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Transverse cracking in continuously reinforced concrete pavement (CRCP) develops over time and may exhibit irregular patterns such as cluster cracks, Y-shaped cracks, and divided cracks. These undesirable cracking patterns can increase the probability of premature spalling and punchouts. Ideally, a uniform transverse cracking pattern with small crack widths leads to favorable long-term performance in CRCP. An experimental field project was constructed with internally cured concrete and active cracking to control crack initiation timing, patterns, and properties. Prewetted fine lightweight aggregate was used for internal curing, and edge notches of 2 in. depth and 2 ft length every 4 ft along the test section were sawcut for active crack control. The three experimental CRCP sections in Illinois were monitored for crack spacing, crack width, and formation of undesirable cracks over a 4-year period. Internally cured concrete significantly reduced the undesirable crack patterns relative to the control section. Internally cured concrete coupled with active crack concrete produced superior crack patterns and properties, that is, uniform crack spacing of 3.6 ft without cluster cracks, 0.2 mm surface crack width, and only a small number of undesirable cracks. Active crack control produced a higher number of transverse cracks near the terminal joint (last 150 ft) compared with the control section. Moisture and temperature management with active crack control during construction of the CRCP provided a desirable crack pattern and properties that should increase the overall service life of a pavement.

Transverse cracking and delamination are two of the most common failure modes in cross-ply composite laminates. The initiation and combination of these two failure mechanisms lead to catastrophic f...

The influence of carbon nanofibers (CNFs) on carbon fiber (CF) reinforced polymer (CFRP) is investigated in this study. A program is developed to generate the finite element model (FEM) for the nan...

This paper presents an experimental study of tensile properties, using a carbon–polypropylene uni-directional sheet with a thickness of 0.15 mm, which shows that highly non-linear stress–strain curves can be achieved with cross-angle-ply laminates. Generally, these properties are studied from the scanning electronic microscope and X-ray computed tomography. Cross-ply laminates with fiber orientation angles from 15 to 60° are investigated and it is found that there are the pseudo-ductile behavior with the fiber rotation, especially at fiber orientation angles from 30° to 60°.The Pseudo-ductile behavior is a phenomenon in which the apparent strain increases after yielding with strain hardening. It is greatly affected by the fiber reorientation in the loading direction. The fiber reorientation is allowed the plasticity of the polypropylene and thickness of each layer.

The influence of linear and non-linear temperature and moisture concentration distribution on the stress distribution was studied for metal/ceramic sandwich plate with transverse cracks. An interlaminar adhesive layer between two different layers is taken into account which transferring the normal stress and the interlaminar shear stress. The validation of the used model was done with the comparison of the stiffness reduction as a function of crack density and the experimental data. A comparison showed that a satisfactory qualitative and quantitative agreement was obtained. The temperature and moisture concentration variation are studied using the linear and non-linear distribution around the cracks to predict the stress distributions along the axis x. Finally, it observed through this study that the variations of the thermal and moisture concentration distribution largely impact the stress distribution for a sandwich plate with transverse cracks in the central layer and also with different mechanical properties of each layers.

A weld cracking of the outlet pipe occurred during the operation of a low-pressure steam super-heater in the purification device. It was found that many cracks were perpendicular to the weld, which affected the equipment safe operation. In order to investigate the failure cause, the samples containing weld and cracks in the outlet pipe were cut. The experiments, including chemical composition analysis, mechanical properties testing, scanning electron microscope observation, energy spectrum analysis and metallographic analysis, were performed. The results showed that the corrosion products had loose structure, mainly consisting of iron, sodium and phosphorus oxides. The metallographic results of the fracture section indicated that there existed a mixed cracks of trans-granular and inter-granular mode, along with stepped crack characteristics. Therefore, it is believed that the weld transverse cracking in the outlet pipe may be resulted by both of alkali stress corrosion cracking and the hydrogen induced cracking. According to the failure cause analysis, the corresponding suggestions are given, such as welding, operation process and inspection.

The concept of the “effective stiffness” for plies in laminates containing intralaminar cracks is revisited presenting rather accurate fitting expressions for the effective stiffness dependence on crack density in the ply. In this article, the effective stiffness at certain crack density is back-calculated from the stiffness difference between the undamaged and damaged laminate. Earlier finite element method analysis of laminates with cracked 90-plies showed that the effective longitudinal modulus and Poisson’s ratio of the ply do not change during cracking, whereas the transverse modulus reduction can be described by a simple crack density dependent function. In this article, focus is on the remaining effective constant: in-plane shear modulus. Finite element method parametric analysis shows that the dependence on crack density is exponential and the fitting function is almost independent of geometrical and elastic parameters of the surrounding plies. The above independence justifies using the effective ply stiffness in expressions of the classical laminate theory to predict the intralaminar cracking caused stiffness reduction in laminates with off-axis plies. Results are in a very good agreement with (a) finite element method calculations; (b) experimental data, and (c) with the GLOB-LOC model, which gives a very accurate solution in cases where the crack face opening and sliding displacements are accurately described.

The crack opening and crack sliding displacements of both faces of an intralaminar crack are the main parameters defining the significance of each crack in laminate stiffness degradation, according to the previously published GLOB-LOC approach for symmetric laminates with an arbitrary number of cracks in all plies. In the exact stiffness expressions of this approach, the crack density is always multiplied by crack opening displacement and crack sliding displacement. The dependence of crack opening displacement on geometrical and elastic parameters of adjacent plies was studied previously and described by simple fitting functions. The crack sliding displacement has been analyzed for low-crack densities only and the proposed finite element method-based fitting expressions are oversimplified not including the out-of-plane ply stiffness effects. Based on finite element method analysis, more accurate expressions for so-called non-interactive cracks are suggested in the presented article. For the first time the shear stress perturbations are analyzed and interaction functions are presented with the feature that they always lead to slightly conservative predictions. The presented simple fitting functions, when used in the GLOB-LOC model, give predictions that are in a good agreement with finite element method results and with experimental data for laminates with damaged off-axis plies in cases when crack face sliding is of importance. The significance of including crack sliding displacement in stiffness predictions is demonstrated.

Being immune to corrosion, and having a tensile strength up to three times higher than structural steel, glass fiber reinforced polymer (GFRP) bars are suitable for reinforcing concrete structures exposed to aggressive environmental conditions. However, a relatively low elasticity modulus of GFRP bars (in respect to the steel) favors the occurrence of relatively large deformability of cracked reinforced concrete. Lack of ductility and degradation of properties under high temperature can be also identified as debilities of GFRP bars over steel ones. Combining GFRP and steel bars can be a suitable solution to overcoming these concerns. Nevertheless, the application of such hybrid reinforcement systems requires reliable material models. The influence of the relative area of GFRP and steel bars on the tensile capacity of cracked concrete (generally known as tension-stiffening effect), was never investigated from the experimental point of view, mainly crossing results from different tools on the assessment of the cracking process. This paper experimentally investigates deformations and cracking behavior of concrete prisms reinforced with steel bars and GFRP bars in different combinations. The test results of 11 elements are reported. A tensile stress-strain diagram is conceptually proposed for modelling the tension-stiffening effect in elements with such hybrid combination of the reinforcement. The cracking process in terms of crack width and crack spacing is analyzed considering the hybrid reinforcement particularities and a preliminary approach is proposed for the prediction of the crack width for this type of reinforced concrete elements, Research Council of Lithuania (Research Project S-MIP-17-62). The second author also 590 wish to acknowledge the support provided by FCT through the PTDC/ECM591 EST/1882/2014 project

Thermal cracking is a non-load associated distress mode of asphalt pavements. Finite element models (FEM) were first introduced in this study to determine the thermally induced J-integral at the tip of thermal crack. After extensive runs of the FEM, artificial neural network models were constructed to predict the J-integral, which was used in the Paris’ law to calculate the cumulative thermal crack growth over time and thermal cracking fatigue life. Additionally, Long-term pavement performance data was collected to characterize the thermal cracking in different climatic zones. The calculated fatigue life was well correlated with the observed transverse cracking field performance.

Transverse crack formation in epoxy based unidirectional composites is treated by means of a percolation concept. A previously proposed criterion for brittle cavitation in epoxies is used as the criterion for fibre/matrix debonding. Then, neglecting the details of debond linkups, a transverse crack is assumed to form when the intensity of the linkup process crosses a threshold analogous to the percolation threshold. The predicted applied strain to transverse crack formation based on this assumption agrees well with experimental data. A parametric study is conducted to reveal the effects of thermal cooldown temperature, fibre volume fraction and fibre elastic properties on the percolation threshold for transverse crack formation.

У цьому дослідженні вивчається динамічний модуль асфальтового матеріалу та продуктивність його перероблення за допомогою даних про експлуатацію та лабораторних випробувань. Кафедра транспорту Колорадо має 37 проектів з використання даного матеріалу площею більше 8 км 2. Для відстеження результатів і збирання дослідних матеріалів для лабораторних досліджень було відібрано зразки з десяти проектів. Тестування динамічного модуля для даного матеріалу відбувалось у лабораторії кафедри транспорту Державного університету Колорадо. Результати свідчать про те, що досліджувані показники якості є переважно нижчими за порогові значення впродовж періоду експлуатації. Зокрема, міжнародний показник шорсткості та поперечне розтріскування ніколи не перевищували порогові значення впродовж усього періоду дослідження. Лише два асфальтні покриття перевищили порогові показники для втомних тріщин після 8–10 років експлуатації. Грунтуючись на технічних міркуваннях, виміряні показники аналогічні до показників для звичайних тротуарів. Результати лабораторних досліджень показали, що матеріал має приблизно на 50 % менший динамічний модуль порівняно з традиційною асфальтовою сумішшю. This study investigates the dynamic modulus of cold-in-place recycling (CIR) asphalt material and its performance using pavement performance data and laboratory dynamic modulus testing. Colorado Department of Transportation (CDOT) has 37 projects with over 8 million square yards using CIR materials. Sites from ten projects were selected to monitor the performances and collect samples for laboratory testing. Dynamic modulus testing on the CIR cores was conducted by the CDOT. Results show measured distresses of CIR rehabilitation techniques are mostly below the threshold values during the service period. International Roughness Index, rutting, and transverse cracking never exceeded the threshold values during the studied period. Only two CIR pavements exceeded the threshold values for fatigue cracking after 8-10 years of service. Measured distresses of CIR rehabilitation techniques are similar to conventional pavements based on engineering judgment. The laboratory dynamic modulus test results show CIR has about 50 % less dynamic modulus compared to the traditional asphalt mixture.

Many states have problems with transverse cracking of the concrete bridge decks. These cracks occur in negative and positive moment regions and can affect the serviceability of the decks. ...

Transverse cracking and crack induced delaminations growth are generally considered as the most relevant damage modes developing during the fatigue loading of composite laminates. So far, non-interactive damage progression schemes have been considered, arguing that transverse cracks saturate before the initiation of induced delaminations, despite concurrent damage accumulation has been experimentally acknowledged, also suggesting mutual interaction. In the present paper a simultaneous and interactive damage progression scheme based on fracture mechanics is proposed. A two-dimensional variational mechanics analysis approach is used to obtain the individual energy release rates and the interaction between damage modes is theoretically acknowledged. Also, a unique parameter is proposed accounting for both the damage modes accumulation levels, ruling the growth rates of the individual damage modes, and the characteristic damage state is questioned. Theoretical findings are then verified using multi-scale fatigue damage data from GFRP cross-ply laminate specimens subjected to uniaxial fatigue loading.

With the increased usage of recycled materials and various evaluation techniques being utilized to evaluate them, it is becoming increasingly important to be able to obtain consistency between the various techniques. Given the wide range of recycled materials as well as treatments or additive materials being used and the complex interactions resulting between them, it is becoming increasingly important to continually verify the field performance related to the findings of the various evaluation techniques. Therefore, this effort utilized binder blending, mortar procedure, and the uniaxial thermal stress and strain test (UTSST) to examine several mixtures containing recycled asphalt pavement (RAP) and recycled asphalt shingles (RAS) along with example recycling agents. The methodologies were compared to each other to seek similarity in findings as well as preliminary comparisons to relevant field performance. The results indicated general agreement between certain parameters of each methodology, while the UTSST showed promising relationships to measured longitudinal and transverse cracking in the observed field test sections.

Field pavement transverse cracking typically can be grouped into two categories, namely thermal cracking that initiates at the surface of the pavement and propagates downward, and reflective cracking that initiates at the pavement layer above the existing pavement cracks or joints and propagates upward. Recently, another transverse cracking phenomenon was noticed in some field investigations but was less studied. Cracks were observed from both the surface and the bottom of field cores, but they cannot be visually observed from the middle layer. In addition, the surface and the bottom cracks lined up well, showing the tendency of meeting each other. This study aimed to evaluate the causes of such transverse cracking phenomena by laboratory tests. Hamburg equipment was used as the evaluation equipment. Some samples were prepared with a saw cut notch 0.33 inches in depth and 0.25 inches in width, and some samples were prepared without the notch at the bottom. The results showed that such a crack type could have happened when samples are aged, the base below the sample is soft, and a notch exists in the bottom layer. A potential mechanism is when the wheel load moves on one side of the existing transverse cracking (the near side), as the specimen on this side tends to bend downward under the wheel load, especially when the support is relatively soft. If without constraint, the other side of the specimen (the far side) should consequently be tilted upward. However, the bonding with the base layer and the self-weight of the specimen restrict the upward movement of the far-side specimen. Therefore, the tensile stress at the surface of the specimen directly on top of the bottom crack is created. At the same time, the bottom crack has the potential of being squeezed and pushed together.

Asphalt concretes are made from aggregates, binders, and modifiers. In this chapter, a brief description is given on the ingredients of asphalt concretes. Different modes of deterioration in asphalt concretes including cracking (i.e., fatigue cracking, longitudinal cracking, transverse cracking, block cracking, slippage cracking, reflective cracking, and edge cracking), surface deformation (i.e., rutting, corrugation, shoving, depression, and swell), disintegration (i.e., pothole and patch), and surface defects (i.e., raveling, bleeding, polishing, and delamination) are then introduced.

This manuscript presents a computationally efficient method based on a geometric model to simulate the transverse cracking of a 90∘ cross-ply in a composite laminate. The model expands on existing homogenized solutions of transverse cracking by accounting for the random microstructure of the transverse ply extracted from optical micrographs of a hybrid [0∕90∕0]T glass/carbon/epoxy composite laminate. The chapter summarizes the three steps of the method, which allows to model the creation of multiple transverse cracks in realistic transverse plies composed of tens of thousands of fibers. The model is calibrated against experimental measurements of the critical values of the applied transverse strain corresponding to the appearance of transverse cracks and then used in a statistical analysis of the impact of the interface strength distribution on the evolution of the transverse cracking process.

In this work, an analytical model is developed to calculate the electrical resistance of a conductive symmetric multidirectional laminate with cracks in multiple layers. To this end, initially, an analytical solution is derived for laminates with cracks in a single layer and, subsequently, the case of cracks in multiple layers is treated using a superposition approach. The accuracy of the analytical model is checked by comparison with the results of several numerical analyses. Later on, the electrical model is used in combination with an existing stiffness degradation model, documenting that a well-defined correlation does exist between the electrical resistance and the stiffness loss of a multidirectional damaged laminate. This allowed damage charts to be drawn, that can be used to assess the stiffness degradation of composites based on electrical measurements.

This paper presents an experimental investigation to better understand the mechanisms of delamination migration in multidirectional End Loaded Split (ELS) specimens. A stacking sequence susceptible to delamination migration was selected for this study and subjected to pure mode II static and fatigue loading. The static and fatigue results gave comparable migration mechanisms, however, differences were noted regarding the damage sequence, the fracture surface , the migration angle and the horizontal distances of migrated location to the front of pre-crack. Scanning Electron Microscopy (SEM) results indicated that fibre imprints and cusps were two dominant micro-features on the fracture surfaces for all specimens. Interactions between delamination and ply splits were observed and confirmed by X-ray CT scanning. Furthermore, comparison was made to understand the effects of loading modes (mode I and II) on delamination migration.

Application of a continuum damage mechanics formulation rests on the ease with which the material constants involved in the formulation can be determined. For an initially linear elastic material, the changes in elastic constants induced by damage depend on certain damage related material constants that are commonly determined by experiments in addition to those required to determine the initial properties. This additional experimental task can render the continuum damage mechanics theory less attractive. The present paper will only deal with those associated with damage representation. We propose here a procedure for analytically determining seven out of eight damage related material constants for unidirectional composites assumed initially transversely isotropic and containing a parallel array of matrix cracks along fibres. The remaining constant can be determined experimentally or by a numerical experiment proposed here for the purpose. The analytical expressions derived are in terms of initial elasticity constants of a unidirectional composite and are verified for their accuracy by numerical experiments. Since a unidirectional composite forms a building block in composite laminates, the results obtained here can be naturally used for damage in laminates.

A model to predict transverse cracking in cross-ply laminates in the presence of residual thermal stresses is developed here. This model is based on the coupled criterion of the finite fracture mechanics. This criterion has been successfully used for different materials, structures and scales to predict crack initiation. It is based on two main hypotheses: (i) crack initiation occurs as a finite-length crack onset and (ii) the crack onset requires that both stress and energy criteria are fulfilled simultaneously. The present model is developed under the generalized-plane-strain hypotheses combining the results obtained using the laminate theory and a boundary element code. The present analysis shows that the residual thermal stresses affect both the stress and the energy criteria in the form of adding a residual elastic-strain to the strain imposed by external mechanical loads. An explicit expression for this residual elastic-strain is provided. For certain composite materials as carbon/epoxy the value of this residual elastic-strain is shown to be relatively large in comparison with the nominal critical transverse strain of the material. The comparison with experiments shows that considering the residual thermal stresses using the strategy proposed here improves drastically the accuracy of the model predictions.

The cast-in-place concrete base plate is a main member of the China Railway Track System (CRTS) III ballastless track structure that is prone to generating early transverse cracking. Such cracks can dramatically affect the performance and service life of the railway track structure. This study investigated the influence of temperature and moisture boundary conditions on early cracking behavior of the CRTS III base plate by using approaches of both in situ measurements and numerical modelling. In-site measurements of strain and temperature were made in four test series of CRTS III base plates under the same natural environmental condition but cured with different regimes, and a total of 96 measuring positions were monitored for up to 150 days. The results showed that the strain magnitude and distribution in the field base plate, the initial time at cracking, and the observed cracking pattern varied significantly between the different test series. In order to understand the mechanisms that create these transverse cracks and to provide guidelines for the current curing strategy during construction, the characteristics of temperature-induced and moisture-induced stresses were analyzed by using 3D numerical modelling and by considering early-age concrete creep properties, meteorological factors, and the influence from environmental boundary conditions. The calculated results revealed that early-age transverse cracking in CRTS III base plate depends more on drying shrinkage stress than temperature stress. By conducting this study, we expect to provide guidance for reducing or eliminating early cracks of CRTS III concrete base plate.

International audience; The influence of water ageing on the evolution of damage during tensile loading in woven hemp/epoxy composites is studied. First, the water uptakes of several types of samples are compared. Micro-CT observations show that, from the beginning of desorption but not during the water ageing, damage appears in the composites. At macroscopic scale, tensile tests reveal a significant modification of mechanical properties of the composite after water ageing. Then, an original test, combining tensile loading and X-ray microtomography, is performed on a ±45 hemp/epoxy composite material. The volume of damage inside two specimens (with and without water ageing) at several steps during a tensile test can be quantified. Results highlight significant differences in the evolution of the volume of damage between the two samples. This work shows how the mechanisms of deformation and damage of plant fibre composites are governed by their moisture exposure history.

Stress field in the ceramic layer containing multiple transverse cracks is determined using a modified 2-D shear lag approach and a finite element method.

This study predicted transverse cracking progression in laminates including 90° plies. The refined stress field (RSF) model, which takes into account thermal residual strain for plies including transverse cracks is formulated, and the energy release rate associated with transverse cracking is calculated using this model. For comparison, the energy release rate based on the continuum damage mechanics (CDM) model is formulated. Next, transverse cracking progression in CFRP cross-ply laminates including 90° plies is predicted based on both stress and energy criteria using the Monte Carlo method. The results indicated that the RSF model and the CDM model proposed in this study can predict the experiment results for the relationship between transverse crack density and ply strain in 90° ply. The models presented in this paper can be applied to an arbitrary laminate including 90° plies.

The coupled effect of transverse cracking and cyclic drying–wetting conditions on chloride penetration in concrete is explored in this paper. The transport mechanisms of chloride in cracked concrete subjected to drying–wetting cycles are described and simplified. An experimental investigation was conducted for sustained cracked concrete beams and the results are reported here. It is found that the depth interval of the convection region in cracked concrete varies from approximately 10 to 20 mm, which is slightly greater than that found in sound concrete. Also, it increases with the increase in crack width and decreases with the increase in fly ash content. At the cracked sections, the speed of chloride penetration is increased by the presence of cracks. It is shown that the modified diffusion model is still practicable for describing the chloride distribution in transversely cracked concrete when the crack width is within a range close to 0·30 mm. Finally, a regressive relationship between equivalent chloride diffusion coefficient, DCleq, and crack width, wcr, is proposed with a quadratic function of crack effect.

International audience; Multi-cracking of brittle thin layers and coating is a phenomenon difficult to model especially because of the large number of cracks that may occur. It is overcome herein by conducting calculations, not on the whole structure, but only on a simplified cell that is representative of the structure by periodic duplication. The coupled criterion is applied within this representative cell (RC) and allows to predict the crack density under an increasing applied load, the length of the RC being a variable parameter of the model. Based on the simultaneous fulfilment of an energy and a stress conditions, it allows to take into account thin layers where the crack onset is energy driven and thicker layers where the stress condition governs the transverse cracking. Results are in a good agreement with various experiments found in the literature, conducted on cross-ply laminates and coated substrates.

The characterisation of fatigue damage evolution in constrained glass fibre reinforced plastic off-axis laminates is presented. A newly developed imaging technique known as Automatic Crack Counting (ACC) is used to quantify the off-axis crack state in constant amplitude (CA) and variable amplitude (VA) block loading tension-tension fatigue tests and constant amplitude compression-tension tests. The quantified crack states are analysed by combining the newly developed ACC method with a data mining approach and applying these to large data sets obtained during fatigue tests. It is shown that for a constant stress level, the stochastic nature of off-axis crack initiation and crack growth is accurately modelled by the Weibull distribution, with the distribution parameters being efficiently derived using the developed approach. The data-rich characterisation provides new insight in the crack density evolution process for VA and C-T loading, as well as derived Weibull distribution parameters in combination with the classical S-N curves and Paris’ Law relationship. Hence, providing an improved approach that includes the stochastic and deterministic information for physically based modelling of crack density evolution for fatigue loading.

This paper presents a numerical study evaluating the influence of nonlinear material behavior on the stiffness reduction due to inter-fiber cracks. It is shown that the relation between crack density and damage variables changes as the load level increases. A three-dimensional nonlinear material model is used in a representative volume element study to accurately calculate the local stress distribution around cracks. The studies show that as the load increases the stress recovers to the far-field level within a shorter distance, and consequently the plastic deformation causes a decrease in the crack-induced stiffness reduction. To provide damage variables for a coupled elastoplastic-damage material approach at the homogenized ply level, the results of a systematic representative volume element study are used for interpolation. For verification, the response curves of several laminates influenced by inter-fiber cracks are simulated and compared to experimental results. The presented procedure enables the constitutive laminate response under large deformations to be accurately predicted.

The purpose of this paper is to investigate the moisture absorption effect on the stress distribution of the cross-ply laminates with transverse matrix cracks. Two analytical models were used to evaluate the stress distribution, Shear Lag and the variational approach. The results show that a complete parabolic variation of displacement gives a good approximation of the stress distribution compared to the finite element analysis. Furthermore, the cracked cross ply laminate is submitted different temperature and moisture concentration distribution. The predicted model shows that moisture absorption has a significant effect on the stress distribution especially at the higher crack density.

Transverse cracking is probably the first and most dominant mode of damage in composite materials. In this paper, transverse cracking of cross-ply [02/90n]s (n = 2,3,4) laminates under uniaxial tension load was studied by means of experimental and numerical methods. In the numerical simulations, a simplified computational strategy only focusing on the damage of the resin was proposed and the mechanical response of the cracking cross-ply laminates was studied by finite element analysis of multi-scale representative volume elements (RVEs). In the RVEs, the longitudinal 0&deg, plies were represented by macro-scale, homogeneous, orthotropic elastic solids while the 90&deg, plies were modeled by the discrete fibers and the surrounding matrix resin in micro-scale. Based on researching the critical longitudinal mechanical strain &epsilon, x which initiates the cracks, the in-situ transverse ply strength and the stiffness degradation of the transverse plies, the simplified computational strategy proposed was proven correct. In addition, the crack initiation is sensitive to residual stress. Higher process-induced residual stress levels are dangerous to laminates, leading to early crack initiation.

© 2018 Elsevier Ltd Voids are an important type of manufacturing defects in fiber-reinforced composites. Matrix cracking is sensitive to the presence of voids. Although this cracking occurs at the ply scale, its dynamics is strongly affected by ply's microstructure, in particular, fiber distribution, fiber content, and the presence of voids. In the current study, a computational approach to simulate the influence of intra-laminar voids on cracking in composite laminates is developed. The approach combines finite element models of two scales: a micro-scale model, where the fibers and voids are modeled explicitly, and a meso-scale model, where the cracking phenomenon is captured on the ply scale. The micro-scale model, incorporating plasticity and damage in the matrix, provides input for the meso-scale model, which simulates the progressive cracking by means of the extended finite element method. The methodology is applied to investigate the effect of voids on the density of transverse cracks in cross-ply laminates in function of the quasi-static tensile load. Different sizes and contents of voids, which are chosen based on experimental micro-computed tomography data, are simulated. The numerical experiments show that the presence of voids leads to earlier start of the cracking, with the crack density evolution less sensitive to voids. ispartof: COMPOSITES PART A-APPLIED SCIENCE AND MANUFACTURING vol:117 pages:180-192 status: published

The performance of jointed plain concrete pavement is affected by various design parameters including mechanical and thermal properties of concrete. Out of these, coefficient of thermal expansion, elastic modulus and modulus of rupture are a few important ones and to evaluate the effects of these material properties on pavement performance, simulations were carried out in MEPDG. All other design parameters such as traffic, design life, climate and road bed soil conditions were considered as constant and pavement performance was evaluated. The simulation results appreciated that with an increase in coefficient of thermal expansion of concrete, the pavement performance was adversely affected. In addition, with an increase in elastic modulus and modulus of rupture values of concrete, the strength of concrete increases and resultantly an improved pavement performance was obtained. It became evident that these material parameters should be carefully considered while designing a rigid pavement. Keywords: Coefficient of thermal expansion (CTE), Modulus of rupture (MOR), Jointed plain concrete pavement (JPCP), Mechanistic empirical pavement design guide (MEPDG), Transverse cracking, Joint faulting

A novel nonlocal discrete model is proposed in this paper to study the deformation and failure behaviors of cross-ply laminated composite plate under static or quasi-static mechanical loadings. Different from existing numerical approaches, the proposed model accounts for the material anisotropy at both constitutive and structural level. To achieve this purpose, the proposed model rotates the underlying topological structure, rather than transforming the material’s tangent stiffness matrix as in the continuum-based simulations. Thus, different failure behaviors can be modeled as the natural outcome of the breakage of connecting springs. The proposed model is verified and validated by comparing the simulation results with analytical solution and experimental observations from open literature.

The long-term performance of asphalt concrete (AC) overlays using mixtures containing reclaimed asphalt pavements (RAP) is compared with the performance of overlays using virgin mixtures. Data from 18 sites of the long-term pavement performance (LTPP) program are used for analysis. Each site consists of 8 side-by-side experimental sections that vary in overlay thickness and pre-overlay treatment method. The selected performance indicators include fatigue cracking, longitudinal cracking, transverse cracking, rutting, and roughness. Explorative data analysis, non-parametric survival analysis, and pair- t tests are used to compare possible performance differences. The analysis results suggest that there are interactive effects between the use of RAP-containing mixtures, overlay thickness, and pre-overlay treatment method. With relatively thin (51 mm) overlay and minimal pre-overlay treatment, undesirable performance of RAP-containing mixtures is expected. Conversely, with relatively thick (127 mm) overlay and intensive pre-overlay treatment, RAP-containing mixtures outperform virgin mixtures in rutting and roughness, without inducing additional cracking-related distresses. The field performance of RAP-containing mixtures is believed to be driven by their fundamental properties, i.e., the reduced cracking resistance and increased stiffness.

The first damage mode to appear in continuous fibre-reinforced composite laminates subjected to in-plane loading is usually transverse cracking, i.e. matrix cracking in the off-axis plies of the laminate. Since the density of transverse cracks has a great influence on the subsequent failure steps like delaminations, it is important to be able to predict it accurately. In this paper, the evolution of crack density with increasing external load is predicted using a combination of the Coupled Criterion of Finite Fracture Mechanics and the Equivalent Constraint Model.

A method for assessing the susceptibility of a weld to transverse cracking is proposed based on a newly designed test specimen featuring a transverse gap in the centre to control restraint and produce a large residual stress in the weld metal. Through FEM simulation of the effects of the weld bead length on the longitudinal residual tensile stress (σx) after welding, it is confirmed that the transverse gap can significantly increase σx after welding. Furthermore, with a fixed transverse gap length, σx increases monotonically with the length of the weld bead. Two different commercial weld wires were used to check the effectiveness of this method; the experimental results obtained indicate that the critical cracking length of the weld bead differs depending on the weld wire used. The critical length of the weld bead can therefore be used as an effective index of its susceptibility to transverse cracking.

Metal/ceramic composites with lamellar microstructures are a novel class of metal-matrix composites produced by infiltration of freeze-cast or ice-templated ceramic preforms with molten aluminium alloy. The cost-effectiveness of production and relatively high ceramic content make such composites attractive to a number of potential applications in the automotive, aerospace and biomedical engineering. A hierarchical lamellar microstructure exhibited by these composites, with randomly orientated domains in which all ceramic and metallic lamellae are parallel to each other, is the result of the ice crystal formation during freeze-casting or ice templating of preforms from water-ceramic suspensions. In this paper, a single-domain sample of metal/ceramic composite with lamellar microstructure is modelled theoretically using a combination of analytical and computational means. Stress field in the sample containing multiple transverse cracks in the ceramic layer is determined using a modified 2-D shear lag approach and a finite element method. Degradation of stiffness properties of the sample due to multiple transverse cracking is also predicted.

Defects such as out-of-plane wrinkles are known to strongly affect in-plane strength but there has been very little research on their effect on out-of-plane properties. Experimental and numerical studies of multi-directional curved-beam laminates were thus carried out to understand the effects of out-of-plane wrinkles on through-thickness tensile strength. The initially selected layup saw free-edge delamination interacting with transverse cracking, which is undesirable. After suppressing the free-edge delamination by dispersing the plies near the specimen surfaces, through-thickness tensile failure was observed near the mid-plane. The effects of out-of-plane wrinkles could be studied with this appropriate layup, showing a 16% reduction in strength. A High-fidelity Finite Element Method (Hi-FEM) has been used to distinguish between the different failure modes and to understand the effects of wrinkles. Good agreement was achieved between the numerical and experimental results in terms of through-thickness tensile strengths and delamination locations.

The fatigue crack density evolution in a cross-ply laminate where edge finish and stitching are taken into account is investigated. Diamond saw and water jet cutting are used to produce the test specimens and some of the specimens are polished afterwards. The crack density evolution and crack initiations are tracked automatically. It is shown that the number of cracks initiating at the edges for non-polished specimens are similar, whereas the diamond saw cut and polished specimens have fewer cracks at the edges, and the water jet cut and polished specimens have even fewer. In addition it is shown that the crack density is higher in the stitching areas than in the rest for polished specimens. This indicates that the stitching is highly governing of where cracks initiate and propagate in the specimens with limited edge defects. The same applies to real composite structures, which are negligibly affected by edge defects.

Open graded friction course (OGFC) is used to reduce noise, improve friction, and for faster drainage of surface water of an asphalt pavement. However, OGFC’s contribution to low-temperatur...

Delamination migration is particularly critical in multi-directional composite laminates and is often observed in different loading scenarios and components. Further understanding on the migration mechanism, especially the similarities and differences in the quasi-static and fatigue delamination migrations, is important for the design of composite structures. In this study, the process of delamination migration under mode I quasi-static and fatigue loadings was experimentally investigated for specimens with a +θ/−θ centreline interface. Specimens, with a specially designed stacking sequence, which allows migration events using a simple Double Cantilever Beam set-up, were tested for θ = 75° and 60°. Delamination migration via intralaminar ply splitting has been observed and this was confirmed by the X-ray computed tomography scan results. All the specimens from both quasi-static and fatigue loadings had a fairly similar sequence of damage events; delamination grows through the −θ and +θ ply block successively until it reaches the 0° ply that prevents further migration. The delamination paths and shape of fracture surfaces were observed to be the same, while the Scanning Electron Microscope fractography results showed that the quasi-static fracture surface was rougher in comparison with that of fatigued specimens. In addition, the distances of migration points from the pre-crack tip were slightly smaller in the fatigue specimens, which may indicate a greater propensity for migration under fatigue loading. This study provides important guidelines to the damage tolerance design of multidirectional composite structures and the verification of advanced numerical modelling technologies.