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Integrating a mortar model into discrete element simulation for enhanced understanding of asphalt mixture cracking
Computer-Aided Civil and Infrastructure Engineering
Abstract
Cracks impact the performance and durability of asphalt pavements, necessitating a comprehensive understanding of the mixture cracking behavior. While discrete element modeling has been implemented, many studies oversimplify the simulation of asphalt mortar, a critical component affecting mixture cracking resistance. This study proposes a mortar model that is applicable to both two-dimensional (2D) and, to a preliminary extent, three-dimensional (3D) simulations. The model incorporates a geometric representation of mortar distribution and a mechanical softening model to simulate damage accumulation and fracture. Laboratory and virtual Superpave indirect tensile tests were performed on asphalt mixtures with varying gradations at different aging levels. The virtual simulations successfully mirrored indoor test results in volumetric parameters , load-displacement behavior, and stress distribution. Minor differences in strength, strain, and fracture energy between virtual and indoor tests confirmed the accuracy of the mortar model. Notably, the 3D simulations provided a more accurate reconstruction of the cracking process, showing smaller discrepancies between virtual and indoor results, compared to the 2D simulations, with errors in stress, strain, and fracture energy of 5.6%, 5.7%, and 4.7%, respectively. Employing the mortar model in discrete element simulation revealed insights into fracture angle distribution and tendencies, enabling meticulous analysis of mixture damage characteristics and cracking behavior. This allows for the improved design of mixtures with excellent cracking performance and contributes to advancing computational methods that could complement laboratory testing.
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The constraint action of the unbound aggregate layer underneath plays an important role in affecting the temperature strains in the top asphalt layer. The focus of the present paper is to investigate the interactive thermal contraction mechanisms between the asphalt mixture and granular base layers to offer a new perspective in promoting the understanding of the thermal cracking disease. In this paper, both experiments and simulations were conducted for the thermal contraction tests. A novel numerical modeling of virtual composite structures was proposed using wall‐zone coupling operation based on the finite difference and discrete element coupling method. The experimental composite structures containing three types of asphalt mixture overlays and five types of unbound aggregate base layers were developed for verification. The thermal contraction and restraint mechanism were revealed from both macro and microscopic scales. The proposed numerical modeling shows a 94% high accuracy. The particle displacement vector and contact force chain could explain the thermal contraction behavior of composite structures. Smaller particle motion displacement or stronger contact force chain result in a higher restraint strain of the asphalt overlay. The thermal contraction behavior can be coordinated through the compaction and loosening of unbound aggregates. The material parameters and cooling temperature differences in the asphalt overlay have slight effects on the constraint action of a base layer, while the gradation and mechanical parameters of the unbound aggregate layer show significant impaction. The parameters, cohesion C and friction angle φ, show a quadratic function with the restraint coefficient. This work has significant guidance on the selection of pavement structure and materials to improve the thermal cracking problem and lay the basis for the mechanical theoretical calculation to predict thermal cracking.
When an impact load is sufficiently small, its influence on the pavement structure is mainly from the surface layer material. To explore the influence depth of an impact load and back‐calculation of the pavement surface modulus, both numerical calculation and experimental testing were conducted, and the results are presented in this paper. The numerical calculation was performed through a DEM‐FDM‐coupled model. After a new modulus back‐calculation algorithm is formed by analyzing the numerical modeling results, experimental tests were also conducted for verification, and the results were analyzed. The max value of the falling weight impact force was closely related to the elastic modulus of the material, and the influence depth was controllable. Finally, it is proved that the method can be used to calculate the surface layer modulus and estimate the surface layer thickness.
The characteristic indicators of aggregate contacts in asphalt mixtures, including the number, orientation, and area of contact regions, significantly affect skeleton morphology and mixture stability. To investigate the influence of indicators on mixture stability, structures with diverse characteristics of aggregate contacts are required. This study proposes an algorithm for the virtual modeling of asphalt mixture beams, which supports the density and distributional controls of aggregate contacts in the microstructure. The methodology comprises three main steps: (1) three‐dimensional models of coarse aggregates conforming to the predefined gradation and volumetric content are randomly selected from a digital library of realistic aggregates, (2) contact relations of aggregates are established during the adaptive arrangement of aggregates in samples with prescribed control parameters of aggregate contact using self‐developed codes, and (3) air voids are randomly scattered in the sample without overlapping aggregates according to the volumetric content of the air voids, and an asphalt mortar model is then constructed using Boolean operations. Four beam samples with different contact characteristics were obtained using the proposed method to conduct simulations of three‐point bending tests. The number and spatial distribution of aggregate contacts in beam models are consistent with the prescribed parameters, showing the reliability of the proposed method for the control of aggregate contact in asphalt mixtures. A comprehensive comparison of the results of the laboratory test and simulations validates the ability of the digital beam to capture the macroscale response of asphalt mixtures. Furthermore, simulation results indicate that the sample with the greatest number and distribution uniformity of aggregate contacts has the largest peak strength and fracture energy, which is beneficial for the understanding of the relationship between the indicators of aggregate contacts and the rutting and fatigue resistance of mixtures.
A three‐dimensional (3‐D) locally homogeneous model for asphalt mixtures is presented in this study, which can effectively balance the simulating accuracy and computational effort. Moreover, the locally homogeneous model accounts for various aggregate gradations to allow for the mesoscale analysis of the asphalt concrete (AC) under loading. In the first step of the locally homogeneous model development, weighted Voronoi tessellation technology was employed to divide the volume of asphalt mixture into several local parts in terms of the aggregate gradations and random particle locations with each part containing one or a few aggregates particles. Subsequently, the mesomechanical Mori–Tanaka method was used to calculate the homogeneous mechanical properties for each local space. Finally, 3‐D models of asphalt mixtures were developed, which were further used for numerical simulations. The finite element method was used for the asphalt mixture mesoscale investigations. Two asphalt mixtures were studied consisting of dense‐ and gap‐graded aggregates and labeled, respectively, AC‐13 and stone mastic asphalt (SMA)‐11. The efficacy of the numerical analysis was demonstrated by comparing model‐generated responses and performance with compressive dynamic loadings test results. The models demonstrated the ability to characterize the linear viscoelastic performance for both asphalt mixtures. Furthermore, the locally homogeneous models of AC‐13 and SMA‐11 mixtures were coupled into global asphalt pavements to identify the influence of aggregate particles on their mechanical responses. The results indicated that the locally homogeneous models are able to consider both the pavement structure at the global scale and the internal feature of asphalt mixtures at the local scale.
In order to obtain more accurate parameters required for the simulation of asphalt mixtures in the discrete element method (DEM), this study carried out a series of cross-functional asphalt mixture experiments to obtain the DEM simulation meso-parameters. By comparing the results of simulation and actual experiments, a method to obtain the meso-parameters of the DEM simulation was proposed. In this method, the numerical aggregate profile was obtained by X-ray CT scanning and the 3D aggregate model was reconstructed in MIMICS. The linear contact parameters of the aggregate and the Burgers model parameters of the asphalt mastic were obtained by nanoindentation technology. The parameters of the parallel bonding model between the aggregate and mastic were determined by the macroscopic tensile adhesion test and shear bond test. The results showed that the meso-parameters obtained by the macroscopic experiment provide a basis for the calibration of DEM parameters to a certain extent. The trends in simulation results are similar to the macro test results. Therefore, the newly proposed method is feasible.
Fine aggregate matrix (FAM) refers to the mixture of asphalt binder and fine aggregate in asphalt mixture. The viscoelastic properties, such as the complex modulus of FAM, directly affect the performance of asphalt pavement. In this study, finite element (FE) simulation by coupling random aggregate distribution algorithm and steady‐state dynamic (SSD) analysis was applied to predict the complex modulus of FAM. Both the dynamic moduli and phase angles of FAM were predicted and compared with those obtained from laboratory tests. The modeling and testing results indicated that the complex interface layer between asphalt mastic and aggregate can significantly affect the viscoelastic performance of FAMs. Considering the interface layer into the FE model can improve the prediction accuracy. Besides, the simulation results showed that the SSD method is 576 times more efficient in predicting the dynamic moduli and phase angles of FAMs than the conventional transient dynamic method, indicating its high potential for multi‐scale modeling of asphalt mixture.
The stress-absorption layer in cement concrete pavement delays the development of reflection cracks and is good at fatigue resistance. Laboratory investigations of the anti-crack performance of the high viscous asphalt sand stress-absorption layer (HVASAL) and rubber asphalt stress-absorption layer (RASAL) were carried out by force-controlled fatigue crack propagation tests, for which three types of overlay structures with three types of pre-crack (i.e., the middle crack, the side crack, and the 45° inclined crack) were designed. A probability model was established to describe the propagation of the fatigue cracks. The fatigue crack propagation, the fatigue life, the crack propagation rate, and the crack propagation mechanism of the three types of overlay structure were compared and analyzed. The results show that the stress-absorption layers have good anti-crack fatigue performance, and that the RASAL is better than the HVASAL. The crack propagation patterns of the three types of overlay structure were found. In the double logarithmic coordinate, the curves of the three types of cracks are straight lines with different intercepts and slopes. The probability model quantifies the relationship between the crack propagation rate and ∆K. The influences of the three types of crack on the fatigue properties of the asphalt overlays are different.
Interstitial component (IC), referring to the finer portion of asphalt mixture, is primarily responsible for tensile properties and thereby strongly affects mixture cracking performance. Whereas mixture tests are usually complex and labor-intensive, determination of fracture properties with a simpler test on the IC portion will add values in terms of ranking mixtures and predicting mixture fracture properties. An interstitial component direct tension (ICDT) test, which was derived from the dog bone direct tension test originally developed for asphalt mixtures, was applied to determine the fracture energy density (FED) of mixture IC portion. FED describes the damage tolerance before fracture occurs and it is also a component associated with crack propagation. Two methods of strain determination were evaluated including a digital image correlation (DIC) system and a predictive equation derived from finite element analysis with load-head displacement as input. ICDT tests were conducted on the IC portion of two sets of four mixtures, which had identical coarse aggregate structure. The DIC system yielded greater failure strain than those based on load-head displacement. However, the ratios between the two values for all mixtures were almost constant, supporting the use of the predictive equation as a surrogate. Moreover, IC FED ranked these mixtures in the same order as mixture FED and more importantly, an excellent correlation was observed between IC FED and mixture FED of these mixtures. In conclusion, the ICDT test can be used to determine the IC FED, which provides valuable insights regarding the effect of IC characteristics on mixture FED.
This study aimed to design and evaluate asphalt mixtures by considering various factors including different binders, aggregate types, and gradation characteristics of the fine portion of mixtures, referred to as the inter-stitial component (IC). The mixtures were compacted to 93% of maximum theoretical density to prepare specimens for Superpave IDT tests, which included resilient modulus, creep compliance, and fracture tests. Parameters such as failure limit (fracture energy), damage rate (dissipated creep strain energy per cycle), and the relative cracking performance indicator (number of cycles to failure) were assessed for test specimens subjected to the long-term oven aging and the cyclic pore pressure conditioning. The results showed that mixtures with styrene-butadiene-styrene modified binders exhibited slightly higher failure limits but significantly lower damage rates compared to mixtures with unmodified binders, indicating improved cracking performance. Similarly, the limestone mixtures demonstrated equivalent failure limit but much lower damage rate to the granite mixtures, attributed to the porous surface morphology and inherent weakness of limestone aggregates. Notably, even small changes in the IC characteristics of the mixtures yielded substantial differences in fracture properties and performance, a phenomenon believed to be linked to the distribution of asphalt binder and the structure of air voids within the mixture. In conclusion, a thorough examination confirmed the impact of polymer modification and aggregate type on fracture properties and, notably, highlighted the pivotal role of the fine portion's characteristics in determining mixture cracking performance.
This research aimed to investigate the crack resistance of asphalt mixtures via laboratory tests and discrete element modelling. For the construction of virtual cracking model, the interactive 2D modeling method based on various software and the establishment method of 3D aggregate are proposed. The description method of crack path is also improved.When establishing the 2D model, considering the mesostructural characteristics of an AC-20 asphalt mixture, the aggregate-asphalt mortar-void three-phase structure was established based on PFC2D software and image processing. Taking into account the gradation and form of coarse aggregate, a 3D model incorporating real aggregate shapes was constructed by PFC3D. Based on the numerical model, semi-circular bending and tensile tests of specimens with pre-cut slits of different lengths were conducted to analyse their stress levels, cracking process and crack locations under low-temperature conditions. Taking the fracture performance parameters as an evaluation index, the feasibility of the numerical simulations was verified in comparison to laboratory test data. In the early phase of model loading, the stress distribution has the characteristics of a compression-tension zone. Crack formation undergoes a process of smooth expansion and rapid penetration, and cracks in the compression zone pass through the aggregate. The failure state presented by the particle flow program was in general agreement with the crack evolution results obtained from the tests. Additionally, the fracture parameters of the simulations had a favourable overlap with the experimental observations, indicating that the discrete element simulations can adequately represent the crack propagation process in asphalt mixes. This approach is effective for in-depth and efficient exploration of the cracking performance of asphalt mixtures.
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Cemented granular materials, formed by pouring self-compacting cement in coarse aggregate, have been widely used in geotechnical engineering. In this study, we developed a mesoscale bond model to study the mechanical behavior of cemented granular particles, considering the amount and distribution of cement. A discrete element method with clumped particles is used to simulate irregularly shaped particles. The Voronoi tessellation is used to analyze the void structure, which forms the basis for determining the cement distribution and geometry properties of the cement bond between the clumped particles. Numerical simulations are compared with experimental uniaxial compression tests, with the cement ratio ranging from 5 to 50%. The numerical model is also used to study the fracture development and breakage patterns of cemented granular samples. The numerical results are consistent with the experimental ones, indicating that this numerical model can simulate the behaviors of cemented granular materials with a wide range of cement ratios.
There are some deficiencies in the current understanding of the influence of gradation size on the crack resistance of asphalt mixtures. This study first uses the particle flow code (PFC) to perform virtual semi-circular bending (SCB) tests to explore the effect of gradation changes on the fracture properties of asphalt mixtures and determine the related influence rules. The conclusions are then verified through indoor tests. The results show that for samples with the same nominal maximum particle size and different gradations, the crack resistance of the asphalt mixtures cannot be improved by simply increasing or decreasing the coarse aggregate content. Changes in both the coarse aggregate content and specific surface area have a parabolic correlation with the fracture properties of the asphalt mixtures. Based on these relationships, the reference value ranges of the coarse aggregate content and specific surface area of AC-20 asphalt mixtures for optimal crack resistance can be calculated as 52.02%–54.02% and 5.72–6.06 m²/kg, respectively. Calculation methods and suggestions are provided based on the presented research conclusions for improving the crack resistance of asphalt mixtures by optimising the gradation in pavement engineering and these conclusions have a certain promotion significance.
In order to investigate creep mechanism of asphalt mixtures from the mesoscopic level, a virtual dynamic creep test of asphalt mixture was conducted with two-dimensional discrete element method (DEM). Based on the probability theory and the Monte-Carlo method, a random generation algorithm was used to generate aggregate particles with irregular shapes. The virtual dynamic creep test, including the modeling of a virtual asphalt mixture specimen, the selection of contact models and mesoscopic parameters, and the realization of semi-sine wave intermittent dynamic loading, was simulated based on DEM. Then the simulation results were verified via the experimental dynamic creep test. It is demonstrated that the discrete element model effectively simulated the dynamic creep test, in which the relative error is less than 10% in general. During the simulation test, the contact force in the asphalt mixture was evenly distributed at the beginning of loading, but part of the contact bond was broken, and then redistributed and stress concentration appeared in the failure period. In addition, with the increase of temperature or contact pressure, the axial strain of asphalt mixture increased, and the resistance to permanent deformation decreased, which is consistent with law of the laboratory test. Moreover, the relation between the elastic modulus and axial strain in Burgers model indicates that the modulus of Burgers model is closely correlated with permanent deformation of asphalt mixture.
Semi-circular Bending (SCB) test has been widely used to evaluate the fracture performance of asphalt mixtures, but its potential in evaluating the low-temperature performance of asphalt mixtures at mortar scale has been seldom investigated. This study aims to explore the feasibility and evaluate the performance of SCB tests in evaluating the low-temperature performance of asphalt mortar. To quantify the influence of the crushing and local creep at the top of the SCB test samples on testing results, the Digital Image Correlation (DIC) method was used to characterize the displacement field of mortar samples during the test under different loading rates at −10 °C. The effects of binder film thickness, filler content, and aging condition on low-temperature performance of asphalt mortar were investigated by SCB test. The experimental design set a fixed nominal maximum aggregate size of 4.75 mm. The test matrix considered three binder film thicknesses (9, 10 and 11 µm) and four filler contents (8.5%, 9.4%, 10.5% and 11%) at two aging conditions (short-term and long-term aging). Two cracking indexes including before-peak slope (Sbp) and fracture energy (Gf) were used to evaluate the low-temperature performance. According to the results of DIC analysis, the loading rate of 3 mm/min was proposed to be the optimum for the SCB mortar test at −10 °C. It was concluded that the SCB mortar test can effectively differentiate the low-temperature cracking performance of different asphalt mortars under different aging conditions. Thicker binder film thickness can significantly decrease the aging rate of asphalt mortar from short-term aging to long-term aging, whereas the effect of filler content on ageing rate is not statistically significant.
The fracture of Cement Treated Base (CTB) is greatly influenced by its mesoscale structure and characteristics. The Discrete Element Method (DEM) was adopted to build a mesoscale Semicircular Bending (SCB) model of CTB. The DEM models were built based on two methods including the Digital Image Process (DIP) of actual aggregate distribution and randomization algorithm to generate aggregates. The mesoscale heterogeneity of the model consisted of aggregates, cement mortar, Interface Transition Zone (ITZ) and air voids. Analysis results showed that the DEM models based on both DIP and randomization with the Linear Parallel Bond Model (LPBM) presented satisfying results, compared with laboratory tests. It was found that the main cracks occurred along ITZ between mortar and aggregates. The gradation and distribution of aggregate, and air voids have all significant influence on the fracture resistance and the crack propagation of the CTB. The lime-ash treated material simulation results showed relatively higher fracture toughness over strength ratio.
The discrete element method (DEM) requires an enormous amount of computational resources when applied to asphalt mixture simulation. Reducing material modulus is recognized as an efficient method to cut down the computational cost. However, over-reduced material modulus would case unacceptable calculation errors for DEM models, and the allowable modulus reduction range is not clear. Based on the small displacement assumption in the DEM modeling, the overlap ratio between particles should be small enough to ensure efficient force transition and discrete system stability. Combining this assumption with time step determination and force-displacement law, a theoretical inference that specified a material modulus reduction range without causing an exceeded overlap ratio can be derived. To verify this theoretical inference, a three-step DEM compaction model, including gravity fall, static compaction, and gyratory compaction processes was established for asphalt mixtures. Three groups of asphalt mixtures with different mixture designs were tested both in the laboratory and in simulation. To evaluate the effects of the reduced material modulus on the internal-structure of asphalt mixture specimen under three compaction states, this study proposed 4 categories of internal-structure indexes in respect of specimen’s height, average coordination number, rotation angles of coarse aggregates, and spatial distribution of mastic particles. In the presented case, when the modulus reduction was 1/100 times, the maximum simulation error of internal-structure indexes (except the average coordinate number) was around 4% compared to the control group. Meanwhile, the model’s calculation efficiency was increased by 8–10 times depending on the mixture design.
To solve the concrete mixture design problem, engineers have traditionally relied on guidelines such as those from ACI, and a conservative, labor-intensive, time-consuming, and costly trial-and-error approach that neglects cost or environmental impact of the mixture in the design procedure. In this paper, the concrete mixture design problem is solved through adroit integration of a nonlinear optimization algorithm (OA) and a computational intelligence-based classification algorithm (CA) used as a virtual lab to predict whether desired constraints are satisfied in each iteration or not. The model is tested using previously collected data, three OAs, and three CAs. The outcome of this research is an entirely new paradigm and methodology for concrete mixture design for the twenty-first century. The most cost-effective solutions are achieved by the combination of neural dynamics model of Adeli and Park and enhanced probabilistic neural networks. The cost savings for large-scale concrete projects can be in the millions of dollars.
A detailed analysis and evaluation of 22 field test sections throughout the state of Florida resulted in the development and verification of energy-based criteria for top-down cracking of hot mix asphalt. There was no single mixture property or characteristic that could reliably predict top-down cracking performance of hot mix asphalt. A parameter termed the Energy Ratio, which was derived using the HMA Fracture Mechanics Model developed at the University of Florida, was determined to accurately distinguish between pavements that exhibited top-down cracking and those that did not, except for mixtures with excessively low or unusually high dissipated creep strain energy thresholds. A discussion covers the description of field test sections; effect of mixture properties on cracking performance; development of energy-based criteria for top-down cracking performance; and development of mixture specification criteria. This is an abstract of a paper presented at the Association of Asphalt Paving Technologists 2004 Technology Sessions (Baton Rouge, LA 3/10-18/2004).
Using X-CT technique, digital graphic processing technique and fractal theory, the influences of mineral aggregate gradation on air void percentage, air void diameter, air void quantity, air void fractal dimension were analyzed. The result indicates that the air void equivalent diameters decrease from 3.9-4.8 mm with 18.8% air void percentage to 1.5-2.9 mm with 4% air void percentage as air void percentage decreases, and the average values of air void equivalent diameters decrease from 4.3 mm to 2.0 mm. The distribution rules of air void quantity, air void percentage and air void equivalent diameter along depth direction are consistent. The fractal dimension of air void profile increases as air void percentage decreases and there exists functional relationship between fractal dimension of air void profile and air void percentage. The air void percentage of 14% is considered to be the dividing value between porous asphalt mixture and common asphalt mixture. Air void quantities of porous asphalt are less, but the air void equivalent diameters are larger.
A finite element model is described to study interlaminar stresses within polymer composite laminated materials. This model is based upon a global-local model proposed by Pagano and Soni in 1983. The development of solution procedures includes an out-of-core memory solving technique. The numerical results generated for simple plate problems with and without holes in the center under uniaxial loading are reported. Comments regarding the finite-element mesh-size, numerical stability, problem size and sensitivity of results to substructuring of the laminate into global and local regions have also been discussed.
The theoretical fundamentals used in evaluating Poisson's ratio and elastic modulus of materials using the indirect diametral tensile test are evaluated. With the current state of practice (ASTM D4123), the material properties are evaluated by the two-dimensional stress equations for a circular element supporting short-strip loading along the vertical diameter. Because of the inability of these equations to study misalignment of the specimen, the planar solution is analyzed. The analysis of the above two approaches indicates that the material properties predicted are relatively insensitive to specimen size and misalignment. However, the influence of aggregate inclusions in the vertical plane may cause significant propagation of errors in the vertical measurements outside the central half-radius that significantly affects the value of the predicted Poisson's ratio. The influence of aggregate inclusions in the horizontal plane does not appear to be a significant factor contributing in the horizontal displacement variations. Thus, determination of the elastic modulus from horizontal displacements alone has great potential in providing consistent, reasonable results with an assumed Poisson's ratio. In addition, a means of estimating the magnitude of the displacements and the required sensitivity of the measuring devices based upon expected Poisson's ratio and gauge length is presented. Finally, test control parameters based upon the ratio of vertical to horizontal deformations have been developed to check if the material being tested is within the elastic range as the test progresses.
With increasing traffic loads and changes in crude petroleum refining techniques, cracking in asphalt pavements continues to be a major cause of structural and functional deterioration of these systems, particularly in cold climates. Although modern design tools such as the AASHTO Mechanistic Empirical Pavement Design Guide have recognized the need to predict pavement cracking in pavement life cycle cost analyses, the development of true fracture tests and associated models is hampered by a lack of fundamental knowledge of the physical nature of cracking in asphalt concrete materials. A clustered discrete element method (DEM) was employed as a means to investigate fracture mechanisms in asphalt concrete at low temperatures. The DEM approach was first verified by comparing elastic continuum theory and the discontinuum approach using uniform axial compression and cantilever beam models. A bilinear cohesive zone model was implemented into the DEM framework to enable simulation of crack initiation and propagation in asphalt concrete. Verification of the cohesive zone fracture model was carried out using a double cantilever beam. The main advantage of the DEM approach was that a mesoscale representation of the morphology of the material could be easily incorporated into the model using high-resolution imaging, image analysis software, and by developing a relatively simple mesh generation code. The simulation results were shown to compare favorably with experimental results, and moreover, the simulations provide new insight into the mechanisms of fracture in asphalt concrete. The modeling technique can provide more details of the fracture process in laboratory fracture tests, the influence of heterogeneity on crack path, and the effects of local material strength and fracture energy on global fracture test response.
We present distributed algorithms for the finite-element (FE) analysis of large structures on a loosely coupled multicomputer such as a cluster of inexpensive workstations. The focus is on the development of a coarse-grained preconditioned conjugate gradient (PCG) solver based on the element-by-element approach to solve the resulting system of linear equations. To account for the slow communication speed of the ethernet network connecting workstations, techniques such as redundant computations to eliminate communication, efficient data distribution, and algorithmic restructuring to reduce communication frequency have been developed to coarsen task granularity. We present a data distribution and data movement strategy based on set theory. Due to the general nature of the data distribution scheme, the algorithms are versatile and can be applied to the analysis of unstructured FE domains consisting of a combination of various types of elements.
An object-oriented finite element modeling approach is presented for solution of complex engineering systems. For efficient processing of a myriad of data types generated in such analyses an object-oriented enhanced entity relationship (EER) data model is developed. A class library is created for performing object-oriented finite element analysis in C + +. These classes model the basic concepts and tools needed for finite element analysis of engineering problems. As an example, the models and class library developed in this research are applied to interlaminar stress analysis of composite structures. This research lays the foundation for development of a new generation of highly modular, reusable, and easily maintainable finite element software systems.
The distinct element method is a numerical model capable of describing the mechanical behavior of assemblies of discs and spheres. The method is based on the use of an explicit numerical scheme in which the interaction of the particles monitored contact by contact and the motion of the particles modelled particle by particle. The main features of the distinct element method are described. The method is validated by comparing force vector plots obtained from the computer program BALL with the corresponding plots obtained from a photoelastic analysis.
Cracks in asphalt pavements create irreversible structural and functional deficiencies that increase maintenance costs and
decrease lifespan. Therefore, it is important to understand the fracture behavior of asphalt mixtures, which consist of irregularly
shaped and randomly oriented aggregate particles and mastic. A two-dimensional clustered discrete element modeling (DEM) approach
is implemented to simulate the complex crack behavior observed during asphalt concrete fracture tests. A cohesive softening
model (CSM) is adapted as an intrinsic constitutive law governing material separation in asphalt concrete. A homogenous model
is employed to investigate the mode I fracture behavior of asphalt concrete using a single-edge notched beam (SE(B)) test.
Heterogeneous morphological features are added to numerical SE(B) specimens to investigate complex fracture mechanisms in
the process zone. Energy decomposition analyses are performed to gain insight towards the forms of energy dissipation present
in fracture testing of asphalt concrete. Finally, a heterogeneous model is used to simulate mixed-mode crack propagation.
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