Estimation of ultimate tension load of methylmethacrylate bonded steel rods into concrete

This paper introduces an alternative method of predicting ultimate tension load of methylmethacrylate (MMA) bonded steel rods into concrete. In general, the elastic model is found to predict many of the major experimentally observed characteristics of adhesively bonded steel rods. This theory gives quite reasonable results when applied to epoxy adhesives, but does not agree with data of MMA adhesives. It is necessary, therefore, to modify the analysis in order to bring the elastic model into agreement with test data. This is done by assuming that c, which is a parameter in the analysis, is a function of the shear strain. The solution based on this concept leads to a more general equation which includes as a special case the elastic model previously used to represent the dependence of ultimate tension load on the bond length. Experimental evidence appears to indicate that the ultimate tension load of a MMA bonded steel rod can be predicted, to a good approximation, using this model.     

NEW ALANINE/EPR DOSIMETER USING EVA COPOLYMER/PARAFFIN AS A BINDER FOR HIGH-DOSE RADIATION DOSIMETRY: PERFORMANCE CHARACTERIZATION

Alanine/EPR rods (3 × 10 mm) for routine use in high-dose radiation applications have been prepared by a simple technique in the laboratory where alanine powder was mixed with molten mixture of paraffin wax and ethylene vinyl acetate copolymer (EVA). The binding mixture EVA/Paraffin does not present interference or noise in the EPR signal before or after the irradiation. The rods show good mechanical properties for safe and multi-use handling. The rods can be used with good precision in the dose range from 1 to 125 kGy. The overall uncertainty for calibration of the EVAPA rod dosimeters at 2σ was found to be 4.56%. The dose response, influence of humidity and temperature during irradiation, energy dependence as well as post–irradiation storage at different conditions are discussed.     

Modeling of the compression behavior of foam cores reinforced with composite rods

This article models the energy‐absorbing characteristics of polymer foams reinforced with either carbon or glass fiber reinforced epoxy rods. Initially, the compression response of 20 mm thick foams containing rods of equal length was modeled and the resulting predictions were compared with experimental data. The FE models have been shown to accurately predict the load–displacement responses of the reinforced foams in most cases. It has been shown that the energy absorbed by the reinforced cores increases linearly with foam density and that it also increases with increasing rod diameter. The energy values were normalized by the mass of the reinforced core to determine specific energy absorption (SEA) values. It has been shown that the SEA increases rapidly with increasing rod diameter and more slowly with increasing foam density. The validated models were used to predict the compression response of foams of different thickness, where it was shown that increasing the thickness of the core results in a reduction in the SEA. In addition, the FE model was used to model graded cores based on composite rods of different lengths. Using differently sized rods allows for the controlled energy absorption as well as the more gradual increase in the sustained crushing load. POLYM. COMPOS., 38:2301–2311, 2017. © 2015 Society of Plastics Engineers     

新型铸铁冷焊法焊条及其焊接工艺

一种由结构钢焊条简单改性而成、且具有较好抗裂等性能的新型铸铁冷焊焊条,配套采用相应独特的焊接工艺,可快速焊接(修复)的白口、灰口、可锻、球墨铸铁机件,其焊接质量能达到或超过目前的铸铁冷焊法焊条。与其它铸铁焊条相比,拥有较好的综合优势,已在化工、化肥、机械行业铸铁机件的焊接中得到成功应用。     

The impact endurance of polycrystalline graphite

Repeated impact tests have been carried out on a wide range of polycrystalline graphites. Two modes of test were employed using centrally impacted rods and discs with the rods supported horizontally at their ends and the discs supported around the circumference. The resulting impact endurance curves for all the different graphites under repeated impacts of constant energy were found to have a substantially common shape in both the disc and the rod tests. The absolute levels of the endurance curves differ considerably and correlate well with other mechanical properties of graphites, in particular the strain energy density at failure in bend. Measurement of impact forces on the single impact failure of graphite rods supports this correlation by showing that the dynamic stresses generated at failure in a single impact are the same as the corresponding static 3-point bend strengths in the same test mode. Measurement of impact forces at energies less than those required to cause failure in a single impact show that the fraction of energy absorbed as specimen strain energy is dependent on specimen size and shape but is not very sensitive to impact energy. A fracture mechanics model based on incremental crack growth and previously used to interpret stress-cycling fatigue data for graphite is proposed to describe also the endurance of polycrystalline graphite under repeated impacts. The model describes available experimental data obtained under both impact and fatigue conditions. On this model, the difference between the two cyclic stressing modes is the rate of crack growth per stress cycle, this being greater under repeated impacts than under fatigue cycles of the same stress amplitude.     

Incorporation of inorganic bioceramics into electrospun scaffolds for tissue engineering applications: A review

Today, the integration of medical and engineering principles for producing biological replacements has attracted much attention. Tissue engineering is an interdisciplinary field introduced for recovery, preservation, and improvement of tissues' function. During the process of reproduction, scaffolds with the support of cells and biological materials and growth factors underlie the effective regeneration of the target tissue. Among the numerous methods, the electrospinning method has the great ability to mimic the extracellular matrix by creating a network of polymer fibers with a high surface area at the nanoscale in order to provide more binding sites for cells. Considering the capabilities and limitations of different polymers, the use of ceramics as a reinforcement phase is a promising approach. Over the past few decades, electrospun scaffolds have been developed by adding different ceramics in terms of their nature, bioinert, bioactive, and biodegradable properties. The main results are related to enhancing the mechanical properties and biological behavior of the polymeric scaffolds after the incorporation of ceramics. Enhanced hydrophilicity, antibacterial and antioxidant properties are other aspects caused by chemical interactions of ceramics and polymers. In this review, the effect of adding inorganic ceramic structures incorporated into polymeric electrospun scaffolds is discussed by highlighting the most recent studies in tissue engineering applications.     

Equilibrium Point Defect and Electronic Carrier Distributions near Interfaces in Acceptor-Doped Strontium Titanate

A mathematical model based on Frenkel's theory for charged defect segregation at interfaces is used to calculate the equilibrium grain boundary depletion layer widths and conductivity profiles in acceptor-doped SrTiO₃ ceramics. The calculations examine the effect of oxygen vacancy equilibration during annealing at moderate temperatures (∼1000 K) on the development of interfacial charge that influences grain boundary electrical properties at lower temperatures. Good agreement is demonstrated between the model predictions and experimental results reported in the literature.     

Strength Behavior of Polycrystalline Alumina Subjected to Thermal Shock

Theoretical predictions of crack propagation behavior in brittle solids under conditions of thermal shock were verified by water quenching of cylindrical polycrystalline alumina rods followed by strength testing. The calculated quenching temperature difference (Δ T _O) required to initiate thermal-stress fracture agreed fairly well with experiment. When fracture was initiated, strength decreased catastrophically, in agreement with theory. An expression for the strength remaining after thermal stress fracture was derived in terms of the pertinent physical parameters. Values of surface fracture energy similar to those reported in the literature agreed with experiment. Strength after thermal shock was predicted to be inversely proportional to the 1/4 power of the rod diameter; this prediction was supported by experimental data for two rod sizes. Over a range of quenching temperature differences Δ T Δ T ₀ strength remained constant, in agreement with the theoretical expectation that the newly formed cracks were subcritical. Only at the highest quenching temperature differences could further decreases in strength be observed; the quantitative changes, however, were masked by nonlinear deformation (evidenced by permanent crack opening). It was concluded that, although thermal shock behavior of brittle ceramics can be approximated fairly well, reliable quantitative estimates require considerably more information about strength and surface fracture energies as a function of environment, stress distribution, strain rate, and temperature and specimen size effects.     

Mechanical properties of individual phases of ZrB2-ZrC eutectic composite measured by nanoindentation

Zr-based ceramics are of interest for applications in aerospace propulsion, owing to their high hardness and stability. Application of these ceramics requires better understanding of their mechanical behavior in small scales and at elevated temperatures. Here, we prepared a ZrB₂-ZrC ceramic eutectic composite, consisting of self-assembled ZrC rods grown within a single-crystalline ZrB₂ matrix, and studied the mechanical properties of the individual eutectic phases using nanoindentation at both room and elevated-temperatures. The Vickers hardness of the eutectic composite was measured at room temperature. These data provide insight into the understanding of the mechanical behavior of the individual phases of non-oxide ceramic eutectic composites for high-temperature applications.     

Numerical simulations of bioextruded polymer scaffolds for tissue engineering applications

Scaffolds provide a temporary mechanical and vascular support for tissue regeneration while shaping the in‐growth tissues. These scaffolds must be biocompatible, biodegradable, enclose appropriate porosity, pore structure and pore distribution, and have optimal structural and vascular performance, with both surface and structural compatibility. Surface compatibility means a chemical, biological and physical suitability to the host tissue. Structural compatibility corresponds to an optimal adaptation to the mechanical behaviour of the host tissue. Recent advances in the design of tissue engineering scaffolds are increasingly relying on computer‐aided design modelling and numerical simulations. The design of optimized scaffolds based on fundamental knowledge of their macro microstructure is a relevant topic of research. This research work presents a comparison between experimental compressive data and numerical simulations of bioextruded polymer scaffolds with different pore sizes for the elastic and plastic domain. Constitutive behaviour models of cellular structures are used in numerical simulations to compare numerical data with the experimental compressive data. Vascular simulation is also used in the design process of the extrusion‐based scaffolds in order to define an optimized scaffold design. © 2013 Society of Chemical Industry     

Er对Ti(C,N)基金属陶瓷结构和力学性能的影响

了添加稀土金属Ｅｒ对Ｔｉ（Ｃ,Ｎ）基金属陶瓷结构和力学性能的影响。结果表明,加入稀土ｒ能有效地提高金属陶瓷的硬度,抗弯强度和断裂韧性。     

Rods glued in engineered hardwood products part I: Experimental results under quasi-static loading

Glued-in Rods (GiR) represent an adhesively bonded structural connection widely used in timber engineering. Up to now, common practice largely focused on softwood. Most structural adhesives have been, accordingly, specifically formulated to perform on softwood, in particular spruce. The increased use of hardwood, and corresponding engineered wood products (EWP), calls for deeper insights regarding GiR for the connection thereof. This paper, the first of a two part series, presents an overview over extensive research carried with 9 adhesives, 3 EWP, and 4 types of rods. Investigations started at component level, by fully characterising all adhesives, EWP, and rods. They were then extended to characterise the behaviour of interfaces, providing by this a methodology for selecting adhesives. Investigations at full scale followed, involving 5 different adhesives, 3 EWP, and 4 rod types. A total of 180 individual samples were tested. The results allowed to draw conclusions about the relationship between performance of GiR connections, and mechanical properties of their components. This relationship, however, has been found to be relatively weak. The companion paper will present a design methodology based on the material properties determined herein, and explain the ambiguous relationship between performance of the GiR and the mechanical properties of the adhesive, wood, and rods     

Silk fibroin/chitosan/heparin scaffold: preparation,antithrombogenicity and culture with hepatocytes

Antithrombogenicity is very important for tissue engineering scaffolds used in situations involving contact with blood. A silk fibroin/chitosan (SFCS) scaffold has been developed for liver tissue engineering with porous structure, suitable mechanical properties and biocompatibility. Because the interaction between silk fibroin and blood coagulation factors can lead to blood coagulation, the anticoagulant property of the SFCS scaffold should be improved. Heparin was added into SFCS scaffold under mild conditions. The effects of heparin on the morphology, swelling properties, structure, porosity, mechanical properties, antithrombogenicity and cytocompatibility of the SFCS scaffold were studied. SFCS scaffold containing heparin maintains the porous structure and good mechanical properties of the fibroin‐based scaffold; moreover, it is not cytotoxic. Addition of heparin leads to the SFCS scaffold being blood‐compatible and an effective heparin‐delivering system. The anticoagulant property of the SFCS scaffold can be improved by the addition of heparin, which may be helpful for scaffolds used in situations involving contact with blood. Copyright © 2009 Society of Chemical Industry     

Three-dimensional printing of triply periodic minimal surface structured scaffolds for load-bearing bone defects

The porous and cellular architecture of scaffolds plays a significant role in mechanical strength and bone regeneration during the healing of fractured bones. In this present study, triply periodic minimal surface (TPMS)-based gyroid and primitive lattice structures were used to design the cellular porous biomimetic scaffolds with different unit cell sizes (4, 5, and 6). The fused filament fabrication-based 3D printing technology was used for the fabrication of polylactic acid scaffolds. The surface morphology and mechanical compressive strength of differently structured scaffolds were observed using scanning electron microscopy and a universal testing machine. The unit cell size of 4 showed higher compressive strength in both gyroid and primitive structured scaffolds compared to unit cell sizes 5 and 6. Moreover, the gyroid structured scaffolds have higher compressive strengths as compared to primitive structured scaffolds due to the higher bonding surface area at the intercalated layers of the scaffold. Hence, the mechanical strength of scaffolds can be tailored by varying the unit cell size and cellular structures to avoid stress shielding and ensure implant safety. These TPMS-based scaffolds are promising and can be used as bone substitute materials in tissue engineering and orthopedic applications.     

Synthesis,characterization and in-vitro behavior of natural chitosan-hydroxyapatite-diopside nanocomposite scaffold for bone tissue engineering

Composite materials based on a combination of biodegradable polymers and bioactive ceramics, including chitosan and hydroxyapatite are discussed as suitable materials for scaffold fabrication. Diopside is a member of bioactive silicates; it is a good choice for hard tissue engineering because of its biocompatibility with host tissue and high mechanical strength. Chitosan and hydroxyapatite were extracted from shrimp shell and bovine bone, respectively and diopside nanoparticles were prepared by the sol-gel method. The present study reports on a chitosan composite which was reinforced by hydroxyapatite and diopside; the scaffolds were fabricated by the freeze-drying method. The so-produced chitosan-hydroxyapatite-diopside (CS-HA-DP) scaffolds were further cross-linked using tripolyphosphate (TPP) to achieve enhanced mechanical strength. The ratios of the ceramic components in composites were 5-58-37, 10-55-35, and 15-52-33 (diopside-hydroxyapatite-chitosan, w/w %). The physicochemical properties of scaffolds were investigated using Fourier-transform infrared spectrometry (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) techniques. The effect of scaffolds composition on bioactivity and biodegradability were studied well. To investigate mechanical properties of samples, compression test was done. Results showed that the composite scaffold with 5% DP has the highest mechanical strength. The porosity of composites dropped from 92% to 76% by increasing the amount of DP. Cytocompatibility of the scaffolds was assessed by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, alkaline phosphatase (ALP) activity, and cell attachment studies using human osteoblast cells. Results demonstrated no sign of toxicity and cells were found to be attached to the pore walls within the scaffolds; moreover, results illustrated that the developed composite scaffolds could be a potential candidate for tissue engineering.     

Modelling the anisotropic thermal conductivity of 3D logpile structures

Assessing and predicting the thermal conductivity (κ) of macroporous materials is particularly important for additive manufactured 3D structures, as they offer considerable potential for tuning architectures and properties. In this work, finite element methods (FEM) are used to simulate the transient plane source test in 3D logpile lattices, approaching the effect of interfacial thermal contact resistances on κ measurement. Besides, the influence of different geometrical parameters (rod diameter, macropore size and overlapping between rods in consecutive layers) and the κ of the strut material on the anisotropic thermal conductivity of 3D lattices are investigated. The models are validated using experimental data for 3D composite structures of γ-Al₂O₃ with graphene nanoplatelet contents up to 18 vol%, as well as with reported data for alike scaffolds, all printed by robocasting. Results have strong impact for the application of novel 3D structures in energy production and storage, catalysis and heat transfer-related fields.     

Multiscale Modeling for Predicting the Mechanical Properties of Silicon Carbide Ceramics

Silicon carbide (SiC) is one of the advanced ceramics, which is widely used in industries due to its excellent mechanical properties. Understanding the relations between its microstructure and the mechanical properties is critical to adopting SiC ceramics in different applications. In this paper, a multiscale model incorporating a cohesive zone model is proposed to predict the mechanical properties of SiC ceramics. Interatomic potentials are developed using ab initio calculation to more accurately calculate the SiC behaviors in molecular dynamics modeling. The proposed multiscale model is used to predict the mechanical properties of SiC ceramics and their relations with the grain size distribution in the finite element framework. A good agreement is found between prediction results and experimental measurements. Successfully predicting its mechanical behaviors could help selection of parameters during processing of SiC ceramics under different conditions.     

Phase mixture modeling of the grain size dependence of Young’s modulus and thermal conductivity of alumina and zirconia ceramics

The grain size dependence of Young’s modulus and thermal conductivity of alumina and zirconia ceramics is predicted via phase mixture modeling, using both analytical and numerical approaches. Using typical values for the thickness and properties of the grain boundaries, the equivalent volume fraction of “grain boundary phase” is calculated for a given grain shape. Based on this volume fraction estimate and a rough estimate of the grain boundary properties, the effective properties of the polycrystalline materials are calculated and compared in terms of volume-equivalent sphere diameters. For grains of cubic and tetrakaidecahedral shape excellent agreement is found between numerical calculations and analytical predictions based on the lower Hashin-Shtrikman bound. The grain size dependence is extremely weak for Young’s modulus, but can be more significant for thermal conductivity, especially when the intrinsic conductivity of the material is high. The predictions are compared to literature data.     

The influence of specimen size and mode of loading on the fracture of graphite

Predictions of graphite strength under tensile and bending loads using fracture mechanics have been compared with experimental data and the currently used Weibull method. The methods are comparable for similar specimens but Weibull's method fails to predict the observed effects for large specimen size differences. Discussion of this failure indicates that the basis of Weibull's theory (a volumetric flaw distribution) may be inapplicable to failure of materials resulting from surface defects. Examination of graphite rods has shown a defect size distribution across the material which leads to prediction of lower strengths for the inner rod regions with respect to the outer regions. Experimental results follow the predicted trend but it is considered that further examination of the fracture mechanics technique must be undertaken before it can be recommended as a design method for graphite materials.     

Ceramics for medical applications: A picture for the next 20 years

High-tech ceramics have always been associated to medical devices: they are used today as femoral heads and acetabular cups for total hip replacement, dental implants and restorations, bone fillers and scaffolds for tissue engineering. Here, we describe their current clinical use and propose a picture of their evolutions for the next 20 years. The need for tough, strong and stable bioinert ceramics should be met by either nano-structured, alumina and zirconia based ceramics and composites or by non-oxide ceramics. Nano-structured calcium phosphate ceramics and porous bioactive glasses, possibly combined with an organic phase should present the desired properties for bone substitution and tissue engineering. The position of ceramics in a gradual medical approach, from tissue regeneration to conventional implants, is discussed.