and the experimental results showed that the dielectric constant and the dielectric loss factor decreased as the frequency increased for all polymer blend films. Moreover, the above-mentioned properties increased with increasing salt weight ratios at the same frequency. The experimental results also showed an increase in AC electrical conductivity with increasing frequency, for all polymer blend films, and the AC electrical conductivity also increased with an increase in the weight ratio of the salt at the same frequency. The effect of the salt weight ratio on the mechanical properties of the salt-reinforced PVA:PVP polymer blend films was also studied. The experimental results obtained from the tensile test of the salt-reinforced polymer blend films show significant change in the values of tensile strength, elongation at break, and Young’s modulus with increasing salt weight ratios; the hardness value first increases then decreases with increasing salt weight ratios, and the fracture energy value increases with increasing salt weight ratios, thus they could be good candidates for hard adhesives with low flexibility.

Investigation the effect of short term aging on thermodynamic parameters and thermal cracking of asphalt mixtures modified with nanomaterials

Thermal or low temperature cracking is among the most common distresses in asphalt pavements, occurring in cold regions and exerting a detrimental effect on the quality and life of the pavement. Hardening or aging of asphalt binder in the process of production and service life of asphalt mixtures is known as a major factor impacting the durability of asphalt mixtures. This study investigated the effect of asphalt binder modification with two types of mineral nanomaterials, nano calcium carbonate (NCC) and nano hydrated lime (NHL), on the aging and thermal cracking of asphalt mixtures using thermodynamic and mechanical methods. To this end, 24 asphalt mixtures were prepared using limestone and granite aggregates with different mineralogical properties, two types of asphalt binder with PG of 64–16 and 58-22, and two types of nanomaterials, including NHL and NCC. Thermal cracking of asphalt mixtures was evaluated by mechanical semicircular bending (SCB) test based on AASHTO TP105, and thermodynamic tests of sessile drop and universal sorption device based on surface free energy (SFE) methods. The results of the SCB test indicated that aging significantly affected the values of maximum load, fracture energy, and fracture toughness. In addition, asphalt binder modification using NCC and NHL significantly increased the values of all three parameters mentioned above in both the control and aged samples. On the other hand, the results of thermodynamic tests demonstrated that the free energy of cohesion of PG 64–16 in both control and aged states was higher than that of PG 58-22. Accordingly, aging and modification of the control and aged asphalt binder using nanomaterials increased the cohesion energy of asphalt binder. Results also indicated that mixtures made with granite aggregates, in both aged and control states, had higher values of free energy of adhesion compared to mixtures made with limestone aggregates. Aging caused a decrease in the free energy of adhesion, which was much lower in the nano material modified samples in comparison with the control samples. The results of ANOVA and linear regression analysis also revealed that there was a significant and strong correlation between thermodynamic parameters of cohesion and adhesion energy and the maximum load, fracture energy, and fracture toughness parameters in examining the effects of aging and additives on thermal cracking. This indicates the high potential of thermodynamic methods in thermal cracking examination in asphalt mixtures.

The influence of aging on the fracture characteristics of recycled aggregate concrete through three methods

AbstractIn this research, to assess the impact of aging on the fracture properties of recycled aggregate concrete (RAC), three‐point bending tests were carried out on 260 specimens. Then, work of fracture method (WFM), size effect method (SEM), and boundary effect method (BEM) were utilized for analysis of fracture parameters. The result showed that fracture energy values for RAC were 4.2%, 7.1%, 22.7% and 24.2% less than natural aggregate concrete (NAC) ones at 3, 7, 28 and 90 days, respectively. Based on calculation of the characteristic length, the behavior of RAC is more ductile than NAC at early ages. However, through time, the ductility of RAC becomes less than NAC. On average, the ratio of fracture energy achieved from WFM (GF) to initial fracture energy achieved from SEM (Gf) for RAC and NAC was 2.38 and 2.14, respectively. The comparison of fracture energy obtained by BEM and modified WFM showed that these values were close to each other.