Influence Of Specimen Thickness Research Articles

Effect of specimen thickness on fracture toughness and adhesive properties of hydroxyapatite-filled polycaprolactone

Abstract The fracture toughness of hydroxyapatite (HAP)-filled polycaprolactone (PCL) biocomposites was investigated using the technique of essential work of fracture (EWF). The influence of specimen thickness on the toughness parameters was investigated. The specific essential work of fracture ( w e ) was found to decrease with the increase in filler loading and with the thickness of the specimen. The testing procedure used for the EWF measurement obeyed the validity criteria of the concept and w e determined can be considered to be a good measure of the plane-stress toughness of the composite. The adhesive strength between the HAP and the PCL phase was determined using T-peel tests. The layer of the laminates in the PCL–HAP–PCL peel test specimens was varied to study the influence of laminate thickness on the interfacial work of fracture. The effect of temperature on the interfacial work of fracture was also evaluated. The parameters were varied to determine the effect of the plastic deformation on the peel strength. The interfacial work of fracture between HAP and PCL was found to be relatively strong; however, the effect of temperature and PCL laminate thickness did not significantly vary the adhesion strength.

The Influence of Specimen Thickness on the High Temperature Corrosion Behavior of CMSX-4 during Thermal-Cycling Exposure

CMSX-4 is a single-crystalline Ni-base superalloy designed to be used at very high temperatures and high mechanical loadings. Its excellent corrosion resistance is due to external alumina-scale formation, which however can become less protective under thermal-cycling conditions. The metallic substrate in combination with its superficial oxide scale has to be considered as a composite suffering high stresses. Factors like different coefficients of thermal expansion between oxide and substrate during temperature changes or growing stresses affect the integrity of the oxide scale. This must also be strongly influenced by the thickness of the oxide scale and the substrate as well as the ability to relief such stresses, e.g., by creep deformation. In order to quantify these effects, thin-walled specimens of different thickness (t = 100−500 μm) were prepared. Discontinuous measurements of their mass changes were carried out under thermal-cycling conditions at a hot dwell temperature of 1100 °C up to 300 thermal cycles. Thin-walled specimens revealed a much lower oxide-spallation rate compared to thick-walled specimens, while thin-walled specimens might show a premature depletion of scale-forming elements. In order to determine which of these competetive factor is more detrimental in terms of a component’s lifetime, the degradation by internal precipitation was studied using scanning electron microscopy (SEM) in combination with energy-dispersive X-ray spectroscopy (EDS). Additionally, a recently developed statistical spallation model was applied to experimental data [D. Poquillon and D. Monceau, Oxidation of Metals, 59, 409–431 (2003)]. The model describes the overall mass change by oxide scale spallation during thermal cycling exposure and is a useful simulation tool for oxide scale spallation processes accounting for variations in the specimen geometry. The evolution of the net-mass change vs. the number of thermal cycles seems to be strongly dependent on the sample thickness.

Mechanical characterization of bovine periodontal ligament.

This study is part of a research program that aims to develop a constitutive three-dimensional model of the periodontal ligament (PDL) through the identification of pertinent material parameters. As part of this program, bovine PDL was utilized to establish stress-strain responses under tensile and compressive loading conditions. Fresh bovine molars were secured, frozen and prepared to appropriate dimensional specifications. Bar-shaped specimens that comprised portions of dentine, PDL and bone were produced. Push-pull tests were conducted using a specifically constructed loading machine. Full range monotonic stress-strain diagrams were generated. The effect of a rate increase on cyclic S-E diagrams was also determined. The influence of specimen thickness was expressed in terms of modulus of elasticity, strength, uniaxial maximizer strain, and strain energy density. The overall load-response was heavily hysteretic in compression. On the tensile side, after a steep rise, the curve tended to flatten out asymptotically. Variations in rate that spanned four orders of magnitude had no effect on reciprocal load responses. The E-modulus was in the 4-8 MPa range, the strength of the PDL was 1-2 MPa, the maximizer strain was at 45-60% and the strain energy density ranged between 0.3 and 0.4 MPa.

Polycarbonate and co-continuous polycarbonate/ABS blends: influence of specimen thickness

The influence of specimen thickness on the fracture behaviour of polycarbonate (PC) and co-continuous PC/ABS (50/50) blends was studied in single edge notch tensile tests at 1m/s and different temperatures (−80 to 130°C). Specimen thickness ranged from 0.1 to 8mm. In the co-continuous PC/ABS blends the rubber concentration in the ABS was 0, 15 and 30wt%. The change in fracture toughness was typified by the change in brittle-to-ductile transition temperature (Tbd).Tbd of pure PC depended strongly on specimen thickness, leading to very low transition temperatures for thin PC specimens. PC/ABS 0%, a 50/50 blend of PC and SAN (i.e. ABS without polybutadiene (PB)), was a brittle blend and showed a very high Tbd close to the Tg of SAN. Tbd did not seem to be influenced by specimen thickness. PC/ABS blends with 15 and 30% PB in ABS showed improved Tbd compared to PC/SAN and PC, indicating effective rubber toughening. Tbd decreased with decreasing thickness for PC/ABS specimens thicker than 1.5mm. However, Tbd increased with decreasing thickness for specimens below 1.5mm thickness. In thin specimens, the rubber-filled blend is less effective rubber toughening. The plane strain stress condition needed for rubber cavitation is apparently not present in thin specimens.

Transverse tension fatigue life characterization through flexure testing of composite materials

The transverse tension fatigue life of S2/8552 glass–epoxy and IM7/8552 carbon–epoxy was characterized using flexure tests of 90-degree laminates loaded in 3-point and 4-point bending. The influence of specimen polishing and specimen configuration on transverse tension fatigue life was examined using the glass–epoxy laminates. Results showed that 90-degree flexure specimens with polished machined edges and polished tension-side surfaces had lower fatigue lives than unpolished specimens when cyclically loaded at equal stress levels. The influence of specimen thickness and the utility of a Weibull scaling law were examined using the carbon–epoxy laminates. The influence of test frequency on fatigue results was also documented for the 4-point bending configuration. A Weibull scaling law was used to predict the 4-point bending fatigue lives from the 3-point bending curve fit and vice versa. Scaling was performed based on maximum cyclic stress level as well as fatigue life. The scaling laws based on stress level shifted the curve fit S–N characterizations in the desired direction, however, the magnitude of the shift was not adequate to accurately predict the fatigue lives. Furthermore, the scaling law based on fatigue life shifted the curve fit S–N characterizations in the opposite direction from measured values. Therefore, these scaling laws were not adequate for obtaining accurate predictions of the transverse tension fatigue lives of heterogeneous, fiber reinforced, polymer matrix composites.

Essential work of fracture on PET films: influence of the thickness and the orientation

This paper presents the fracture behaviour of films of a bioriented poly(ethylene terephthalate) (BOPET), that was studied by the Essential Work of Fracture (EWF) method. The influence of specimen thickness and molecular orientation was investigated. The results show that this method is a useful alternative for studying the plane-stress fracture of this material, finding that the specific essential work of fracture is strongly affected by the orientation [we was smaller in the direction of extrusion (MD) than in the perpendicular one (TD)], but independent of the specimen thickness in a range from 50 to 250 μm. On the other hand, the plastic work item is sensitive to variations of thickness but does not depend on orientation.

The influence of size effects and dynamic loading on the fracture toughness of commercial GRP materials

The influence of specimen thickness and the effect of dynamic rates of testing on fracture toughness behaviour of laboratory-prepared and commercial glass-reinforced plastic materials have been investigated. The four materials, from different sources, gave similar fracture toughness data. The results show that the fracture toughness increases with specimen size, for specimens with nominal thicknesses in the range 10 to 25 mm; this is thought to be associated with the length of fibres in the testpiece ligament. Dynamic tests produced higher fracture toughness values than those obtained statically. This was believed to be due to a change in fracture mode from fibre fracture to fibre pull-out.

Measurement of London penetration depth from holographic images of superconducting vortices: The influence of specimen thickness

High-resolution holographic data of superconducting vortices are presented and analyzed in order to extract a measurement of the London penetration depth by fitting the reconstructed phase across the core using an analytical one-dimensional London model. The resulting value of $50\ifmmode\pm\else\textpm\fi{}5\mathrm{nm}$ for the London penetration depth is obtained, which is about two times larger than the commonly accepted value of 30 nm used in previous simulations. It is shown that this discrepancy can be removed by taking into account the influence on the phase shift of the specimen thickness and of the associated broadening of the field lines near the surface. These results highlight the importance of the assumed model in order to extract from the analysis of experimental data reliable quantitative estimates of critical parameters such as the London penetration depth.

Influence of specimen thickness on change of waveform in ultrasonic measurement : Journal of JSNDI, Vol. 45, No. 11 (November 1996) p. 811 Shen, Liming; Kato, Hiroshi

Influence of specimen thickness on change of waveform in ultrasonic measurement : Journal of JSNDI, Vol. 45, No. 11 (November 1996) p. 811 Shen, Liming; Kato, Hiroshi

On the Influence of Specimen Thickness in TEM Images of Super-Conducting Vortices: II

Abstract In our previous papers on the same topic we have shown how the finite thickness of the specimen influences the magnetic field distribution associated to a single superconducting vortex. Fortunately, Clem found an approximate, but analytical, solution for this problem predicting that the field lines are bent within the specimen and fan out near the surfaces, giving an external field topography broader than the bulk one. This is shown in Figure 1 (a) which reports the projected phase maps of the magnetic field, i.e., the phase shift experienced by a coherent electron plane wave in an ideal experiment where the beam direction is parallel to the specimen surface and the apparent infinite thickness of the specimen is overlooked. The specimen thickness has been taken equal to 2 λL, the bulk London penetration depth. Figure 1 (b) shows the trends of the z-component of the magnetic field calculated up to a distance from the core of 5 λL at the film surface (lower curve), at the film center (intermediate curve) and, for reference, the bulk Clem model (upper curve).

An experimental study to validate tests used to determine mixed mode failure criteria of glass/epoxy composites

Abstract This paper presents results from an experimental study to assess the reliability of the tests commonly used to determine mixed mode fracture initiation envelopes of composites. The material studied is a unidirectional glass/epoxy composite manufactured by hand lay-up. The influence of specimen thickness is examined for mode I(DCB), mode II(ENF) and mixed mode I/II(MMB) loading. Crack initiation was carefully monitored and different criteria for the definition of initiation are applied. Data analysis of the MMB test has been performed using both beam theory and also an experimental method based on direct displacement measurements. Fracture toughness values and mixed mode partitioning given by both methods are shown to give similar results. However, the 5% offset delamination initiation definition widely used for pure mode loadings is not suited to the MMB test and acoustic emission correlates more closely with non-linearity on the load-displacement curve.

Influence of Specimen Thickness and Projectile Material on Crater and Spalling of an Electrode-grade Graphite by the Impact of a Projectile

An electrode-grade polycrystalline graphite material, G151A, was used for impact test by a 4mm-diameter sphere made of Mn-Zn ferrite or steel. The impact velocity was 900m/s to 1700m/s. Influence of specimen thickness and projectile material on the initiated crater and spalling was investigated in this study. Material and thickness did not affect crater volume. However, crater area by Mn-Zn ferrite was larger than that by steel at the same kinetic energy. The spall area and the depth were almost constant in all the thicknesses when the material spalled.

Influence of specimen thickness and projectile material on crater and spalling of an electrode-grade graphite by the impact of a projectile

An electrode-grade polycrystalline graphite material, G151A, was used for impact test by a 4mm-diameter sphere made of Mn-Zn ferrite or steel. The impact velocity was 900m/s to 1700m/s. Influence of specimen thickness and projectile material on the initiated crater and spalling was investigated in this study. Material and thickness did not affect crater volume. However, crater area by Mn-Zn ferrite was larger than that by steel at the same kinetic energy. The spall area and the depth were almost constant in all the thicknesses when the material spalled.

On the influence of specimen thickness in TEM images of super-conducting vortices

The successful observation of superconducting flux lines (fluxons) in thin specimens both in conventional and high Tc superconductors by means of Lorentz and electron holography methods has presented several problems concerning the interpretation of the experimental results. The first approach has been to model the fluxon as a bundle of flux tubes perpendicular to the specimen surface (for which the electron optical phase shift has been found in analytical form) with a magnetic flux distribution given by the London model, which corresponds to a flux line having an infinitely small normal core. In addition to being described by an analytical expression, this model has the advantage that a single parameter, the London penetration depth, completely characterizes the superconducting fluxon. The obtained results have shown that the most relevant features of the experimental data are well interpreted by this model. However, Clem has proposed another more realistic model for the fluxon core that removes the unphysical limitation of the infinitely small normal core and has the advantage of being described by an analytical expression depending on two parameters (the coherence length and the London depth).

The influence of specimen thickness on fatigue crack growth retardation following an overload

Abstract The influence of specimen thickness on the fatigue crack growth response of a carbon manganese structural steel following a single tensile overload has been investigated. The results show that a linear relationship exists between the retardation, in terms of the logarithm of the delay cycles, and specimen thickness. Crack closure measurements show that the regardation is predominantly a plane stress phenomenon and it is demonstrated that plasticity-induced crack closure is the principal retardation mechanism.

Application of the instrumented impact test to the toughness characterization of high impact thermoplastics

The toughness behaviour of some blends and a PA/CF composite under dynamical loading (1 m/s) based on the J-integral was studied. Different methods were used for the tests. It can be shown that the multiple specimen stop-block technique gives the most conservative results. Furthermore the influence of specimen thickness on crack resistance behaviour was studied. The instrumented Charpy impact test enables the determination of valid crack resistance curves on plastics with small specimen geometries. The advantages and disadvantages of using the known standards for metallic materials in comparison to the ESIS TC4 testing protocol were discussed and a physical concept is compared with the empirical description of R-curve behaviour with the standards.

Influence of specimen thickness on the deformation and fracture behaviour of wide plates

The influence of specimen thickness on the deformation behaviour and the load bearing capacity has been investigated with large scale double edge notched tension specimens (DENT). The difference of the state of stress can be modelled by simplifications (plain strain, plain stress). Equations for the calculation of plastic limit loads taking into account the defect ratio a/W have been derived based on analytical, numerical and experimental investigations. Already existing equations may lead to unsafe prediction in special situations. The difference between plastic limit and maximum load is smaller for the thicker specimens due to higher toughness requirements. The toughness requirements have been quantified for the DENT specimens using the J-integral analysis. The requirements mainly depend on the overall dimensions ( W, B), the thickness ratio ( B/W) and the defect ratio ( a/W).

Influence of the scale factor on the cyclic crack resistance of plastic steels in the low-amplitude area of loading

The authors study the rules of the influence of specimen thickness on fatigue crack kinetics and the threshold range of the stress intensity factor in plastic steels. Steel 10GN2MFA was used in the investigations.

Influence of specimen thickness on isothermal crystallization kinetics. A theoretical analysis

In the DSC technique, isothermal crystallization experiments are usually performed on thin flat specimens, but their interpretation generally uses theories developed for an unbounded volume. In this paper, isothermal crystallization of spherical entities in the volume limited by two parallel infinite planes is considered. Our model, derived from Avrami's theory, gives an analytical expression for the transformed volume fraction as a function of time. It is shown that the influence of thickness becomes important when thickness becomes of the order of or smaller than the average spherulite radius. The main effects of a decreasing thickness are a slower crystallization kinetics and a decrease in the Avrami exponent. These results can be used to interpret experimental data obtained in isothermal polymer crystallization.

The influence of specimen thickness in quantitative electron energy loss spectroscopy: II

In a previous paper it was shown that the influence of specimen thickness on quantitative electron energy loss spectroscopy (EELS) can be judged by measuring the intensity ratio of any two characteristic EEL edges as a function of thickness. If the specimen is homogeneous and thickness effects are neglegible then, one can show from Egerton’s formulation that this intensity ratio should be a constant. Any departure from a constant value indicates a breakdown of the quantitative theory due to thickness related effects. It was shown that if the ratio of Ip/IO (Ip = intensity of plasmon loss, IO = intensity of zero loss) exceeds ∼ 0.3 then quantitative analysis can be in significant error. In subsequent work Egerton showed that a better measure is the ratio of ℓn(It/IO) which is related to the ratio of t/λ. Here It is the total energy loss intensity, t the specimen thickness and λ the mean-free path for total inelastic scattering.