Angular Crack Research Articles

Effect of nano-reduced graphene oxide (NRGO) on long-term fracture behavior of Warm Mix Asphalt (WMA)

Recent studies have shown that in addition to ambient temperature, time-dependent factors such as temperature cycles and freeze–thaw cycles (FTCs) affect the speed of creation and growth of low-temperature cracks (LTCs) and intermediate-temperature cracks (ITCs) by creating the aging process in the asphalt mixture. Therefore, it is necessary to study the cracking behavior of asphalt mixtures by considering these factors. In the present study, an attempt was made to evaluate the long-term fracture behavior of Warm Mix Asphalt (WMA) modified with nano-reduced graphene oxide (NRGO) containing vertical and angular cracks under mode I loading conditions at low and intermediate temperatures using Semi-circular bend (SCB) geometry. In order to simulate long-term performance, two conditions of 3 FTC and aging process (for 6 days) were applied to the mixtures with and without NRGO, and the results were compared with samples subjected to 0 FTC (short-term performance). The results showed that adding 0.3% and 0.6% NRGO to the WMA mixture increased fracture toughness (KIC), fracture energy (GF), and stiffness under mode I at low and intermediate temperatures. At +15 °C and for the geometry containing the vertical crack, the NRGO-modified WMA mixture had better flexibility under 3 FTC than 0 FTC; while, the flexibility of the NRGO-modified WMA mixture decreased under aging process. For geometry containing angular crack, flexibility indices improved for NRGO-containing mixtures under 3 FTC and aging process (at +15 °C temperature). On the other hand, the results showed that the addition of NRGO to the WMA mixture, while increasing the maximum load at the moment of fracture, caused a decrease in the displacement at the fractured moment at low and intermediate temperatures. This result was obtained for the mixtures that were conditioned under aging process. However, the results showed that applying 3 FTCs decreased the maximum load at the moment of fracture and increased the displacement at the fractured moment. Finally, the results showed that the reduction of fracture indices was higher for WMA and NRGO-modified WMA mixtures under 3 FTCs (at temperatures ±15 °C); therefore, applying 3 FTC instead of aging process can be used to evaluate the long-term performance of asphalt mixtures.

Evaluation of long-term fracture behavior of amorphous poly alpha olefin (APAO)-modified Hot Mix Asphalt (HMA) under modes I and II at low and intermediate temperatures

Opening and in-plane sliding cracks are among the most important cracks in flexible pavements, resulting from tensile and sliding deformations, respectively. Loading and freeze–thaw damage (FTD) are the two main factors for the initiation and growth of these types of cracks, which may lead to two types of cracks, intermediate-temperature cracks (ITCs) and low-temperature cracks (LTCs), depending on the ambient temperature. Therefore, in order to simulate the tensile and sliding deformations of mixtures containing ITCs and LTCs, two geometries called symmetric sample SCB (containing vertical cracks) and classical-modified sample SCB-2 (containing angular crack) resulting from mode I loading, as well as two geometries named modified sample SCB-1 (containing vertical crack) and modified sample SCB-2 (containing vertical crack) resulting from mode II loading at temperatures of + 15 and −15 °C were evaluated. In order to control and reduce the cracking potential of Hot Mix Asphalt (HMA), the amorphous poly alpha olefin (APAO) additive was used in percentages of 3, 6, and 9 % and compared with the mixture without additives. Also, all specimens were under 0 and 3 FTD cycles. In order to measure and evaluate the fracture behavior results of unmodified and APAO-modified specimens, fracture toughness indicators (KIC and KIIC) and fracture energy (GF) were calculated. Eventually, to investigate the fracture behaviors of mixtures before the maximum loading, two indicators of tensile stiffness index (TSI) and tensile strength (TS) were evaluated. The results showed that at −15 °C and from the perspective of KIC (or KIIC) and GF (under modes I and II) indicators, the fracture resistance in specimens comprising 6 and 9 % APAO under 0 and 3 FTD cycles was higher compared to the base specimen. At + 15 °C and from the perspective of KIC (or KIIC) indicator, the fracture resistance of mixtures containing 6 and 9 % APAO in 0 and 3 FTD cycles was higher than the unmodified specimen; however, from the point of view of GF (under modes I and II) indicator, the mixture containing 9 % APAO represented greater fracture resistance. Also, it was indicated that mixtures modified with APAO represented higher TSI as well as TS values; therefore, APAO additive increased the resistance to elastic deformation by increasing the fracture performance before the maximum loading. Finally, mixtures containing 6 and 9 % APAO were chosen as the best mixture; however, the use of these mixtures in areas with temperatures lower than −15 °C should be done with caution due to the relative reduction in flexibility of the mixture containing APAO additive.

Effect of hospital waste pyrolysis hydrocarbon (HWPHC) on fracture behavior of Warm Mix asphalt (WMA) under freeze–thaw damage (FTD)

Warm mix asphalt (WMA) is more susceptible to macroscopic cracks than other mixtures due to insufficient aggregate-bitumen adhesion, especially at low temperatures. In this study, the behavior of low-temperature cracking (LTC) and intermediate temperature cracking (ITC) of WMA mixture with and without the environmentally friendly additive called hospital waste pyrolysis hydrocarbon (HWPHC) was evaluated at −15 and +15°C under mode I loading conditions using three geometries: symmetric specimen SCB, classical-modified specimen SCB-1, and symmetric specimen ENDB. In order to determine the effect of freeze–thaw damage (FTD) on the mixtures, samples with and without the HWPHC additives were subjected to 0 and 3 FTD cycles. The results showed that adding 3 % and 6 % of HWPHC additive increased the fracture resistance of the samples, i.e., fracture energy (GF) and fracture toughness (KIC) at temperatures of ±15 °C using all three mentioned geometries under 0 and 3 FTD cycles. At temperatures of ±15 °C and for all mixtures with and without additives, the average GF and KIC for symmetric specimen ENDB (vertical crack) are lower and higher than for symmetric specimen SCB (vertical crack) and classical-modified specimen SCB-1 (angular crack), respectively. Therefore, the complete fracture potential and crack initiation for the ENDB geometry were higher and lower than the other two geometries (under 0 and 3 FTD cycles). Also, at temperatures of ±15 °C and under 0 and 3 FTD cycles, the flexibility indices showed that adding HWPHC reduced the flexibility of the WMA mixture slightly. Finally, the increase in the fracture resistance and resistance to elastic deformation of the mixtures modified with HWPHC additive was achieved using two Tensile Stiffness Index (TSI) and Tensile Strength (TS) indices. Therefore, in addition to helping to reduce the amount of environmental waste and increase cleaner production, the mentioned mixtures can be used to improve the LTC and ITC fracture performance of the WMA mixture under mode I and FTD conditions.

Tomographic Reconstruction of Rolling Contact Fatigues in Rails Using 3D Eddy Current Pulsed Thermography

The detection and quantification of the rolling contact fatigue (RCF) in rail tracks are essential for rail safety and condition-based maintenance. The tomographic reconstruction of the rolling contact fatigue is challenging work. The x-ray is unable to do in-situ inspection effectively. This paper proposes a new approach for RCF construction using 3D eddy current pulsed thermography. A differential time-square-root (sqrt) of temperature drop (DTSTD) is proposed as a mean to construct the sectional images and to reconstruct the thermal tomography image. The proposed method is validated through artificial angular crack slots as well as natural RCF crack. The thermal tomographic reconstruction is compared with the x-ray computed tomography on a rail track head cut-off with RCF cracks.

Mechanical and Scratch behaviour of TiAlN Coated and 3D Printed H13 Tool Steel

ABSTRACT This investigation focuses on the manufacturing of H13 tool steel samples using the selective laser melting (SLM) process. The sample with the highest part density (99% relative density) and lowest porosity was obtained with 733.3 J/mm3 volumetric energy density and other process parameters such as 203 W of laser power, 92.3 m/s of scan speed, 50 µm of layer thickness, and 60 µm of hatch spacing. The SLM sample was tempered at 550°C and dwelled for 2 hours, followed by furnace cooling. Tempering transformed the retained-austenite into tempered austenite, ferrite, and few carbides with BCC structure. Further, TiAlN coating was deposited over both the samples (as-SLM and tempered-SLM) resulting in improved surface quality and mechanical properties. Microhardness of the as-SLM sample was improved by 1.51 and 3.99 times on post-tempering and coating deposition, respectively. Moreover, the ratios of hardness and Young’s modulus (H/E and H3/E2) also got improved. What is more, in the adhesion test, typically, three different cracks (parallel crack, angular crack and transverse crack) were observed as the failure mechanism of coating with both the samples. Nevertheless, TiAlN coating showed better adhesion with tempered-SLM sample compared to the as-SLM sample.

Pure mode I and pure mode II fracture resistance of modified hot mix asphalt at low and intermediate temperatures

AbstractAngular cracks are one of the types of cracks in asphalt mixtures that can be created due to the location of coarse aggregates as well as the weakness of the soft asphalt matrix (SAM). In this study, pure mode I was modeled to simulate the fracture behavior of hot mix asphalt (HMA) mixture containing angular cracks using the extended finite element method (XFEM). To improve HMA performance, calcium lignosulfonates (CL) additive and polyester fiber (PE), which were both environmentally and economically justifiable, were used. Numerical and experimental results showed that the proposed samples in both pure mode I (angular crack) and pure mode II (vertical crack) were able to model the fracture behavior of HMA; therefore, it can be used as suitable samples to study the pure mode crack deformation of HMA at low and intermediate temperatures. Also, the presence of coarse aggregate in the ligament section of the samples turned out to be an important factor in increasing fracture energy, fracture toughness, and reducing brittleness.

Evaluation of fracture behavior of modified Warm Mix Asphalt (WMA) under modes I and II at low and intermediate temperatures

Cracking is considered to be one of the most important distress of the Warm Mix Asphalt (WMA) mixture, which can occur in different climatic conditions due to a lack of proper bonds between aggregate and bitumen. Since the WMA mixture consists of coarse aggregates in different parts of the asphalt layer, cracks can develop and grow at an angular position. Therefore, this study investigates the fracture behavior of WMA mixtures under vertical (Pure mode II) and angular (Pure mode I) cracking states using a semi-circular bend (SCB) sample at −18 °C and +25 °C using the fracture mechanics method. To improve the WMA mixture's performance, additives of Calcium Lignosulfonate (CL) and waste Polyester (PE) fibers, which were economically justifiable, were used separately and simultaneously in different percentages. According to numerical-experimental results, the proposed samples in both pure mode I (angular crack) and pure mode II (vertical crack) were able to model the WMA's fracture behavior and therefore can be used as suitable specimens for studying the pure mode crack deformation of WMA at intermediate and low temperatures. The results also showed that the coarse aggregate distribution in the ligament section of the specimen had a significant contribution in improving the WMA mixture's fracture performance. As a result, fracture energy (GF), fracture toughness (KI and KII), The Flexibility Index (FI), Cracking Resistance Index (CRI), and the Toughness Index (TI) depended on the type of additive used in the WMA mixture. Finally, 0.25PE-6CL, 0.25PE, and 6CL mixtures had the best results in terms of fracture mechanics.

Numerical study of fatigue behavior of the aluminum 7075-T6 cantilever beam with angular cracks in different stress ratios

The numerical simulation of fatigue behavior of the Aluminum 7075-T6 cantilever beam with an angular crack has been investigated. Cracks are located separately in three different positions of the investigated beam. To predict the fatigue behavior of the cantilever beam the crack propagation was manually simulated. Compression load is applied in different stress ratios between zero and one; then, the obtained numerical results of this research are compared with the experimental results. It is observed that increasing the stress ratio increases the percentage of the fatigue life of the sample significantly. Ascending growth of fatigue life is slow and more severe by increasing of the stress ratio for the first and the third position, respectively. By increasing the stress ratio, the rate of deviation of the crack decreases and it converges to 0° in parallel to the width of the beam. This result is also observed with an increase in the distance from the support of beam. Furthermore, it is also revealed that by the increase in the initial length of the crack, the fatigue life initially reduces with smaller ratios. However, along the larger cracks, the decreasing ratio of fatigue life increases significantly. © 2021 Growing Science Ltd. All rights reserved.

Fracture resistance of asphalt mixtures under mixed-mode I/II loading at low-temperature: Without and with nano SiO2

Increasing traffic congestion especially in cold climates has increased the damage caused by low-temperature cracks (LTCs) in the asphalt mix where the constituents are not able to withstand the loads required in these climates lonely and using the modifier is undeniable. In recent years, some research fields have been conducted on the use of nanomaterials as a modifier in asphalt mixtures to improve their properties. In accordance with previous researches, one of the nanomaterials that have appropriate effects on the performance of asphalt mixtures is Nano-SiO2. In this study, the effect of Nano-SiO2 on the incident of low-temperature cracks in asphalt mixtures is experimentally investigated. For this purpose, the semicircular bending test (SCB) under mixed-mode I/II loading is used for investigating the effect of Nano-SiO2 on forming cracks in asphalt (i.e., vertical and angular crack) at different temperatures of −5℃, −15℃, and −25℃. Results show that the maximum stress intensity factor (SIF) of the modified asphalt mixtures is related to specimens which have angular crack under pure opening mode, while the maximum critical SIF is improved when Nano-SiO2 is added to specimens which have vertical cracks under mixed-mode I/II with Me = 0.6 at −25℃. Furthermore, the critical SIF of all specimens having both vertical and angular cracks is significantly improved by adding 1.2% of Nano-SiO2 at all temperatures.

Investigation of crack repair using piezoelectric material under thermo-mechanical loading

This article presents an experimental investigation of repair of a crack in a structure using piezoelectric material under thermo-mechanical loading environment. The cyclic mechanical load is applied on a plate with a straight and angular crack under uniform temperature environment. Two cases have been considered for the repair of crack under (a) mechanical loading and (b) thermo-mechanical loading environment. A piezoelectric sensor is utilized to measure voltage. The measured voltage is used to calculate the stress intensity factor in passive and active modes. The effect of a single and double piezoelectric patch in the repair of the plate is investigated. The double piezoelectric patch is found to be more effective as compared to single patch when placed symmetrically offset from the crack. An optimal value of voltage and phase difference is evaluated for most effective crack repair. Location of the piezoelectric patch is varied with respect to crack location, and best-suited position for effective crack repair is proposed. The viability of piezoelectric used for repair under thermo-mechanical loading is discussed. The active mode of repair by piezoelectric is found to be effective under thermo-mechanical loading environment.

Modeling of crack repair using piezoelectric material: XFEM approach

PurposeThe purpose of this paper is to analyze the repair of a straight and angular crack in the structure using a piezoelectric material under thermo-mechanical loading by the extended finite element method (XFEM) approach. This provides a general and simple solution for the modeling of crack in the structure to analyze the repair.Design/methodology/approachThe extended finite element method is used to model crack geometry. The crack surface is modeled by Heaviside enrichment function while the crack front is modeled by branch enrichment functions.FindingsThe effectiveness of the repair is measured in terms of stress intensity factor and J-integral. The critical voltage at which patch repair is most effective is evaluated and presented. Optimal patch shape, location of patch, adhesive thickness and adhesive modulus are obtained for effective repair under thermo-mechanical loading environment.Originality/valueThe presented numerical modeling and simulation by the XFEM approach are of great benefit to analyze crack repair in two-dimensional and three-dimensional structures using piezoelectric patch material under thermo-mechanical loading.

Investigation of the effect of nanosilica on mechanical, structural, and fracture toughness of polyvinylidene fluoride films

This work presented fabrication and characterization of the polyvinylidene fluoride (PVDF) composite material containing various contents of nano-silica (SiO2). The effects of SiO2 contents and notched forms, e.g., V-notched and U-notched single tensile, on the mechanical properties of composite films are investigated. The experimental results show that when an inevitable crack appears in the material and can’t be repaired, trimming the sharp angular crack into a circle can increase the tensile strength by 10%–35%. The stress of the film reaches the maximum value of 35.872 MPa, the elastic modulus is 2.131 GPa and fracture toughness is 2.747 MPa•m1/2 when the filling amount of SiO2 is 6%. But with increasing of SiO2 content, failure behavior of the materials becomes more and more brittle. Then, morphology of the micro-structures is analyzed by electron scanning electron microscope. It is found that the addition of SiO2 doesn’t affect the structure of the films, and it is helpful to increase the number of film pores.

Analysis of Vibration Natural Frequencies of Rotationally Restrained and Simply Supported Circular Plate with Weakened Interior Circle Due to an Angular Crack

An exact solution for the problem of vibration of a circular plate weakened along an internal concentric circle due to the presence of an angular crack, rotationally restrained and simply supported along an edge of the plate is derived. Frequencies for the first six modes of plate vibrations are computed for varying values of the elastic rotational edge restraint, radius of an angular crack and the extent of weakening duly simulated by considering an angular crack as an elastic rotational restraint on the plate. Internal weakening due to crack is found to cause decrease in fundamental frequency of the plate by around as high as 30%. Exact method of solution and the results presented in this paper are expected to be of specific use in analyzing the effect of an angular crack on fundamental frequency of the circular plate in the presence of a rotational restraint with simply supported boundary along the outer edge of the plate. These exact solutions can be of use in checking numerical or approximate results obtained through numerical methods such as finite element method.

Ultimate shear strength of intact and cracked stiffened panels

The present paper focuses on the ultimate shear strength analysis of intact and cracked stiffened panels. Several potential parameters influencing the ultimate shear strength of intact panels are discussed, including the patterns and amplitudes of initial deflection, the slenderness and aspect ratios of the plates, and the boundary conditions defined by the torsional stiffness of support members. An empirical formula for the ultimate shear strength of intact stiffened panels is proposed based on parametric nonlinear finite element analyses in ANSYS. Furthermore, the ultimate shear strength characteristics of cracked stiffened panels are investigated in LS-DYNA with the implicit method. Three types of cracks are considered, namely vertical crack, horizontal crack and angular crack. A simplified method is put forward to calculate the equivalent crack length. And the formula for the ultimate shear strength of cracked stiffened panels is derived on the basis of the formula for intact stiffened panels.

Vibration Analysis of a Rotating Disk with a Crack

This paper studies the vibrational behaviour of a rotating disk with a radially or circumferentially oriented crack. The disk rotates with a constant angular speed. To treat this problem, the finite element method is employed. The disk is discretised into finite elements, and the crack is considered as nonpropagating and always open. The solutions to this problem's governing equations yield the natural frequencies and mode shapes. The frequency response due to dynamic loading is also yielded to determine the crack's effect on the frequency domain. For both crack orientations, parametric studies are conducted to investigate the sensitivity of the vibrational behaviour to the disk's angular speed and radial crack length or circumferential crack angle and distance from the disk's centre. The accuracy of the results is validated through comparisons with results available from the literature.

Nonlinear Dynamic Characteristics of a Simple Blade with Breathing Crack Using Ansys Software

Nonlinear dynamic response represents the most important studies for structures subjected to a dynamic mo-tion so that it provides the researcher by an excellent information especially at critical design levels. The un-predictable nonlinearity in the structure appears when damage is inherited. Most times, the failure of the structure is related to the dynamic nonlinearity. With regard to the breathing phenomena for nonlinear struc-tural systems, very little is known about how the nonlinearities influence the response and the dynamic char-acteristics of cracked structures. In this research, dynamic nonlinearity is presented in damaged structure due to presence of a crack. The crack is assumed to be open and close simultaneously and then breathing. Effect of breathing phenomenon was studied deeply. Crack breathing is simulated at the crack surfaces using con-tact elements. The contact, geometrical, penalty, and spin stiffnesses are taken in consideration. In addition, effect of several important parameters such as rotor angular velocity and crack ratio are studied. The study showed that the breathing natural frequency of any structure is ranged between opened (no contact) and closed crack natural frequencies. The larger crack length, the more nonlinear disturbance in the dynamic re-sponse behavior. Also, at a critical crack length, some mode shapes tend to exchange and pass over with other modes. The presence of the mode interchanging and mode crossover was a guide on the nonlinear re-sponse for the cracked structure. The numerical modeling is achieved using ANSYS finite element program. Experimental data are used for validating the accurate use of contact elements in ANSYS environment.

CRACK DETECTION USING A HYBRID FINITE DIFFERENCE FREQUENCY DOMAIN AND PARTICLE SWARM OPTIMIZATION TECHNIQUES

A hybrid technique based on finite-difference frequency domain (FDFD) and particle swarm optimization (PSO) techniques is proposed to reconstruct the angular crack width and its position in the conductor and ability to detect the crack width, position, and its depth in single and multilayer dielectric objects. FDFD is formulated to calculate the scattered field after illuminating the object by a microwave transmitter. Two-dimensional model for the object is used. Computer simulations have been performed by means of a numerical program; results show the capabilities of the proposed approach. This paper presents a computational approach to the two dimensional inverse scattering problem based on FDFD method and PSO technique to determine the crack position, width and depth. By using the scattered field, the specifications of the crack are reconstructed.

Structure of Plasma-Sprayed Zirconia Coatings Tailored by Controlling the Temperature and Velocity of the Sprayed Particles

The correlation between particle temperature and velocity with the structure of plasma-sprayed zirconia coatings is studied to determine which parameter most strongly influences the coating structure. The particle temperature and velocity are measured using an integrated optical monitoring system positioned normal to the spraying axis. The total porosity, angular crack distribution, and thermal diffusivity are correlated with the particle temperature and velocity. Results show that the temperature of the sprayed particles has a larger effect on the coating properties than the velocity in the conditions investigated.

Fatigue-Crack Propagation in Heat-Resistant Alloys under Thermomechanical Loading. Part 1. Experimental Method and Results of the Investigation of Crack-Propagation Rates

We propose a calculation and experimental method for studying the influence of cyclic thermomechanical loading, wherein the object under investigation is subjected to the simultaneous action of a cyclically varying mechanical load and temperature varying with time and resulting in the occurrence of thermal stresses, on fatigue-crack propagation in specimens of triangular cross section. We present results of the calculation of the stress-intensity factors in elastic formulation for an angular mode-I crack in the case of loading by pure bending and temperature varying with time. We studied crack-growth resistance of alloys KhN70VMTYu (Eacute;I617) and KhN73MBTYu (Eacute;I698) at a constant temperature and under thermomechanical loading. Kinetic fracture diagrams da/dN vs KI have been constructed for the alloys at a constant temperature and for two regimes of thermal cycling within a near-threshold and mean-amplitude portions of the curve da/dN vs KI .

Alumina Coatings by Plasma Spraying of Monosize Sapphire Particles

A series of plasma sprayed coatings of controlled microstructure was obtained by spraying three monosize sapphire powders using an axial injection torch in which the plasma gas composition and nozzle diameter were the only processing parameters varied. The effects of changes in these parameters on the coating splat morphology, porosity, angular crack distribution, and hardness are reported. The uniform, dense microstructure and the high hardness of 14 GPa (a level usually only associated with chromia thermal spray coatings) of the best alumina coatings resulted from using tightly controlled processing conditions and monodispersed precursor powders. The microstructural quality of plasma sprayed coatings and, hence, the coating properties can be improved significantly by minimizing variations in processing and raw material parameters.