Mechanical properties of thin and thick coatings applied to various substrates. Part II. Young's modulus determination of coating materials*

To determine Young's modulus of coating materials when they are applied to substrates, theoretical and experimental analyses are performed. Significant residual stresses are generated within thin and thick coatings applied to substrates. As a result of these stresses, the bi-material strip assumes a certain curvature. The curved beam theory was used to establish the equivalent bending stiffness of bi-layer materials as functions of (a) the initial radius of curvature generated by residual stresses, (b) the mechanical radius of curvature during flexure testing, and (c) mechanical (Young's moduli) and geometrical (widths and thicknesses) characteristics of bi-layered systems. The relevant expression was transformed to a second- or third-order equation in order to calculate Young's modulus of the coating undergoing residual stresses (using models developed in Part I and by Stoney, Röll, and Inoue).     

On the elastic constants of amorphous carbon nitride

Elastic and thermomechanical properties of amorphous carbon nitrite thin films as a function of nitrogen concentration are reported. The films were prepared by ion beam assisted deposition with nitrogen concentrations ranging from 0 to 33 at.%. By using a combination of the thermally induced bending technique and nano-indentation measurements it was possible to calculate independent values for the Young's modulus, the Poisson's ratio, as well as the thermal expansion coefficient of the films. The hardness and elastic recovery are discussed in terms of the Young's modulus and the Poisson's ratio.     

Tensile behaviour of magnesia carbon refractories

The determination of the Young's modulus and the tensile strength of heterogeneous refractories are the subjects of this paper. Great differences have been observed for a similar material according to both the usual tests performed and the interpretation proposed to define these properties. The causes of the discrepancies of the Young's modulus under compression and tensile loading are examined in detail. Then, it is shown that (i) the accuracy measurement of the deflexion in the bend test with a particular device and (ii) the integration of the shearing distorsion in the calculation of the deflexion by the classical beam theory, allow for finding the appropriate value of the Young's modulus. The classical definition of the modulus of rupture (M.O.R.) is also examined. Considering a nonlinear behaviour of the refractory, it is shown by finite element analysis of the beam, that the M.O.R. overestimates the tensile strength.     

Preparation and properties of LixLa0.5TiO3 perovskite oxide electrolytes

Solid electrolytes with high lithium ionic conductivity and outstanding mechanical stability are essential for all solid‐state lithium ion batteries. Perovskite Li_xLa_0.5TiO₃ is one of the most promising as solid electrolytes candidates. Li_xLa_0.5TiO₃ with various initial Li₂O (0.5≤x≤0.569) is synthesized by traditional solid‐state reaction at high temperatures. The crystal structure is not remarkably affected by the Li₂O quantity, yet higher porosity is obtained as a result of excess Li₂O. The Young's modulus, hardness, and fracture toughness are evaluated with indentation method. The Young's modulus increases from 72 to 148 GPa with increasing Li₂O, which means that a small variation of Li quantity in Li_xLa_0.5TiO₃ results in over a 100% change in Young's modulus. However, the fracture toughness exhibits an opposite trend with that of the Young's modulus. The high Young's modulus and fracture toughness could guarantee the structural integrity during cycle operations.     

Regeneration efficiency of composites containing two‐sized capillaries

The aim of this work is to develop a composite material containing a regeneration system and to demonstrate its self‐healing properties. For this purpose, we will study the self‐healing behavior of composites that are fabricated with a regeneration system consisting of two‐sized capillaries filled with epoxy resin and hardener. Composites with restorative systems containing identical microtube diameters can be found in the literature, but until now no comparative studies with multiple diameter structures have been published. We will prove that a regeneration system containing two types of capillaries with diameters of 100 and 50 μm is more efficient (68% recovery of bending strength and Young's modulus after third regeneration) than a regeneration system containing capillaries with the same diameter (44% recovery of bending strength and 44% recovery of Young's modulus after third regeneration). POLYM. COMPOS. 37:1223–1230, 2016. © 2014 Society of Plastics Engineers     

Predictions of young's modulus of inorganic fibrous particulate‐reinforced polymer composites

In this study, the factors affecting the Young's modulus of inorganic fibrous particulate‐reinforced polymer composites were analyzed, and a new expression of the Young's modulus was derived and was based on a simplified mechanical model. This equation was used to estimate the composite Young's modulus. The estimated relative Young's modulus increased nonlinearly with increasing filler volume fraction. Finally, we verified the equation preliminarily by quoting the measured Young's modulus values of poly(butylene terephthalate)/wollastonite, polypropylene/wollastonite, and nylon 6/wollastonite composites reported in the literature. Good agreement was shown between the predictions and the experimental data of the relative Young's modulus values for these three composite systems. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 2957–2961, 2013     

Structure and mechanical properties of isotactic polypropylene and iPP/talc blends functionalized by electron beam irradiation

The structure and mechanical properties of isotactic polypropylene (iPP) functionalized by electron beam irradiation are investigated by differential scanning calorimetry, wide‐angle X‐ray diffraction, thermogravimetry, thermomechanical analysis, melt index and mechanical measurements. The experimental results show that the degree of crystallinity, the thermal degradation temperature and the dimensional stability increase with dose in the range 0–5 kGy. At 5 kGy, the initial and final degradation temperatures of the irradiated iPP are raised by 66 °C and 124 °C, respectively. The melt index increases with increasing dose. The mechanical measurements show that the stiffness of iPP is greatly enhanced by electron beam irradiation. A small dose of irradiation (0.75 kGy) can increase the Young's modulus to 1284 MPa compared with 1112 MPa for unirradiated iPP. Adding 10 % by weight of irradiated iPP powder into iPP/talc (70/20 % by weight) blends, changes the processing parameters significantly and makes the Young's modulus rise substantially. At a dose of 40 kGy the Young's modulus of iPP/talc blend jumps to 3611 MPa against the original 2201 MPa. © 2000 Society of Chemical Industry     

Study on the Viscoelastic Poisson‘s Ratio of Solid Propellants Using Digital Image Correlation Method

Digital image correlation methods were used for further studies of the viscoelastic Poisson's ratio of solid propellants. The Poisson's ratio and the Young's relaxation modulus of solid propellants were separately determined in a single stress relaxation test. In addition, the effects of temperature, longitudinal strain, preload and storage time on the Poisson's ratio of solid propellants were discussed. The Poisson's ratio master curve and the Young's relaxation modulus master curve were constructed based on the time‐temperature equivalence principle. The obtained results showed that the Poisson's ratio of solid propellants is a monotone non‐decreasing function of time, the instantaneous Poisson's ratio increased from 0.3899 to 0.4858 and the time of the equilibrium Poisson's ratio occurred late when the temperature was varied from −30 °C to 70 °C. The Poisson's ratio increased with temperature and longitudinal strain, decreased with preload and storage time, while the amplitude Poisson's ratio increased with preload, decreases with longitudinal strain and storage time. The time of the equilibrium Poisson's ratio occurred in advance with the increase of longitudinal strain, preload and storage time.     

Relationship between Young's modulus and temperature in porcelain tiles

A focused research was conducted on samples prepared from an industrial porcelain tile composition containing quartz, used to produce ceramic floor tiles, with the aim of evaluating the variation of fired specimens’ Young's modulus with temperature. These samples were fired in controlled laboratory conditions so that specimens with pre-existing cracks were obtained and subject to non-destructive in situ thermo-mechanical measurements (impulse excitation technique) in the 22–700 °C temperature range during heating and cooling processes in order to find evidences to explain the hysteresis phenomenon in the Young's modulus versus temperature curve. The observed irreversible Young's modulus may be directly related to the pre-existent cracks that on heating and cooling are closed and opened up respectively, changing thus the Young's modulus which is well characterized by a hysteresis cycle.     

Mechanical properties of individual fiber segments of electrospun lignocellulose‐reinforced poly(vinyl alcohol)

The influence of lignocellulosic nanofibers (LCNF) additive on the inherent mechanical properties of submicron electrospun poly(vinyl alcohol) (PVA) fibers is reported. LCNF with a diameter of 25 ± 15 nm and a length of 220 ± 90 nm obtained from hemp shives were dispersed in aqueous PVA solutions to produce homogeneous nanocomposite fibers with 0, 5, and 10 w/w % LCNF loads in solid PVA. Tensile tests on mats show that LCNF additive causes up to sevenfold increase in stiffness and significant decrease in elongation at yield. AFM‐based 3‐point bending tests on single LCNF‐doped fibers reveal up to 11.4 GPa Young's modulus in the diameter range of 300 to 500 nm, indicating a 2.4 times increase compared to neat PVA fibers. Mechanical properties of both neat and LCNF‐doped PVA fibers are found to be strongly size‐dependent at lower fiber diameters, with Young's modulus values exceeding 100 GPa at below 100 nm diameters. The results can be explained by extensive restructuration of hydrogen bonding network due to the LCNF additive. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44361.     

Thermomechanical properties of Y-substituted SrTiO3 used as re-oxidation stable anode substrate material

Re-oxidation robustness is important to warrant a reliable operation of anode-supported solid oxide fuel cell systems. The current work concentrates on the mechanical properties of re-oxidation stable Y-substituted SrTiO₃ ceramic for the use as anode substrate material. Room temperature micro-indentation yielded Young's modulus and hardness of 160 and 7 GPa, respectively, whereas the temperature-dependent modulus was measured with a resonance-based method up to ∼950 °C. The effective Young's modulus as a function of porosity was measured at room temperature and compared with fracture strength data. The fracture toughness was assessed using a combination of pre-indentation cracks and bending test. Creep rates were measured at 800 and 900 °C in a 3-point bending configuration. Post-test fractographic analysis performed using stereo, confocal and scanning electron microscopy, revealed important information on fracture origins and critical defects in the material. A methodology to assess the mechanical properties of porous materials is suggested.     

Grafting of telechelic poly(lactic‐co‐glycolic acid) onto O2 plasma‐treated polypropylene flakes

An operating window, which is bounded by two temperatures and draw ratios, defines the stable and defect‐free stretching region of a polymer film. Physical properties including the coefficient of thermal expansion (CTE), birefringence, and Young's modulus of a recyclable polyimide (PIR) film were measured under stretching conditions. While values of birefringence and Young's modulus increased with increasing stretching stress in the machine direction, the CTE was found to decrease. A semiempirical model for the prediction of birefringence and Young's modulus under stretching conditions was developed, from which the CTE could be estimated from the Young's modulus data. Theoretically evaluated physical properties were found to be in qualitative agreement with the experimental data. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Development of simplified Tandon‐Weng solutions of Mori‐Tanaka theory for Young's modulus of polymer nanocomposites considering the interphase

The known Tandon‐Weng model originated from Mori–Tanaka theory commonly underestimates the Young's modulus of polymer nanocomposites containing spherical nanofillers. This phenomenon is attributed to disregarding the nanoscale interfacial interaction between polymer and nanoparticles, which forms a different phase as interphase in polymer nanocomposites. In this paper, the simplified Tandon‐Weng model is developed assuming interphase and the predictions of the developed model are compared with the experimental data. The calculations of the developed model completely agree with the experimental results at reasonable levels of interphase properties. Additionally, the effects of main material and interphase properties on the predictions of modulus are evaluated. The developed model predicts that a high‐content, thick, and strong interphase creates a high modulus in polymer nanocomposites. These logical observations demonstrate the correctness of the developed model for Young's modulus of polymer nanocomposites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43816.     

Young's Modulus of Elasticity of Carbon‐Bonded Alumina Materials up to 1450°C

Investigating Young's modulus at elevated temperatures supports the understanding of microstructural changes as a function of application temperature. A sintered alumina and three carbon‐bonded alumina materials with carbon contents of 20 and 30 wt% and alumina grain size of 0.6–3 mm were investigated. Young's modulus was measured in a temperature range from 25°C to 1450°C by the impulse excitation technique. The Young's modulus of carbon‐bonded materials increases up to 140% at 1450°C. After one cycle, a decrease of the Young's modulus up to 50% is registered at room temperature. There is a strong hysteresis behavior during one cycle. Thermal expansion measurements show highest expansion for the highest graphite content material. The expansion of alumina grains and graphite flakes, resulting in microcrack generation during cooling and microcrack healing during heating, is reflected in the registered values of the Young's modulus as a function of the temperature. It is assumed, that higher graphite amounts as well as coarse grains lead to lower sintering effects of the microstructure at elevated temperatures and as a result lower values of the Young's modulus have been registered.     

Bending and breaking fibers in sheared suspensions

An experimental study was made of single fibers rotating and bending in Couette flow of a Newtonian liquid. A previous result for critical fiber buckling was re-tested and found satisfactory, and the transition between ‘springy’ and ‘snake’ rotation was delineated. The minimum radius, of curvature achieved during rotation in the “snake orbit” regime was measured as a function of fiber aspect ratio, Young's modulus, and fluid shear stress. Two correlations are presented which are constrained to satisfy limiting conditions for very stiff and very flexible fibers. Together with a result from thin rod theory, these correlations may be used to predict breaking conditions for fibers of known Young's modulus and ultimate tensile strength. Predictions are tested in experiments where two types of glass fiber are broken in suspension and found satisfactory. Results show that several reinforcing materials will probably break within the range of conditions covered by our experiments, or in a region which can be treated by extrapolation from our results.     

Three-dimensional finite element analysis of stress response in adhesive butt joints subjected to impact bending moments

The stress wave propagation and the stress distribution in adhesive butt joints of T-shaped similar adherends subjected to impact bending moments are calculated using a three-dimensional finite-element method (FEM). An impact bending moment is applied to a joint by dropping a weight. The FEM code employed is DYNA3D. The effects of the Young's modulus of adherends, the adhesive thickness, and the web length of T-shaped adherends on the stress wave propagation at the interfaces are examined. It is found that the highest stress occurs at the interfaces. In the case of T-shaped adherends, it is seen that the maximum principal stress at the interfaces increases as Young's modulus of the adherends increases. In the special case where the web length of T-shaped adherends equals the flange length, the maximum principal stress at the interfaces increases as Young's modulus of the adherends decreases. The maximum principal stress at the interfaces increases as the adherend thickness decreases. The characteristics of the T-shaped adhesive joints subjected to static bending moments are also examined by FEM and compared with those under impact bending moments. Furthermore, strain response of adhesive butt joints was measured using strain gauges. A fairly good agreement is observed between the numerical and the experimental results.     

Measurement of in‐plane elastic moduli of composites with a circular disk specimen and piezoelectric sensors

Many test specimen configurations and test methods have been used for measuring the in‐plane elastic constants of orthotropic composites. While the measurement of the Young's modulus is straightforward, the shear modulus determination is more difficult. Most of the experimental methods require more than one specimen for the measurement of all the in‐plane elastic constants. In the proposed method, a single test specimen in the form of a circular disk is sufficient. The Young's modulus and the shear modulus are measured with piezoelectric sensors that produce and detect dilatational and shear waves, respectively. The experimental techniques involved and the possible methods of interpreting the results are explained. The results obtained were compared with those determined for bar specimens of the same material, using piezoelectric sensors and strain gauges. The comparisons are encouraging. POLYM. COMPOS., 26:542–551, 2005. © 2005 Society of Plastics Engineers     

Factors affecting young's modulus — Porosity relation of hydrated portland cement compacts

Two series of compacts are studied, one d-dried before and one after compaction. Measurements of absolute density, helium flow characteristics and Young's modulus indicate that high pressures can force the layers of d-dried material closer together, giving a Young's modulus double that displayed when no interlayer water is present and identical to that when spaces are occupied by water molecules. Water can re-enter between the layers, however, and on redrying Young's modulus is reduced by 50 per cent to the normal value for the d-dried material. The interlayer water must be regarded as part of the solid.     

Derivative stress-strain curves of polyacrylonitrile fibers

Derivative stress-strain curves at constant strain rate for polyacrylonitrile copolymer fibers have been obtained by simple modification of conventional tensile testing apparatus. These derivative curves, considerably more complex and eventful than stress-strain curves, have been interpreted as direct records of changes undergone by the apparent Young's modulus during experiments which extend from infinitesimal strain to failure. Analysis of the data shows that these changes in the apparent Young's modulus cannot be accounted for to any significant extent by viscoelastic time effects and must therefore be consequences of the deformation process itself. In the light of this analysis, it is concluded that polyacrylonitrile fibers “soften” considerably in the strain range 0.5–3% and that they exhibit moderate “hardening” in the strain range which extends from ca 3% to the breaking strain (10%).     

A two-dimensional stress analysis of single-lap adhesive joints subjected to external bending moments

The stress distributions in single-lap adhesive joints of similar adherends subjected to external bending moments have been analyzed as a three-body contact problem using a two-dimensional theory of elasticity (plain strain state). In the analysis, both adherends and the adhesive were replaced by finite strips. In the numerical calculations, the effects of the ratio of Young's moduli of the adherends to that of the adhesive and the adhesive thickness on the stress distribution at the interfaces were examined. It was found that the stress singularity occurs at the edges of the interfaces and that the peel stress at the edges of the interfaces increases with decreasing Young's modulus of the adherends. It was noticed that the singular stress decreases at the edges of the interfaces as the adherend thickness increases. In addition, photoelastic experiments and FEM (finite element method) calculations were carried out and fairly good agreement was found between the analytical and the experimental results.