Numerical Simulation of Impact Rollers for Estimating the Influence Depth of Soil Compaction

The use of impact rollers has increased for many decades over a wide variety of applications in various parts of the world. Many manufacturers have made claims that impact compaction rollers could have an effect to 1 m or more. In addition, other positive features such as greater depth of influence and faster travel speed than conventional rollers are being reported from the field. However, there is a lack of theoretical explanations or scientific research information for how to operate these rollers. Hence, this study will focus on a geotechnical modeling that describes the behavior of soils during ground compaction using various impact rollers (e.g., triangular, Landpac 3-sided, Landpac 5-sided, and octagonal shapes). In addition, this study will estimate more precisely the depth of influence for impact rollers. To do so, the general purpose finite element computer program LS-DYNA is used for numerical predictions. The finite element study is carried out with three-dimensional models. A simplified elastic perfectly plastic model with the Druker-Prager yield criterion is used for soil modeling and rollers are treated as a rigid body (i.e., incompressible material). The result of this study compares well with existing field experiment data for estimating vertical stress profile and compaction features, and demonstrates that the impact rollers are appropriate for thick layers

Photo-patternable and transparent films using cellulose nanofibers for stretchable origami electronics

Substantial progress in flexible or stretchable electronics over the past decade has extensively impacted various technologies such as wearable devices, displays and automotive electronics for smart cars. An important challenge is the reliability of these deformable devices under thermal stress. Different coefficients of thermal expansion (CTE) between plastic substrates and the device components, which include multiple inorganic layers of metals or ceramics, induce thermal stress in the devices during fabrication processes or long-term operations with repetitions of thermal cyclic loading-unloading, leading to device failure and reliability degradation. Here, we report an unconventional approach to form photo-patternable, transparent cellulose nanofiber (CNF) hybrid films as flexible and stretchable substrates to improve device reliability using simultaneous electrospinning and spraying. The electrospun polymeric backbones and sprayed CNF fillers enable the resulting hybrid structure to be photolithographically patternable as a negative photoresist and thermally and mechanically stable, presenting outstanding optical transparency and low CTE. We also formed stretchable origami substrates using the CNF hybrid that are composed of rigid support fixtures and elastomeric joints, exploiting the photo-patternability. A demonstration of transparent organic light-emitting diodes and touchscreen panels on the hybrid film suggests its potential for use in next-generation electronics.ope

High-Resolution 3D Printing of Freeform, Transparent Displays in Ambient Air

Direct 3D printing technologies to produce 3D optoelectronic architectures have been explored extensively over the last several years. Although commercially available 3D printing techniques are useful for many applications, their limits in printable materials, printing resolutions, or processing temperatures are significant challenges for structural optoelectronics in achieving fully 3D-printed devices on 3D mechanical frames. Herein, the production of active optoelectronic devices with various form factors using a hybrid 3D printing process in ambient air is reported. This hybrid 3D printing system, which combines digital light processing for printing 3D mechanical architectures and a successive electrohydrodynamic jet for directly printing transparent pixels of organic light-emitting diodes at room temperature, can create high-resolution, transparent displays embedded inside arbitrarily shaped, 3D architectures in air. Also, the demonstration of a 3D-printed, eyeglass-type display for a wireless, augmented reality system is an example of another application. These results represent substantial progress in the development of next-generation, freeform optoelectronics

Stretchable and transparent electrodes based on in-plane structures

Stretchable electronics has attracted great interest with compelling potential applications that require reliable operation under mechanical deformation. Achieving stretchability in devices, however, requires a deeper understanding of nanoscale materials and mechanics beyond the success of flexible electronics. In this regard, tremendous research efforts have been dedicated toward developing stretchable electrodes, which are one of the most important building blocks for stretchable electronics. Stretchable transparent thin-film electrodes, which retain their electrical conductivity and optical transparency under mechanical deformation, are particularly important for the favourable application of stretchable devices. This minireview summarizes recent advances in stretchable transparent thin-film electrodes, especially employing strategies based on in-plane structures. Various approaches using metal nanomaterials, carbon nanomaterials, and their hybrids are described in terms of preparation processes and their optoelectronic/mechanical properties. Some challenges and perspectives for further advances in stretchable transparent electrodes are also discussed. © 2015 The Royal Society of Chemistry.open0

A Pilot Experiment to Develop a Lightweight Non-Nuclear EMP Shelter Applying Civil-Military Cooperation in a Sustainability Policy

The goal of future wars is to incapacitate national core infrastructures through cyberattacks and electronic wars. The use of high-tech arms including high-power electronic weapons, laser weapons, and railguns to achieve a precise strike, minimum cost, and neutralization is gradually increasing. Considering the nuclear provocation and non-nuclear electromagnetic pulse (NNEMP) threats from North Korea, it has become urgent for Korea to expand its EMP protection systems. Hence, the need for developing a protective technology lighter than the conventional EMP protection technology is continuously being raised. However, no facility has applied such a lightweight protection technology thus far. Thus, this study tests the performance of a lightweight electromagnetic (EM) shielding material and evaluates the possibility of building a lightweight NNEMP shelter by installing the material. Among the commercially available EM shielding materials, only those appropriate for lightweight purpose are selected. Accordingly, the EM shielding performances of nine fabric types, five film types, and four wallpaper types are tested. For testing, a pan-type EM shielding room 2.5 m × 3.0 m × 2.5 m was constructed with a shielding performance of 80 dB at 18 GHz. The measurement method was based on the IEEE-STD-299 standard, and 10 frequencies from 14 kHz to 18 GHz were used. The result showed that the shielding performance was the highest in the 100 MHz band in most cases. In the high-frequency band above 1 GHz, the shielding performance was almost equal to, or slightly lower than, that in the 100 MHz band. This study confirms the feasibility of building lightweight NNEMP shelters in major military and civil facilities. If the NNEMP shelters to be constructed in military and civil facilities are replaced with lightweight shelters, approximately 49,862.4 tons of CO2 emissions due to the concrete saved can be reduced per shelter. Assuming the Korean carbon transaction price to be USD 50/ton-CO2, the saving amounts to US $2,493,120, contributing to the green growth policy of Korea

Feasibility Study on the Development of a Deployable Tactical EMP Tent for a Sustainable Military Facility

The Korean peninsula is under increasing threat of electromagnetic pulses (EMPs) from neighboring countries; EMP protection facilities are an essential means of ensuring the operational readiness of the military. However, existing EMP protection facilities are manufactured as fixed-weight structures, which limit the mobility of military operations and lead to the misconception of EMP protection as something only required for higher command. The current military and official EMP protection standards require only a uniform shielding effectiveness of 80 dB. Therefore, this study aims to differentiate the existing uniform level of shielding effectiveness of 80 dB into 80 dB, 60 dB, 40 dB, etc. Further, it seeks to derive the factors to be considered when applying various methods, such as shielding rooms, shielding racks, site redundancy, spare equipment, and portable lightweight protective tents, for recovery of failure, instead of the existing protection facilities that rely on shielded rooms by the Delphi analysis. Then, the applicability of lightweight EMP protection is determined after selecting lightweight materials to build a facility. The electromagnetic shielding performance of 21 types of materials was measured in the 30 MHz–1.5 GHz frequency band using ASTM-D-4935-10. The results showed the possibility of developing a lightweight EMP shielding facility, which would save approximately 316,386 tons of concrete, reducing the CO2 emissions by approximately 9,972,489 tons. Assuming that the Korean carbon transaction price is USD 50/ton CO2, the savings are equivalent to USD 49,862,435

Numerical Simulation of the Degree of Protection for K9 Artillery Position under Explosion Scenario Using METT+TC

This study proposes a method to evaluate the protective performance of an existing K9 artillery position according to various explosion scenarios. Thus, a commercial software package AUTODYN was used to create a 3D model of the existing artillery position. Following the mission, enemy, terrain and weather, troops and support available, time available, and civil consideration (METT+TC) analysis, a total of three blast loading scenarios were selected. According to the results, the wall rotation angle of a near-miss explosion was within the standard of 2°; considering contact explosions, the rotation angles were also within 2°. This confirmed that the K9 artillery position under examination for protective performance was within the elastic design range. Considering the final evaluation and combining the results, the walls and slabs of the K9 artillery position were determined to be able to withstand the corresponding blast pressures and have no issues in protective performance. Meanwhile, due to the limitations of the actual blast tests for evaluating the protective performance of civilian protective structures and those of the ROK Armed Forces, these tests were replaced with numerical analysis-based evaluations. However, due to the lack of specified procedures for numerical analysis based on finite element analysis, there were several difficulties in practice. Therefore, this study aims to provide a basic procedure for evaluating the protective performance of protective structures in the future by presenting analytical and blast loading conditions which are necessary for evaluating protective performance

Effectiveness of Dominant Aggregate Size Range–Interstitial Component (DASR-IC) Criteria for Consistently Enhanced Cracking Performance of Asphalt Mixtures in the Field

This study primarily focused on evaluating the effectiveness of Dominant Aggregate Size Range-Interstitial Component (DASR-IC) criteria established for purpose of asphalt mixture design and construction specifications leading to better and consistently enhanced field cracking performance using the Enhanced Hot-Mix Asphalt Fracture Mechanics-based performance prediction model (HMA-FM-E model) plus field performance evaluation. Results indicated that the mixtures meeting all DASR-IC criteria, including DASR porosity, Disruption Factor (DF), Effective Film Thickness (EFT), and Fine Aggregate Ratio (FAR), will have relatively better and consistently enhanced field cracking performance. The mixtures not meeting all DASR-IC criteria show inconsistent field cracking performance, including either cracked or uncracked status. Thereby, it is important to design asphalt mixtures that meet all DASR-IC criteria. The DASR-IC criteria were found to be effective and their implementation will help ensure consistently enhanced cracking performance in the field.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Optimization of Parameters Affecting Horizontal Cracking in Continuously Reinforced Concrete Pavement (CRCP)

Field evaluation of distresses in continuously reinforced concrete pavement (CRCP) indicated punch-out distress associated with horizontal cracking at the depth of the longitudinal steel is the most severe performance problem in CRCP. The developed 3-D model was used to perform a parametric analysis to determine the effects of critical loading location, concrete properties, and longitudinal steel design on horizontal cracking potential. The maximum vertical tensile stresses in the concrete were slightly affected by the coefficient of thermal expansion of the concrete. The critical tensile stresses in the concrete were observed to decrease as the base modulus, slab-base friction, slab thickness, and transverse crack spacing increase. The vertical tensile stresses significantly decreased when the longitudinal steel spacing decreased. The use of varying longitudinal steel spacing and reducing the depth of steel may be one of the ways to reduce the horizontal cracking potential without changing the steel ratio of the slab.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author