Crack Opening Behavior Research Articles

The influence of high temperature exposure on the tensile and cracking behavior of crimped-textile reinforced mortar composites (TRMs)

The use of textile reinforced mortar/concrete composites (TRM) in strengthening applications and new constructions necessitates understanding its behavior after exposure to high temperatures. Therefore, in this study, the residual tensile and cracking behavior of carbon based TRMs was studied. A total of 96 TRM samples were tested in the temperature range of 25–450 °C. The main parameters studied were the textile crimp, textile orientation, textile coating, multiple textile layers and hybrid reinforcement. The hybrid TRM was formed with a combination of uncoated and styrene butadiene (SBR) coated textile layers. This study served as one of the first experimental campaigns to use digital image correlation (DIC) for understanding the residual crack opening behavior of TRMs. The results demonstrated that the properties of the TRMs were noticeably influenced by temperature exposure of 450 °C. Unlike the uncoated or hybrid textile TRMs, the SBR coated textile TRMs demonstrated curvature and cracking after 450 °C exposure. The study showed that the load aligned crimped yarn TRMs were always associated with larger deformation irrespective of the exposure temperature. The crack openings also increased significantly after exposure to 450 °C. Whereas the presence of heat formed cracks caused higher initial rate of crack openings. The evolution in the crack spacing with increasing temperature fluctuated due to the possible relative degradation of cracking strength vs interfacial mortar textile bonding. Finally, the proposed empirical equation showed a good fit to the residual average crack opening vs. stress relations.

Cracking and failure mode behavior of hybrid FRP strengthened RC column members under flexural loading

AbstractStrengthening of reinforced concrete (RC) members in bridges and buildings is often required to improve flexural performance. Strengthening using fiber‐reinforced polymer (FRP) composites has become popular as FRPs offer multiple advantages compared with conventional strengthening practices like steel jacketing and concrete enlargement. External bonding (EB) using carbon FRP (CFRP) laminates/fabric has become a common strengthening practice. The effectiveness of the EB strengthened system is reduced due to possible debonding of FRP from concrete substrate. The near‐surface mounting (NSM) of FRP laminates is efficient in reducing the debonding failure, but it is not effective under dominant compression loading. Hybrid FRP (HYB) strengthening combines the advantages of both the NSM and EB techniques. HYB strengthening can enhance the performance of RC members under all loading combinations. The main objective of this study is to understand the flexural crack opening behavior of control and hybrid FRP strengthened RC column members under pure bending. The digital image correlation (DIC) analysis shows that the crack width and its propagation are significantly reduced due to hybrid FRP strengthening. The crack widths measured using the DIC are compared with the analytical predictions based on Eurocode 2 and fib bulletin 90. HYB FRP strengthening increased the strength and post‐cracking stiffness of RC elements under flexure without compromising the ductility. In addition, the HYB strengthening distributed the damage under flexural loading, unlike localized damage observed in control RC elements.

Quantifying 3D crack propagation in nodular graphite cast iron using advanced digital volume correlation and X-ray computed tomography

Advanced digital volume correlation (DVC) combined with X-ray computed tomography (XCT) was utilized to investigate the 3D crack propagation in nodular graphite cast iron under tensile loading. The objective of this work was to quantify crack growth at the voxel-scale and extract fracture mechanics parameters such as the 3D crack front, crack opening displacements (CODs), and stress intensity factors (SIFs). By employing a crack growth updating strategy and an adaptive multiscale mesh, the 3D crack shape and propagation were accurately captured throughout the entire process. Von Mises strain and COD fields were characterized to provide insights into plastic zones and variations in crack opening behavior. Estimation of SIFs revealed a mode I dominant regime and limited influence from modes II and III. This study provides comprehensive insights into crack propagation and crack opening behavior, providing valuable information to fracture mechanics.

Crack face closure effect and opening behaviors of fatigue pre-crack treated by laser peening

The present work investigates the generation process of crack face closure under laser shock and its effect on the crack opening behavior to reveal the underlying reason for the high-level crack closure induced by laser peening (LP) on the initial fatigue crack. It is found that crack face closure generates a firm compression to the crack face, causing the significant elongation in the crack wake during the crack opening process to prevent crack faces from separating even under the high-level external load. The contribution of crack face closure to crack retardation is comparable to LP-induced residual stress.

Integrated approach to diagnose structural behaviour of dam

The objectives of this study are to: (1) develop an approach for extracting representative information from dam behaviour data and (2) diagnose deformation and crack opening behaviour by integrating techniques in transfer entropy (TE), chaos theory and wavelet transform (WT). First, TE is employed to map the information flow between measuring points to select the representative measuring point. The phase space reconstruction of observation data on dam behaviour is implemented, where lag time τ and embedding dimension m are identified by the statistical C–C method. The non-linear structural dynamical behaviour of the dam is then quantified in the form of the largest Lyapunov exponent representing system chaoticity. In addition, a moving window formula is employed to scan along the observation data to ensure an on-line continuous diagnosis. WT may be employed to assist in detecting the time where significant changes occur. A simple 4 degrees of freedom spring-mass-damper (K-M-C) system is employed to illustrate the performance of the proposed approach. The approach is then applied to an actual dam using monitoring data. From the deformation and crack opening behaviour, it is concluded that the studied dam is performing with no significant changes in behaviour over time. HIGHLIGHTS Transfer entropy is applied to map the information flow between measuring points. The representative information on structural behaviour of an actual dam is identified. TE and chaos theory are combined to diagnose the dam behaviour. A moving window is adopted to facilitate online statistical diagnosis.

Cellulose nanofibers to improve the mechanical and durability performance of self-healing Ultra-High Performance Concretes exposed to aggressive waters

The effects of including cellulose nanofibers (CNFs) in Ultra High Performance Concretes (UHPCs) have been studied in this paper in terms of recovery of both durability and mechanical properties because of the stimulated self-healing behavior. To this purpose, flexural tests on 4-point bending on 30 mm thin and 100 mm wide beam specimens have been carried out to evaluate the mechanical recovery due to self-healing, together with Double Edge Wedge Splitting tests that have been performed to identify the tensile stress crack-opening behavior. Moreover, water permeability and chloride diffusion tests have been performed to evaluate the recovery of durability properties on healed specimens subjected to extremely aggressive environments rich in chlorides and sulfates. Microstructural analysis has been also performed to confirm the enhancement on durability performance due to the presence of CNFs. The presence of CNFs has improved self-healing performance of UHPC since for the same crack width value and same healing period (1, 3 or 6 months) the specimens with CNFs reached higher crack sealing rates compared to those without nano-additions. As a matter of fact, the total sealing of the cracks over the 6-month investigated period was only observed on specimens with CNFs.

Full-life growth behavior of a naturally initiated internal fatigue crack in beta titanium alloy via in situ synchrotron radiation multiscale tomography

The full-life growth behaviors of an internal fatigue crack in a beta titanium alloy were non-destructively monitored using in situ synchrotron radiation multiscale computed tomography. The crack fronts at various cycles were superimposed on the fracture surface from the perspective of crack growth stages. The crack propagation process consisted of multiple facets formation and subsequent growth into the matrix and was dominated by the former process. The crack opening and blunting behaviors triggered crack growth from the facets to the surrounding matrix. The overall crack propagation rate of the internal crack was revealed to be slower than the surface crack.

Stress-dependent matrix crack opening in SiC/SiC composites: theory and analytical prediction

ABSTRACT In the present work, stress-dependent matrix crack opening behavior of SiC/SiC composites was analyzed considering stochastic fragmentation in fibers. The stochastic matrix multiple fragmentation model was adopted to determine the fragmentation lengths of three different types, the accompanying interface debonding process was assessed by the fracture mechanics theory, and stochastic fiber fragmentation was determined by the global load sharing (GLS) criterion. Considering the aforementioned multiple micro-damage mechanisms, matrix crack opening displacements (CODs) in different matrix fragmentation states were determined using a micromechanical technique. Relationships between CODs and the constituent properties of SiC/SiC composites with fiber fragmentation were established. The crack opening behavior of SiC/SiC composites was also analytically predicted. Effects of fiber stochastic fragmentation on crack opening-related damage parameters were examined.

S0 Lamb Mode Scattering Studies in Laminated Composite Plate Structures with Surface Breaking Cracks: Insights into Crack Opening Behavior

Ultrasonic-guided waves are attractive for rapid inspection of laminated composite structures, where cracks developed transverse to the loading direction are the severe type of damage. This paper presents studies of the interaction of fundamental symmetric S0 Lamb mode with vertical surface-breaking cracks in laminated composite plate structures. Finite element simulations and experimental investigations are used to study the effect of crack depth on S0 wave reflection behavior. Results show a monotonic rise of the reflection coefficient for different crack depths in a manner that is strongly dependent on the orientation of the plies and transverse ply location in the vicinity of the crack. Scattered wave packets in the reflection regime are captured using an in-plane laser. The S0 Lamb mode's sensitivity is numerically presented for the different crack depths in the long wavelength limit. We also observed that the reflected wave mode depicts the information of the corresponding broken interfaces. An attempt was made to show that this behavior relates to the crack-opening behavior in response to in-plane excitation. The reflection coefficient as a characteristic polynomial is proposed for various orientations. It was observed that the dispersion at receiver nodes makes the analysis challenging for distinguishing the signal from crack faces due to the smaller dimension. The study outcomes show its prospect as a promising NDE tool for crack damage detection in thin laminated plate structures.

A simple apparatus for tensile testing of rock

Measuring tensile strength of a quasi-brittle material such as rock is a challenging task. Indirect tensile testing methods such as the Brazilian and flexural tests rely on the assumption of linear elastic behavior, which is not valid close to the peak stress. The direct tensile testing method is independent of the constitutive response of the material and should provide more realistic data. Nevertheless, the test set up in direct tensile testing is time consuming and the results can depend on the applied boundary conditions. In this work, a new apparatus is introduced that can measure tensile strength of quasi-brittle materials and provide information regarding the crack opening behavior. The apparatus, which is an aluminum or steel beam with a cut-out and central notch, acts as both the loading fixture and load cell. The specimen is attached to the central part of the apparatus using an epoxy adhesive . Strain gages mounted on the two sides of the apparatus provide the necessary information about the tensile behavior of the specimen. The device is also capable of detecting and quantifying the intensity of asymmetric failure (crack growth) in the specimen, as identified by digital image correlation . The apparatus, its calibration, and some tests results are presented and discussed. • A new apparatus for tensile testing of rock is introduced. • Uniaxial tensile strength and critical crack opening of Charcoal granite are measured. • Comparison is made between the data collected using the new and conventional uniaxial tensile testing devices. • Digital image correlation is used to study the failure process.

Interface wear effects in ceramic composite crack opening

For fiber-reinforced ceramic-matrix composites (CMCs), crack opening behavior controls oxidation atmosphere ingress into the internal composite, which affects the operation reliability and durability of engineering CMC components. Under cyclic fatigue loading, interface wear affects the crack opening behavior in CMCs. In this paper, the stress/cyclic-dependent crack opening behavior in CMCs is analyzed considering interface wear effect. The analytical crack opening displacement (COD) and related damage parameters (e.g., interface debonding ratio (IDR)) are determined based on the microstress analysis in the fiber and the matrix. Experimental CODs of different matrix cracks in SiC/SiC minicomposite are predicted under tensile loading. Considering cyclic-dependent interface wear effect, CODs and related damage parameters are analyzed for different cycles. Theoretical relationships between the COD, peak stress level, cycle number, and composite constitutive properties are established. Effects of constitutive properties, peak stress level, and damage state on cyclic-dependent COD and related damage parameters are discussed. Under tensile loading, with increasing tensile stress, COD first increases nonlinearly and then linearly with applied stress corresponding to change of the interface debonding from partial to complete debonding. The increasing rate of COD curve is relatively low upon initial loading due to short interface debonding range. However, the increasing rate of COD curve decrease again at high stress level at the condition of complete interface debonding. Under cyclic fatigue loading, the change of interface debonding condition with increasing applied cycles affects the COD and IDR curves.

A temperature- and conversion-dependent cohesive zone approach for the calculation of process-induced damage in adhesive bondlines of multi-material structures

Adhesive bondlines in multi-material car bodies underlie various influences from the production process. Especially the mismatch of the coefficient of thermal expansion during the oven process of cathodic dip coating can cause damage and weaken the joint strength. Temperature-dependent mechanical properties and the increasing conversion that describes the degree of cure of the adhesive are important parameters affecting the adhesive bondlines during production. To take these effects into account in numerical simulations, a cohesive zone approach, which is commonly used to model adhesive bondlines in structural simulations, is adapted to a one-component, hot curing, structural epoxy adhesive for body-in-white manufacturing and is extended with a reaction kinetic model of the curing reaction, conversion-dependent material properties, and temperature dependency. The investigation of the material properties using a rheometer and differential scanning calorimetry experiments is described. Furthermore, the cohesive zone model is presented and an experimental validation of the model using customized tapered-double-cantilever-beam specimens to investigate the crack opening behavior of incompletely cured adhesives shows a good agreement with the numerical data.

An approach to estimate crack opening displacement in two-dimensional plain-woven silicon carbide fiber-reinforced silicon carbide composite considering different matrix cracking modes

Understanding of cracking opening behavior is important for the prediction of residual strength and lifetime of silicon carbide fiber-reinforced silicon carbide ceramic–matrix composites at elevated temperatures. Under tensile loading below the proportional limit stress, multiple matrix cracking modes in the longitudinal and transverse yarns of a two-dimensional plain-woven silicon carbide fiber-reinforced silicon carbide composite appear in the matrix with debonding at the fiber/matrix interface. Crack opening displacement is a key parameter to characterize the crack opening behavior in silicon carbide fiber-reinforced silicon carbide composites and is affected by the multiple matrix cracking modes. In this article, a damage-based micromechanical crack opening displacement model for two-dimensional plain-woven silicon carbide fiber-reinforced silicon carbide composites is developed considering different matrix cracking modes. Two typical matrix cracking modes in a two-dimensional plain-woven silicon carbide fiber-reinforced silicon carbide composite, that is, cracking mode III with cracking in the matrix of the longitudinal and transverse yarns and cracking mode V with cracking only in the matrix of the longitudinal yarns, are considered. Micro stress field in the fiber, matrix of the longitudinal yarns, and transverse yarns are obtained. The crack opening displacement and related damage parameters are determined. Relationships between composite's crack opening displacement, constitutive properties, woven parameters, and damage state are established. Experimental crack opening displacements of cracking modes III and V in a two-dimensional plain-woven melt-infiltration silicon carbide fiber-reinforced silicon carbide composite from the published literature are predicted. For cracking mode III with partial interface debonding, the crack opening displacement increased nonlinearly with applied stress; and for cracking mode V with complete interface debonding, the crack opening displacement increased linearly with applied stress.

Improved Hybrid Model for Predicting Concrete Crack Openings Based on Chaos Theory

Conventional statistical models provide inaccurate predictions of concrete crack openings because they do not consider the nonlinear temperature response and the residual characteristics of concrete. To address this problem, this study introduces a nonlinear temperature factor and develops an improved statistical model of crack openings. The chaotic characteristics of residual time series of the improved statistical model are analyzed based on chaos theory and phase-space reconstruction theory. These theories are integrated with back-propagation (BP) artificial neural networks and genetic algorithms (GAs) to establish a GA-BP neural network model for predicting residuals. Finally, a hybrid model is developed for predicting the concrete crack opening behavior. The predictions of the conventional statistical model, the statistical model considering nonlinear temperature component, and the hybrid model are compared using the case study on the crack openings of a regulating sluice. The results show that the proposed hybrid model in this study for predicting concrete crack openings is significantly more accurate than the conventional statistical model and the statistical model considering nonlinear temperature component.

Measurement of fracture toughness based on atomic-resolution observations of crack opening behavior

Crack nucleation and propagation in SrTiO3 single crystal were observed at the atomic level by in situ scanning transmission electron microscopy (STEM) loading experiment with a MEMS loading device. It was found that a crack initiated from the bottom of a notch and propagated along the {110} plane. The fracture toughness for the {110} crack was estimated to be KIC=1.4MPam1/2 based on the measured crack opening displacement. In addition, an atomic structure model of the {110} fracture surface was constructed based on the experimental observations, and first-principles calculations showed that its cleavage energy was γ=3.8Jm-2. From the relationship of KIC=(2γE)1/2 (E: Young’s modulus), the fracture toughness is estimated to be =1.4MPam, which agrees well with the experimental value.

An experimental-analytical scale-linking study on the crack-bridging mechanisms in different types of SHCC in dependence on fiber orientation

A scale-linking, experimental study complemented by an analytical model was carried out to investigate the influence of fiber orientation on the crack-opening behavior of strain-hardening cement-based composites (SHCC). Three SHCC compositions were investigated with polyvinyl alcohol (PVA) and ultra-high molecular weight polyethylene (UHMWPE) fibers in combination with normal- and high-strength matrices. The micromechanical experiments with fiber inclinations of 0°, 30°, 45°, and 60° involved fiber embedment in plain and fiber-reinforced specimens. The experimentally derived micromechanical parameters were input into an analytical crack-bridging model to assess the upscaling accuracy of the micromechanical results by comparing the predicted crack-bridging laws to the single-crack opening behavior of equivalent miniature SHCC specimens with controlled fiber orientation. This study yields new insights into the effect of fiber orientation on the crack-bridging properties of different types of SHCC, assesses the link between micromechanical and composite scale properties, offers a solid experimental basis for refining the analytical models, and developing anisotropic materials models for SHCC in dependence on fiber orientation.

Shear slip post-cracking behaviour of polyolefin and steel fibre reinforced concrete

The most significant structural concrete codes consider the shear contribution of fibres in structural design when using fibre reinforced concrete (FRC) if certain requirements are met. However, instead of obtaining such a contribution based on the results of shear tests, the structural codes establish that the parameters used in the structural design be obtained from bending tests. In order to assess the accuracy of such an approach, this study analyses the shear contributions of fibres in FRC by means of shear push-off tests. The influence of two of the most common structural fibres is examined: hooked-end steel and polyolefin fibres. The paper includes the description of the experimental campaign and the push-off tests. In addition, the analysis of the cracking patterns by means of digital image correlation (DIC) is also included. The experimental results are compared with a shear crack opening behaviour model. The significance of the research relies in the comparison of the shear residual capacity of the concrete reinforced with two main types of structural fibres, the cracking patterns and suitability of the shear-friction theory for reproducing the opening-sliding of the crack under push-off testing of FRC.

Modeling of Bridging Law for Bundled Aramid Fiber-Reinforced Cementitious Composite and Its Adaptability in Crack Width Evaluation.

Tensile performance of fiber-reinforced cementitious composite (FRCC) after first cracking is characterized by fiber-bridging stress–crack width relationships called bridging law. The bridging law can be calculated by an integral calculus of forces carried by individual fibers, considering the fiber orientation. The objective of this study was to propose a simplified model of bridging law for bundled aramid fiber, considering fiber orientation for the practical use. By using the pullout characteristic of bundled aramid fiber obtained in the previous study, the bridging laws were calculated for various cases of fiber orientation. The calculated results were expressed by a bilinear model, and each characteristic point is expressed by the function of fiber-orientation intensity. After that, uniaxial tension tests of steel reinforced aramid-FRCC prism specimens were conducted to obtain the crack-opening behavior and confirm the adaptability of the modeled bridging laws in crack-width evaluation. The experimental parameters are cross-sectional dimensions of specimens and volume fraction of fiber. The test results are compared with the theoretical curves calculated by using the modeled bridging law and show good agreements in each parameter.

Analysis and experiment on DCB specimen using I-fiber stitching process

Several studies related to the reinforcement of composite structures in the through-thickness direction have been conducted recently. In this study, a new reinforcement process is proposed based on previous experimental results; the proposed novel process involves the stitching of T-joints and one-stitched specimens. The need for additional analysis was established under standard DCB tests, for better understanding. Finite element modeling (FEM) results were compared after performing mode I interlaminar fracture toughness tests, using different stitching patterns, for analyzing the through-thickness strength, using reference laminates without stitching. The stitching patterns were defined as 2 × 2 and 3 × 3, where the upper and lower head of the non-continuous stitching process (I-fiber) was shown to strongly affect the through-thickness strength of the laminate. To design a numerical model, cohesive parameters were required for defining surface-to-surface bonding elements using the cohesive zone method (CZM) and for simulating the crack-opening behavior from the DCB test.

Influence of work-hardening on fatigue crack growth, effective threshold and crack opening behavior in the nickel-based superalloy Inconel 718

In this study, the influence of rotary swaging induced cold work on long fatigue crack growth, threshold and opening behavior in the nickel-based superalloy Inconel 718 was investigated. Ambient temperature experiments were carried out using arc-shaped tension specimens according to ASTM standard E399. The direct current potential drop (DCPD) method was used for crack length measurements and crack opening force evaluation. Fatigue crack growth rates (FCGR) measured at load ratios of R=0.2,R=0.5 and R=0.7 were found to increase due to work-hardening in continuous (increasing ΔK) and load shedding (decreasing ΔK) tests. Effective fatigue crack growth thresholds (ΔKth,eff) were determined according to the Kmax=const. procedure and found to decrease monotonically with increasing degree of work-hardening. Compared to the non-deformed material, crack opening stress intensities Kop were reduced in work-hardened states at three different crack lengths. To quantify the detrimental effects of cold work, the effective stress intensity factor range (ΔKeff) model was applied. SEM and TEM micrographs were taken to complement the study.