Influence Of Specimen Thickness Research Articles

An Experimental Study on Welding Distortion in High-Density Polyethylene (HDPE) Welded Structures

High-density polyethylene (HDPE) is increasingly recognized as an eco-friendly material for small crafts. However, there is limited research on welding distortion in HDPE welded structures. This study investigates the deformation behavior of HDPE fillet-welded specimens, focusing on global out-of-plane distortions such as angular and bowing distortions. Experimental analysis, conducted using an optical 3D scanner, reveals similarities between the observed deformation patterns in HDPE fillet-welded specimens and those commonly found in other fillet-welded structures. Angular and bowing distortion modes are primarily observed, resulting from the contraction forces that occur during the cooling process after the melting and solidification of the HDPE welding rod. Additionally, the influence of specimen thickness on deformations is examined. This research contributes valuable knowledge about welding distortions in HDPE, providing directions for optimization of welding processes and the enhancement of structural performance in HDPE welded structures.

Electromagnetic interference shielding of 3D-printed graphene–polyamide-6 composites with 3D-printed morphology

Graphene–polyamide-6 composite (GC) filament was 3D-printed via melt extrusion (ME). The influence of specimen thickness and internal geometric designs on electromagnetic interference shielding effectiveness (EMI SE) and dielectric properties in the X-band frequency range (8.2–12.4 GHz) was investigated. Increasing specimen thickness from 1 to 5 mm did not improve EMI SE due to impedance matching and the associated reductions in electromagnetic (EM) wave reflection. It was demonstrated that the introduction of suitable internal geometric assemblies avoided impedance matching and significantly improved EMI SE. A material model for simulating EM response of 3D-printed GC was developed and experimentally verified. It was found that different internal geometric designs each displayed unique EM responses. However, geometrical inaccuracies in printed specimens resulted in differences between experimental EM response and that predicted by simulations. These inaccuracies stem from the small size of the features relative to the printer resolution and the ME printing methodology. Therefore, the limitations of a printer when replicating complex geometries must be considered to effectively apply internal geometric designs for enhancing EMI SE of 3D-printed components.

Influence of Specimen Thickness on the Acquisition of Al6061-T6 Material Properties Using SHPB and Verified by FEM.

The Split-Hopkinson pressure bar (SHPB), which is used for acquiring material properties at high strain rates (102–104 s−1), requires proper specimen size selection. Under the same applied pressure, an increased S-S curve is obtained as the thickness of the specimen decreases. In this study, 1.5 t, 2.0 t, 3.0 t, 5.0 t, and 7.0 t specimens of Al6061-T6 material were tested under 1.0 bar to understand the influence of specimen thickness on the acquisition of material properties. To grasp the behavior of the SHPB test in real time, Finite Element Method (FEM) was performed using the LS-DYNA program. During the SHPB test, the impedance is increased due to the variation in the specimen area. Because of the influence of impedance, the transmitted pulse increases, and the reflected pulse decreases. As a result, the specimen is deformed in the high-strain rate region, and the S-S curve is increased as the thickness decreases. In addition, by performing the test under different pressure conditions that created similar strain rate regions, the material properties remained constant with thickness variations.

An application of FEM in the determination of tensile properties for work-hardened carbon steel by means of small punch test

The determination of tensile properties from a small punch (SP) test by using a finite element method (FEM) has been studied. First, a finite element (FE) simulation of the SP test using true stress-strain curves including post-necking strain data of work-hardened SM490A carbon steel specimens was conducted. The simulation was validated with actual experimental results, which showed that the FE model can effectively reproduce the load-displacement curves without using a damage modeling technique. The FE model was then used to investigate an empirical correlation between the punch loads and the material parameters, including yield strength and ultimate tensile strength. The results indicated that the empirical constants are dependent on specimen thickness and may be valid for only a limited range of test configurations and materials. To expand the applicability of the SP test in the assessment of tensile properties, an inverse finite element method (iFEM) consisting of the iterative finite element calculation, bisection method, and Ludwik’s constitutive model was developed. Through the procedure, true stress-strain curves were constructed from the simulated load-displacement curves of hypothetical materials based on the SM490A steel specimens. Finally, yield strengths and ultimate tensile strengths of the carbon steel specimens were determined and found to be within 5.2% and 2.8% discrepancies, respectively, from the uniaxial tensile test results. iFEM provides consistent estimations of tensile properties with almost no influence of specimen thickness.

Investigating creep rupture and damage behavior of 41Fe-25.5Cr-23.5Ni alloy small punch creep specimens using a novel microstructure meshing approach

The Voronoi tessellation technique was used to model an idealized polycrystalline microstructure. This novel meshing approach was also implemented to study the crack initiation and growth behaviors of Sanicro25 alloy through small punch creep tests using a modified creep damage constitutive model. Furthermore, the influence of specimen thickness on crack fracture mechanics was examined. The suitability of this novel method was validated on the basis of the accuracy of simulation results. Transgranular fracture patterns were found at the primary stage, which were transformed into intergranular cracks as the creep time progressed. Cracks in small punch specimens were predominantly initiated on the outer surface, where high stress triaxiality occurred. Simultaneously, the high stress and stress triaxiality deviation controlled crack growth behaviors were determined by considering the various stress states.

A new method to determine the beam bending creep critical displacement of three-point bending specimen with fixed constraints

Three-point bending specimen with fixed constraints (TPBSF) can be used to obtain uniaxial creep parameters from small samples of material. Conversion relationships between TPBSF and uniaxial creep data are based on the beam bending model. For large loads and longtime creep test, the specimen deformation can be large, which may be contrary to the small deformation assumption of the beam bending model. So it is necessary to define the critical deformation, below which the beam bending model holds. In this study, a new method to define this critical deformation was proposed by displacement. Based on the relationship between the maximum rotation angle and displacement at the elastic and creep stages, three procedures to determine the critical displacement were first proposed. Then it was verified by the creep test of P91 steel at 566 °C and 66 N. The results show that the critical displacement obtained by finite element method is in good agreement with the experimental result, and the maximum error is 4.5%. Creep parameters were regressed and compared with those in the literature on the basis of critical displacement, it can be seen that creep parameters regressed by the new proposed method are much closer to uniaxial creep than the literature, which indicates that beam bending model holds below this critical displacement. Finally, the finite element method was used to investigate the relationship between the time correction parameter and specimen geometric parameters. It can be found that the specimen width has little influence on the time correction parameter. However, the influence of specimen thickness and span can be significant.

Simultaneous determination of local thickness and composition for ternary III-V semiconductors by aberration-corrected STEM

Scanning transmission electron microscopy (STEM) is a suitable method for the quantitative characterization of nanomaterials. For an absolute composition determination on an atomic scale, the thickness of the specimen has to be known locally with high accuracy. Here, we propose a method to determine both thickness and composition of ternary III-V semiconductors locally from one STEM image as shown for the example material systems Ga(AsBi) and (GaIn)As. In a simulation study, the feasibility of the method is proven and the influence of specimen thickness and detector angles used is investigated. An application to an experimental STEM image of a Ga(AsBi) quantum well grown by metal organic vapour phase epitaxy yields an excellent agreement with composition results from high resolution X-ray diffraction.

Influence of specimen thickness on fatigue behavior of a steel subjected to alternative bending

Influence of specimen thickness on fatigue behavior of a steel subjected to alternative bending

Influence of specimen thickness on the creep behavior of a directional solidification nickel-based superalloy

The effects of thickness and surface signature on the creep life of a directionally solidified nickel based superalloy were investigated. The creep tests of ground specimens in the thickness of 0.61 mm and 0.89 mm, as well as polished ones with 0.66 mm and 0.87 mm in thickness were performed at 980 °C/160 MPa. Based on the experimental results, the thin ones had inferior creep life compared with thick specimens. XRD exhibited that all the specimens were oxidized during the creep tests, however, the non-loading bear zones which caused by oxidation was insufficient to explain the creep life of specimens under different wall thicknesses. On the other hand, the morphology of fracture sections indicated that the interaction of cracks and creep damage could reveal this phenomena. It worth noting that the cracks played a more important role in the creeping of thin specimens, but creep damage influenced the thick specimens more effectly. In addition, the polished specimens had a better behavior during creep tests than the ground ones.

Influence of specimen thickness on the fatigue behavior of notched steel plates subjected to laser shock peening

The influence of specimen thickness on the fatigue crack initiation of 2205 duplex stainless steel notched specimens subjected to laser shock peening (LSP) was investigated. The purpose was to examine the effectiveness of LSP on flat components with different thicknesses. For the LSP treatment a Nd:YAG pulsed laser operating at 10 Hz with 1064 nm of wavelength was used; pulse density was 2500 pulses/cm2. The LSP setup was the waterjet arrangement without sample coating. Residual stress distribution as a function of depth was determined by the hole drilling method. Notched specimens 2, 3 and 4 mm thick were LSP treated on both faces and then fatigue loading was applied with R = 0.1. Experimental fatigue lives were compared with life predictions from finite element simulation. A good comparison of the predicted and experimental fatigue lives was observed. LSP finite element simulation helps in explaining the influence of thickness on fatigue lives in terms of equivalent plastic strain distribution variations associated with the change in thickness. It is demonstrated that specimen size effect is an important issue in applying LSP on real components. Reducing the specimen thickness, the fatigue life improvement induced by LSP is significantly increased. Fatigue life extension up to 300% is observed on thin specimens with LSP.

Influence of the aspect ratio of magnetic metallic additives on the microwave absorbing performance

This work aims to show the behavior of radar absorbing materials (RAM) based on magnetic metallic additives with different aspect ratios. For this, two materials, carbonyl iron, constituted of spherical iron particles, and carbon-steel filaments were used. These additives were characterized considering their morphological and structural features. X-ray diffraction analysis shows that the two additives have the same crystallographic structure, but their morphologies are quite different in micrometer scale. Epoxy resin/metallic additive composites using the neat additives and their mixtures were prepared. The electromagnetic characterization of the composites evaluated the permittivity, permeability and reflectivity behaviors in the frequency range of 8.2–12.4 GHz. The results show that the samples obtained with the mixture of the two additives resulted in composites with high complex parameters of permittivity and permeability. Better RAM performance is observed for samples based on metallic filaments and for more concentrated mixtures containing the two additives (values up to −14 dB or ~96% of attenuation). The influence of specimen-thickness on the RAM performance is also observed.

The influence of specimen thickness and alignment on the material and failure properties of electrospun polycaprolactone nanofiber mats.

Electrospinning is a versatile fabrication technique that has been recently expanded to create nanofibrous structures that mimic ECM topography. Like many materials, electrospun constructs are typically characterized on a smaller scale, and scaled up for various applications. This established practice is based on the assumption that material properties, such as toughness, failure stress and strain, are intrinsic to the material, and thus will not be influenced by specimen geometry. However, we hypothesized that the material and failure properties of electrospun nanofiber mats vary with specimen thickness. To test this, we mechanically characterized polycaprolactone (PCL) nanofiber mats of three different thicknesses in response to constant rate elongation to failure. To identify if any observed thickness-dependence could be attributed to fiber alignment, such as the effects of fiber reorientation during elongation, these tests were performed in mats with either random or aligned nanofiber orientation. Contrary to our hypothesis, the failure strain was conserved across the different thicknesses, indicating similar maximal elongation for specimens of different thickness. However, in both the aligned and randomly oriented groups, the ultimate tensile stress, short-range modulus, yield modulus, and toughness all decreased with increasing mat thickness, thereby indicating that these are not intrinsic material properties. These findings have important implications in engineered scaffolds for fibrous and soft tissue applications (e.g., tendon, ligament, muscle, and skin), where such oversights could result in unwanted laxity or reduced resistance to failure. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 104A: 2794-2800, 2016.

Influence of Specimen Thickness on Thermal Desorption Spectrum of Hydrogen in High Strength SCM435 Steel

Influence of Specimen Thickness on Thermal Desorption Spectrum of Hydrogen in High Strength SCM435 Steel

Influence of specimen thickness on the nanoindentation of hydrogels: Measuring the mechanical properties of soft contact lenses

Nanoindentation offers a convenient method for the testing of thin hydrogel specimens, such as contact lenses, to directly assess their mechanical properties. Here we investigate the mechanical properties of poly(hydroxyethyl methacrylate) (pHEMA) specimens of a range of uniform thickness values and demonstrate that, with 50 and 100μm radius spherical indenters, a significant increase in apparent elastic modulus is seen when the specimen thickness is smaller than 500μm at indentation depths <1μm. This is a manifestation of the well known indentation thickness effect but occurring at larger critical thicknesses than seen with other materials. A simple empirical relation is determined for the variation in apparent elastic modulus with normalised thickness. The empirical thickness correction function obtained from pHEMA specimens was subsequently used to correct for the thickness variation within a range of contact lenses supplied by a number of different manufacturers fabricated from both pHEMA and silicone polymers, with a range of optical strengths and hence thickness profiles. The correction function is seen to compensate for the variation in apparent elastic modulus with lens thickness for all four contact lens types, irrespective of lens material. The measured Young's modulus of the contact lens material, corrected for thickness, was compared with that quoted by the manufacturers of the contact lenses, obtained by conventional bulk mechanical testing, to find good agreement.

The effects of thickness and Poisson’s ratio on 3D mixed-mode fracture

The effects of specimen thickness and Poisson’s ratio are investigated on mixed mode fracture parameters of a test sample using numerical analyses. A large number of three dimensional finite element models of semicircular bend specimen containing an inclined edge crack are analyzed to compute mixed mode fracture parameters (i.e. KI, KII and T). While for the two dimensional models the fracture parameters are independent of thickness and Poisson’s ratio, the three dimensional results showed that the stress intensity factors (KI and KII) and the T-stress are generally increased by increasing Poisson’s ratio. The T-stress decreases when the thickness of specimens is increased. A comparison between the two and three dimensional solutions shows that the available KI, KII and T results obtained from two dimensional conditions, present lower estimate data for the real three dimensional cracked semicircular bend specimen. Also, the influence of specimen thickness and Poisson’s ratio, is more pronounced for dominantly mode I condition in the semicircular bend specimen.

Thickness influence on creep properties for Ni-based superalloy M247LC SX

Abstract The influence of specimen thickness on creep behavior of coated and uncoated specimens was investigated. Creep experiments were carried out on the single crystal Ni-base superalloy M247LC SX at 980 °C and 1100 °C. Tests were performed at different stress levels for 0.3 mm and 1.0 mm flat specimens in vacuum and ambient air. A decrease in creep strength with decreasing thickness was observed. Aluminized specimens showed less scatter in creep behavior in terms of both, rupture times and minimum creep rates. If only the initial two-phase area is considered (without interdiffusion zone and coating layer) the influence of specimen thickness on creep behavior were found to be negligible. The results show, that for turbine blade design the influence of wall thickness has to be considered. Thin-walled structures (below 1.0 mm) should be aluminized in order to reduce scatter in material behavior and to minimize the influence of oxidation on matrix/γ′-microstructure in order to form γ′ reduced or γ′ depleted zones.

Influence of the specimen thickness on low velocity impact behavior of composites

Abstract In this work, the influence of specimen thickness on low velocity impact behavior of carbon-epoxy composite laminates is studied. Plates with different thicknesses were tested under low velocity impact using a hemispherical impactor. The internal damage was mainly constituted by delaminations which were evaluated through the inspection of the impacted plates by the ultrasonic C-scan technique. It was observed that delaminations increase with plate thickness. In order to better understand the physical phenomenon explaining this result, a progressive damage model was used to simulate composites behavior under low velocity impact. In this context, a three-dimensional numerical analysis considering interface finite elements, including a cohesive mixed-mode damage model, which allows simulating delaminations onset and growth between layers, was performed. Good agreement was obtained between experimental and numerical analysis, which validated the proposed procedure. In addition, the proposed numerical methodology allowed identification of physical phenomena related to the influence of plate thickness on delamination size.

Influence of specimen thickness with rectangular cross-section on the tensile properties of structural steels

Abstract Specimens with a rectangular cross-section are commonly used to measure the tensile properties of materials. However, the specimen size may influence the results. In this study, the tensile properties of FH550 and X80 steels were investigated using rectangular cross-section specimens with different thicknesses and the same width. Both an experimental study and a 3D finite element method (FEM) study have been conducted. The results show that the uniform elongation is independent of specimen size, but the post-necking elongation increases dramatically as specimen thickness increases, which was attributed to the stress distribution near neck region. Single factor analysis results show that both the yield and the ultimate tensile strength of the specimens are independent of the thickness when the specimen thickness is larger than 1 mm.

Fracture mechanics approach to compare laser sintered parts and injection mouldings of nylon-12

In comparison to equivalent parts made by injection moulding, components manufactured by laser sintering are often perceived to offer inferior mechanical properties, yet the evidence for this is rarely based upon systematic research studies. In this paper, attempts have been made to conduct a fundamental study of the fracture behaviour of both injection moulded and laser sintered parts, based upon a modification of a standard technique used to determine linear elastic fracture mechanics parameters. The influence of specimen thickness (in the range 2–10 mm) was also included in the experimental plan, which concentrated upon the testing of single-edge notch bending (SENB) beam specimens. Force-displacement characteristics demonstrated significant plastic deformation in nylon (PA12) specimens, so that the J-integral method was used to obtain quantitative fracture parameters, including the energy requirements for crack growth. Comparisons of this parameter showed thickness-dependent ‘geometry-sensitive’ data for each set of samples. For the injection moulded SENB specimens, energy absorption decreased with increasing thickness, a result attributed to the influence of plane-strain-dominated conditions. In contrast, laser sintered samples exhibited increased toughness as specimen thickness increased towards 10 mm; this could not be explained by density or particle melting data and may be interpreted by changes in molecular structure that occur during the additive manufacturing process.

Fatigue Crack Propagation in Thin Structures

The influence of specimen thickness on fatigue crack behaviour has been investigated. To this aim the fatigue crack propagation rate has been measured on two different types of test specimens with varying thickness. The change of stress singularity exponent for the crack front due to vicinity of the free surface is considered. To explain the effect of stress singularity changes on obtained experimental results a methodology based on generalized stress intensity factor and strain energy density concept has been used. It is shown that for materials with Poisson’s ratio of about 0.3 the free surface effect does not play a decisive role for specimens with a low level of in-plane constraint but can influence fatigue crack propagation rate in the case of geometries with a high level of the constraint.