Total Fracture Energy Research Articles

Assessment of concrete-to-concrete shear bond behavior using 3-D direct shear testing

The interfaces that develop when fresh concrete is poured onto existing substrates are noted for their vulnerability and influence on the durability and integrity of the composite structure. Studies on the shear bond properties and failure mechanisms of such composite concrete-to-concrete joints under normal stress are essential for developing predictive and numerical models that accommodate various levels of joint substrate roughness. This study aims to use an innovative 3D shearing box, BCR3D, to analyze the shear behavior of concrete-to-concrete joints under direct shear tests at a constant normal stress. The influence of the degree of surface roughness on the pure shear behavior of these joints was assessed at a normal stress level of 1 MPa. The substrate post-hardening surface morphology was evaluated using a high-resolution laser profilometer. Statistical surface roughness parameters were computed using MATLAB. A parametric study was carried out involving bond strength, residual shear stress, contractive-dilative behaviors, and total fracture energy. Results showed that bond strength, dilative normal displacement, and total fracture energy were proportional to the substrate surface roughness. Residual shear stress was not affected by the initial surface roughness. Dilative normal displacements were more significant for specimens with higher surface substrate roughness due to interlocking, with values reaching up to 1.77 mm. Joints with high substrate surface roughness exhibited similar bond strength and fracture energy to those obtained from the monolithic specimens, underscoring the significance of substrate preparation before casting new concrete layers.

Analysis of fracture mechanism and fracture energy prediction of lightweight aggregate concrete

The fracture energy of lightweight aggregate concrete (LWAC) is comparatively lower than that of normal weight concrete (NWC), primarily due to the propensity for fracture exhibited by lightweight aggregates and their characteristics that modify the damage softening mechanism at the crack tip. Few studies have been done on how to precisely predict the LWAC fracture energy. In this work, 111 sets of three-point bending test data were gathered, and the impact of aggregate types and size, concrete density, water-cement (w/c) ratio, and compressive strength on the total average fracture energy (GF) and the initial fracture energy (Gf) was thoroughly evaluated. Five fracture energy prediction methods’ applicability were compared, and a fracture energy prediction expression appropriate for LWAC was presented. Finally, the three-point bending test was used to confirm the prediction. The results show that the fracture energy of LWAC is significantly influenced by changes in aggregate and mortar characteristics. The compressive strength has substantial correlations with the fracture energy of LWAC. After adjusting the aggregate and mortar coefficients, the prediction formula can correctly predict Gf and GF.

Effect of fiber content on flexural fracture parameters of high-performance steel fiber-reinforced concrete

This study deals with the effect of fiber content on fracture parameters of high-performance steel-fiber-reinforced concretes through a bending test program. All the high-performance steel-fiber-reinforced concretes flexural specimens were tested under configuration of three-point loading. The fracture parameters were hardening energy, softening energy and length of cohesive crack. Two steel fiber types were employed in the studied high-performance steel-fiber-reinforced concretes, including 35 mm long hooked fiber and 13 mm short smooth fiber. The high-performance steel-fiber-reinforced concretes were produced from the same matrix but added different fiber contents as follows: 0.0 vol.%, 0.5 vol.%, 1.0 vol.%, and 1.5 vol.%. The experimental resultsdemonstrated that two parameters, including the hardening energy and softening energy, were observed to increase with increasing of fiber content, regardless of fiber type. The hardening energy was lower than thesoftening energy at any fiber content. The short smooth fibers generally produced the higher fracture energyparameters than the long hooked fibers. The highest total fracture energies of the high-performance steel-fiber-reinforced concretes were observed at 1.0 vol.% as follows: 58.25 kJ/m2 for using short smooth and 59.16 kJ/m2 for using long hooked fibers. Besides, the addition of reinforcing fibers considerably improved the length of the cohesive crack of the high-performance steel-fiber-reinforced concretes: from 0.58 mm using no fiber to 519.85 mm using short smooth fibers 0.5 vol.%.

Full-temperature performance characterisation of super tough resin concrete for steel bridge deck paving

ABSTRACT The severe service environment of steel bridges put forward strict requirements for the deck pavement, especially the flexibility of paving materials. In this study, a new super tough resin-based concrete (STRC) was introduced and a comparative study of STRC and epoxy asphalt concrete (EAC) performance was conducted. Specifically, the high-temperature stability, low- and intermediate-temperature flexibility, fracture resistance, and fatigue properties were characterised by the dynamic creep test, beam bending test, semi-circular bending test, and semi-circular fatigue test, respectively. According to the results, at 70°C, the cumulative strain after 10,000 cycles of loading is about 2700μϵ and 900μϵ for STRC and EAC, respectively. At −10°C, the maximum tensile strain of EAC is only 2419 μϵ, which is significantly lower than that of STRC (17000 μϵ). For the cracking resistance, STRC exhibits larger total fracture energy, pre-peak and post-peak fracture energies, which indicates the excellent cracking resistance of STRC. Furthermore, the fatigue life and accumulated dissipated energy of STRC are higher than that of EAC. Besides, the tensile strain growth rate of EAC is significantly greater than that of STRC, which implies a lower crack propagation rate and better fatigue resistance of STRC.

Dynamic Analysis of a Long Run-Out Rockslide Considering Dynamic Fragmentation Behavior in Jichang Town: Insights from the Three-Dimensional Coupled Finite-Discrete Element Method

To clearly realize the dynamic process as well as the dynamic fragmentation behavior of a long run-out rockslide, a novel numerical method for landslide simulation of the coupled finite-discrete element method (FDEM) was applied and the Jichang rockslide was used as a case. The calibrated simulation result of the FDEM in a rockslide deposit corresponds well with the real rockslide deposit. The main run-out process of the rockslide lasts for 75 s and can be divided into acceleration and deceleration stages, which last for 33 s and 42 s, respectively. The maximum overall rockslide movement speed is 35 m/s while the partial sliding mass reaches 45 m/s. The fracturing, fragmentation, and disintegration processes of the sliding mass can be clearly observed from the dynamic scenarios. Fracture energy generated by rock fracturing constantly increases with time in a non-linear form. Of the total fracture energy, 54% is released in the initial 5 s because of fracturing, and 39% of the total fracture energy is released because of fragmentation and disintegration in the last 35 s. The accumulated friction energy increases in the whole run-out process, and its magnitude is much greater than the kinetic energy and fracture energy of the sliding mass.

Testing the impact energy and determination of the brittleness temperature of the welded joint of steel A516 Gr.70

Most problems with steel structures occur in the welded joint or its immediate vicinity. For this reason, special attention is paid to testing the properties of the welded joint. Fractures of welded steel structures in operating conditions have led to the need to study the influence of temperature on the behavior of steel and welded joints. For the purpose of these tests, the critical test conditions (temperature) that cause brittle fracture are defined. The paper will present the results of experimental tests of the impact energy of the welded joint of steel A516 Gr.70. Impact energy testing at different temperatures was done with the aim of determining the brittleness transition temperature of the base metal and components of the welded joint. Also, these tests should give an assessment of the influence of temperature on the ratio of the crack formation energy Wiu, and the crack propagation energy Wa in the total fracture energy Wt. This test procedure determines the tendency to brittle fracture, that is, the tendency to increase brittleness during exploitation. The obtained results are most often used for ongoing quality control and evaluation of material homogeneity.

Processing of lithium aluminium silicate glass-ceramics and investigations of fracture behaviour and its correlation with the microstructural features

Lithium Aluminium Silicate (LAS) samples were fabricated through a melt casting process using Lithium carbonate, Aluminium hydroxide, Silica and other additives as raw materials. The melt was drain casted at 1300 °C in a pre-heated mould followed by annealing and ceramization at 850 °C. Ceramized samples were subjected to X-ray diffraction. The density of the samples was found to be in the range of 2.53–2.54 g/cm3. The sample was found free from bubbles and inclusions after optically polishing. Mechanical properties including hardness, flexural strength, fracture toughness and compressive strength of LAS samples were evaluated. Knoop hardness of the LAS samples was found to be 597–669 kg/mm2. LAS sample exhibited a peak flexural strength of 110–114 MPa and compressive strength of 221 MPa before fracture. Additionally, the total fracture energy release rate (Jc) of LAS samples along with R-curve and fractography were also studied. R-curve exhibited an increasing trend of Jc with respect to normalised displacement without any sign of saturation indicating the scope for optimisation of quantification of crystals fraction in the glass matrix to obtain the predominant toughening behaviour. Finally, the physico-chemical, microstructural and optical properties were measured and correlated with the mechanical properties observed. Near to theoretical density, high crystallinity and superior mechanical properties of processed LAS glass-ceramic can be used in strategic and civilian applications.

Low temperature cracking behavior of modified asphalt mixture under modes I and III

The study of the short- and long-term cracking behavior of asphalt pavement under tensile and tear deformations, and the production of sustainable mixtures using recycled additives, were the two main goals of this study. For this purpose, two types of additives, namely pyrolysis carbon black (PCB) and pyrolysis hydrocarbon (PHC), which were made from hospital waste recycling as a result of the COVID-19 pandemic, were used to study the fracture behaviour of asphalt mixture under modes I and III (at −15 °C). For simulating the actual pavement conditions with the Edge Notched Disc Bend (ENDB) samples, 0 and 3 freeze–thaw damage (FTD) cycles were applied to mixtures. Laboratory findings indicated that the addition of 6, 12, and 18 % PCB, 1.25, 2, and 2.75 % PHC, and 18 % PCB + 2.75 % PHC into the asphalt mixtures resulted in an increase in the total fracture energy of mixtures at −15 °C by increasing the GIfpre-peak and GIIIfpre-peak as well as increasing the fracture toughness, for both FTD cycles. Also, the results of brittleness indices revealed that using 18 % PCB + 2.75 % PHC in the asphalt mixture had more flexible behaviour than the mixture containing PCB (due to a higher average brittleness index) and more brittle behaviour than the mixture containing PHC (due to a lower average brittleness index) under mode I. While the mixtures containing PCB, PHC, and 18 %PCB + 2.75 %PHC were more flexible under mode III. Finally, the mixture containing 18 % PCB + 2.75 % PHC had the best fracture performance under mode I. It increased the asphalt mixture's fracture energy and toughness respectively under 3 FTD cycles by 62 and 54 %, in comparison with the unmodified mixture and without applying FTD cycles. Also, it was indicated that the modified mixture with 18 %PCB + 2.75 %PHC can compensate for 97 % of the fracture energy decrease due to the influence of FTD cycle (under mode III), while in terms of the fracture toughness index, a 12 % increase was obtained.

Evaluation of the initial and total fracture energy of concrete: novel hybrid SVR analysis

Evaluation of the initial and total fracture energy of concrete: novel hybrid SVR analysis

Comparison of regression analysis for estimation of initial and total fracture energy of concrete

Comparison of regression analysis for estimation of initial and total fracture energy of concrete

Experimental and numerical investigation of fracture behavior of ultra high performance concrete

The fracture behavior of ultra-high performance concrete (UHPC) with different depths of notches and curing ages were investigated using a three-point bending test. The ratio of total fracture energy to initial fracture energy raises from 5.9 to 8.3, and then drops to 7.8 with the increases of depth of notch. The fracture energy of UHPC beams with different depths of notches has size effect based on comprehensive analysis. Furthermore, the ratio of total fracture energy to initial fracture energy diminishes from 17.9 to 8.2. The two types of fracture energy of UHPC grow rapidly as the curing age increases, and the influence of curing ages on the fracture energy is mainly reflected in the energy growth within 14 days. In addition, a more suitable improved softening curve model for UHPC is proposed based on the above experimental results and analysis of fracture process. The model could not only better predict the peak load in the rising section of the crack mouth open displacement (CMOD) curve, but also simulate the failure process in the descending section curve.

Evaluation of Fracture Mechanics Parameters of Light-weight Concrete by Implementing Natural Pumice Stone as Coarse Aggregate

The concrete material softening response curve is essential for accurate numerical analysis of concrete. The tensile strength, initial fracture energy, and total fracture energy are the three parameters of interest in defining such softening response. Among them, the fracture energy is usually regarded in any analytical program that attempts to model reinforced concrete (RC) structures' behavior. The brittleness and fracture characteristics of lightweight concrete (LWC) produced from 19 mm maximum size natural pumice stone aggregate were investigated via testing notched beam specimens under three-point bending test. Fracture parameters were analyzed and explained using the size effect method (SEM) and the work of fracture method (WFM), and the results were compared to those found in the published literature. The results show mean total fracture energy (GF) of 145.65 N/m and a mean characteristic length (Lch) of 590.34 mm. Later, by correlating the result obtained via this method to the SEM approach, the initial fracture energy (Gf) was determined with a mean value of 58.26 N/m and the fracture toughness (KIC) was found to be 38.47 MPa.mm0.5. Lightweight concrete was found to be more ductile and need more energy to propagate fracture across the specimen, as shown by a comparison of current data to that acquired from literature.

Improvement of size effect simulation based on an energy-balanced exponential softening bond model and fracture energy regularization

Although the Mode I fracture of rock demonstrates a noticeable size effect, current contact models in the discrete element method cannot simulate the size effect very well. An exponential softening bond model is proposed to address this issue based on an exponential damage law and an elliptic yield criterion. Its basic formulas are established on energy balance to ensure that the total fracture energy of the normal and shear springs always equals the fracture energy dissipated by the resultant contact force. The simulations of uniaxial tensile and three-point bending tests were conducted to demonstrate the performances of the proposed model on the fracture simulations. The particle size dependency is successfully eliminated by fracture energy regularization, in which the force–displacement relationship is adjusted based on fracture energy and particle size. The simulation results show that the exponential softening bond model effectively simulates the whole load–displacement curves of experimental tests. It also demonstrates a perfect energy balance among external work, internal energy, and fracture energy. Besides, compared with the other two bond models, the exponential softening bond model is more precise in representing the fracture toughness, the fracture process zone, and the size effect of the Mode I fracture of limestone.

A Simple Principle for Fracture Toughness Assessment of Ductile Materials by Ball Indentation Technique

A simple principle for determining fracture toughness (FT) of ductile materials by ball indentation (BI) technique is suggested here. The principle is based on the consideration that the total fracture energy of a material is equivalent to the indentation energy corresponding to a critical plastic strain (CPS); the latter can be estimated from the true fracture strain in tensile test and stress triaxiality ratio in tensile and BI test. Fracture toughness values of 304LN stainless, 316LN stainless, interstitial free (IF), 0.14% C and SA333 steels have been determined by the modified BI technique as well as by standard J-integral test for two steels. A comparative assessment indicates that the equivalent FT values determined by the suggested BI technique is within 5% of the estimated or reported values of J-integral FT of the materials, and thus validates the consideration behind the principle of the suggested BI technique.

Evaluation of fracture performance of Polyvinyl Alcohol fiber reinforced hot mix asphalt

• Fracture performance of reinforced HMA was significantly affected by Gradation type, binder grade, and PVA fiber dosage. • Coarse graded reinforced HMA exhibited 25% higher strength than fine graded HMA at 0.3% fiber content. • FE and FI doubled for lower grade asphalt reinforced HMA than control. • Coarse graded HMA showed higher fracture growth rate. • SEM and DIC analyses revealed effective crack bridging and enhanced strain distribution due to fiber reinforcement. Several studies have been conducted over the past two decades to evaluate the fracture and fatigue performance of hot mix asphalt (HMA) reinforced with different fiber types, dosages, and aspect ratio. However, a few studies focused on the impact of aggregate gradation and binder grades on the fracture performance of fiber reinforced mixtures. This study adopted a systematic approach to evaluate the impact of three different coarse and fine aggregate gradations with different nominal maximum sizes using three different binder grades and varying Polyvinyl Alcohol (PVA) fiber content. Semicircular bending beam (SCB) test was performed to evaluate several fracture characteristics of PVA fiber reinforced HMA. Experimental results revealed that binder grades and gradation significantly affect the fracture performance of such mixtures. Total fracture energy, flexibility index, and stiffness of 0.3% PVA reinforced PG 58-22 mixtures were doubled relative to control ones. However, fiber reinforced PG76-22 mixtures exhibited up to 50% improvements. The fracture growth rate reduced by 250% at 0.3% fiber content in coarse graded mixture while cumulative energy per unit crack length increased by 190% in fine graded mixture. Digital Imaging Correlation analyses revealed more twisted and convoluted fracture path and higher strain distribution in lower grade asphalt reinforced mixtures with lower nominal maximum size gradation. Scanning electron microscopy micrographs showed proper fiber coating of asphalt and effective fiber bridging across the cracks indicating enhanced resistance to post-peak deformation under load.

Incorporating 3D image analysis and response surface method to evaluate the effects of moisture damage on reinforced asphalt mixtures using glass and polypropylene fibers

• Incorporation of up to a certain amount of combined fibers can beneficially enhance load bearing capacity and reduce the proportion of broken aggregate. • Fibers can increase the total fracture energy (particularly post-peak G f ) and consequently reduce the fragility index by obstructing crack propagation. • Integration of fibers can improve mixtures' moisture susceptibility and reduce the negative effects of moisture damage. • The destructive impact of an increase in temperature is more dominant compared to the number of freeze and thaw cycles. • The combination of the response surface method and image analysis techniques exhibited a great capability to detect and quantify adhesion and cohesion failures. This paper evaluates the performance of fiber-reinforced mixtures subjected to moisture damage. Response Surface Method was used to design an experimental matrix based on the central composite design. The amounts of fibers, number of freeze and thaw cycles, and testing temperatures were considered as factors, while maximum load, stiffness, indirect tensile strength, CT index , fragility index, broken aggregate, and adhesion failure were regarded as the responses. Indirect tensile strength test and 3D image analysis were conducted to characterize mixtures’ fracture properties and moisture susceptibility, respectively. The results show that temperature exhibits the highest influence on mixtures’ mechanical properties as well as adhesion and cohesion failures. An increase in the number of freeze and thaw cycles deteriorated the mixtures’ performance. Although higher beneficial impacts of glass fiber were reported earlier, this study proved that the performance of the mixtures prepared with combined fibers is comparable with the previous study. This finding brings forth the advantage in cost reduction of reinforced mixtures production due to the replacement of part of the glass fiber with polypropylene fiber. In addition, it was found that a combination of utilized fibers up to approximately 0.2% by weight of aggregates exhibited beneficial impacts on load bearing capacity, indirect tensile strength, and proportion of broken aggregate while exceeding this amount was not favorable which was correlated to the jeopardizing of cohesion level between mixtures constituents. Moreover, it was observed that fibers slightly reduced the fragility index by obstructing crack propagation. It was finally concluded that a higher amount of fibers enhanced mixtures' moisture resistance and diminish the negative effects of freeze and thaw cycles.

Experimental Study on Size Effect and Fracture Properties of Polypropylene Fiber Reinforced Lightweight Aggregate Concrete

In this experimental research, the effects of polypropylene fibers on size effect and fracture properties of lightweight aggregate concrete were studied. Two methods, including size effect method and work of fracture method, were used to investigate and analyze the size effect and fracture properties on different sizes of notched beams. The polypropylene fiber contents were 0.5%, 0.75%, and 1% by volume fraction. The obtained results revealed that increasing the polypropylene fibers in lightweight aggregate concrete relatively decreased the dependence of strength on the size effect parameter, while the addition of polypropylene fibers exhibited significant influence on decreasing the size dependency of ductility and fracture energy in lightweight aggregate concrete. Moreover, the increase of polypropylene fibers improved the total fracture energy (GF), initial fracture energy (Gf), characteristic length (lch), length of fracture process zone (cf), and critical stress intensity factor (KIc) of lightweight aggregate concrete in both size effect method and work of fracture method. This increase was more significant in work of fracture method because of considering the post-peak behavior. The size effect method was suitable and accurate for plain lightweight aggregate concrete. The GF ⁄ Gf ratio increased from 2.88 in plain lightweight aggregate concrete to 12.26 in polypropylene fiber reinforced lightweight aggregate concrete.

Determination of the fracture energy under mode I loading of a honeycomb/carbon-epoxy sandwich panel using the asymmetric double cantilever beam test

The asymmetric double cantilever beam (ADCB) test was used to measure the fracture energy of a honeycomb/carbon-epoxy sandwich panel under mode I loading. A data reduction scheme based on equivalent crack length theory was developed for this case. The experimental Resistance-curves were obtained using exclusively data ensuing from the load-displacement curves avoiding the usual and non-rigorous crack length monitoring during the test. Furthermore, a mode partitioning methodology lying on cohesive zone modelling was adopted, aiming to estimate the fracture energy under mode I loading from the total fracture energy under mixed-mode I+II ensuing from the ADCB test. Numerical simulations of the ADCB test considering cohesive zone modelling were performed for the sake of validation of the followed procedure.

Fibre bridging: Continuum modelling of extrinsic toughening in double cantilever beam tests

Extrinsic toughening, such as fibre bridging, acts behind the crack tip to increase toughness in composite laminates. Computational studies have captured this phenomenon; however, the uniqueness of fit between computational results (which vary based on the interface traction-separation relationship) and experimental results has not been explored in detail. Here, detailed exploration of the parameter space for various traction-separation laws (TSL) using finite elements is presented to investigate the role of fibre bridging. In the absence of extrinsic toughening, a linear softening TSL is sufficient to capture the key R-curve features, the total input fracture energy is of primary importance. Where extrinsic toughening is present, the ratio between intrinsic and extrinsic energy dictates the shape of the crack growth resistance curve (where fracture toughness (energy) increases with increasing crack growth). The influence of fibre bridging length on the crack growth required to reach a plateau in toughness is examined. A strategy for determining key cohesive properties from a double cantilever beam test is presented and applied to experimental results.

Gradient strengthening effects in mode I tearing of ductile plate at the engineering scale

The present study aims to quantify the influence of void size effect on crack initiation and growth in mode I tearing of large ductile plates. Specifically, the aim is to demonstrate how size effects influence the transition from crack initiation to steady-state tearing and reveal the evolution in both the traction-separation relation and the fracture energy dissipated in the tearing process when related to large-scale cohesive modeling. The study investigates mode I tearing by adopting the gradient enriched Gurson–Tvergaard–Needleman (GTN) model by Niordson and Tvergaard (2019), where the novelty lies in accounting for strain gradient hardening near growing micro-voids in relation to large-scale plate tearing. The steady-state crack growth conditions are compared to a 2D plane strain model setup, while the transition from crack initiation to steady-state is analyzed using full 3D plate tearing calculations. A discussion about the 2D versus 3D models’ capability, their differences, and agreement is presented. The results are related to the traction-separation relations fit for efficient large-scale simulations, e.g., using cohesive zone modeling. The present study shows that the material length parameter incorporated into the constitutive model has a negligible impact on the onset of plate thinning (or necking) but delays the onset of shear localization and, thus, increases the total cohesive fracture energy.