Effect Of Transverse Cracks Research Articles

Effects of Transverse Cracks on the Backcalculated Layer Properties of Asphalt Pavements from Non-destructive Testing Data

Effects of Transverse Cracks on the Backcalculated Layer Properties of Asphalt Pavements from Non-destructive Testing Data

Modelling the corrosion mechanism of steel bars in chloride-contaminated concrete with transverse cracks

The development of cracks in reinforced concrete structures can accelerate structural deterioration and reduce service life. A numerical model was established to analyse steel bar corrosion in chloride-contaminated concrete with transverse cracks. In the model, the dynamic distinction between anode and cathode regions on the steel surface is considered by introducing an empirical formula for the anodic Tafel slope related to chloride concentration. The time-dependent characteristics of the corroded region were examined using the proposed corrosion prediction model and the corrosion process of steel bars in cracked concrete was revealed. The effects of crack width and crack spacing on steel corrosion were analysed in detail in terms of the corrosion area and corrosion rate. The results showed a variation in the corrosion area adjacent to cracks over time and a positive correlation between corrosion area and the square root of time. According to the micro-cell and macro-cell contributions to the corrosion rate, the process of steel bar corrosion was determined to occur in three stages. The effects of transverse cracks on the corrosion rate were found to vary with exposure time and to depend on the control steps of the micro- or macro-cells.

Effect of pre-existing longitudinal and transverse corrosion cracks on the flexural behaviour of corroded RC beams

Assessing the residual capacity of corroded reinforced concrete (RC) beams depends on quantifying the corrosion cracks and rebar cross-section loss, and understanding their influence on the structural behaviour. Relations between corrosion crack widths and cross-section loss have been developed in the literature, and experimental studies have shown a decrease in the flexural capacity of corroded RC beams. However, their results were only related to longitudinal cracks and rebar cross-section loss. In real structures, corrosion of stirrups causes transverse cracks. In this paper, their influence on rebar pitting and failure of corroded beams is investigated through an experimental test programme in which RC beams are corroded and then tested in bending. Firstly, the effect of transverse cracks on the relation between crack widths and cross-section loss is studied. Secondly, the role of each type of corrosion damage on the flexural failure of the beams is investigated. It is found that transverse cracks lead to localized cross-section loss causing non-linearity in the relation between the longitudinal crack widths and the cross-section loss. Additionally, it is found that longitudinal corrosion cracks decrease the number of flexural cracks, while transverse cracks form weak spots to initiate the beam failure. Furthermore, it is observed that beams fail at the location of either the transverse cracks or the minimum rebar cross-section or both. Moreover, transverse corrosion cracks may lead to misaligned minimum cross-sections on the tensile rebars, which cause a skewed critical cross-section during bending failure. Finally, the study concludes that pre-existing longitudinal corrosion cracks deteriorate the tension-stiffening effect, while transverse cracks cause local pits in the tensile rebars and affect the failure mechanism of the beams.

A new predictive model to estimate the frequencies for beams with branched cracks

Detecting damage by using vibration signals is popular because it permits evaluating the structural integrity without being necessary scanning of the whole structure. The effect of transverse cracks is presented in detail in the literature, but in reality, the cracks can shift the direction of propagation and even split, resulting in the so-called branched crack. The effect of this type of crack is less investigated due to its complexity. We herein propose a simple model to predict frequency changes that occur due to branched cracks. Initially, we present the effect of stiffness reduction along the damaged section on the structure’s natural frequency. Next, we show that the predicted frequency drop is smaller that happens in reality. This is caused by the sudden cross-section reduction in the slice on which the transverse crack branch is. The phenomenon is similar to the stress concentration for static loads. We propose for dynamic systems a factor that considers the energy stored at the delamination ends. Considering this factor and the stiffness reduction on the damaged segment, we obtain accurate frequency changes due to any type of crack that extends in the longitudinal direction. The model is implemented in Python and tested successfully against simulation with dedicated software.

КОНЦЕНТРАЦІЯ НАПРУЖЕНЬ В ОКОЛІ ТРІЩИНИ В ДОРОЖНЬОМУ ПОКРИТТІ ПРИ ДІЇ ТРАНСПОРТНИХ НАВАНТАЖЕНЬ

The problem of stress concentration in the vicinity of a crack under the action of transport loads is posed. Its analysis takes place in an elastic (thermoelastic) formulation using the given modules that correspond to a given state of the system at a given load level. Cases where the coating has no cracks and has them in the upper and inner layers are considered. The effect of transverse cracks on the redistribution of stress fields under the action of transport loads is analyzed. In the case where the coating has no cracks, the greatest compressive stresses occur on the top plane of the coating. Tensile stresses predominate in the zone of the third layer. They increase as they approach the contact plane of the third and fourth layers. The maximum values of the tangent stresses are realized at the boundary of the second and third layers, thus being a potential cause of the coating delamination in this zone. If the crack penetrates the first two upper layers, then the greatest compression stress has moved to the fracture mouth, and the tensile stress remains almost unchanged. In the case where a vertical crack penetrates the inner layer, the maximum values of the normal and tangent values occur in the central and edge zones of the load distribution. A finite element analysis of the effect of the crack on the stress-strain state of the multilayer system is performed. The stress concentration in the crack zones depends largely on the geometry of the crack and its structure at its mouth. KEYWORDS: AUTOMOBILE ROAD, ROAD COATING STRUCTURE, TRANSPORT LOADS, NORMAL VOLTAGE, TENSION VOLTAGE, TENSION-DEFORMED CONDITION

Study on the Corrosion Length of Steel Bars in Concrete with Transverse Cracks Under the Dry-wet Circulation Environment

In the paper, the effect of transverse cracks on the corrosion length of steel bars in concrete under the dry-wet circulation environment has been studied. Specimens of reinforced concrete with different width of transverse cracks were used in the drywet circulation environment test. After a certain number of cycles, carry out the study on the state of reinforcement corrosion in concrete. Main results are as follows: the steel corrosion length in the specimens soaked in chloride solution was much longer than the steel corrosion length of those specimens soaked in water. Besides, the corrosion length of steel bars increased along with the increase of crack width. When the crack width was more than 0.3mm, the reinforced steel showed the sustained corrosion mechanism; but when the crack width was less than 0.3mm, the reinforced steel showed the crack sealing mechanism. The phenomenon illustrated that the corrosion rate was fast at the early stage, and slowed down or even stopped later. The relationship between steel corrosion length and the period of dry-wet circulation applied to the linear relationship. In the paper, the prediction model of steel corrosion length has been built after the relationship between steel bars corrosion length and the dry-wet cycles has been analyzed.

A new two-staged model to predict corrosion degree of steel bars in cracked concrete area

In order to quantitatively describe the local corrosion process of steel bars in cracked concrete area, a new two-staged utility model is established, and the effect of transverse cracks on the reinforcement corrosion is analyzed from the angle of long-term service performance evaluation for reinforced concrete structure. Moreover, based on the principle of spectral analysis for environmental action of concrete, an equivalent relationship is established between the corrosion rate in the natural environment and that under the standard temperature and relative humidity condition according to the principle of equivalent annual corrosion depth. Comparison between the inspection results from some references and the calculated values by the two-staged utility model validates the feasibility of the proposed model. The model was applied to Chinese Railway Track System (CRTS)II ballastless track slab with transverse dummy joints, from which satisfactory results of corrosion degree of steel bars were obtained.

The effect of transverse crack upon parametric instability of a rotor-bearing system with an asymmetric disk

It is well known that either the asymmetric disk or transverse crack brings parametric inertia (or stiffness) excitation to the rotor-bearing system. When both of them appear in a rotor system, the parametric instability behaviors have not gained sufficient attentions. Thus, the effect of transverse crack upon parametric instability of a rotor-bearing system with an asymmetric disk is studied. First, the finite element equations of motion are established for the asymmetric rotor system. Both the open and breathing transverse cracks are taken into account in the model. Then, the discrete state transition matrix (DSTM) method is introduced for numerically acquiring the instability regions. Based upon these, some computations for a practical asymmetric rotor system with open or breathing transverse crack are conducted, respectively. Variations of the primary and combination instability regions induced by the asymmetric disk with the crack depth are observed, and the effect of the orientation angle between the crack and asymmetric disk on various instability regions are discussed in detail. It is shown that for the asymmetric angle around 0, the existence of transverse (either open or breathing) crack has attenuation effect upon the instability regions. Under certain crack depth, the instability regions could be vanished by the transverse crack. When the asymmetric angle is around π/2, increasing the crack depth would enhance the instability regions.

Analysis of the transverse cracking in hybrid cross-ply composite laminates

Abstract A modified shear-lag analysis, taking into account the concept of interlaminar shear stress, is employed to evaluate the effect of transverse cracks on the stiffness reductions in different glass/epoxy and graphite/epoxy hybrid cross-ply laminates. The modified shear-lag model is proposed that assumes interlaminar adhesive layer between two neighbouring layers transferring not only interlaminar shear stress but also normal stress. The stress distribution is solved by the used model which rigorously satisfies the stress equilibrium equations, boundary conditions and the traction continuity at interfaces between layers.

High-cycle fatigue characteristics of quasi-isotropic CFRP laminates over 10 8 cycles (Initiation and propagation of delamination considering interaction with transverse cracks)

High-cycle fatigue features of over 10 8 cycles, particularly the initiation and propagation of edge delamination considering the effects of transverse cracks, were investigated using quasi-isotropic carbon-fiber-reinforced plastic (CFRP) laminates with a stacking sequence of [45/0/−45/90] s in this study. In the relationship between a transverse crack density and initiation and growth of edge delamination, it was found that fatigue damage growth behavior varied depending on applied stress. It was observed that edge delamination initiated and grew at parts where transverse cracks were dense at ordinary applied stress, whereas it was observed that edge delamination grew before or simultaneously with transverse crack propagation at a low applied stress and high-cycle loading. In addition, the critical transverse crack density where delamination begins growing was calculated to evaluate the interaction between transverse crack and edge delamination growth.

Effect of transverse cracking on stiffness reduction of hygrothermal aged cross-ply laminates

An analytical model based on the notion of the stress perturbation function is developed and applied to study the effect of multiple cracks in aged cross-ply laminates on the stiffness of a laminated composite. The material properties of the composite are affected by the variation of temperature and moisture, and are based on a micro-mechanical model of laminates. This hygrothermal effect is taken into account to assess the changes in the longitudinal modulus due to transverse cracking. The obtained results represent well the dependence of the degradation of elastic properties on the cracks density and hygrothermal conditions. Through this theoretical study, we hope to contribute to the understanding of damage of aged composite materials.

Tensile strength of CFRP cross-ply laminates containing transverse cracks

The effect of transverse cracks on the ultimate tensile strength (UTS) was experimentally and analytically studied for carbon fiber reinforced plastic (CFRP) cross-ply laminates. For coupon specimens of various cross-ply stacking sequences, quasi-static tensile tests were carried out and transverse cracks were observed. The experimental results showed that the measured fiber bundle strength of 0° ply was almost constant, which indicated that transverse cracks had little influence on the notch sensibility of the bundle strength. Then, we proposed a new numerical model based on the finite element method to investigate the damage extension to the fracture. This model considered the elastoplastic behavior of epoxy matrix and the fiber breakages. Using this model, we applied a Monte-Carlo method to the damage extension simulation. It was found that the plastic region at the tip of the transverse crack reduced the stress concentration due to the crack, and that the bundle strength was barely affected by transverse cracks.

An investigation of non-linear elastic behavior of CFRP laminates and strain measurement using Lamb waves

This paper investigates the non-linear elastic behavior of unidirectional and cross-ply CFRP laminates and proposes a new method to measure tensile strain using Lamb waves. Young’s modulus was measured as a function of strain in situ using Lamb wave velocity during a tensile test. The stiffening effect of the carbon fibers on [0] 8 specimens and the softening effect of the epoxy matrix on [90] 8 specimens were accurately evaluated. Young’s modulus of the 0° ply was obtained as a quadratic function of strain. Using the function and the rule of mixture, the dependence of Young’s modulus on strain was accurately predicted for cross-ply laminates. Based on the results, the tensile strain was quantitatively correlated with the corresponding arrival time of the Lamb waves. The strains obtained from the proposed method agreed well with those from the strain gauge. Finally, the effect of transverse cracks on the in situ Young’s modulus of the cross-ply laminate under a tensile load was investigated. This method clearly detected even a small decrease in the Young’s modulus due to the transverse cracks in stiffening cross-ply laminate.

OS11W0019 Fatigue damage development and growth in fiber reinforced polymeric composites

Damage initiation and growth under quasi-static and cyclic loading of cross-ply and multidirection laminates are presented. Damage states such as initiation of matrix cracking, onset of delamination and fiber fracture are identified. A linear relationship is found between the maximum applied cyclic stress and logarithm of number of cycles for each damage mode. The effect of transverse cracks on the stiffness reduction has been quantified. Again a linear relationship between the normalized stiffness and crack density is shown to be a good representation of the test data, irrespective of the applied maximum cyclic load. Under cyclic loading matrix cracks initiated at a lower stress compared to the quasi-static loading. Also higher crack densities were observed under cyclic loading than that of quasistatic one. A major difference between the two types of loading is in the initiation and growth of delamination.

Lamb wave evaluation and localization of transverse cracks in cross-ply laminates

This paper investigates the effect of transverse cracks on the S0 mode velocity in GFRP and CFRP cross-ply laminates, and proposes a new AE source location method that considers the change in the S0 mode velocity due to the transverse cracks. We found experimentally that the stiffness and the velocity decreased as the transverse crack density increased. Analytical predictions deduced from the combination of the complete parabolic shear-lag analysis, the classical plate theory and the laminated plate theory are in good agreement with the experimental results. Utilizing this relationship between the velocity and the mechanical damage, we located AE sources of transverse cracks in cross-ply laminates with the calculated in situ velocity. We were able to show that highly accurate source location requires the reduction of the in situ value of the velocity. The present method is simple but quantitative and useful in health-monitoring for detecting and localizing the damage in composite structures.

Dynamic Stability of Rotating Blades with Transverse Cracks

In this paper, the main objective is to examine the effects of transverse cracks on the dynamic instability regions of an axially loaded rotating blade. The blade is modeled as an Euler-Bernoulli beam. To reduce the governing equations to a set of ordinary differential equations in matrix form, Hamilton's principle is used in conjunction with the assumed-mode method. The crack is accounted for by considering the energy release rate and the parametric instability regions are obtained using Bolotin's first approximation. Benchmark results are presented for cracked rotating blades at different rotating speeds, crack lengths and crack positions.

Effect of transverse cracks on lamb wave velocity in CFRP cross-ply laminates

In the case of cross-ply laminates subjected to uniaxial loading, transverse cracks initiate in the 90◦ plies at the specimen edge and extend across the laminates. As the applied load increases, the crack density increases, resulting in stiffness reduction until it reaches to a limiting value. Therefore, it has been a subject of considerable interest to analyze the effect of the crack density on the stiffness reduction [1] and to monitor the cracks nondestructively, For example, with acoustic emission [2] and embedded fiber Bragg grating sensors [3]. Among the various techniques available, ultrasonic Lamb waves offer a convenient approach for evaluating the damaged composite laminates. As the Lamb were velocity depends on the in-plane stiffness of the laminate, the transverse cracks that cause the stiffness reduction can be monitored by the measurements of the velocity [4]. The acoustic emission method is also useful due to its ability of sensitive detection and source location for damages and impacts [5]. For the accurate AE source location, the in-situ wave velocity should be used in the calculation if the laminate is damaged. So combining the active sensing of measuring the in-situ Lamb wave velocity and the passive sensing of detecting acoustic emission is ideal to monitor the transverse cracks. However, as far as we know, there have been no studies considering the reduced wave velocity for the AE source location. In the present letter, the stiffness and the velocity of the lowest order symmetric (S0) mode for CFRP crossply laminates with various transverse crack densities were measured. The reduction of the stiffness and the S0 mode velocity as a function of the crack density were calculated theoretically and then the predicted values were compared with the experimental results. Furthermore, linear AE source locations were conducted on the damaged specimen and the effect of the reduction of S0 mode velocity on the accuracy of the source location was investigated. The materials studied were CFRP (T300/F593) cross-ply with two stacking sequences of [0/906/0] and

Effect of cracks on the dynamic response of a simple beam subject to a moving load

The effect of transverse cracks on the dynamic behaviour of simply supported undamped Bernoulli-Euler beams was determined. Crack presence in the beam results in higher deflection and alters the beam response patterns. In particular, for a given speed, the largest deflection in the beam takes longer to build up, and a discontinuity appears in the slope of the deflected shape of the beam at the crack location. In addition, for certain speeds the beam changes its pattern of deflection from downwards to upwards as the load leaves the beam. Crack effects become more noticeable as crack depth increases.

Damage accumulation in composite laminates during quasi-static transverse loading

A mechanism of damage accumulation in composite laminates subjected to a quasi-static concentrated load is numerically studied by using the finite element method to disclose the impact damage problem. The energy release rate distributions are calculated along the delamination edges in square composite laminates with various stacking sequences. Not only circular delaminations but also more realistic impact damage models are investigated to explain the reason why the typical impact damage must be created. The effects of transverse cracks and stacking sequence on the energy release rate are discussed.

Transverse cracks in cross-ply laminates. 1. Stress analysis

During service loading of cross-ply laminates, transverse cracks occur in plies. The cracks parallel to the fiber direction are extended over the full thickness of transverse plies and often cross the entire test specimen width. It is widely recognized that the changes of laminate thermomechanical constants, caused by the transverse cracking of composite laminates, can be significant. Theoretical stress analysis in the cross-ply laminates in the vicinity of cracks is performed using numerical (FE) and analytical methods. The effect of transverse cracks on the degradation of elastic properties will be discussed in Part 2 [1]. Approximate analytical micromechanical models based on shear lag predictions, variational analysis, and numerical 2D finite element calculations were verified in their predictive abilities. The three variational models used are based on the principle of minimum complementary energy and have different degrees of accuracy with respect to the stress assumptions used (Hashin's, 2D 0° and 2D 0°/90° models). Using FEM, the plane stress and strain state were analyzed. The effect of material properties and layer thickness on the stress distribution in a 90° layer was evaluated by varying the crack spacing. The crack opening displacement (COD), normalized with respect to the far field strain, is proposed as a measure of reduction of the mechanical properties. Since the CODs are rather insensitive to the crack spacing (crack density) in a wide region, they will be used in modeling the stiffness reduction in these laminates [1].