The effect of loading rate on fracture energy of asphalt mixture at intermediate temperatures and under different loading modes

At intermediate service temperatures hot mix asphalt (HMA) concretely are subjected to different loading rates due to movement of vehicles which can significantly affect their mechanical characteristics and final service load. Hence, in this paper the effect of loading rate on intermediate temperature fracture resistance of HMA materials is investigated experimentally in different modes of cracking. Different hot mix asphalt mixtures made of various compositions were subjected to asymmetric threepoint bend loading in the form of edge cracked semi-circular bend (SCB) specimens. The effect of aggregate type and air void were studied on the fracture energy values for three mode mixities (including pure mode I, mixed mode I/II and pure mode II) and at different temperatures of 5°C, 15°C and 25°C. Trends of change in fracture energy values revealed noticeable influence of loading rate on the low and intermediate temperature cracking behavior of tested asphalt mixtures with different air void contents and aggregate types subjected to mixed mode I/II loading. Also, a change observed in fracture resistance of asphalt mixtures at nearly zero (5°C) and intermediate temperatures (25°C) that was due to change in the behavior of bitumen from elastic to viscoelastic. © 2018, Gruppo Italiano Frattura. All rights reserved

Engineering Solid Mechanics Determination of fracture parameters for a bi-material center cracked plate subjected to biaxial loading using FEOD method

Fracture parameters of a bi-material plate containing a cener crack and subjected to biaxial tensile loading was calculated numerically. Based on the crack tip stress field obtained numerically in a bi-material joint and using the finite element over deterministic (FEOD) method, the stress intensity factors (KI and KII) and also non-singular T-stress terms, were determined for different material properties and biaxial loading cases. Due to asymmetry of loading and material properties in the investigated dissimilar plate, the center crack experinces mixed mode I/II fracture in general. By increasing the bi-material constant value, which shows the difference between the mechanical properties of two materials, the amplitude of stress intensity factor decreases. The obtained results from this method were in good agreement with the displacment field method prevousiuly reported by other researchers

The role of mix design and short glass fiber content on mode-I cracking characteristics of polymer concrete

Suitable resistance against fracture and cracking is a primary requirement for using polymeric concrete materials in practical applications. The main aim of this research is to investigate the effect of mix-design on mode I cracking behavior. A total number of 72 different Polymer Concrete (PC) mix-designs made of four ingredients (epoxy resin, coarse silica aggregate, fine sand filler and chopped strand E-glass fibers) were considered for conducting fracture experiments using the Semi-Circular Bend (SCB) specimen. The weight percentages of the ingredients were varied in the following range: 17–25% resin, 75–81% fine and coarse aggregates and 0–2% glass fibers. The investigated mix-designs were categorized into six groups (ultra-high, high, medium-high, medium-low, low and ultra-low) in terms of the adhesive agent content (i.e. the ratio of resin plus fiber content to the weight of the whole mixture). The experiments showed the noticeable dependency of both fracture toughness and fracture energy values (KIf and GIf) on the PC mix-design. In addition, the effect of substituting 1 and 2% of resin content with glass fiber was investigated. It was found that adding the fiber cannot necessarily enhance the performance of PC mixture against cracking and for some mix-designs; the addition of fiber can even reduce both KIf and GIf values

Application of an average strain energy density criterion to obtain the mixed mode fracture load of granite rock tested with the cracked asymmetric four-point bend specimens

Mixed mode brittle fracture behaviour of granite rock is studied experimentally and theoretically using Asymmetric Four Point Bend (AFPB) specimens containing pre-cracks subjected to different mixed mode loading conditions, ranging from pure mode I to pure mode II. The main aim of this paper is twofold. First, to present a complete set of experimental results on fracture of pre-cracked granite samples under various in-plane loading mixities, and second, to predict the fracture loads of the tested rock samples under mixed mode I/II conditions using an energy-based criterion, namely the Average Strain Energy Density (ASED) criterion. Good agreement is found between the experimentally obtained fracture loads and the theoretical predictions based on the constancy of the mean strain energy density over the material volume. It is shown that the ASED criterion is able to provide well predictions for the fracture loads of the investigated rock material containing a pre-crack. © 2017 Elsevier Lt

Investigation of fracture toughness for a polycrystalline graphite under combined tensile-tear deformation

In the present contribution, mixed mode I/III fracture toughness of a polycrystalline graphite is studied experimentally, numerically and theoretically using a new designed test specimen. A simple disc shape specimen subjected to three-point bending named herein edge notched disc bend (ENDB), is successfully employed for fracture toughness experiments on graphite. This specimen can introduce full combination of modes I and III including pure mode I, pure mode III and complete intermediate mode mixities. Fracture toughness values (KIc and KIIIc) of investigated graphite are obtained for six different mode mixities for and the obtained experimental data are compared with theoretical predictions of two conventional mixed mode I/III fracture theories namely: maximum tangential stress (MTS) and maximum tangential strain energy density (MTSED). It has been observed that the fracture toughness results are in good agreement with the mixed mode I/III curve of MTSED criterion. Consequently, the suggested ENDB specimen can be proposed as a suitable specimen for mixed mode I/III fracture toughness study of based on graphite materials. © 2017 Elsevier Lt

EMTSN criterion for evaluating mixed mode I/II crack propagation in rock materials

This paper investigates the results of brittle fracture in rock materials subjected to the mixed mode I/II loading using different fracture criteria. Two sets of mixed mode fracture test data in the entire range of mode mixity, from pure mode I to pure mode II, reported in the literature for semi-circular and triangular shape specimens and subjected to three point bend loading (i.e. SCB and ECT specimens) are utilized to study the brittle fracture in two marble rocks. First, the onset of fracture initiation is examined by different conventional fracture criteria including Maximum Tangential Stress (MTS) and Maximum Tangential Strain (MTSN) criteria. It is shown that these two conventional fracture criteria, which only consider singular crack tip stress/strain terms, are not able to accurately predict the mixed mode fracture test data. The experimental mixed mode fracture toughness data are then predicted by an extended version of the maximum tangential strain (EMTSN) criterion which takes into account the effect of first nonsingular strain term as well as the singular strain components. It is found that both mixed mode fracture toughness results of the investigated rock materials and the crack propagation direction can be predicted successfully by the EMTSN criterion. (C) 2017 Elsevier Ltd. All rights reserved

Design and validation of simple bend beam specimen for covering the full range of I+II fracture modes

Using short beam specimen containing an edge crack (perpendicular to the beam axis) and subjected to asymmetric three-point bend loading a new test configuration (called ASBB) was suggested for investigating the mixed mode I/II fracture. Despite the conventional beam specimen with high aspect ratio of length to width that is not able to produce mode II or dominantly mode II conditions, complete mode mixities were obtained using the proposed three-point bend asymmetric short beam specimen. The fracture parameters including modes I and II stress intensity factors and T-stress were determined numerically for this test specimen with different crack lengths and bottom rollers distances relative to the crack. The practical ability of the ASBB specimen was examined experimentally by conducting several mixed-mode I/II fracture tests on PMMA material. The critical stress intensity factors, the direction of fracture kinking and the path of fracture trajectory were investigated both experimentally and theoretically using MTS and GMTS criteria. The fracture toughness of PMMA tested with the ASBB specimen was increased by increasing the contribution of mode II component. The effects of beam length aspect ratio, crack type and loading type on the mixed mode fracture of cracked beam samples subjected to three-point bend loading were also examined

Strain-based criteria for mixed-mode fracture of polycrystalline graphite

The mixed-mode brittle fracture of two types of commercial graphite is investigated focusing on strain-based fracture criteria. The previously published experiments using centrally-cracked Brazilian disk specimens subjected to mixed-mode loadings are simulated by two strain-based fracture criteria: the traditional maximum tangential strain (MTSN) criterion only considering the singular terms, and the extended maximum tangential strain (EMTSN) criterion, which considers the first nonsingular strain term as well as the singular terms. Numerical simulations on the centrally-cracked Brazilian disk specimen show that the first nonsingular tangential strain term significantly influences the tangential strain distribution around the crack tip. The comparison of the evaluations by the MTSN and EMTSN criteria with the experimental data shows that the EMTSN criterion is more capable of successfully estimating the fracture resistance of graphite materials rather than the traditional MTSN criterion. In addition, when the first nonsingular term is considered, the strain-based fracture criterion provides better predictions for near mode II loadings than the stress-based fracture criterion

A comprehensive study on ring shape specimens under compressive and tensile loadings for covering the full range of I+II fracture modes of gypsum material

Using ring-shape specimens containing two aligned cracks on the internal surface of the ring, two test configurations subjected to tensile or compressive loads namely (i) diametrically compressed ring (DCR) and (ii) diametrically tensile ring (DTR) specimens were suggested to investigate the full mixed-mode I/II fracture problem. The fracture parameters, including modes I and II stress intensity factors and T-stress, were determined numerically for these two test specimens with different crack lengths and crack angles. Also, the ability of the specimens was examined by conducting experimental fracture tests on gypsum material. In addition, the direction of fracture kinking was investigated both experimentally and theoretically. The experimental results were then compared and predicted using the mixed mode fracture criteria such as maximum tangential stress (MTS) and generalized maximum tangential stress (GMTS). The normalized fracture toughness (KIIc/KIc) ratios of the tested DCR and DTR specimens were about 0.72 and 0.95, respectively. Such difference was related to the considerable effect of T-stress values and it was shown that the GMTS criterion provides more accurate predictions for the test results of both DCR and DCT samples compared to the MTS criterion