Due to the long-term coupling effect of a train load and groundwater, the surrounding rock at the tunnel bottom will soften in a certain range and the mechanical parameters of the surrounding rock will decrease, causing the uneven distribution of the confining pressure at the tunnel bottom and affecting the base concrete structure service life. In this research, the method of combining field tests and numerical simulation is adopted, and the vertical displacement, vertical acceleration, and maximum and minimum principal stresses are used as evaluation indicators. The dynamic response law of the base structure with the softened surrounding rock of the heavy-duty train is analyzed, and the Miner linear cumulative damage theory is introduced to obtain the service life of the tunnel bottom structure under different softening conditions. The results show that with the decrease in the softening coefficient and the increase in the softening thickness of the bedrock, the displacement, acceleration, and principal stress response indexes of the structure increase by varying degrees, and the service life of the base structure decreases almost linearly. The maximum vertical displacement, acceleration, and tensile stress are located directly below the track, and the maximum compressive stress is located at the connection between the inverted arch and the side wall. According to the predicted value of the service life, the reliability of the base structure is divided into four levels safety, warning, danger, and serious danger.Composites can be engineered to exhibit high strength, high stiffness, and high toughness. Composite structures have been used increasingly in various engineering applications. In recent decades, most fundamentals of science have expanded their reach by many orders of magnitude. Currently, one of the primary goals of science and technology seems to be the quest to develop reliable methods for linking the physical phenomena that occur over multiple length scales, particularly from a nano-/micro-scale to a macroscale. The aim of this Special Issue is to assemble high quality papers that advance the field of multiscale simulation of composite structures, through the application of any modern computational and/or analytical methods alone or in conjunction with experimental techniques, for damage assessment or mechanical analysis and prediction.An innovational self-reduction molecular-level-mixing method was proposed as a simplified manufacturing technique for the production of carbon nanotube copper matrix composites (CNT/Cu). Copper matrix composites reinforced with varying amounts of (0.1, 0.3, 0.5 and 0.7 wt%) carbon nanotubes were fabricated by using this method combined with hot-pressing sintering technology. The surface structure and elemental distribution during the preparation of CNT/Cu mixing powder were investigated. The microstructure and comprehensive properties of the CNT/Cu composites were examined by metallography, mechanical and electrical conductivity tests. The results revealed that the CNT/Cu could be produced by a high temperature reaction at 900 degrees under vacuum, during which the carbon atoms in the carbon nanotubes reduced the divalent copper on the surface to zero-valent copper monomers. The decrease in the ratio of D and G peaks on the Raman spectra indicated that the defective spots on the carbon nanotubes were wrapped and covered by the copper atoms after a self-reduction reaction. The prepared CNT/Cu powders were uniformly embedded in the grain boundaries of the copper matrix materials and effectively hindered the tensile fracture. The overall characteristics of the CNT/Cu composites steadily increased with increasing CNT until the maximum at 0.7 wt%. The performance was achieved with a hardness of 86.1 HV, an electrical conductivity of 81.8% IACS, and tensile strength of 227.5 MPa.This paper aims to find out the effect of different weight percentages of geopolymer filler in glass-reinforced epoxy pipe, and which can achieve the best mechanical properties and adhesion between high calcium pozzolanic-based geopolymer matrices. Different weight percentages and molarities of epoxy hardener resin and high calcium pozzolanic-based geopolymer were injected into the glass fiber. By manually winding filaments, composite samples were produced, and they were then allowed to cure at room temperature. To determine how well the geopolymer matrices adhere to the fiber reinforcement, the microstructure of the composites’ surfaces and perpendicular sections were examined. Maximum values of compressive strength and compressive modulus were 94.64 MPa and 2373.58 MPa, respectively, for the sample with a weight percentage of filler loading of 30 wt% for an alkali concentration of 12 M. This is a relatively wide range of geopolymer weight percentage of filler loading from 10 wt% to 40 wt%, at which we can o the melted epoxy.From a technical and economic point of view, our aim is to provide viable solutions for the replacement of fossil fuels which are currently used in internal combustion diesel engines. In this research, two new biofuels composed of second-generation vegetable oils (SVO),used oil sunflower (SO) or castor oil (CO), and the ABE blend (acetone/butanol/ethanol) were evaluated. ABE is an intermediate product from the fermentation of carbohydrates to obtain bio-butanol. Besides, the ABE blend exhibits suitable properties as biofuel, such asvery low kinematic viscosity, reasonable energy density, low autoignition temperature, and broad flammability limits. Diesel/ABE/SVO triple blends were prepared, characterized and then, tested on a diesel engine, evaluating power output, consumption, and exhaust emissions. The power output was slightly reduced due to the low heating values of ABE blend. Also, engine consumed more fuel with the triple blends than with diesel under low engine loads whereas, at medium and high loads, the fuel consumption was very similar to that of diesel. Regarding exhaust gas emissions, soot wasnotably reduced, and nitrogen oxides (NOx) and carbon monoxide (CO2) emissions were lower or comparable to that of diesel, while the CO emissions increased. The use of these biofuels allows the replacement of high percentagesof diesel without compromising engine power and achievinga significant reduction in pollution emissions. Furthermore, a notable improvement in cold flow properties of the fuel blends is obtained, in comparison with diesel.Para-aramid materials such as Twaron® and Kevlar® are commonly used for ballistic-resistant body armor, which are designed to protect human life and health. For this reason, the materials from which body armor are made should be thoroughly investigated in the area of long-term reliability, particularly with regard to exposure to UV light, humidity and temperature, as these are known causes of degradation in commonly used ballistic materials. This research presents the durability of soft and hard ballistic inserts designed using para-aramid (Twaron®) materials. Para-aramid ballistic inserts not subjected to accelerated aging processes and also ones subjected to laboratory aging for 63, 129 and 194 days, which corresponded to 2, 4 and 6 years of aging in real conditions, were tested. The selected para-aramid inserts were verified in terms of ballistic and physico-mechanical properties as well as changes in chemical structure of the ballistic materials. Ballistic tests were carried out with the use of a 1.1 g FSP.22 fragment according to STANAG 2920. Changes in the microstructure of the para-aramid materials were evaluated using infrared spectroscopy and scanning electron microscopy. The obtained results indicate that despite the changes which took place at the molecular level in the Twaron® materials, accelerated aging processes do not affect the fragmentation resistance properties of ballistic inserts made of para-aramid materials.In the rotational moulding industry, non-used, scrap, and waste purge materials have tremendous potential to be reprocessed and applied in skin-foam-skin sandwich structures to replace and reduce the use of virgin polymers. This approach not only encourages the re-use of these waste materials but also significantly contributes to reduce environmental impacts associated with the use of virgin polymers in this sector. The demand of rotationally moulded sandwich structures is rapidly increasing in automotive, marine, and storage tanks, where investigating their impact and after-impact responses are crucial. Hence, this study investigated the low-velocity impact (LVI) and flexure-after-impact (FAI) responses of rotationally moulded sandwich structures manufactured using reprocessed materials. Results obtained from LVI induced damage at two different incident energy levels (15 J, 30 J), and the residual flexural strength of impacted structures evaluated by three-points bending tests were compared with non-reprocessed sandwich structures (virgin materials). The impact damage progression mechanism was characterized using the X-ray micro-computer-tomography technique. Reprocessed sandwiches demonstrated 91% and 66% post-impact residual strength at 15 J and 30 J respectively, while for non-reprocessed sandwiches, these values were calculated as 93% and 88%. Although reprocessed sandwich structures showed a lower performance over non-reprocessed sandwiches, they have a strong potential to be used in sandwich structures for various applications.The confinement of concrete enhances its strength and ductility by restraining lateral dilation. The accuracy of a confinement model depends on how well it captures the dilation of concrete. In the current paper, a mesoscale model is established to study the dilation properties of concrete in active confinement, where the heterogeneity of concrete is considered. The stress-strain and lateral-axial strain curves of concrete in active confinement were used to demonstrate the validity of the mesoscale model. Subsequently, the distribution of lateral strain and the influences of the strength grade and confinement ratio on the dilation of concrete were investigated in a simulation. The results show that the distribution of the lateral strain along the radial or longitudinal directions is not uniform on the specimen when compressive failure occurs. The confinement ratio has a more significant influence on the concrete’s transverse dilation than the strength grade. Finally, an expression of the lateral-axial strain relationship of concrete in active confinement is proposed. The proposed formula can reflect the simulation results of the mesoscale model and is in good agreement with the prediction of existing formulas.This study proposes test methods for assessing the printability of concrete materials for Additive Manufacturing. The printability of concrete is divided into three main aspects flowability, setting time, and buildability. These properties are considered to monitor the critical quality of 3DCP and to ensure a successful print. Flowability is evaluated through a rheometer test, where the evolution of shear yield strength is monitored at a constant rate (rpm), similar to the printer setup. Flowability limits were set based on the user-defined maximum thickness of a printed layer and the onset of gaps/cracks during printing. Setting time is evaluated through an ultrasonic wave pulse velocity test (UPV), where the first inflection point of the evolution of the UPV graph corresponds to the setting time of the concrete specimen. The results from this continuous non-destructive test were found to correlate with the results from the discrete destructive ASTM C-191 test for measuring setting time with a maximum difference of 5% between both sets of values.