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Background: Fiber-matrix debonding is a precursor for transverse cracking and several other types of damage in fiber composites. However, to date, there are limited experiment-based reports that study the fundamental mechanisms of fiber-matrix debonding. Objective: This work aims to uncover the governing mechanisms of fiber-matrix interface debonding by full-field measurements supplemented by numerical simulations. In particular, the application of a dual-vision image-based characterization approach on single glass macro fiber samples is discussed and proven useful in understanding the in-plane and out-of-plane debonding characteristics at the fiber-matrix interface. Methods: Full-field strain and displacement measurements based on digital image correlation are performed on model single-fiber composites. The use of a dual-vision system allows strain measurements in the vicinity of the fiber-matrix interface, also allowing for the identification of critical strain and stress values corresponding to the initiation and propagation of debonding damage. The experimental data are used to calibrate an inverse identification approach that outputs the shape of the debonded interface along the fiber length. Results: Full-field measurements allow for establishing correlations between local and global strain fields. Observation of debonding propagation along the fiber axis seems to be representative of the crack tunneling during the early stages of the failure process, i.e., when the crack tip is subjected to opening mode only. Conclusions: Side view measurements are useful as a first-order approximation of the debonding propagation velocity along the fiber axis but fail to provide accurate measurements for the debonding shape, esp. in areas where the crack is under a dominantly shear stress state. This issue can be resolved by full-field measurements coupled with computational simulations. [ABSTRACT FROM AUTHOR]

It is well known within the dam engineering profession that the potential for earthquake-induced cracking is a key consideration in the design and construction of dams. Transverse cracking of embankment dams is a major concern of engineers involved in dam safety management and commonly represents a potential failure mode for such dams. If transverse cracking extends below the reservoir level, it may lead to leakage from the reservoir, internal erosion of the embankment soils, and dam failure. Considerable effort has been made in the engineering profession during the last few decades to study the nature and effects of dam earthquake cracking and to develop design measures to mitigate its potential occurrence. However, few studies exist on earthquake-induced cracking of embankment dams, and the profession's ability to accurately predict its characteristics is limited. Thus, it seems useful to review key aspects of earthquake cracking of embankment dams and some of the lessons learned about cracking from the past performance of dams during earthquakes. This paper aims to fulfill this objective by providing an overview of the observed effects of earthquakes on embankment dams, discussing the potential for embankment dam failure by cracking, reviewing basic concepts about the mechanics of cracking in soils, discussing the analysis of embankment dam cracking in practice, and presenting two case histories of cracking of embankment dams. The case histories describe (1) the performance of Matahina dam during construction, reservoir filling, and the 1987 Edgecumbe earthquake in New Zealand and (2) the performance of Lenihan dam during the 1989 Loma Prieta earthquake in California and an analysis of the dam for that earthquake. [ABSTRACT FROM AUTHOR]

The influence of Ti on the behavior of hot ductility was examined in four different Ti-containing micro-alloyed steels with a constant content of Nb. Thermomechanical investigations using a dilatometer were carried out to simulate the conditions during casting and cooling in the strand of a continuous caster with temperatures in the range of 650–1100 °C, strain rates of 0.01 s−1 and 0.001 s−1, and reheating rates between 60 and 180 Kmin−1. To understand the fracture mechanism, optical (LOM) and scanning electron microscopy (SEM), elemental analysis via energy dispersive X-ray spectroscopy (EDX), MatCalc "Scheil–Guilliver" calculations, and precipitation kinetics calculations were carried out for the critical conditions, showing low hot ductility between Ar3 and Ae3 temperatures and a brittle to ductile transition temperature at 900 °C. The existence of TiNb(CN), thin ferrite formation, and grain boundary sliding (GBs) due to limited dynamic recrystallization (DRX) has been documented and discussed. As a result, the reheating rate has no sufficient effect on the ductility. The existence of Nb-rich TiNb(CN) of sizes below ~1 μm triggers brittle fracture by increasing the frequency of micro-voids around grain boundaries. It can be stated that if the conditions in the hot ductility trough are avoided, the addition of Ti and high strain support minimize the risk of crack formation. [ABSTRACT FROM AUTHOR]

Laminates with ultra-thin plies is a promising new development for polymeric composite materials expected to provide superior resistance to intralaminar crack propagation. The ply thickness effect on the crack initiation stress that according to some theoretical studies on fiber/matrix debonding does not depend on the ply thickness was investigated. Ultra-thin ply carbon fiber/epoxy cross-ply laminates subjected to tensile loading at room, –50, and –150°C temperatures relevant for cryogenic fuel storage, aeronautical, and aerospace applications were studied. The stochastic nature of the crack initiation stress in the 90°-plies was analyzed using Weibull strength distribution. The results obtained show delayed transverse crack initiation only in the thinnest plies with a clear trend that the scale parameter is much larger. This thickness effect on initiation is different than that for crack propagation which is observable in much larger ply thickness range. Regarding crack propagation, it was found that in most cases even at very high applied strain levels (1.5%) only a few transverse cracks have propagated from the specimen edges to its middle. [ABSTRACT FROM AUTHOR]

Over the years, thicknesses of continuously reinforced concrete pavement (CRCP) increased to accommodate rising truck traffic. With a fixed percentage of longitudinal reinforcement relative to the concrete cross-sectional area, thicker slabs necessitate more reinforcement and reduced bar spacing, potentially hindering consolidation. To address this issue, two-mat steel design was implemented in Texas for pavements with thickness of 330 mm (13 in.) or larger. Performance evaluations of thick CRCPs revealed that horizontal cracking developed at the depth of reinforcement where one-mat steel was placed, while no horizontal cracking was observed where two-mat steel was used. Pavement responses with one-mat and two-mat reinforcements with different depths were analysed by three-dimensional modelling with a finite element analysis (FEA) programme for the wide range of environmental loadings. Maximum concrete vertical tensile stresses around longitudinal reinforcement at transverse crack area are a good indicator of horizontal cracking potential; those stresses were evaluated, along with concrete stresses at top of the slab, which are responsible for top-down transverse cracking. The results show that the two-mat design causes higher concrete stresses at the top of the concrete slab and lower concrete stresses around the longitudinal reinforcement, leading to increased transverse cracks and a reduction in horizontal cracking potential. [ABSTRACT FROM AUTHOR]

Transfer learning (TL) offers a convenient methodology for exploiting the capability of deep convolutional neural networks (DCNNs) for many image classification tasks including the classification of pavement distresses. Seven state-of-the-art DCNNs were retrained to classify asphalt pavement distresses grouped into eight classes using TL techniques. The aim was to evaluate the predictive performances of the selected DCNNs in order to provide some guidelines on selection of DCNNs for pavement application. The results show some existing DCNN's are better than others for developing pavement distress classification models using the specific TL approach adopted in the study. The predictive ability of each model varied depending on distress class as some models with very low overall accuracy showed excellent results for individual distress class(s). Based on a combination of various performance metrics including F1-score, area under ROC curve, optimal operating threshold, training time, and model size, the best performing network had a relative score that was found to be significantly higher than the next two top-performing models. The best-performing networks were characterised by lower proportions of false negative values, low ambiguity scores, and well-defined t-SNE clusters that showed clear separation between the eight different pavement distress classes considered. [ABSTRACT FROM AUTHOR]

The Mechanistic-Empirical Pavement Design Guide (MEPDG) is a comprehensive method, including models and guidance, developed in 2002 by the American Association of State Highway and Transportation Officials (AASHTO) to analyze and design both flexible and rigid pavements. The MEPDG is implemented in a software called Pavement ME. The MEPDG models were calibrated using data from the Long-Term Pavement Performance (LTPP) sections from throughout the United States, including some from California. The MEPDG recommends that nationally calibrated models be validated using local data and, if necessary, recalibrated. This recommendation is particularly applicable to the Caltrans road network, considering the climate and materials differences between California and the rest of the nation. The first step in recalibrating Pavement ME is to perform a sensitivity analysis to identify which variables are most important and to look for results that do not match expected performance. This was the subject of a previous report titled Pavement ME Sensitivity Analysis. Based on the sensitivity analysis, the decision was made to perform a new calibration of the MEPDG models as implemented in Pavement ME software. A new approach was developed for the calibration. This new approach uses network-level performance data from the pavement management system (PMS) with orders of magnitude more observations and length of pavement than are used in the traditional approach and in the national calibration of the MEPDG models. The framework does not require sampling of materials from specific sections in the network. Rather, it uses the statewide median values from mechanistic testing from a representative sample of materials across the network. Variability of performance and reliability of design (probability that the design will meet or exceed the design life) is accounted for through separate consideration of within-project and between-project variability. The calibration reduced significant bias in the application of the nationally calibrated models to California. This report presents the results of the application of the new procedure to calibrate the Pavement ME transverse cracking model for jointed plain concrete pavements (JPCP). The California pavement management system (PaveM) database—with about 4600 lane-miles of JPCP built on 446 lane replacement projects completed between 1947 and 2017—was used to calibrate the transverse cracking model in Pavement ME. The nationally calibrated Pavement ME transverse cracking model prediction on the PaveM performance database has bias and standard error of 13.3% and 23.03%, respectively. After calibration, the bias and standard error of the locally calibrated model decreased to 0.039% and 5.69%, respectively.

A new approach that utilizes Thermoelastic Stress Analysis (TSA) is proposed to investigate fatigue-induced material degradation in laminated fiber-reinforced polymer composites (FRP). The proposed model accounts for non-adiabatic conditions, the effects of the material temperature on the material properties, and the effects of stiffness material degradation due to damage. Experimental data from the literature is used to validate the part of the model that simulates the heat transfer, which results in a non-adiabatic contribution to the thermoelastic response. Specimens made from E-glass FRP representative of those used in wind turbine blade manufacture are used in the study, which make a challenging proposition for TSA. The evolution of tunneling cracks caused by cyclic loading causes stiffness degradation and changes in the thermoelastic response. The added features of the proposed model are shown to be necessary to interpret the thermoelastic response. The model improves correspondence with experimental data compared to previous TSA methods. Hence a generalized framework is proposed for incorporating the mechanisms that affect the thermoelastic response as materials degrade due to fatigue loading.

The American Association of State Highway and Transportation Officials Mechanistic-Empirical Pavement Design Guide (AASHTO M-E) offers an opportunity to design more economical and sustainable high-volume rigid pavements compared to conventional design guidelines. It is achieved through optimizing pavement structural and thickness design under specified climate and traffic conditions using advanced M-E principles, thereby minimizing economic costs and environmental impact. However, the implementation of AASHTO M-E design for low-volume concrete pavements using AASHTOWare Pavement ME Design (Pavement ME) software is often overly conservative. This is because Pavement ME specifies the minimum design thickness of concrete slab as 152.4 ​mm (6 in.). This paper introduces a novel extension of the AASHTO M-E framework for the design of low-volume joint plain concrete pavements (JPCPs) without modification of Pavement ME. It utilizes multi-gene genetic programming (MGGP)-based computational models to obtain rapid solutions for JPCP damage accumulation and long-term performance analyses. The developed MGGP models simulate the fatigue damage and differential energy accumulations. This permits the prediction of transverse cracking and joint faulting for a wide range of design input parameters and axle spectrum. The developed MGGP-based models match Pavement ME-predicted cracking and faulting for rigid pavements with conventional concrete slab thicknesses and enable rational extrapolation of performance prediction for thinner JPCPs. This paper demonstrates how the developed computational model enables sustainable low-volume pavement design using optimized ME solutions for Pittsburgh, PA, conditions.

The influence of Ti on the behavior of hot ductility was examined in four different Ti-containing micro-alloyed steels with a constant content of Nb. Thermomechanical investigations using a dilatometer were carried out to simulate the conditions during casting and cooling in the strand of a continuous caster with temperatures in the range of 650–1100 °C, strain rates of 0.01 s−1 and 0.001 s−1, and reheating rates between 60 and 180 Kmin−1. To understand the fracture mechanism, optical (LOM) and scanning electron microscopy (SEM), elemental analysis via energy dispersive X-ray spectroscopy (EDX), MatCalc “Scheil–Guilliver” calculations, and precipitation kinetics calculations were carried out for the critical conditions, showing low hot ductility between Ar3 and Ae3 temperatures and a brittle to ductile transition temperature at 900 °C. The existence of TiNb(CN), thin ferrite formation, and grain boundary sliding (GBs) due to limited dynamic recrystallization (DRX) has been documented and discussed. As a result, the reheating rate has no sufficient effect on the ductility. The existence of Nb-rich TiNb(CN) of sizes below ~1 μm triggers brittle fracture by increasing the frequency of micro-voids around grain boundaries. It can be stated that if the conditions in the hot ductility trough are avoided, the addition of Ti and high strain support minimize the risk of crack formation.

This study investigates the field performance of Warm Mix Asphalt (WMA) road overlays containing various amounts of RAP and binder. Rutting, the International Roughness Index (IRI), and transverse, longitudinal and alligator cracking are the key parameters considered here. Our research is based on a Specific Pavement Study-10 experiment (SPS-10) conducted in nine states of North America (eight in the USA and one in Canada) that included 31 road sections in dry and wet regions. Road overlays were evaluated 1 and 4 years after their placement in terms of anti-cracking behavior and were compared with the pre-treatment status of the road. The best rutting resistance occurred at 15% and 12% RAP in dry and wet regions, respectively. For IRI, 30% and 0.0% RAP were the best for dry and wet regions as well. The maximum longitudinal crack recovery rates were found at site 3 (BA01, Arizona; dry region) and site 26 (AA65, Missouri; wet region), with RAP contents of 20% and 36%, respectively. In addition, alligator cracking did not occur post-overlay, so optimal RAP and binder contents cannot be suggested. The greatest improvements were found at site 15 (AA01, Washington state; dry) and site 30 (AA63, Oklahoma; wet). The response surface method (RSM) was also developed to explore the optimal models for RAP and selection of binder contents to minimize the rutting, IRI, and transverse and longitudinal crack lengths.

There is considerable interest in improving the resistance of fully austenitic TWIP steels to hydrogen embrittlement; one potential route is to use V additions to promote hydrogen trapping by V(C,N) precipitates. This has the dual benefit of increasing the yield strength through precipitation strengthening and grain refinement. However, the effect on slab quality during continuous casting has not been determined. In this study, the hot ductility of two twinning-induced plasticity (TWIP) steels, Fe-0.6C-22Mn and Fe-0.6C-22Mn-0.2V, was examined over the temperature range 650–1200 °C. Tensile samples were taken from continuous cast 225 mm slabs and from 36 mm transfer bars. The addition of V caused the ductility trough in the temperature range 650–900 °C to deepen and widen and the lowest reduction in area (RA) recorded in the as-cast condition was 30%. This deterioration of hot ductility was due to V(C,N) precipitation. Even though the minimum RA was below the value often accepted to avoid cracking, no transverse cracking was observed in industrial trials and the surface quality was acceptable. The RA values of Fe-0.6C-22Mn were found to be very sensitive to the P level. However, this sensitivity was less evident when V was added, possibly due to P trapping by VC at austenite boundaries. No transverse cracking was observed in industrially produced slabs with P in the range examined (0.02 to 0.04 wt.% P). [ABSTRACT FROM AUTHOR]

This study utilized synchrotron radiation X-ray computed tomography to investigate the initiation and propagation of microcracks in cross-ply carbon fiber-reinforced polymer (CFRP) laminates under mechanical loading. Initially, static tensile loads were applied to detect microcracks within a ply thickness of 160 μm. The crack propagation was subsequently characterized, extending across adjacent carbon fibers and along the interfaces of individual fibers into the material's interior. The experiment was repeated with cyclic loading, where the laminates were imaged periodically. Analysis of the images revealed the presence of microcracks and provided insights into their progression from the point of initiation. Notably, microcracks exhibited the initiation toward the interior of the material rather than across the neighboring carbon fibers, whereas their propagation is more significant across the adjacent carbon fibers particularly under the static loading. Under cyclic loading, however, the crack propagation toward the interior of the material was more pronounced, implying different propagation behavior than when under static loading. These findings were also validated through the distribution of energy release rate and stress triaxiality along the crack tip calculated by finite element analysis. [Display omitted] [ABSTRACT FROM AUTHOR]

The R-curves for transverse cracking could be determined based on the size effect law using SENB specimens, where the R-curves determined by the size effect law were consistent with those determined by the compliance method. The crack growth resistance in the steady-state and the crack extension at the onset of the steady-state of carbon-fiber/epoxy laminates, T800S/2592, were determined to be 0.22 N/mm and 0.36 mm, respectively. The crack growth stability in SENB specimens depended not only on the load control method but also on the specimen geometry, whereas a unique R-curve could be obtained regardless of the crack growth stability. • The R-curve for transverse cracking in composite laminates was "experimentally" determined based on the size effect law. • The validity of the above method was not only theoretically predicted but also numerically and experimentally proven. • The R-curves obtained by the size effect law were demonstrated to be independent of the load control method. • The R-curves obtained by the size effect law were demonstrated to be compatible with those obtained by the compliance method. • A practical data reduction scheme was proposed to reduce the evaluation error in the size effect study. [ABSTRACT FROM AUTHOR]

• Crack density growth in cross-ply laminates during fatigue loading is analyzed. • Transverse cracking is influenced by local stress ratio in the 90-layer. • Equivalent stress is introduced to include the effect of local stress ratio. • Equivalent stress concept is validated against two different cross-ply layups. Presented test results on transverse cracking in cross-ply laminates upon tension–tension cyclic loading show that the increase of crack density depends not only on the maximum transverse stress in the cycle but also on the local cyclic stress ratio R T loc in the analyzed layer. To include the effect of the R T loc in the model with statistical failure stress distribution for crack initiation (based on Weibull distribution) adapted for fatigue, an equivalent stress is introduced in a similar manner as the equivalent strain energy release rate has been used for delamination crack propagation. The equivalent stress in the layer is defined as a power function of the maximum stress and the stress ratio in the layer. It was found, testing laminates with two different fiber contents that higher the local stress ratio in 90-layer, higher the transverse cracking resistance. Transverse crack density simulation using the developed equivalent stress model has been validated against test results. [ABSTRACT FROM AUTHOR]

This study investigates the field performance of Warm Mix Asphalt (WMA) road overlays containing various amounts of RAP and binder. Rutting, the International Roughness Index (IRI), and transverse, longitudinal and alligator cracking are the key parameters considered here. Our research is based on a Specific Pavement Study-10 experiment (SPS-10) conducted in nine states of North America (eight in the USA and one in Canada) that included 31 road sections in dry and wet regions. Road overlays were evaluated 1 and 4 years after their placement in terms of anti-cracking behavior and were compared with the pre-treatment status of the road. The best rutting resistance occurred at 15% and 12% RAP in dry and wet regions, respectively. For IRI, 30% and 0.0% RAP were the best for dry and wet regions as well. The maximum longitudinal crack recovery rates were found at site 3 (BA01, Arizona; dry region) and site 26 (AA65, Missouri; wet region), with RAP contents of 20% and 36%, respectively. In addition, alligator cracking did not occur post-overlay, so optimal RAP and binder contents cannot be suggested. The greatest improvements were found at site 15 (AA01, Washington state; dry) and site 30 (AA63, Oklahoma; wet). The response surface method (RSM) was also developed to explore the optimal models for RAP and selection of binder contents to minimize the rutting, IRI, and transverse and longitudinal crack lengths. [ABSTRACT FROM AUTHOR]

This study aims to investigate the effects of transverse cracking on the deflections of asphalt pavements. 3D finite element models were developed to simulate various intact and cracked asphalt pavements. The deflections of intact and cracked pavements under falling weight deflectometer (FWD) loading were computed and compared. In most cases analyzed, the deflections of cracked pavements are greater than those of intact pavements. For pavements with thermal cracking, the deflections can be 12% and 25% greater than those of intact pavements for cement treated base (CTB) and granular base (GB), respectively. For pavements with reflective cracking, the deflections of cracked pavements can be 98% greater than those of intact pavements, and the deflection decreases sharply across the reflective crack and in some cases it can even increase with increasing distance from the loading center. Crack location and width mainly affect the deflections on the loaded side of crack. Both thermal and reflective cracking have greater influences on the deflections of pavement with a thicker AC layer and a weaker subgrade. The effects of reflective cracking on the deflections are significantly greater than thermal cracking. LTE30–60cm is recommended as a deflection index to distinguish reflective cracking from thermal cracking. [ABSTRACT FROM AUTHOR]

The inter-fiber failure of glass fiber-reinforced epoxy specimens with four different fiber angles was analyzed. Flat specimens were subjected to static and fatigue loading considering different load levels and load ratios. Damage investigation in terms of crack density measurement was performed by transmitted white light imaging using a digital camera and LED illumination from the back of the specimen on a servo-hydraulic testing machine. Static and fatigue results were examined with respect to crack initiation and crack growth, considering the special case of bonding yarns parallel to the fiber directions. The bonding yarns act as stress concentrations, influencing the early cracking behavior, and complicate the detectability of cracks growing underneath or next to the bonding yarns. In cyclic loading, the influence of load level, load ratio, mean stress, fiber orientation, and ply thickness was the focus of the experimental campaign. Cyclic cracking behavior in terms of initiation and growth was analyzed based on the applied loading conditions and laminate configurations. It was found that halving the ply thickness nearly doubled the amount of microcracks in case of high loads. For low loads, no such effect was observed up to 5 × 10 5 loading cycles. Experimental findings on individual crack growth confirmed that crack interaction started for crack spacings less than four times the ply thickness and that subsequent crack growth shifted into regions of larger local crack spacing. [ABSTRACT FROM AUTHOR]

Cold-in-Place Recycling (CIR) asphalt material is gaining increased popularity due to its innovative properties, performance and recycling values. However, detailed material properties of this material are required to design pavement using the CIR materials. This study finds out an equivalent conventional Hot-Mix Asphalt (HMA) which behaves very similar to the CIR material. As a first step, detailed properties of the CIR materials used in Colorado has been measured in the laboratory. Then, the performances of ten pavements which are built using the CIR are predicted using the AASHTOWare Pavement Mechanistic-Empirical (ME) Design (PMED) software. Then, different HMA mixes are used to run the PMED software and are compared with the performance of the CIR material. Results show that the PMED software analysis showed the PMED-predicted IRI and rutting values are close to the values measured in the field. However, the PMED-predicted fatigue cracking values are less than values measured in the field. CIR material behaves very similar to the HMA SX (75) PG 58-28 mix and thus may be used in place of CIR while analyzing a pavement using the PMED software.

The process of formation and subsequent propagation of transverse cracks in 90° plies of carbon-fiber laminated composites was studied using modal acoustic emission approach and digital image correlation techniques. The results from modal acoustic emission approach, which included a newly developed processing tool for acoustic emission waveforms, provided information for identification and subsequent characterization or localization of signals originating from transverse cracking by analysis of the separated flexural and extensional Lamb wave modes in terms of their modal parameters. The digital image correlation method served as a verification tool of the acoustic emission data outputs in the terms of activity of significant localized events originating from the formation of the transverse crack in the 90oply. This made it possible to specify more locally the accompanying activity belonging to the formation or propagation of the magistral transverse crack. The manuscript also presents results related to the evolution of flexural/extensional wave modal parameters as the function of loading force for both [0/0/0/90]S and [90/0/0/0]S panels. It can be concluded that the detection of transverse cracks requires the need for applying a more complex acoustic emission data analysis methodology, while the standard parametric analysis, including the waveform peak frequency, is not sufficient. The presented methodology may serve as a basis for development of robust analysis tool capable of detecting the investigated phenomena. [Display omitted] [ABSTRACT FROM AUTHOR]

This work is concerned with extracting characteristic features of transverse crack formation in cross ply laminates under axial tension considering nonuniform distribution of fibers in the ply cross section. The fiber-matrix debond crack initiation sites are determined first by the dilatation induced cavitation criterion for an epoxy matrix. The growth of the debond cracks is analyzed by calculating the energy release rates using the virtual crack closure technique. The kink-out of the debond cracks into the matrix is determined in short incremental steps by the maximum energy release rate criterion. Different scenarios are considered for the linking up of the kinked-out cracks to form continuous transverse cracks. By studying two different degrees of fiber distribution nonuniformity, the interactive effects due to the fiber distribution on the transverse crack formation are clarified. [Display omitted] [ABSTRACT FROM AUTHOR]

The ability of carbon fibre reinforced polymers to respect functional requirements such as permeability is strongly related to their damage state. In order to identify the fracture properties on which transverse cracking kinetics depend, we combine experimental and virtual tests by explicitly modelling all transverse cracks. Two modelling methods are compared, the cohesive zone model (CZM) and finite fracture mechanics (FFM). Both models are based on a double criterion of energy and strength. Each potential crack is assigned a couple of material properties (fracture energy and strength) derived from a probability distribution. This study focuses on how modelling choice implies assumptions on energy dissipation and the cracking behaviour represented. The relevance of both modelling methods is also discussed. A methodology is provided for identifying fracture properties and predicting damage accumulation in an isolated ply. [Display omitted] [ABSTRACT FROM AUTHOR]

Matrix microcracking is considered the main factor responsible for the gas permeation in linerless pressure vessels and storage tanks. The addition of halloysite nanotubes (HNTs) to them at different concentrations was studied in order to enhance their microcrack resistance. A 50% increase in the cracking onset stress was found at a 5% addition of HNTs to the epoxy matrix. Moreover, a 60% increase was observed at a similar level of microcrack density compared with that of neat epoxy. A reactive diluent was used as an alternative to keep the viscosity suitable for the filament winding process and to offset the rise in viscosity by HNT incorporation. Despite the fact that the matrix fracture toughness increased even to 10% of HNTs, no growth in the microcrack resistance was found at more than 5% of HNTs. As a result, it was concluded that the microcracking phenomenon can be affected not only by the matrix fracture toughness, but also by the residual thermal stresses. [ABSTRACT FROM AUTHOR]

In this study, the rate dependency of transverse cracking evolution in cross-ply laminates is investigated for several 90° plies thicknesses. The crack detection methodology is based on a recently proposed protocol relying on the use of infrared thermography. A new analysis methodology is proposed to make it more robust and to directly link the spatial localization of the crack with the stress level at which it occurs. Based on this methodology, the results obtained for various loading rates and 90° ply thicknesses are analysed. The crack density evolution with respect to stress apply to the laminate exhibits a rate dependency only for the [0/90]s configuration. This rate dependency is finally discussed based on transverse crack onset theories in cross-ply laminates.

The modeling of the structural behavior of composite materials is an interesting but complex task since the response of the material to loading structural may be difficult to predict, and the failure may be manifested in different forms. In cross-ply fiber-reinforced composites, the major failure mechanisms include: (i) the failure of the matrix material (transverse cracking), (ii) delamination and (iii) the breakage of the fibers. The process of the transverse cracking is a well studied damage mechanism and can be used in numerical simulations, in order to study the effects of various parameters on the crack density. In this paper, the finite element modeling of a cross-ply composite under uniaxial loading in tension is performed using ABAQUS software, considering all the potential damage mechanisms. The model takes into account shear-lag effect for the determination of the stress transfer and furthermore it adopts a homogenization procedure for the calculation of elastic and viscoelastic material properties. Stochasticity is introduced by assigning various interfacial strengths that follow a Gaussian distribution, so as to predict the cracking sequence up to saturation in the transverse to the 0 ∘ layers. The results are directly compared with available experimental measurements showing reasonable agreement. Finally, a cross-ply RVE model was created and loaded in uniaxial tension and crack propagation is modelled with the Extended Finite Element Method (XFEM). The stress concentration calculations around the crack tips are in agreement with the mesoscale model. [ABSTRACT FROM AUTHOR]

This article investigates transverse cracking in embankment dams resulting from cross-valley differential settlements during and post-construction, in which concentrated leak erosion may initiate. Based on case studies and numerical analyses, it is shown that valley profiles with a step in the upper part of the abutment and subject to large post-construction settlements within the embankment, or within compressible soil in the foundation, are most likely to be subject to cracking. Estimated localised strains at the crest > 1%, and in particular >2%, are likely to be indicative of conditions conducive to transverse cracking. Smaller strains but greater than about 0.25% may also result in cracking but they are likely to be narrower and shallower. The article also gives general guidance on the likely width and depth of cracking. The information presented is only suitable for preliminary dam safety assessments. For detailed dam safety assessments and risk assessments where decisions are to be made on whether risks are tolerable, or upgrades required, site-specific cross-valley numerical analyses should be carried out. These detailed analyses should model the cross-valley profile accurately, material parameters more rigorously than has been done in the parametric studies reported in this article. [ABSTRACT FROM AUTHOR]

Cracking is one of the primary forms of distress suffered by hot-mix asphalt (HMA) overlay of composite pavements. Pavement cracking affects the ride quality and pavement service life by allowing water and debris to penetrate through the pavement structure. This paper presents the development of transverse cracking and longitudinal cracking performance models for overlay treatment of composite pavements in the state of Louisiana. Various factors that affect the cracking performance of overlay treatment were identified. Such factors include equivalent single axle load (ESAL), thickness of HMA and Portland cement concrete (PCC), functional classification of roadways, and newly developed temperature indexes. Regression analyses were performed to identify those factors and to develop cracking prediction models. In order to better predict the pavement service life, the existing condition of the pavement was also utilised through the models. The developed models provided an acceptable agreement between the measured and predicted crack values. It was found that the predictions were improved when the existing pavement condition was incorporated in the models. The resulting cracking models could be used by Louisiana Department of Transportation and Development (LADOTD) as a good pavement management tool for timely pavement maintenance and rehabilitation actions to maximise benefits, driver's comfort, and safety. [ABSTRACT FROM AUTHOR]

There is considerable interest in improving the resistance of fully austenitic TWIP steels to hydrogen embrittlement; one potential route is to use V additions to promote hydrogen trapping by V(C,N) precipitates. This has the dual benefit of increasing the yield strength through precipitation strengthening and grain refinement. However, the effect on slab quality during continuous casting has not been determined. In this study, the hot ductility of two twinning-induced plasticity (TWIP) steels, Fe-0.6C-22Mn and Fe-0.6C-22Mn-0.2V, was examined over the temperature range 650–1200 °C. Tensile samples were taken from continuous cast 225 mm slabs and from 36 mm transfer bars. The addition of V caused the ductility trough in the temperature range 650–900 °C to deepen and widen and the lowest reduction in area (RA) recorded in the as-cast condition was 30%. This deterioration of hot ductility was due to V(C,N) precipitation. Even though the minimum RA was below the value often accepted to avoid cracking, no transverse cracking was observed in industrial trials and the surface quality was acceptable. The RA values of Fe-0.6C-22Mn were found to be very sensitive to the P level. However, this sensitivity was less evident when V was added, possibly due to P trapping by VC at austenite boundaries. No transverse cracking was observed in industrially produced slabs with P in the range examined (0.02 to 0.04 wt.% P).

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Cold-in-Place Recycling (CIR) asphalt material is gaining increased popularity due to its innovative properties, performance and recycling values. However, detailed material properties of this material are required to design pavement using the CIR materials. This study finds out an equivalent conventional Hot-Mix Asphalt (HMA) which behaves very similar to the CIR material. As a first step, detailed properties of the CIR materials used in Colorado has been measured in the laboratory. Then, the performances of ten pavements which are built using the CIR are predicted using the AASHTOWare Pavement Mechanistic-Empirical (ME) Design (PMED) software. Then, different HMA mixes are used to run the PMED software and are compared with the performance of the CIR material. Results show that the PMED software analysis showed the PMED-predicted IRI and rutting values are close to the values measured in the field. However, the PMED-predicted fatigue cracking values are less than values measured in the field. CIR material behaves very similar to the HMA SX (75) PG 58-28 mix and thus may be used in place of CIR while analyzing a pavement using the PMED software. [ABSTRACT FROM AUTHOR]

The inter-fiber failure of glass fiber-reinforced epoxy specimens with four different fiber angles was analyzed. Flat specimens were subjected to static and fatigue loading considering different load levels and load ratios. Damage investigation in terms of crack density measurement was performed by transmitted white light imaging using a digital camera and LED illumination from the back of the specimen on a servo-hydraulic testing machine. Static and fatigue results were examined with respect to crack initiation and crack growth, considering the special case of bonding yarns parallel to the fiber directions. The bonding yarns act as stress concentrations, influencing the early cracking behavior, and complicate the detectability of cracks growing underneath or next to the bonding yarns. In cyclic loading, the influence of load level, load ratio, mean stress, fiber orientation, and ply thickness was the focus of the experimental campaign. Cyclic cracking behavior in terms of initiation and growth was analyzed based on the applied loading conditions and laminate configurations. It was found that halving the ply thickness nearly doubled the amount of microcracks in case of high loads. For low loads, no such effect was observed up to 5×105 loading cycles. Experimental findings on individual crack growth confirmed that crack interaction started for crack spacings less than four times the ply thickness and that subsequent crack growth shifted into regions of larger local crack spacing.

This study investigates the relation of quality measures of asphalt mixture properties during production and construction to long-term in-service performance of flexible pavements. Data from flexible pavement sections taken from the Long-Term Pavement Performance (LTPP) program along with the pavement sections of 30 Wisconsin projects were compiled in a single relational database to establish a georeferenced architecture that embraces the natural variability within the database. An in-depth analysis was performed on seven selected projects using two modeling programs that are based on statistical regression and mechanistic-empirical methods. The three research approaches allowed for assessing the effects of the variation in quality measures during construction and production: air void (Va); voids in mineral aggregates (VMA); and in-place density. The analysis showed that the deviation from the standard target for in-place density influences fatigue, longitudinal, and transverse cracking, as well as the International Roughness Index (IRI). The study showed the shortcomings of over-averaging pavement characteristics in the modeling of predicted in-service performance. Last, this study showed that implementing the proposed georeferenced relational database architecture within LTPP would increase the impact of this program. [ABSTRACT FROM AUTHOR]

The modeling of the structural behavior of composite materials is an interesting but complex task since the response of the material to loading structural may be difficult to predict, and the failure may be manifested in different forms. In cross-ply fiber-reinforced composites, the major failure mechanisms include: (i) the failure of the matrix material (transverse cracking), (ii) delamination and (iii) the breakage of the fibers. The process of the transverse cracking is a well studied damage mechanism and can be used in numerical simulations, in order to study the effects of various parameters on the crack density. In this paper, the finite element modeling of a cross-ply composite under uniaxial loading in tension is performed using ABAQUS software, considering all the potential damage mechanisms. The model takes into account shear-lag effect for the determination of the stress transfer and furthermore it adopts a homogenization procedure for the calculation of elastic and viscoelastic material properties. Stochasticity is introduced by assigning various interfacial strengths that follow a Gaussian distribution, so as to predict the cracking sequence up to saturation in the transverse to the 0∘ layers. The results are directly compared with available experimental measurements showing reasonable agreement. Finally, a cross-ply RVE model was created and loaded in uniaxial tension and crack propagation is modelled with the Extended Finite Element Method (XFEM). The stress concentration calculations around the crack tips are in agreement with the mesoscale model.

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]