Mechanical properties and electrical resistivity of multiwall carbon nanotubes incorporated into high calcium fly ash geopolymer
Mechanical properties and electrical resistivity of multiwall carbon nanotubes incorporated into high calcium fly ash geopolymer-2021
High calcium fly ash (HCF) is a pozzolan material and is available in large quantity in Thailand due to the existence of coal-based electrical power plants. It is used as a supplemental material to partially replace cement content in concrete as a movement toward concrete sustainability. In order to lift the sustainability level, a cementitious material without Portland cement called ‘geopolymer’ was introduced. Geopolymer can be produced from raw materials containing high alumina and silica, for example fly ash, blast furnace slag, and metakaolin. For high calcium fly ash geopolymer (HCFG), the unique properties include fast setting, and high early strength. In this study, in order to enhance the properties of HCF geopolymer, multiwall carbon nanotubes (MWCNTs) were introduced into the matrix. In addition to the investigation into basic properties, the effect of MWCNT on electrical resistivity was also investigated to determine its potential use in piezoelectric sensor applications. The results showed that the addition of MWCNTs improved the mechanical properties of HCFG. The maximum compressive and flexural strengths were obtained with a mix containing 0.2% MWCNTs. The EDS test also indicated the increase in geopolymerization and hydration products with the addition of MWCNTs. To investigate the piezoelectricity potential, the electrical resistivity under different levels of compression loads was investigated. The resistivity decreased with the increasing load level up to the first crack, and then decreased. The changes in electrical resistivity indicated the potential use of HCFG incorporated MWCNTs in self-sensing for structural health monitoring.
Keywords: Geopolymer | High calcium fly ash | Multiwall carbon nanotube | Electrical resistivity
A new development of four-point method to measure the electrical resistivity in situ during plastic deformation
توسعه جدیدی از روش چهار نقطه ای برای اندازه گیری مقاومت الکتریکی در محل در طول تغییر شکل پلاستیک-2021
The presented study introduces a new test method to measure the change of the electrical resistivity in situ during plastic deformation to characterize the deformation behavior of metals. This investigation is based on a specially developed four- point method, which determines the change in electrical resistance of sheet samples of an aluminum alloy 6062, a copper alloy CW024A and steel DC04 in situ during deformation in a tensile test. Results show that the strain path, the deformation history, the plastic anisotropy as well as the plastic deformation have a significant influence on the electrical resistivity of all investigated materials. Therefore, this technique is universally applicable for all sheet metals, independent of the crystal structure, the electrical and mechanical properties to characterize structural changes during forming. The obtained data can be used for simulations of metal forming processes, e. g. to predict forming limit curves and damage monitoring under service loading.
Keywords: Plastic deformation | Plastic anisotropy | Plane strain test | Uniaxial tensile test | Electrical resistivity | Four-point method
Effect of graphite and Mn3O4 on clay-bonded SiC ceramics for the production of electrically conductive heatable filter
اثر گرافیت و Mn3O4 بر سرامیک های SiC پیوند خورده با خاک رس برای تولید فیلتر قابل گرمایش رسانای الکتریکی-2021
Electrically conductive porous SiC ceramics are attracting substantial attention due to their application in heatable filters, vacuum chuck, and semiconductor processing parts, etc. The main problem is their high processing cost. Ideal candidates from an engineering ceramic perspective will be mechanically durable and have the required electrical properties with sufficiently low fabrication costs. To decrease the sintering temperature, kaolin has been added, but it tended to render the material an insulator. Graphite was used to effectively decrease the electrical resistivity. Additionally, manganese oxide was used to decrease the quantity of kaolin (the component that leads to an insulator material after sintering) and decrease the electrical resistivity while maintaining the mechanical properties. In our study, we found that SiC with 35% kaolin, 20% graphite and 10% manganese oxide can produce samples with 6.5 × 10− 1 Ω cm electrical resistivity and 43.5 MPa flexural strength at a low sintering temperature of 1200 ◦C.
Keywords: SiC | Mullite | Electrical resistivity | Mechanical properties | Manganese oxide
Analysis of energy dissipation and crack evolution law of sandstone under impact load
تجزیه و تحلیل اتلاف انرژی و قانون تکامل ترک ماسه سنگ تحت بار ضربه-2020
Based on the split Hopkinson pressure bar (SHPB) laboratory tests, the dynamic mechanical properties and failure mode of sandstone are analyzed, and a SHPB numerical model is established by particle flow code (PFC). The dynamic stress equilibrium, stress wave propagation, stress-strain characteristics and failure mode are analyzed, respectively, which verifies the effectiveness of the model. Then we studied the impact failure process form both mesoscopic cracks and energy point of views. The results show that microcracks are activated in large quantities with the increasing of strain rate. When the crack density reaches a certain degree, the interaction between the cracks can not be ignored. The failure mode gradually changes from local tension–shear damage mode to axial splitting failure mode and then to crushing failure mode. During the impact failure process, the energy is mainly consumed by the generation of the cracks and the friction caused by the slip of the particles, namely, broken dissipation energy. As the impact load increases, the broken dissipation energy density shows the high–speed growth and the low–speed growth stage successively with a double exponential growth pattern. The friction energy increases continually by a certain percentage, which indicates it should be considered during the analysis of fracturing process. Moreover, the dynamic strength and fragmentation degrees are closely related to energy dissipation density.
Keywords: Rock dynamics | Split hopkinson pressure bar | PFC2D | Crack propagation | Energy transformation
Dynamic covalent chemistry (DCC) in dental restorative materials: Implementation of a DCC-based adaptive interface (AI) at the resin–filler interface for improved performance
شیمی کووالانسی پویا (DCC) در مواد ترمیمی دندانپزشکی: اجرای یک رابط سازگار مبتنی بر (DCC )هوش مصنوعی در رابط رزین-پرکننده برای بهبود عملکرد-2020
Objective. Dental restorative composites have been extensively studied with a goal to improve material performance. However, stress induced microcracks from polymerization shrinkage, thermal and other stresses along with the low fracture toughness of methacrylate-based composites remain significant problems. Herein, the study focuses on applying a dynamic covalent chemistry (DCC)-based adaptive interface to conventional BisGMA/TEGDMA (70:30) dental resins by coupling moieties capable of thiol–thioester (TTE) DCC to the resin–filler interface as a means to induce interfacial stress relaxation and promote interfacial healing. Methods. Silica nanoparticles (SNP) are functionalized with TTE-functionalized silanes to covalently bond the interface to the network while simultaneously facilitating relaxation of the filler–matrix interface via DCC. The functionalized particles were incorporated into the otherwise static conventional BisGMA/TEGDMA (70:30) dental resins. The role of interfacial bond exchange to enhance dental composite performance in response to shrinkage and other stresses, flexural modulus and toughness was investigated. Shrinkage stress was monitored with a tensometer coupled with FTIR spectroscopy. Flexural modulus/strength and flexural toughness were characterized in three-point bending on a universal testing machine. Results. A reduction of 30% in shrinkage stress was achieved when interfacial TTE bond exchange was activated while not only maintaining but also enhancing mechanical properties of the composite. These enhancements include a 60% increase in Young’s modulus, 33% increase in flexural strength and 35% increase in the toughness, relative to composites unable to undergo DCC but otherwise identical in composition. Furthermore, by combining interfacial DCC with resin-based DCC, an 80% reduction of shrinkage-induced stress is observed in a thiol–ene system “equipped” with both types of DCC mechanisms relative to the composite without DCC in either the resin or at the resin–filler interface. Significance. This behavior highlights the advantages of utilizing the DCC at the resin–filler interface as a stress-relieving mechanism that is compatible with current and future devel- opments in the field of dental restorative materials, nearly independent of the type of resin improvements and types that will be used, as it can dramatically enhance their mechanical performance by reducing both polymerization and mechanically applied stresses through- out the composite lifetime.
Keywords: Adaptive interface | Interfacial stress relaxation | Thiol–thioester exchange | Dynamic covalent chemistries | Composites
A novel biomimetic design of a 3D vascular structure for self-healing in cementitious materials using Murrays law
طراحی biomimetic جدید از ساختار عروقی سه بعدی برای بهبودی در مواد سیمانی با استفاده از قانون موری-2020
Nature has always been a source of inspiration in engineering applications and vascular networks, as in human skin and in a tree leaf, are one attribute that has received attention in the design of resilient structures. A vascular system houses healing agents within its hollow channels or interconnected networks which are incorporated within a cement matrix. It is the only self-healing approach that has the capability to address different scales of damage in cementitious materials. The main aim of this work is to develop a novel vascular network inspired by nature for self-healing in cementitious systems. To achieve this, a biomimetic three-dimensional (3D) vascular networkwas designed and generated followingMurrays lawfor circulatory blood volume transfer. The designed structureswere constructed through 3D printing and assessed in a cement-based matrix. One-dimensional (1D) and two-dimensional (2D) models were also designed, printed and embedded into cement prisms to compare with the 3Dvascular system. Load recoverywas used to assess recovery inmechanical properties after the sample was cracked and pumped with sodium silicate for 28 days. Mechanical testing assessed the compatibility of the system with the surrounding matrix as well as the functionality of the network in delivering and releasing the healing agent at the location of damage. This initial proof of conceptwork confirmed the ability of all vascular systems to deliver the healing agent after a damage event, and the 3D vascular system demonstrated a significantly enhanced healing performance.
Keywords: Vascular networks | Biomimetic structures | 3D printing | Self-healing | Cementitious materials
Degradation model of the dynamic mechanical properties and damage failure law of sandstone under freeze-thaw action
مدل تخریب خواص مکانیکی پویا و قانون شکست خسارت ماسه سنگ تحت عمل ذوب انجماد-2020
In the construction process of alpine regions, the construction zone is often subjected to blasting vibrations, heavy truck transportation vibrations, earthquakes and other dynamic loads. It is of great significance to analyse the dynamic mechanical properties of a rock mass under the coupling action of freeze-thaw cycles and dynamic loading. In this paper, the degradation laws of the static mechanical parameters and dynamic mechanical parameters and the failure modes of the sandstone are studied by static mechanical tests, electron microscopic tests and uniaxial impact compression tests on sandstone samples with different numbers of freeze-thaw cycles under impact loading. The test results show that the dynamic increase factor (DIF) is affected by the number of freezethaw cycles and the strain rate, and the strain rate is the dominant factor. For the dynamic increase factor of the elastic modulus DIFE, the effect of the strain rate on the DIFE is much smaller than that on the DIF, and the variation in the DIFE decreases with the increase in the number of freeze-thaw cycles. When the strain rate is constant, the dynamic compressive strength of the sandstone samples decreases exponentially with an increase in the number of freeze-thaw cycles. When the number of freeze-thaw cycles is constant, the dynamic compressive strength of the sandstone samples increases linearly with increasing strain rate. The dynamic compressive strength degradation model of sandstone considering the number of freeze-thaw cycles and strain rate is obtained by fitting the experimental data. In the early stage of the freeze-thaw cycle, the main dynamic failure mode of sandstone under the action of freeze-thaw cycles and a lower impact load is the axial splitting failure mode, while the dynamic failure mode of sandstone under freeze-thaw action and a higher impact load is the crushing failure mode. The research results can be used to predict the dynamic compressive strength of rock under different strain rates and varying numbers of freeze-thaw cycles and provide a theoretical basis for similar engineering construction.
Keywords: Freeze-thaw cycles | Impact load | Strain rate | Dynamic response
Implications of rectal preconditioning for interpretation of sensory-motor data
پیامدهای پیش شرط رکتوم برای تفسیر داده های حسی- حرکتی-2020
Testing of biomechanical properties of intestine requires the tissue to be preconditioned by applying cyclic loading to obtain repeatable mechanical data. However, little is known about the mechanosensory properties during intestinal preconditioning. We aimed to study the relationship between mechanical preconditioning of the human rectum and sensory response. Three fast rectal bag distensions to the pain threshold were done in seven healthy females. A visual analog scale (VAS) was used for sensory assessment. At each distension, we determined (1) time, bag cross-sectional area (CSA), radius (r), r/r0, pressure and tension to reach VAS = 1, 3 and 5 (pain threshold); (2) the same parameters at induced contraction start; (3) CSA where the pressure started to increase (CSAP>baseline) and (4) the number of contractions. The time, CSA, r/r0 and tension to reach VAS = 1 and VAS = 3 increased from distension 1 to 3 (4.9 < F < 1 1.5, 0.05 > P > 0.007), primarily due to difference between the first and second distension. For VAS = 5, r/r0 was smaller in distension 3 than distension 1 (P < 0.05), whereas time, CSA and tension did not differ between distensions (P > 0.5). Compared with distension 1, CSA, r/r0 and tension at contraction start, and CSAP>baseline were bigger in distensions 2 and 3 (5.5 < F < 10.9, 0.05 > P > 0.009). The pressure to reach the VAS levels, the contraction numbers and pressure at contraction start did not differ among distensions (P > 0.6). During mechanical preconditioning, CSA, tension and deformation increased at subpain levels, reflecting sensory adaptation. The data point to acute remodeling of a strain-dependent mechanism in the rectal wall.
Keywords: Load-dependent effect | Mechanosensation | Preconditioning | Rectum | Sensory-motor properties
Challenges of 3D printing technology for manufacturing biomedical products: A case study of Malaysian manufacturing firms
چالش های فن آوری چاپ سه بعدی برای تولید محصولات زیست پزشکی: یک مطالعه موردی از شرکت های تولید مالزی-2020
Additive manufacturing has attracted increasing attention worldwide, especially in the healthcare, biomedical, aerospace, and construction industries. In Malaysia, insufficient acceptance of this technology by local industries has resulted in a call for government and local practitioners to promulgate the development of this technology for various industries, particularly for biomedical products. The current study intends to frame the challenges endured by biomedical industries who use 3D printing technology for their manufacturing processes. Qualitative methods, particularly in-depth interviews, were used to identify the challenges faced by manufacturing firms when producing 3D printed biomedical products. This work was able to identify twelve key challenges when deploying additive manufacturing in biomedical products and these include issues related to binder selection, poor mechanical properties, low-dimensional accuracy, high levels of powder agglomeration, nozzle size, distribution size, limited choice of materials, texture and colour, lifespan of materials, customization of fit and design, layer height, and, lastly, build-failure. Furthermore, there also are six challenges in the management of manufacturing biomedical products using 3D printing technology, and these include staff re-education, product pricing, limited guidelines, cyber-security issues, marketing, and patents and copyright. This study discusses the reality faced by 3D printing players when producing biomedical products in Malaysia, and presents a primary reference for practitioners in other developing countries.
Keywords: Business | Biomedical products | Additive manufacturing | 3D printing technology
Study on the variation law of bamboo fibers’ tensile properties and the organization structure on the radial direction of bamboo stem
بررسی قانون تغییر خصوصیات کششی الیاف بامبو و ساختار سازمان در جهت شعاعی ساقه بامبو-2020
Bamboo fiber cell wall was layered composite with fine mechanical properties reinforced by cellulose microfibril with lignin and hemicellulose as amorphous matrix. This paper aimed at study the organization structure and tensile properties of natural bamboo fibers extracted by handwork assisted with a laser micrometry device to monitor the deformation of fibers, and the variation law of tensile properties and organization structure on radial direction of bamboo stem. The results were that the average tensile strength, elastic modulus and strain to failure were 523.20 MPa(SD=111.65 MPa), 22.27 GPa(SD=6.29 GPa) and 3.08%(SD=1.57%). From the inner part to the outer part of bamboo stem, tensile strength of bamboo fibers slightly tended to increase on the whole, while the tensile elastic modulus and the strain to failure had obviously increasing tendency and decreasing tendency respectively. The fracture behavior of fibers nearby the inner part was similar to brittle fracture, while that of the fibers nearby the outer part similar to ductile fracture. The phenomena were in accordance with the variation of the tensile properties of bamboo fibers on the radial direction of bamboo stem, which had closely relation with the variation of the organization structure of bamboo fiber cell wall in radial direction.
Keywords: natural bamboo fibers | tensile properties | organization structure | fracture behavior