Influence of Modulus of Base Layer on The Strain Distribution for Asphalt Pavement

In order to investigate the influence of modulus of the base layer on the strain distribution for asphalt pavement, the modulus ratio of the base layer and the AC layer (Rm) is introduced as a controlled variable when keeping modulus of the AC layer as a constant in this paper. Then, a three-layered pavement structure is selected as an analytical model, which consists of an AC layer with the constant modulus and a base layer with the variable modulus covering the subgrade. A three dimensional (3D) finite element model was established to estimate the strains along the horizontal and vertical direction in the AC layer under different Rm. The results show that Rm will change the distribution of the horizontal strains along the depth in the AC layer; the increase of Rm could reduce the maximum tensile strain in the AC layer, but its effect is limited; the maximum tensile strain in the AC layer does not necessarily occur at the bottom, but gradually rises to the middle with the increase of Rm. Rm could significantly decline the bottom strain in the AC layer, and there is a certain difference between the bottom and the maximum strain when Rm is greater than or equal to one, which will enlarge with increasing Rm. Rm could change the depth of the neutral axis in the AC layer, and the second neutral axis will appear at the bottom of the AC layer under a sufficiently large Rm. The average vertical compressive strain in the AC layer will significantly enlarge with the increase of Rm.

Flexible crosslinking of polyurethane using grafted poly(dimethylsiloxane) with Epichlorohydrin and Bisphenol A end groups and its impact on the mechanical properties and low-temperature flexibility

Poly(dimethylsiloxane) (PDMS) was grafted onto polyurethane (PU), and Epichlorohydrin and Bisphenol A were attached to the free ends of PDMS groups and used to link the grafted PDMS to thereby introduce flexible crosslinks between the PU chains. The flexible crosslinks enhanced the crosslink density and solution viscosity of PU but did not change the melting and crystallization behaviors of the soft segments of PU. In particular, the flexible PDMS crosslinks increased the maximum tensile stress by up to 300% and the maximum tensile strain up to 180%. The shape recovery capability at 10°C and the shape retention capability at −25°C were maintained above 90% with the flexible crosslinking. Grafted PDMS moderately improved the low-temperature flexibility of PU due to its flexibility at low temperature. The flexible crosslinks of grafted PDMS successfully improved the tensile strength, shape recovery, and low-temperature flexibility of the PU.

Evaluation of High-Temperature and Low-Temperature Performances of Lignin–Waste Engine Oil Modified Asphalt Binder and Its Mixture

This research aims to explore the high-temperature and low-temperature performances of lignin–waste engine oil-modified asphalt binder and its mixture. For this research, the lignin with two contents (4%, 6%) and waste engine oil with two contents (3%, 5%) were adopted to modify the control asphalt binder (PG 58-28). The high-temperature rheological properties of the lignin–waste engine oil-modified asphalt binder were investigated by the viscosity obtained by the Brookfield viscometer and the temperature sweep test by the dynamic shear rheometer. The low-temperature rheological property of the lignin–waste engine oil-modified asphalt binder was evaluated by the stiffness and m-value at two different temperatures (−18 °C, −12 °C) obtained by the bending beam rheometer. The high-temperature and the low-temperature performances of the lignin–waste engine oil-modified asphalt mixture were explored by the rutting test and low-temperature bending beam test. The results displayed that the rotational viscosity and rutting factor improved with the addition of lignin and decreased with the incorporation of waste engine oil. Adding the lignin into the control asphalt binder enhanced the elastic component while adding the waste engine oil lowered the elastic component of the asphalt binder. The stiffness of asphalt binder LO60 could not meet the requirement in the specification, but the waste engine oil made it reach the requirement based on the bending beam rheometer test. The waste engine oil could enhance the low-temperature performance. The dynamic stabilities of LO40- and LO60-modified asphalt mixture increased by about 9.05% and 17.41%, compared to the control mixture, respectively. The maximum tensile strain of LO45 and LO65 increased by 16.39% and 25.28% compared to that of LO40 and LO60, respectively. The high- and low-temperature performances of the lignin–waste engine oil-modified asphalt LO65 was higher than that of the control asphalt. The dynamic stability had a good linear relationship with viscosity, the rutting factor of the unaged at 58 °C, and the rutting factor of the aged at 58 °C, while the maximum tensile strain had a good linear relationship with m-value at −18 °C. This research provides a theoretical basis for the further applications of lignin–waste engine oil-modified asphalt.

Propaedeutic Study of Biocomposites Obtained With Natural Fibers for Oceanographic Observing Platforms

In response to the pervasive anthropogenic pollution of the ocean, this manuscript suggests the use of biodegradable elastomers in marine applications. The present study characterizes 25 samples of highly biodegradable polymers, obtained blending a base elastomer with natural fibers. Mechanical analysis and Scanning Electron Microscope imaging, reveal how base polymers behave differently depending on the plant fiber chosen, on the external forcing—exposure to water—and on the doses that constitute the final biocomposite. Results suggest that EcoflexTM 00-30 and EcoflexTM 00-50, mixed with potato starch, perform best mechanically, maintaining up to 70% of their maximum tensile strain. Moreover, early signs of degradation are visible on polysiloxane rubber blended with 50% vegetable fibers after 19 hours in distilled water. Analyses demonstrate that highly biodegradable elastomers are good candidates to satisfy the requirements of aquatic devices. Furthermore, the discussed materials can improve the dexterity and biodegradability of marine technology.

Characterization of Natural Rubber (NR), Polybutadiene Rubber (BR) and Styrene-Butadiene Rubber (SBR) Blends Cured in a Vulcanization System

In this work, the mechanical properties of three types of dough rubber NR, NR/BR, and NR/SBR have been investigated using five percentages of materials fill (30, 40, 50, 60, and 70) pphr. Carbon black was used as a filler material. The tensile test was achieved with 300% elongation and strain rates of (100, 200, 300, 400, and 500) mm/min. The tensile strength results indicate that the maximum value of tensile strength for NR Dough carbon black 60 pphr reaches 23.2 MPa; the maximum tensile strain of NR dough (carbon black 50 pphr) reaches 805.5%, and the modulus of elasticity with carbon black 70 pphr reaches 4.3 MPa. It was found that the compression strength decreases with increasing the carbon black, and the maximum value of compression set at NR dough (carbon black 30 pphr) reaches 29.3%. Fatigue crack growth was achieved according to ASTM D 813 for rubber testing. The minimum value of fatigue strength dough (carbon black 70 pphr) reaches 68 (IRHD). For NR dough (carbon black 30,40,50 pphr) reaches 3.5 mm at the number of cycles 15000 cycle. Finally, the maximum hardness of NR.

Middle-Up Cracking Potential in Flexible Pavements with Stabilized Foundations

This investigation presents a new perspective on the structural behavior of stabilized foundation pavements through full-scale testing and simulation where the historical premise of bottom-up fatigue cracking has been challenged. Two full-scale pavement sections were constructed at the National Center for Asphalt Technology Test Track in 2018. One section featured a stabilized foundation under the asphalt layers while the other was a thick-lift asphalt section on conventional base and subgrade materials. Both sections were embedded with pavement response instrumentation and their behavior was observed over time under accelerated truck trafficking. In addition, computational simulations were executed to explain the observed behavior. The strain measurement at the bottom of the asphalt concrete (AC) for the thick-lift section showed a familiar trend in which the tensile strain at the bottom of the AC increased exponentially with temperature. In contrast, the strain at the bottom of the AC in the stabilized foundation pavement was predominantly in compression at elevated temperatures. Further analysis revealed that compressive strain at the bottom of the AC increased exponentially with temperature similar to conventional flexible pavements but with a reversed sign. The results were confirmed by falling weight deflectometer testing that was conducted directly above the embedded pavement sensors. Computational simulations confirmed the behavior and suggested that the maximum tensile strain could occur at shallower depths, possibly mid-depth of the AC, in stabilized foundation pavements. This indicates stabilized foundation pavements could be prone to middle-up cracking and subsequent precautions should be taken to avoid middle-up fatigue cracking.

Multiscale Modeling of Asphalt Concrete and Validation through Instrumented Pavement Section

In this study, macroscale responses of asphalt concrete (AC) are predicted from the responses of its corresponding microscale representative volume element (RVE) within a finite element framework using quasi-static and dynamic analyses. Nanoindentation test was performed on the mastic and aggregate phase of an AC sample to determine the viscoelastic and elastic properties of RVE elements. Aggregate-mastic proportions in the RVE were obtained from the morphological image analysis. Macroscale model responses were compared with the AC pavement responses obtained from an instrumented pavement section subjected to falling weight deflectometer loading and a class 9 vehicle. Model responses are very close to the actual responses. The multiscale analyses show that tensile strain in microscale RVE is 5–10 times higher than that in a macroscale element. Furthermore, multiscale analyses also show that variations in the microscale RVE, such as the reduction in the aggregate-mastic ratio or increment in the voids, can increase the maximum tensile strain at the bottom of the AC in macroscale model by around 25%.

Molecular dynamics simulation of carbon nanotubes and silicon nanowire composites

The deformation behavior of the nanocomposite structure under tension was studied by molecular dynamics (MDs) simulation. This nanocomposite structure is called as SiNW@CNT, which is a silicon nanowire (SiNW) embedded in carbon nanotube (CNT). The simulation results show that the insertion of the SiNW into CNT increases the tensile strength of zigzag CNT and the maximum tensile strain of the armchair CNT. However, it can greatly reduce the maximum tensile strain of the zigzag CNT and the maximum tensile strength of the armchair CNT. In addition, the maximum tensile strain of the SiNW@CNT has little to do with the diameter of the CNT, but is mainly related to the chirality of the CNT. For both hollow CNT and SiNW@CNT, the tensile strength is related to the diameter and chirality, and smaller diameter but greater tensile strength. This findings suggest that the physical properties of the SiNW@CNT can be tailored to specific applications by controlling the CNT diameter and chirality.

Study on Grinding and Deformation Fracture Control of Cold Rolled Titanium Strip

Surface defects of titanium strip need to be removed by local grinding, but local cracking or band breaking then occurs during subsequent cold rolling. Tensile properties and deformation resistance of 3 mm thick commercially pure titanium strip with grinding pits on the surface were simulated by a finite-element method using a multi-pass cold-rolling deformation process. The stress and strain of grinding pits with depths of 0.25–2 mm were analyzed. During cold-rolling deformation, the stress and strain in the center of a grinding pit were larger than at the edge region. The strip was first subjected to tensile stress in the rolling direction, which then decreased and gradually changed to compressive stress. Partial stress was larger in the rolling direction than in the transverse direction. When the tensile stress and true strain both exceeded the stress and strain limits during second-pass rolling, the strip with a grinding depth of 2 mm cracked, but shallower grinding pits were repaired. The criterion for cracking during rolling after grinding is that the maximum tensile strain at the bottom of the pit must be less than the critical strain of the material: ln ( 1 + h / H ) ≤ ε C r . Results of numerical simulation were verified by the data for cold-rolling tests.

Enhanced Stretchable and Sensitive Strain Sensor via Controlled Strain Distribution

Stretchable and wearable opto-electronics have attracted worldwide attention due to their broad prospects in health monitoring and epidermal applications. Resistive strain sensors, as one of the most typical and important device, have been the subject of great improvements in sensitivity and stretchability. Nevertheless, it is hard to take both sensitivity and stretchability into consideration for practical applications. Herein, we demonstrated a simple strategy to construct a highly sensitive and stretchable graphene-based strain sensor. According to the strain distribution in the simulation result, highly sensitive planar graphene and highly stretchable crumpled graphene (CG) were rationally connected to effectively modulate the sensitivity and stretchability of the device. For the stretching mode, the device showed a gauge factor (GF) of 20.1 with 105% tensile strain. The sensitivity of the device was relatively high in this large working range, and the device could endure a maximum tensile strain of 135% with a GF of 337.8. In addition, in the bending mode, the device could work in outward and inward modes. This work introduced a novel and simple method with which to effectively monitor sensitivity and stretchability at the same time. More importantly, the method could be applied to other material categories to further improve the performance.