The Effect of Elevated Temperature on Engineered Cementitious Composite Microstructural Behavior: An Overview

This paper discusses the quantitative bibliographic data derived from scientific publications on Engineered Cementitious Composites (ECC) subjected to elevated temperature, the influence of elevated temperature on the mechanical properties, particularly the compressive strength and microstructure behavior of Engineered Cementitious Composites (ECC) mixtures based on the review of previous pieces of literature. Systematic literature reviews were employed as the methodology in this study. The age of related publications selected to be reviewed was limited to publications for the past ten years, 2010 to December 2020. It was found from available research that exposure of the ECC specimen at the elevated temperature starting from 200oC significantly reduced the compressive strength when the temperature increases, melting of fiber and increase of porosity causes the dramatically increase micro-cracks.

Microstructure and Mechanical properties of transition zone in laser additive manufacturing of TC4/AlSi12 bimetal structure

Ti/Al bimetallic structure (BS) has a good development prospect and broader application potential in aerospace engineering. Considering the limitation that dissimilar welding is only applicable to the thin plate, it is necessary to explore a new manufacturing process for Ti/Al BS. In this study, a TC4/AlSi12 BS was prepared by laser additive manufacturing (LAM). TC4 zone, AlSi12 zone and transition zone were formed in the LAM process. Due to the sufficient diffusion reaction, the transition zone with a width of about 0.8mm was obtained. At the same time, a few micro-cracks were found in the transition zone. The microstructure and phase composition of the transition zone had been emphatically studied. Research results showed that the presence of Si element made the phase composition of the transition zone more complicated. The structure evolution from TC4 to AlSi12 was: α-Ti → Ti3Al → TiAl+(TiAl+Si) → Ti5Si3 → TiAl3+(α-Al+Si) → α-Al+ Si +TiAl3 +(α-Al+Si) → α-Al+Si+(α-Al+Si). The hardness distribution of BS was uneven, with the highest value reaching 524HV. The tensile strength of the TC4/AlSi12 BS was about 110Mpa, and the fracture location was located in the transition zone.

Effects of Graphene on the Wear and Corrosion Resistance of Micro-Arc Oxidation Coating on a Titanium Alloy

In order to improve the wear and corrosion resistance of micro-arc oxidation (MAO) coating on a Ti-5Al-1V-1Sn-1Zr-0.8Mo alloy, 0–0.20 g/L graphene was added to the electrolyte to prepare micro-arc oxidation coating. The thickness, roughness, micro-morphology, and composition of the MAO coating were characterized, and the wear and corrosion resistance of the coating was tested and analyzed. The results show that with 0.05 g/L of graphene in the electrolyte, the roughness of the coating decreased from 56.76 μm to 31.81 μm. With the increase in the addition of graphene, the microstructure of the coating became more compact, the diameter of micro-holes and micro-cracks decreased, and the corrosion resistance of the coating improved. The wear tests showed that the mass loss of the coating at the early wear stage (0~100 revolutions) was greater than that at the later stage (100~250 revolutions), and the wear resistance of the coating obtained by the addition of 0.10 g/L of graphene was the highest. With 0.10 g/L of graphene, the adhesion force between the coating and the substrate alloy is the largest, reaching 57.1 N, which is 9.98 N higher than that without graphene. After salt spray corrosion for 480 h, the coating with graphene has better corrosion resistance than that of a graphene-free coating.

Performance Evaluation On Structural Behaviour Of Sisal Fibre Reinforced Concrete

All over the world, construction industries looking forward for the green materials to meet the structural integrity and sustainability in terms of arresting micro cracks in the concrete and also for a secondary reinforcement materials for addition in the concrete. Internal micro cracks in the concrete will reduce the longetivity of the structure and also it results in structural failure. The use of fibres in the concrete is currently used as a secondary reinforcement for strengthening the reinforced concrete members. To make the concrete as a sustainable material and to improve structural integrity in this research Sisal Fibre was used as a secondary reinforcement. Natural fiber such as sisal fibre, appears as an one of the good alternative since they are available in fibrous form and can be extracted from plant leaves at very low cost. In this work, effect of sisal fiber on the strength of concrete for M 25 grade has been studied by varying the percentage of fibers in concrete. Fiber content were varied by 0.05%, 0.10%, 0.15%, 0.20%, 0.25%, 0.30%, 0.35% and 0.40% by volume of concrete. Cubes, Cylinder and Prism were cast to evaluate the Strength Characteristics and to optimize dosage level of fibre in concrete. The reinforced concrete beam was cast by optimum dosage level of fibre to evaluate structural behavior of concrete such as Load deflection, Ductility factor and Stiffness. The result proven, there is significant improvement in structural behavior of Sisal Fibre added Reinforced Concrete when compared to control concrete.

Thermal Effect on Formation Stability Due to Heterogeneity

This study evaluates physical and chemical changes induced by high thermal gradients on the formation and their impact to the stability. The heat sources that effect the formation’s stability are varied, including drilling (due to drilling bit friction), perforation, electromagnetic heating (laser or microwave), and thermal recovery or stimulation (steam, resistive heating, combustion, microwave, etc.). This study uses an integrated approach to characterize rock heterogeneity and mapping heat propagation from different heat sources. The information obtained from the study is vital to accurately design and enhance well completion and stimulation This is an integrated analysis approach combining different advanced characterization and visualization techniques to map heat propagation in the formation. Advanced statistical analysis is also used to determine the key parameters and build fundamental prediction algorithms. Characterization on the samples was performed before, during, and after the exposure to thermal sources; it comprised thin-section, high speed infrared thermography (IR), differential thermal analysis and thermogravimetric analyzer (DTA/TGA), scanning electron microscope (SEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), uniaxial stress, and autoscan (provide hardness, composition, velocity, and spectral absorption). The results are integrated, and machine learning is used to derive a predictive algorithm of heat propagation and mapping in the formation with reference to the key formation variables and heterogeneity distribution. Rock heterogeneity affects the rate and patterns of heat propagation into the formation. Within the rock sample, minerals, laminations, and cementations lead to a heterogeneous, and sometimes anisotropic, distribution of thermal properties (thermal conductivity, heat capacity, diffusivity, etc.). These properties are also affected by the rock structure (porosity, micro-cracks, and fractures) and saturation distribution. The results showed the impact of heat on the mechanical properties of the rocks are due to clays dehydration, mineral dissociations, and micro cracks. High speed thermal imaging provides a unique visualization of heat propagation in heterogeneous rocks. Statistical analysis identified key parameters and their impact on thermal propagation; the output was used to build a machine learning algorithm to predict heat distributions in core samples and near-wellbore. Characterizing rock properties and understanding how heterogeneity modifies heat propagation in rocks enables the design of optimal completion and stimulation strategies. This paper discusses how advanced characterization and analysis, combined with novel algorithms, can improve this understanding, and unleash innovation and optimization. The data and information gathered are critical to develop numerical models for field-scale applications.

Core Scale FEM Modeling of Thermochemical Fracturing on Cement Cube Samples

Brownfields and depleting conventional resources of fossil fuel energy are not enough to fulfill the tremendously increasing energy demands around the globe. Unconventional oil and gas resources are creating a huge impact on the enhancement of the global economy. Tight rocks are usually located in deep and high-strength formations. In this study, numerical simulation results on a new thermochemical fracturing approach is presented. The new fracturing approach was implemented to reduce the breakdown pressure of the unconventional tight formations. The hydraulic fracturing experiments presented in this study were carried out on ultra-tight cement block samples. The permeability of the block samples was less than 0.005mD. Thermochemical fracturing was carried out by a thermochemical fluids that caused a rapid exothermic reaction which resulted in the instantaneous generation of heat and pressure. Different salts of nitrogen such as sodium nitrite and ammonium chloride were used as a thermochemical fluid. The instantaneous generation of the heat and pressure caused the creation of micro-cracks. The fracturing results revealed that the novel thermochemical fracturing was able to reduce the breakdown pressure in ultra-tight cement from 1095 psi to 705 psi. The reference breakdown pressure was recorded from the conventional fracturing technique. A finite element (FEM) analysis was conducted using commercial software ABAQUS. In FEM, two approaches were used to model the thermochemical fractures namely, cohesive zone modeling (CZM) and concrete damage plasticity models (CDP). The sensitivity analysis of peak pressure and time to reach the peak pressure is also presented in this study. The sensitivity analysis can help in better designing thermochemical fluids that could lead to the maximum generation of micro-cracks and multiple fractures.

The Fracture Behavior of 316L Stainless Steel with Defects Fabricated by SLM Additive Manufacturing

In this paper, the fracture behaviors of 316L stainless steel with defects fabricated by the Selective Laser Melting (SLM) additive manufacturing are studied by a peridynamic method. Firstly, the incremental formulations in the peridynamic framework are presented for the elastic-plastic problems. Then, the pairwise force of a bond for orthotropic material model is proposed according to both the local and the global coordinate systems. A simple three-step approach is developed to describe the void defects that generated in the processing of the SLM additive manufacturing in the numerical model. Next, some representative numerical examples are carried out, whose results explain the validation and accuracy of the present method, and demonstrate that the orthotropic features, micro-cracks and voids of the materials have a significant influence on the ultimate bearing capacity, crack propagation and branching of the corresponding structures. It is also revealed that the crack initiations are induced actively by the defects and the crack branching is contributed to the complex multiple-crack propagation. Finally, the achievements of this paper lay a foundation for the engineering applications of the SLM additive manufacturing materials.

The LAI Coupling Associated with the M6 Luxian Earthquake in China on 16 September 2021

Periodic signals replaced noise that was found in continuous seismic data, particularly in the nighttime, from the broadband seismometer at the MVP-LAI (monitoring vibrations and perturbations in the lithosphere, atmosphere and ionosphere) system before the occurrence of the Luxian earthquake on 16 September 2021. A short distance of ~150 km between the MVP-LAI system and the epicenter of the Luxian earthquake suggests the periodic singles as promising seismo-phenomena, due to that the radius of the earthquake preparation zone is ~380 km for an M6 event. Integration of geophysical parameters, including atmospheric pressure, vertical electric field, radon concentration, groundwater level and precipitation, at the MVP-LAI system provides an excellent opportunity for studying the seismo-LAI coupling associated with the Luxian earthquake. Analytical results show that ground vibrations, atmospheric pressure and total electron content varied from ~10−3 to ~10−2 Hz before the Luxian earthquake. The seismo-LAI coupling in the relatively low frequency band (~10−3 Hz) can be referred to as the acoustic-gravity waves triggered by the amplified ground vibrations. In contrast, the seismo-LAI coupling in a relatively high frequency band (~10−2 Hz) would be caused by micro-cracks and/or the high-mode natural frequency that further drives changes of TEC due to the atmospheric resonance.

Research on Residual Life Estimation Method for KMN Steel Based on Nonlinear Ultrasonic Testing

The testing of KMN steel bending fatigue with different cycles was carried out using a nonlinear ultrasonic detector to obtain its nonlinear coefficient. The experimental results show that the nonlinear coefficient first increases and then decreases with an increase in fatigue cycles. The relationship between the propagation of the micro-cracks inside the material and the nonlinear coefficient was researched by microscopic analysis in the dangerous position of the specimens. As the fatigue cycles increase, the microstructure of the specimen gradually deteriorates and cracks occur, which proves that nonlinear ultrasonic detection can be used to characterize the initiation of micro-cracks in the early fatigue stages of the material and that the nonlinear coefficient β of the material can be used to reflect the fatigue damage degree and fatigue life of the interior of the material. An analysis of the numerical statistics of the fatigue cracks inside the specimens was carried out, and the extreme value of fatigue cracks was calculated using the Gumbel distribution. An empirical formula for the nonlinear coefficient and crack growth size of KMN steel was established and then a method for estimating the fatigue life of KMN steel based on nonlinear ultrasonic testing was proposed.