Mechanistic Design Research Articles

Optimization of Platoons’ Lateral Position Based on Damage Estimation

Truck platooning is one of the upcoming paradigm shifts in roadway-traffic patterns. It is defined as a convoy of trucks moving with short distances between them; truck platoons will change the performance of pavements. This change could practically be realized with the emergence of connected and autonomous trucks, which can control their lateral position. In this study, optimal lateral position of truck platoons is defined. Using an efficient algorithm, pavement damage was estimated assuming a probabilistic position of trucks. Four typical pavement cross-sections were used to apply the algorithm-based optimization developed. The pavement sections varied in thickness and stiffness from thick and strong section to thin and weak. The optimization results showed that different schemes can be optimal for the same cross-section. However, most of these optimal schemes disperse the traffic throughout the lane. Compared with normally distributed truck traffic, up to 18% and 50% reduction in rutting and fatigue cracking, respectively, could be achieved when applying an optimized traffic pattern. When compared with a channelized-platoon traffic pattern, the optimized truck traffic shows prospects of reducing rutting and cracking up to 29% and 70%, respectively. Optimal traffic patterns were used to develop simple platoon factors that could be applied to the Illinois Mechanistic Design Method to incorporate truck platooning.

Characterizing and Predicting the Resilient Modulus of Recycled Aggregates from Building Demolition Waste with Breakage-Induced Gradation Variation.

Building demolition waste (BDW) has been massively stockpiled due to increasingly rapid urbanization and modernization. The use of recycled BDW as unbound granular base/subbase materials is among the sustainable, cost-effective, and environmentally friendly pavement construction alternatives. The resilient modulus is an important mechanical property of BDW-derived aggregates and mechanistic design input of pavements incorporating BDW. This paper presents the results of a comprehensive laboratory study on the shear strength and resilient modulus characteristics of BDW-derived aggregate materials. A series of monotonic triaxial compression tests and repeated-load triaxial (RLT) tests were conducted with five different gradations representing particle breakage and different stress paths. The apparent cohesion and internal friction angle of recycled BDW aggregates under consolidated drained conditions ranged from 35.3 to 57.5 kPa and from 30.2° to 54.3°, respectively. The apparent cohesion and internal friction angle also increased and decreased non-linearly with the increasing relative content of fine particles, respectively. The resilient modulus of recycled BDW aggregates gradually decreased with increasing relative content of fine particles at the same stress level. Both the deviator stress and confining pressure exhibited significant influences on the resilient modulus, while the effect of confining pressure was more profound. Based on laboratory testing data, a mechanistic-empirical model was developed to predict the resilient modulus of recycled BDW aggregates from gradation and stress-state variables. The findings could be useful for extended engineering applications of BDW in unbound granular pavement base/subbase construction.

Impact of Improved Density on Pavement Design Response for Low-Volume Roads/Non-Primary Routes

Hughes said “Compaction is the single most important factor that affects pavement performance in terms of durability, fatigue life, resistance to deformation, strength, and moisture damage.” Past research studies have shown that a 1% decrease in air voids was estimated to improve the fatigue performance of asphalt pavements between 8.2% and 43.8%. Tran et al. quoted: “A 1% decrease in air voids was estimated to extend the service by conservatively 10% .” The objective of this research study is to show the impact of varying density properties using the concept of expected life difference. Fatigue life will be evaluated using the traditional fatigue life prediction equations and an advanced mechanistic empirical model (i.e., AASHTO Pavement ME). Dynamic modulus is the main input for conducting a pavement analysis and/or design when using AASHTO Pavement ME. The dynamic modulus data was generated from an extensive laboratory density study sponsored by Kentucky Transportation Cabinet. The air voids of the dynamic modulus samples varied from 11.4% to 3.9%. This study forms a framework for a highway agency, city, and county engineer if they are looking for an engineering solution as to why they should improve their in-place density specifications and what that impact is, using mechanistic empirical design procedures.

Effects of variability in thickness and elastic modulus on the reliability of flexible pavement structural performance

ABSTRACT This study investigates the effect of variability of layer thickness and elastic modulus of pavement materials on the reliability of flexible pavement structural performance with respect to rutting failure using the mechanistic design approach. Monte Carlo simulation was applied to incorporate the variability of input design parameters in establishing the probability distribution of reliability of multi-layered flexible pavements. Using Matlab 7.0 programming language, a programme named DTC1.0 was developed for calculating the overall elastic modulus and pavement reliability. Data from some National Highways of Vietnam were used to construct statistical distributions of layer thicknesses and elastic moduli. Sensitivity analyses were conducted to identify key input parameters that have the most effect on reliability. The research shows that changing the value of the coefficient of variation (COV) affects the reliability of the flexible pavement at different levels: the higher the COV, the higher the rate of decrease in the reliability. Changes in thickness and elastic modulus of upper layers have more impact on reliability than lower layers. The influence of COVs of the elastic modulus is larger than that of the thickness. It is expected that the study can provide the foundation to develop a reliability-based design procedure following the mechanistic design approach.

Reclaimed Asphalt Pavement (RAP) as an Unbound Base Course Material: A Mechanistic Design Approach Based on Multi-stage Repeated Load Triaxial Tests

Reclaimed asphalt pavement (RAP) and blends of RAP with virgin aggregate (VA) were characterized in this study to be utilized as base course aggregate. Multi-stage and single repeated load triaxial (RLT) tests were conducted in the laboratory to characterize the materials. The results from these tests were used to develop a mechanistic design approach that is suited not only for virgin but also for recycled materials that are prone to excessive plastic deformations under repeated loads. The design approach presented in this study allows the users to select different pavement structure configurations in terms of base course and HMA thicknesses, where the selected configuration can withstand the repeated loads without undergoing significant permanent strains. Such design approach was achieved with the laboratory tests that were conducted with variety of stress ratios (σ1/σ3) that represented different pavement layer configurations and beyond. Principles of shakedown theory were utilized to define the boundaries of plastic shakedown, creep shakedown, and incremental collapse. This study demonstrated that the use of failure and plastic shakedown boundaries were crucial to the proposed mechanistic design approach.

Highly Robust Interfacially Polymerized PA Layer on Thermally Responsive Semi-IPN Hydrogel: Toward On-Demand Tuning of Porosity and Surface Charge.

Hydrogel composites with skin layer that allows fast and selective rejection of molecules possess high potential for numerous applications, including sample preconcentration for point-of-use detection and analysis. The stimuli-responsive hydrogels are particularly promising due to facile regenerability. However, poor adhesion of the skin layer due to swelling-degree difference during continuous swelling/deswelling of the hydrogel hinders its further development. In this work, a polyamide skin layer with strong adhesion was fabricated via gel-liquid interfacial polymerization (GLIP) of branched polyethyleneimine (PEI) with trimesoyl chloride (TMC) on a cross-linked N-isopropyl acrylamide hydrogel network containing dispersed poly sodium acrylate (PSA), while the traditional m-phenylenediamine (MPD)-TMC polyamide layer readily delaminates. We investigated the mechanistic design principle, which not only resulted in strong anchoring of the polyamide layer to the hydrogel surface but also enabled manipulation of the surface morphology, porosity, and surface charge by tailoring interfacial reaction conditions. The polyamide/hydrogel composite was able to withstand 100 cycles of swelling/deswelling without any delamination or a significant decrease in its rejection performance of the model dye, i.e., methylene blue. Regeneration can be done by deswelling the swollen beads at 60 °C, which also releases any loosely bound molecules together with absorbed water. This work provides insights into the development of a physically and chemically robust skin layer on various types of hydrogels for applications such as preconcentration, antifouling-coating, selective compound extraction, etc.

Unlocking the Electrochemical–Mechanical Coupling Behaviors of Dendrite Growth and Crack Propagation in All‐Solid‐State Batteries

AbstractDendrite growth and crack propagation are two major hurdles on the road towards the large‐scale commercialization of lithium metal all‐solid‐state batteries (ASSBs). Due to the high multiphysics coupled nature of the underlying dendrite growth mechanism, understanding it has been difficult. Herein, for the first time, an electrochemical‐mechanical model is established that directly couples dendrite growth and crack propagation from a physics‐based perspective at the cell level. Results reveal that overpotential‐driven stress propels a crack to penetrate through the solid electrolyte, creating vacancies for dendrite growth, leading to the short circuit of the battery. Thus, high lithiation/charging rate and low conductivity of electrolytes can accelerate the electrochemical failure of the battery. It is further discovered that Young's modulus ELLZO of the electrolyte has competing contributions to the fracture and dendrite growth; specifically, when ELLZO = 40–100 GPa, the short circuit is triggered early. A larger toughness value hinders the crack propagation and mitigates the Li dendrite growth. The developed multiphysics model provides an in‐depth understanding of the coupling of crack propagation and dendrite growth within ASSBs and an insightful mechanistic design guidance map for robust and safe ASSB cells.

Using Artificial Intelligence to Estimate Nonlinear Resilient Modulus Parameters from Common Index Properties

The Mechanistic–Empirical Pavement Design Guide (MEPDG) considers a hierarchical approach to determine the input values necessary for most design parameters. Level 1 requires site-specific measurement of the material properties from laboratory testing, whereas other levels make use of equations developed from regression models to estimate the material properties. Resilient modulus is a mechanical property that characterizes the unbound and subgrade materials under loading that is essential for the mechanistic design of pavements. The MEPDG resilient modulus model makes use of a three-parameter constitutive model to characterize the nonlinear behavior of the geomaterials. As the resilient modulus tests are complex, expensive, and require lengthy preparation time, most state highway agencies are unlikely to implement them as routine daily applications. Therefore, it is imperative to make use of models to calculate these nonlinear parameters. Existing models to determine these parameters are frequently based on linear regression. With the development of machine learning techniques, it is feasible to develop simpler equations that can be used to estimate the nonlinear parameters more accurately. This study makes use of the Long-Term Pavement Performance database and machine learning techniques to improve the equations utilized to determine the nonlinear parameters crucial to estimate the resilient modulus of unbound base and subgrade materials.

Lipophilic nanocrystal prodrug-release defines the extended pharmacokinetic profiles of a year-long cabotegravir

A once every eight-week cabotegravir (CAB) long-acting parenteral is more effective than daily oral emtricitabine and tenofovir disoproxil fumarate in preventing human immunodeficiency virus type one (HIV-1) transmission. Extending CAB dosing to a yearly injectable advances efforts for the elimination of viral transmission. Here we report rigor, reproducibility and mechanistic insights for a year-long CAB injectable. Pharmacokinetic (PK) profiles of this nanoformulated CAB prodrug (NM2CAB) are affirmed at three independent research laboratories. PK profiles in mice and rats show plasma CAB levels at or above the protein-adjusted 90% inhibitory concentration for a year after a single dose. Sustained native and prodrug concentrations are at the muscle injection site and in lymphoid tissues. The results parallel NM2CAB uptake and retention in human macrophages. NM2CAB nanocrystals are stable in blood and tissue homogenates. The long apparent drug half-life follows pH-dependent prodrug hydrolysis upon slow prodrug nanocrystal dissolution and absorption. In contrast, solubilized prodrug is hydrolyzed in hours in plasma and tissues from multiple mammalian species. No toxicities are observed in animals. These results affirm the pharmacological properties and extended apparent half-life for a nanoformulated CAB prodrug. The report serves to support the mechanistic design for drug formulation safety, rigor and reproducibility.

(Invited) On the Effective Design of Electrochemical Interfaces for Solar Production of Fuels

Extensive research has been conducted on man-made systems for the solar production of fuels in which many different chemical and physical constructs and prototypes have been assembled to demonstrate the possibility of creating fuels from sunlight. These efforts comprise a broad array of chemical and electrochemical work that originates in the Fujishima and Honda work on photoelectrochemical water splitting and has moved on to molecular-based catalysts for water splitting as well as designed nanostructures of semiconductors for light absorption and charge separation.This presentation examines how the mechanistic design of these systems for solar fuels production constrain and define the chemistry and electrochemistry of the solid and molecular components required for effective operation. It will also identify alternative approaches that show promise. The discussion will begin with design analyses of the photosynthetic system for carbon fixation and man-made photosystems for the oxidation of water as a sacrificial electron donor for fuels production. It will be shown how the kinetics inherent in their operational design imposes demands upon the photosystem components, in particular the catalyst TOF and TON figures. With this collection of designs, full structures for water or carbon dioxide reduction can be composed and consequent demands upon catalysts can be quantified.While many research systems for solar photoconversion are given as examples of “artificial photosynthesis,” few actually take full advantage of the important design principles that underlie the effectiveness of photosynthesis as a means of transducing solar energy into the biochemistry of a life form. A tracing of the flow of energy and charge through the photosynthetic reaction centers and then to RuBisCO for CO2 fixation reveals the significance of impedance matching at various coupling points in the system. A direct coupling of Photosystem II with the oxygen evolving catalyst is evident as is indirect coupling at other points where protons and redox agents are produced and their diffusion creates a Nernstian concentration potential at distant locations to initiate further reaction. These types of coupling are of consequence in man-made systems.The oxidation of water provides the electrons and protons for solar driven reduction reactions, whether it be natural or artificial. Nature has its own oxygen evolving complex in photosynthesis to effect this reaction and there are many man-made structures that have been assembled and studied to oxidize water as well. A kinetic design of the natural system will be drawn in this presentation that will be compared with the kinetic designs of representative artificial systems and a critique will be made. These include semiconductor photoelectrolysis of water, dye sensitized electrochemical water oxidation, molecular water oxidation catalysts, and particulate and nanostructured systems for water splitting. The relationship between the kinetic design of the system and the component solids, catalysts and associated species will be shown.The catalytic reduction of CO2 or water to a fuel are wide spread and dynamic areas of research. Whereas the electrochemistry of water reduction to hydrogen has long been an object of study, the catalysis of CO2 reduction is much less developed. Molecular catalysts are being sought for this role as are interfacial metal deposits with both being accompanied by theoretical backing. Given the recognition and analysis of the various designs identified in this discussion, a more effective effort can be made in the development of photosystems for production of these fuels. They can help define not only the form of the catalyst, be it solid or molecular, but also its required reaction velocity and durability.

N‐Heterocyclic Carbene Catalyzed Benzannulations: Mechanism and Synthetic Utility

AbstractAromatic compounds are ubiquitous in pharmaceutical agents and other functional materials. Therefore, synthetic methods to construct highly functionalized aromatic frameworks have attracted considerable attention, especially when utilizing acyclic precursors instead of pre‐existing benzenoid cores. A plethora of methods exist in the literature for the construction of substituted aromatic products by using transition metal catalysis and base‐promoted benzannulation reactions starting from acyclic precursors. In recent years, organocatalytic approaches such as N‐heterocyclic carbene catalysis have emerged as effective tools for the efficient and regioselective construction of highly functionalized aryl rings under metal‐free and mild reaction conditions. The fundamental objective of this minireview is to highlight the synthetic potential of NHC‐catalyzed benzannulations for the generation of aromatic rings with complex substitution patterns and to discuss these reactions from the perspective of their mechanistic design.

Mechanical performance of rehabilitated bituminous layers with paving fabric under cyclic loading

The application of paving fabric along with a fresh asphalt overlay has proved its effectiveness in terms of delaying the propagation of reflective cracks. Nevertheless, this application requires an in-depth knowledge of its mechanical performance under cyclic loading during the design life. In this context, rutting resistance and fatigue failure are commonly employed as major performance criteria in mechanistic-based design methods. The objective of this study was to understand the necessary changes in distress prediction models embedded in mechanistic design methods in the presence of paving fabric. Rutting resistance was evaluated using the French Laboratory Rut Tester (FLRT) device and adhesion bond at the interface was studied via a method initially developed in Département de Génie Civil et Bâtiment (DGCB). The results showed that the composite structures including paving fabric had lower rutting resistance, especially at higher number of cycles, but 30 percent enhanced adhesion bond at the interface.

Submillimetre mechanistic designs of termite-built structures.

Termites inhabit complex underground mounds of intricate stigmergic labyrinthine designs with multiple functions as nursery, food storage and refuge, while maintaining a homeostatic microclimate. Past research studied termite building activities rather than the actual material structure. Yet, prior to understanding how multi-functionality shaped termite building, a thorough grasp of submillimetre mechanistic architecture of mounds is required. Here, we identify for Nasutitermes exitiosus via granulometry and Fourier transform infrared spectroscopy analysis, preferential particle sizes related to coarse silts and unknown mixtures of organic/inorganic components. High-resolution micro-computed X-ray tomography and microindentation tests reveal wall patterns of filigree laminated layers and sub-millimetre porosity wrapped around a coarse-grained inner scaffold. The scaffold geometry, which is designed of a lignin-based composite and densely biocementitious stercoral mortar, resembles that of trabecula cancellous bones. Fractal dimension estimates indicate multi-scaled porosity, important for enhanced evaporative cooling and structural stability. The indentation moduli increase from the outer to the inner wall parts to values higher than those found in loose clays and which exceed locally the properties of anthropogenic cementitious materials. Termites engineer intricately layered biocementitious composites of high elasticity. The multiple-scales and porosity of the structure indicate a potential to pioneer bio-architected lightweight and high-strength materials.

C-FLEX Advanced Finite Element Analysis Program for Flexible Pavement Analysis and Design

The U.S. Army Engineer Research and Development Center (ERDC) of the U.S. Army Corps of Engineers has initiated an effort to modernize the Department of Defense (DOD) pavement design and evaluation procedures initially developed in the 1950s. Flexible pavement analyses and evaluations are currently performed based on the elastic layered WESLEA and WESDEF software programs. To modernize the current pavement design and evaluation procedures used by the DOD, an advanced axisymmetric Finite Element Method (FEM) based analysis program, named C-FLEX, was developed and is introduced in this paper. The C-FLEX program is designed to feature accurate material models for all pavement layers with the capability to model the cross-anisotropic and nonlinear elastic properties of unbound base/subbase and subgrade layers, the viscoelastic behavior of the asphalt mixture, as well as mechanical reinforcement using geosynthetics in flexible pavements. The FEM formulation in C-FLEX and the program architecture and implementation details are introduced and discussed in this paper. The different analysis schemes and proper models used to characterize the cross-anisotropy and stress-dependent material nonlinearity are also described in detail. The viscoelastic analysis scheme and the geosynthetic characterization are currently under development and so are not included in this paper. Furthermore, two conventional flexible pavements with different layer properties are analyzed to verify the solutions and reliability of the C-FLEX program. Based on this development effort with ERDC, the C-FLEX program is envisioned to eventually serve as the flexible pavement analysis engine for the DOD’s new mechanistic design and evaluation platform.

Estimation of resilient behavior of crushed waste rocks using repeated load CBR tests

Crushed waste rocks (CWR), generated from mining operations, have been widely used for the construction of mine haul roads because of their low-cost, high-strength, and availability. Resilient modulus is a necessary input to mechanistic design for mine haul roads, but its determination usually requires advanced and complex equipment such as repeated load triaxial (RLT) test. Repeated load CBR (RLCBR) tests are simpler and more often available, and were therefore investigated in this study to estimate CWR resilient behavior under low and high stress levels. RLCBR equivalent modulus calculated using various equations were validated using RLT resilient modulus. The MR-θ model showed good representation and prediction of CWR resilient behavior under both low and high stress levels. A new equation was also proposed to predict more precisely the equivalent modulus of CWR based on RLCBR tests. Results showed that the impact of loading frequency and waveform was limited, while the measured equivalent modulus increased significantly with contact stress (especially when contact stress < 10%). The effect of dry density and soaking on equivalent modulus was negligible, but specimen drying resulted in a marked increase of the equivalent modulus. The good agreement between RLCBR equivalent modulus and RLT resilient modulus indicates that RLCBR tests could be an effective alternative to RLT tests to estimate resilient behavior of CWR used in mine haul roads.

A mechanistic perspective on the kinetics of plastic deformation in FCC High Entropy Alloys: Effect of strain, strain rate and temperature

Strain rate sensitivity and activation volume that dictate the kinetics of plastic deformation along with strain hardening response determine the plastic deformation behaviour of novel high entropy alloys. Although, the deformation behaviour of FCC single-phase Cantor alloy exhibits some similarity to that of conventional FCC solid solutions, the deformation behaviour over a wide range of temperature, strain rate, strain and grain size is unexplored. More importantly, theoretical understanding of solid solution strengthening, stacking fault energy and dislocation activation in 100 percent solute high entropy alloys (HEAs) and their flow kinetics is not yet established. This necessitates development of combined experimental and computational approaches to realise the mechanistic design of new single-phase and multi-phase transformative FCC HEAs to achieve optimum combination of strength and ductility in the novel complex concentrated alloys.

Permanent deformation modelling of large-size unbound pavement materials tested in a heavy vehicle simulator under different moisture conditions

ABSTRACT Climate changes alter the environmental conditions which pavement design is based on, invalidating empirical design methods. Transition to mechanistic design requires the ability to model the behaviour of pavement materials under relevant environmental conditions. An accelerated pavement test (APT) is designed to test two instrumented pavement structures under moisture conditions which are altered by raising the groundwater table (GWT). Open-graded and well-graded subbase materials are used to investigate the effect of gradation on moisture dependency. Pavement response behaviour is modelled using a non-linear elastic (NLE) approach. Accumulation of permanent deformation under different moisture conditions is calculated by two models and compared to measured surface rutting. Moisture transport through the structures differs due to the subbase gradation. Increased GWT accelerates the accumulation of permanent deformations in both structures, identified by both models. One model provides a significantly better fit to the subgrade deformations and the width of the rutting profile.

Information Access Equality on Network Generative Models

It is well known that networks generated by common mechanisms such as preferential attachment and homophily can disadvantage the minority group by limiting their ability to establish links with the majority group. This has the effect of limiting minority nodes' access to information. We present the results of an empirical study on the equality of information access in network models with different growth mechanisms and spreading processes. For growth mechanisms, we focus on the majority/minority dichotomy, homophily, preferential attachment, and diversity. For spreading processes, we investigate simple vs. complex contagions, different transmission rates within and between groups, and various seeding conditions. We observe two phenomena. First, information access equality is a complex interplay between network structures and the spreading processes. Second, there is a trade-off between equality and efficiency of information access under certain circumstances (e.g., when inter-group edges are low and information transmits asymmetrically). Our findings can be used to make recommendations for mechanistic design of social networks with information access equality.

A critical review of vehicle-pavement interaction mechanism in evaluating flexible pavement performance characteristics

This paper presents a review of investigations that recognised the effect of vehicle-pavement interaction (VPI) mechanism in estimating flexible pavement performance criteria. This state-of-the-art review highlights the importance of dynamic traffic loads illustrated through vehicular models that have potential in simulating realistic field conditions in the mechanistic pavement design process. Furthermore, this article documents the advanced pavement models along with uncoupled and coupled VPI methods of analyses to predict structural and functional performance characteristics. Based on extensive search, there seems to be an expansive scope to better the current pavement design procedures through the integration of VPI for evaluation of performance criteria. Overall, it is envisioned that the prospects underscored in this detailed note will help advance the design procedures and certainly create a mechanistic-based design template for flexible pavements that exemplifies practical roadway scenarios.

Toward Mechanistic Design of Surrogate Buffers for Dissolution Testing of pH-Dependent Drug Delivery Systems.

The in vivo dissolution of enteric-coated (EC) products is often overestimated by compendial in vitro dissolution experiments. It is of great interest to mimic the in vivo conditions as closely as possible in vitro in order to predict the in vivo behavior of EC dosage forms. The reason behind this is the overly high buffering capacity of the common compendial buffers compared to the intestinal bicarbonate buffer. However, a bicarbonate-based buffer is technically difficult to handle due to the need for continuous sparging of the media with CO2 to maintain the desired buffer pH. Therefore, bicarbonate buffers are not commonly used in routine practice and a non-volatile alternative is of interest. A mathematical mass transport modelling approach was previously found to enable accurate calculation of surrogate buffer molarities for small molecule compounds; however, the additional complexity of polymeric materials makes this difficult to achieve for an enteric coat. In this work, an approach was developed allowing relatively rapid screening of potential surrogate buffers for enteric coating. It was found that the effective buffering pKa of bicarbonate at the surface of a dissolving enteric polymer tended to be around 5.5, becoming higher when the dissolving enteric polymer formed a gel of greater firmness/viscosity and vice versa. Using succinate (pKa 5.2 under physiological ionic strength) and/or citrate (pKa 5.7 under physiological ionic strength) at conjugate base molarities corresponding to bicarbonate molarities in the intestinal segments of interest as an initial “guess” can minimize the number of experimental iterations necessary to design an appropriate surrogate.