Young’s modulus of cast HMS 2112-C f composite—prediction and ultrasonic evaluation

Various models for the prediction of strengthening mechanism of metal matrix composites (MMCs) containing either fibres or particulates are analysed. Assuming that the matrix strengthening by dislocations could be treated as equivalent to the effect of different volume fraction of dispersoids, as well as by considering the effect of morphology of reinforcement on the Young’s modulus, an expression for Young’s modulus for MMCs has been derived. The Young’s modulus values thus predicted, using this model, have been validated by ultrasonically-derived values of Young’s modulus of an Al-alloy matrix composite containing 5, 8 and 12 wt% chopped carbon fibre (C _f) dispersoids, in as cast and extruded conditions. Further, the theoretically- and ultrasonically-derived Young’s modulus of cast Al-alloy-C _f composites with 5 and 8 wt%C _f have been found to be comparable with the reported values of Young’s modulus for these weight fractions.     

Silicon carbide (NicalonTM) fibre-reinforced borosilicate glass composites: mechanical properties

The objective of this study was to assess the applicability of an extrinsic carbon coating to tailor the interface in a unidirectional NicalonTM–borosilicate glass composite for maximum strength. Three unidirectional NicalonTM fibre-reinforced borosilicate glass composites were fabricated with different interfaces by using (1) uncoated (2) 25 nm thick carbon-coated and (3) 140 nm thick carbon coated Nicalon fibres. The tensile behaviours of the three systems differed significantly. Damage developments during tensile loading were recorded by a replica technique. Fibre–matrix interfacial frictional stresses were measured. A shear lag model was used to quantitatively relate the interfacial properties, damage and elastic modulus. Tensile specimen design was varied to obtain desirable failure mode. Tensile strengths of NicalonTM fibres in all three types of composites were measured by the fracture mirror method. Weibull analysis of the fibre strength data was performed. Fibre strength data obtained from the fracture mirror method were compared with strength data obtained by single fibre tensile testing of as-received fibres and fibres extracted from the composites. The fibre strength data were used in various composite strength models to predict strengths. Nicalon–borosilicate glass composites with ultimate tensile strength values as high as 585 MPa were produced using extrinsic carbon coatings on the fibres. Fibre strength measurements indicated fibre strength degradation during processing. Fracture mirror analysis gave higher fibre strengths than extracted single fibre tensile testing for all three types of composites. The fibre bundle model gave reasonable composite ultimate tensile strength predictions using fracture mirror based fibre strength data. Characterization and analysis suggest that the full reinforcing potential of the fibres was not realized and the composite strength can be further increased by optimizing the fibre coating thickness and processing parameters. The use of microcrack density measurements, indentation–frictional stress measurements and shear lag modelling have been demonstrated for assessing whether the full reinforcing and toughening potential of the fibres has been realized. This revised version was published online in November 2006 with corrections to the Cover Date.     

Effect of microstructure on the modulus of PAN-based carbon fibers during high temperature treatment and hot stretching graphitization

The changes of microstructure and Young’s modulus of PAN-based carbon fibers during the high temperature treatment (2400–3000 °C, stretching 0%) and hot stretching graphitization (0–5%, 2400 °C) were compared. It was observed that although the Young’s modulus of the fibers could be increased by the two graphitization techniques, the microstructure parameters determined by X-ray diffraction were different for the same value of modulus. The relationship between microstructure and modulus showed that Young’s modulus not only depended on the preferred orientation, but also related to the crystallite size (L _c and L _a ) and shape (L _a /L _c ). On the other hand, it was found that crystallite size of the fibers was mainly affected by heat treatment temperature and the crystallite shape could be altered by hot stretching graphitization. Further investigation indicated that the fibers were composed of turbostratic carbon structure even after heat treated to 3000 °C, which could be detected from the absence of 101 and 112 peaks in X-ray diffraction pattern, and the interlayer spacing (d₀₀₂) and preferred orientation (Z) were only 0.3430 nm and 14.71°, respectively.     

Tensile strength of windmill palm (Trachycarpus fortunei) fiber bundles and its structural implications

Trachycarpus fortunei (windmill palm) is one of the most widely distributed and widely used palms in East Asia. In order to find further uses for the palm’s fibers, however, more information on their mechanical and anatomical properties is needed. With this in mind, tensile strength and Young’s modulus of windmill palm fiber bundles were investigated and the structural implications considered. The anatomical features in cross-section, the fracture mode, and the microfibril angle (MFA) of natural fiber bundles were determined. The transverse sectional area occupied by fibers in a fiber bundles (S _F) contributes to mechanical strength in practice. It was found that the ratio of S _F to the transverse sectional area of a fiber bundle dramatically increases with a decrease in bundle diameter. Therefore, tensile strength and Young’s modulus of an individual fiber bundle in this species increase in parallel with a decrease in fiber bundle diameter. The observed MFA features might have a relationship with the biomechanical movements of fiber bundles in the windmill palm. The potential uses of windmill palm fibers have been discussed.     

Preparation and characterization of aluminium alloy sheet Aramid fibre-laminated composites

Laminated composites consisting of alternate layers of aluminium alloy sheets and unidirectional Kevlar-49 fibre epoxy composites were prepared using two different aluminium alloys DTD 687 and aluminium-lithium alloy. Tensile, compressive and interlaminar shear strengths of the laminates were measured. The residual stresses in the aluminium alloy sheets arising out of thermal mismatch between aluminium alloys and aramid fibres were also measured. It is found that the laminates have lower density, higher tensile strength and marginally lower Young’s modulus as compared with monolithic alloy sheets.     

复合材料疲劳寿命预测

在疲劳载荷作用下,复合材料的弹性模量会随着载荷循环数的增加而不断下降,而材料中的内部损伤则不断增大。为此,本文提出复合材料的疲劳模量和累积应变的概念,并由此定义出三种预测复合材料疲劳寿命的疲劳损伤模型。文中应用这三种模型对单应力水平和多应力水平下的玻璃纤维增强环氧树脂复合材料的疲劳寿命进行了估算,并同实验结果进行了比较。     

A Stiffness Degradation Based Fatigue Damage Model for FRP Composites of (0/<Emphasis Type="BoldItalic">θ</Emphasis>) Laminate Systems

The present study develops a stiffness reduction—based model to characterize fatigue damage in unidirectional 0˚ and θ° plies and (0/θ) laminates of fiber-reinforced polymer (FRP) composites. The proposed damage model was constructed based on (i) cracking mechanism and damage progress in matrix (Region I), matrix-fiber interface (Region II) and fiber (Region III) and (ii) corresponding stiffness reduction of unidirectional composite laminates as the number of cycles progresses. The proposed model enabled damage assessment of FRP (0/θ) composite laminates by integrating the fatigue damage values of 0˚ and θ° plies. A weighting factor η was introduced to partition the efficiency of load carrying plies of 0° and θ° in the (0/θ) composite lamina. The fatigue damage curves of unidirectional FRP composite samples with off-axis angles of 0˚, 30˚, 45˚, and 90˚ and composite laminate systems of (0˚/30˚), (0˚/45˚) and (0˚/90˚) predicted based on the proposed damage model were found in good agreement with experimental data reported at various cyclic stress levels and stress ratios in the literature.     

Effect of acid and TETA modification on mechanical properties of MWCNTs/epoxy composites

Acid treatment and triethylene-tetramine (TETA) modification of multi-walled carbon nanotubes (MWCNTs) purposing to attain better dispersibility and stronger interfacial bonding between MWCNTs and epoxy matrix have been carried out in this paper. The epoxy and MWCNTs/epoxy composites were produced by cast molding method. Stress–strain curves show that TETA-MWCNTs/epoxy hold the greatest toughness of all samples with 0.5 wt.% nanoparticles. The Young’s modulus of TETA-MWCNTs/epoxy has a significant increase about 38% compared to the neat epoxy, while the Young’s modulus of unmodified MWCNTs/epoxy or acid-modified MWCNTs/epoxy has a bit of decrease. Tensile and impact strength tests reflect that TETA-MWCNTs reinforced epoxy composites have an obvious improvement of tensile strength about 30% and an enhancement of impact strength over 34% compared to the pure epoxy composites with only 0.5 wt.% loading of TETA-MWCNTs. Scanning electron microscopy images of fractured surface of MWCNTs/epoxy indicate homogeneous dispersibility of TETA-MWCNTs and strong interfacial adhesion between the TETA-MWCNTs and the epoxy in the MWCNTs/epoxy composite.     

Gd–Ni–Al bulk glasses with great glass-forming ability and better mechanical properties

A series of Gd–Ni–Al ternary glassy alloys with the maximum diameter of 4 mm were obtained by common copper mold casting. The maximum values of the reduce glass transformation temperature (T _g/T _m) and the distance of supercooling region ΔT _x of these alloys in this study were 0.648 and 50 K, respectively. The compressive fracture strength (σ _f) and Young’s modulus (E) of Gd–Ni–Al glassy alloys were 1,240–1,330 MPa and 63–67 GPa, respectively. The magnetic properties of these BMGs were investigated. The Gd–Ni–Al bulk glassy alloys with great glass forming ability and good mechanical properties are promising for the future development as a new type of function materials.     

Initiation of fatigue cracks near inclusions in elastoplastic materials

We propose a new approach to calculating the period of crack initiation in the neighborhood of elastic inclusions in elastoplastic materials. We have established the factors determining the intensity of fatigue of a material in the neighborhood of an inclusion. These factors are: load amplitude and ratio; geometry of the inclusion surface and its relative rigidity; Young’s modulus, yield point, and ultimate strength of the matrix material; parameters of cyclic strengthening or softening of the material and its ultimate strain. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 6, pp. 12–17, November–December, 2008.     

Mechanical properties of very thin cover slip glass disk

The biaxial flexural strength, Young’s modulus, Vicker’s microhardness and fracture toughness data for very thin, commercial, soda-lime-silica cover slip glass (diameter, D-18 mm, thickness, T-0.3 mm; T/D ≈ 0.02) are reported here. The ball on ring biaxial flexure tests were conducted at room temperature as a function of the support ring diameter (≈ 10–20 mm) and cross head speed (0.1–10 mm min⁻¹). In addition, the Weibull modulus data were also determined. The Young’s modulus data was measured using a linear variable differential transformer (LVDT) from biaxial flexure tests and was checked out to be comparable to the data obtained independently from the ultrasonic time of flight measurement using a 15 MHz transducer. The microhardness data was obtained for the applied load range of 0.1–20 N. The fracture toughnessK _IC data was obtained by the indentation technique at an applied load of 20 N.     

Measurement of the dynamic Young’s modulus of porous titanium and Ti6Al4V

The dynamic Young’s modulus of porous titanium and Ti6Al4V with various porosities was measured using the electromagnetic acoustic resonance method. The dependence of Young’s modulus (E) on the porosity (P) has been analysed in detail based on Phani–Niyogi relation and Pabst–Gregorová relation . We find that both Phani–Niyogi relation and Pabst–Gregorová relation with fixed material constant n = 2 or a = 1 but varying P _C can correctly account for the dependence of Young’s modulus on the porosity for porous titanium and Ti6Al4V.     

Influence of free water content on the compressive mechanical behaviour of cement mortar under high strain rate

The effect of free water content upon the compressive mechanical behaviour of cement mortar under high loading rate was studied. The uniaxial rapid compressive loading testing of a total of 30 specimens, nominally 37 mm in diameter and 18.5 mm in height, with five different saturations (0%, 25%, 50%, 75% and 100%, respectively) were executed in this paper. The technique ‘Split Hopkinson pressure bar’ (SHPB) was used. The impact velocity was 10 m/s with the corresponding strain rate as 10²/s. Water-cement ratio of 0.5 was used. The compressive behaviour of the materials was measured in terms of the maximum stress, Young’s modulus, critical strain at maximum stress and ultimate strain at failure. The data obtained from test indicates that the similarity exists in the shape of strain–stress curves of cement mortars with different water content, the upward section of the stress–strain curve shows bilinear characteristics, while the descending stage (softening state) is almost linear. The dynamic compressive strength of cement mortar increased with the decreasing of water content, the dynamic compressive strength of the saturated specimens was 23% lower than that of the totally dry specimens. With an increase in water content, the Young’s modulus first increases and then decreases, the Young’s modulus of the saturated specimens was 23% lower than that of the totally dry specimens. No significant changes occurred in the critical and ultimate strain value as the water content is changed.     

Influence of temperature gradient and growth rate on the mechanical properties of directionally solidified Sn–3.5 wt% Ag eutectic solder

The Sn–3.5 wt% Ag eutectic alloy was directionally solidified upward with a constant growth rate (V = 16.5 μm/s) at different temperature gradients (G = 1.43–4.28 K/mm) and with a constant temperature gradient (G = 3.93 K/mm) at different growth rates (V = 8.3–500 μm/s) in a Bridgman-type directional solidification furnace. The rod spacings (longitudinal section, λ _L and transverse section, λ _T ) and mechanical properties (microhardness, HV and ultimate tensile strength, σ _UTS ) of Sn–3.5 wt% Ag eutectic alloy were measured. The dependency of the microhardness, ultimate tensile strength on the temperature gradient, growth rate and rod spacings were determined. According to experimental results, the microhardness and ultimate tensile strength of the solidified samples increase with increasing G and V, but decrease with the increasing the rod spacing.     

Young’s modulus evolution at high temperature of SiC refractory castables

The evolution of Young’s modulus versus temperature has been evaluated in SiC-based hydraulically bonded refractories used in waste-to-energy (WTE) plants. Two types of low cement castables (LCC) with 60 and 85 wt% of SiC aggregates have been considered. The study was conducted by the way of a high temperature ultrasonic pulse-echo technique which allowed in situ measurement of Young’s modulus during heat treatment starting from the as-cured state up to 1400 °C in air or in neutral atmosphere (Ar) and during thermal cycles at intermediate temperatures (1000 and 1200 °C). For comparison in order to facilitate interpretation, thermal expansion has also been followed by dilatometry performed in the same conditions. Results are discussed in correlation with phase transformations occurring in the oxide matrix (dehydration at low temperature, crystallization of phases in the CaO–Al₂O₃–SiO₂ system) above 800 °C and damage occurring when cooling. The influence of oxidation of SiC aggregates on elastic properties is also discussed.     

Weibull modulus of nano-hardness and elastic modulus of hydroxyapatite coating

Here we report the microstructural dependence of nano-hardness (H) and elastic modulus (E) of microplasma sprayed (MIPS) 230 μm thick highly porous, heterogeneous hydroxyapatite (HAP) coating on SS316L. The nano-hardness and Young’s modulus data were measured on polished plan section (PS) of the coating by the nanoindentation technique with a Berkovich indenter. The characteristic values of nano-hardness and Young’s modulus were calculated through the application of Weibull statistics. Both nano-hardness and the Young’s modulus data showed an apparent indentation size effect. In addition, there was an increasing trend of Weibull moduli values for both the nano-hardness and the Young’s modulus data of the MIPS-HAP coating as the indentation load was enhanced from 10 to 1,000 mN. An attempt was made in the present work, to provide a qualitative model that can explain such behavior.     

Effects of strain rate on the mechanical properties of tricalcium phosphate/poly(l-lactide) composites

Bioactive ceramic/bioresorbable plastic composites have been expected as materials for the bone fracture fixations which have more biocompatibility than monolithic bioresorbable plastics. Many studies have been conducted on these materials. Most studies, however, focused on the mechanical properties under static loading. In the actual usage, these materials are loaded dynamically. In this study, effects of strain rate on the mechanical properties of tricalcium phosphate/poly(l-lactide) (TCP/PLLA) composites were investigated experimentally and analytically. The TCP/PLLA composites containing three different TCP contents (5, 10 and 15 wt.%) were prepared by injection molding. In order to characterize the mechanical properties, tensile and compressive tests were conducted. The results of tensile tests indicated that the Young’s moduli of composites increased with increasing TCP contents. For each TCP contents, tensile Young’s modulus kept constant up to strain rate of 10⁻¹/s. On the other hand, tensile strength increased with increasing strain rate. The effect of strain rate became larger with decreasing TCP contents, which means the strain rate dependency of the PLLA is more effective than that of TCP. From the results of compressive tests, similar results with tensile tests were obtained. That is, compressive Young’s modulus kept constant up to strain rate of 10⁻¹/s and the 0.2% proof stress increased with increasing strain rate. In order to predict the mechanical behavior of TCP/PLLA composites, the micro-damage mechanics was proposed. In this analysis, 3-phases particle reinforced composites, which include the intact particles, damaged particles and matrix, are assumed. The elastic constants are calculated with micromechanics based on the analyses by Eshelby and Mori and Tanaka. Only the debonding between particle and matrix are assumed as the damage. The nonlinearity in the stress-strain behavior of matrix PLLA is also considered. The debonding particles are assumed as voids. Void formation is calculated based on the energy criterion. The energy release rate associated with void formation was estimated by fitting the analytical results with the experimental results of the composites with 15 wt.% TCP contents for each strain rate. Then the analytical results for the composites with 5 and 10 wt.% TCP contents were compared with the experimental results. The analytical tensile stress-strain curves are in good agreement with experimental results. It is also clarified that the energy release rate associated with void formation increased with increasing strain rate.     

Structure and properties of ultrafine silk fibers produced by <Emphasis Type="Italic">Theriodopteryx ephemeraeformis</Emphasis>

Theriodopteryx ephemeraeformis commonly known as bag worms produce ultrafine silk fibers that are remarkably different than the common domesticated (Bombyx mori) and wild (Saturniidae) silk fibers. Bag worms are considered as pests and commonly infect trees and shrubs. Although it has been known that the cocoons (bags) produced by bag worms are composed of silk, the structure and properties of the silk fibers in the bag worm cocoons have not been studied. In this research, the composition, morphology, physical structure, thermal stability, and tensile properties of silk fibers produced by bag worms were studied. Bag worm silk fibers have considerably different amino acid contents from those of the common silks. The physical structure of the bag worm silk fibers is also considerably different compared with B. mori and common wild silk fibers. Bag worm’s silk fibers have lower tensile strength (3.2 g/denier) and Young’s modulus (45 g/denier) but similar breaking elongation (15.3%) compared with B. mori silk. However, the tensile strength and Young’s modulus of bag worm fibers are similar to those of the common Saturniidae wild silk fibers. Bag worm silk fibers could be useful for some of the applications currently using the B. mori and wild silk fibers.     

Tensile properties and thermal expansion of discontinuously reinforced aluminium composites at subambient temperatures

The effects of temperature on the mechanical properties and thermal expansion of two discontinuously reinforced aluminium composites have been determined over the range 300–100 K. Silicon carbide particulate-reinforced 2009 and 6092 aluminium alloys were studied by tensile testing, in which both longitudinal and transverse strains were recorded, and by thermal expansion measurements. The test results clearly show that cooling to 100 K induces plastic flow in the aluminium alloy matrices due to the thermal expansion difference between aluminium and silicon carbide. At very low temperatures, the linear region of the stress-strain curve is greatly reduced or eliminated and the Poisson’s ratio, ν, increases. For the higher yield strength 2009 matrix composite, ν increases from a room-temperature value of 0.28 to 0.35 at 100 K. For the lower-strength 6029 matrix composite, ν increases from a room-temperature value of 0.33 to a value of 0.5 at 100 K. A Poisson’s ratio of 0.5 is the value characteristic of plastic flow in an incompressable material. Changes in yield strength, Young’s modulus and thermal expansion with decreasing temperature are also consistent with thermally induced plastic flow in the composite matrix. This revised version was published online in November 2006 with corrections to the Cover Date.     

Elastic characteristics of iron-glass materials at low temperatures

We present the results of an investigation of the influence of low temperatures on the elastic characteristics of iron-glass materials with 3, 5, 12, or 20 wt.% of glass at 77–300 K and show that Young’s modulus exponentially decreases as the glass content of the material increases. We suggest a relation for the evaluation of the Young’s modulus of a composite at various temperatures according to its value at room temperature. Institute for Problems of Strength, National Academy of Sciences of Ukraine, Kiev, Ukraine. Translated from Problemy Prochnosti, No. 1, pp. 42 – 46, January – February, 1998.