Increasing Specimen Thickness Research Articles

First study of quantitative relationship between electric polarization and electromagnetic interference (EMI) shielding effectiveness of CFRP

This study investigates the electric polarization, including direct current (DC) and alternating current (AC), and electromagnetic interference (EMI) shielding capabilities within the microwave range (2.5–3.9 GHz) of cross-ply continuous carbon fiber-reinforced polymer (CFRP) composites, constructed by stacking prepreg composites. The DC conductivity of CFRP was evaluated using a multimeter, while the AC relative permittivity was measured with electronic test equipment (LCR meter). To describe the relationship between shielding effectiveness and polarization behavior, the EMI shielding of CFRP was assessed using the waveguide method, presenting a quantitative description of this relationship for the first time. Results indicate a decrease in DC conductivity with increasing specimen thickness due to increasing defects. Conversely, AC permittivity increases with specimen thickness, attributed to a rise in charged carriers and associated carrier-atom interactions. Skin depth δ, at a given thickness, follows a trend of initial decrease and subsequent increase with rising frequency; at a given frequency, it increases with decreasing specimen thickness. The interaction between CFRP and radiation is primarily reflective, with the reflection coefficient being much higher than the absorption coefficient across the frequency range, escalating with specimen thickness. Shielding effectiveness (SET) and absorption loss (SEA) display an initial increase followed by a decrease with rising frequency, whereas reflection loss (SER) sees a slight increase. For the smallest thickness, SEA per unit thickness exceeds 3120 dB/m and 7960 dB/m using specimen and carbon thickness, respectively. The absorption loss predominantly arises from the interaction of the electric field with electric dipoles formed by carrier-atom interaction at defects.

Corrosion resistance of hybrid plasma electrolytic oxidation coatings on AZ31B magnesium alloy in simulated body fluid

This study examines the effects of a hydroxyapatite/anatase TiO2/CeO2 coating on the corrosion of AZ31B magnesium alloy in a simulated body fluid. Plasma electrolytic oxidation (PEO) is used to create the coating, and the surface properties are analysed using X-ray diffraction (XRD), atomic force microscopy (AFM) and field-emission scanning electron microscopy (FE-SEM). Contact angle measurements adapted to compare the uncoated substrate (144.74 ± 2.08°) with the coated substrates, which exhibit contact angles of (107.92 ± 2.16°), (95.88 ± 2.06°) and (66.05 ± 2.09°) for the respective coating durations. Increasing the thickness of the coating improves its corrosion resistance. Specifically, a 6-minute PEO coating significantly increases the thickness and provides better protection against corrosion for the AZ31B magnesium alloy. Cross-sectional scans of the coated samples revealed an increase in specimen thickness from 32.92 μm to77.17 μm. Potentiodynamic polarisation tests in a simulated body fluid reveal that the 6-minute coated sample shows the highest corrosion resistance, with the lowest corrosion current density (1.9037 × 10-06) compared to other coatings, indicating strong protection against corrosion. This research proposes a novel method to enhance the corrosion resistance of PEO coatings on magnesium alloys by depositing a thicker layer of hydroxyapatite, anatase TiO2 and CeO2. This approach results in a stronger and more effective protective system against corrosion.

Study on physical and mechanical properties of cement asphalt emulsified mortar under track slab

PurposeDuring the construction process of the China Railway Track System (CRTS) I type filling layer, the nonwoven fabric bags have been used as grouting templates for cement asphalt (CA) emulsified mortar. The porous structure of nonwoven fabrics endowed the templates with breathability and water permeability. The standard requires that the volume expansion rate of CA mortar must be controlled within 1%–3%, which can generate expansion pressure to ensure that the cavities under track slabs are filled fully. However, the expansion pressure caused some of the water to seep out from the periphery of the filling bag, and it would affect the actual mix proportion of CA mortar. The differences in physical and mechanical properties between the CA mortar under track slabs and the CA mortar formed in the laboratory were studied in this paper. The relevant results could provide important methods for the research of filling layer materials for CRTS I type and other types of ballastless tracks in China.Design/methodology/approachDuring the inspection of filling layer, the samples of CA mortar from different working conditions and raw materials were taken by uncovering the track slabs and drilling cores. The physical and mechanical properties of CA mortar under the filling layer of the slab were systematically analyzed by testing the electrical flux, compressive strength and density of mortar in different parts of the filling layer.FindingsIn this paper, the electric flux, the physical properties and mechanical properties of different parts of CA mortar under the track slab were investigated. The results showed that the density, electric flux and compressive strength of CA mortar were affected by the composition of raw materials for dry powders and different parts of the filling layer. In addition, the electrical flux of CA mortar gradually decreased within 90 days’ age. The electrical flux of samples with the thickness of 54 mm was lower than 500 C. Therefore, the impermeability and durability of CA mortar could be improved by increasing the thickness of filling layer. Besides, the results showed that the compressive strength of CA mortar increased, while the density and electric flux decreased gradually, with the prolongation of hardening time.Originality/valueDuring 90 days' age, the electrical flux of the CA mortar gradually decreased with the increase of specimen thickness and the electrical flux of the specimens with the thickness of 54 mm was lower than 500 C. The impermeability and durability of the CA mortar could be improved by increasing the thickness of filling layer. The proposed method can provide reference for the further development and improvement of CRTS I and CRTS II type ballastless track in China.

Effect of specimen thickness on fatigue crack shape evolution for aluminum alloy

The investigation of fatigue crack propagation and fracture mechanisms in high-thickness metal plates holds pivotal importance in the advancement of a three-dimensional damage tolerance assessment methodology. This research also bears significant implications for ensuring the safe operation of large-scale mechanical equipment. In this study, we examine the influence of specimen thickness on the evolution of fatigue crack shapes in an aluminum alloy. Fatigue crack growth tests were conducted on single-edge notch tension specimens to explore the impact of specimen thickness on the shape of fatigue crack growth. Additionally, we propose a calculation model for crack growth shape based on an energy model in this paper. Both experimental and analytical findings indicate that specimen thickness does indeed exert an influence on fatigue crack shape. Specifically, as the specimen thickness increases, the crack shape transitions from resembling a “fingernail” to a “saddle” shape.

Effect of specimen size on creep crack growth rate in superalloys IN625 and IN783

To further clarify the relation between the intensity of specimen size effect on creep crack growth (CCG) rate and operative creep fracture mechanisms, CCG testing and mechanism observation were carried out for two superalloys IN625 and IN783. Results show that the CCG data of different specimen types for IN625 basically coincide at 650 °C. In contrast, strong specimen size effect was observed in IN783 at 560 °C, that is, the CCG rate increases with the increase in specimen thickness, producing the largest CCG ratio of approximately seven. The load-line displacement and fracture mechanism analyses indicate that the IN625 specimens failed in a ductile and intergranular manner, while the IN783 specimens in a brittle and intergranular manner. The present study suggests that the influence of creep fracture mechanisms should be considered in the characterization of the specimen size effect on CCG rate.

Experimental and simulation study on compressive failure evolution of multidirectional laminates with different dimensions

The composite strength refers to the ultimate local value rather than the average value of local strength, thus the effect of size effect needs to be considered. In this study, experimental and numerical approaches are used to evaluate the influence of size effect on the compressive characteristics and failure process of multidirectional carbon fiber reinforced composites. The representative failure modes of specimens with different thicknesses are described. The reasons for the difference in failure modes are analyzed by microstructure analysis, and the crack propagation process of specimens with different gauge lengths is identified. The simulation results and microscopic mechanism analysis reveal that with the increase of specimen thickness, the final failure mode develops from longitudinal cracking to multidirectional delamination, and finally evolves into shear failure through the thickness. Influenced by the free edge effect, the specimen thickness significantly affects the final failure mechanism by influencing the location of the initial cracking, and the size of the gauge section affects the site of matrix compression failure leading to a change in the final failure mode. These findings provide some helpful guidance for the design and fabrication of thick composite structures.

The effect of Pd and Ni coatings on hydrogen permeation experiments of as-quenched martensitic steel

Abstract Hydrogen permeation technique is a widely used testing method for the determination of hydrogen diffusion coefficient (D), which is an important parameter considering hydrogen embrittlement. A palladium (Pd) or nickel (Ni) coating is often utilised on the hydrogen detection side of the test specimens. Here, we investigate the effect of Pd and Ni coatings on hydrogen diffusion in a martensitic 500 HBW hardness low-alloy steel in the thickness range of 0.5 – 0.8 mm using a refined successive transient method and compare against an uncoated reference specimen. Both coatings yield similar average D values (6 – 6.6 × 10−7 cm2/s), but the best repeatability is achieved with Pd coating. With Ni coating, D values decrease with the increasing specimen thickness, which is partly caused by a slower hydrogen diffusion in Ni, and therefore a concentration gradient at the specimen-coating interface. The uncoated specimen has a poor transient fit, and significantly lower D (2.1 × 10−7 cm2/s) due to surface oxidation. With both coatings, the steepness of the last decay transient was highly affected by specimen thickness, and therefore the density of reversible hydrogen traps is only comparable for similar thicknesses.

Effect of Loading Rate on Fracture Behaviour and Shear Lips Formation of Al6061 Alloy

Aluminiumalloys are widely used in many engineering industries due to their mechanical and material properties. It is used in many applications, especially automotive parts, like automobile cylinder heads, engine blocks, and chassis. It is important to obtain the behaviour of fracture of this material. Several materials testing has been conducted on aluminium 6061 alloy to fulfil the requirement in industries. However, the effect of specimen thickness on shear lip ratio and plastic zone size on fracture specimens for aluminium 6061 under the three-point bending test is hardly studied. Also, the fracture behaviour of this material has only sometimes been clarified. The objective of this paper is to study the effect of the thickness of the sample as well as the loading rate on the formation of shear lips for aluminium 6061. To find out whether shear lips occur on the fracture surface of aluminium 6061, a three-point bending test was performed on a Single Edge Notched Bending (SENB) specimen. Analysis has been made to determine the shear lips ratio dependence on specimen thickness and loading rate. Based on the result of the analysis, the shear lips ratio decreases as the specimen's thickness increases. Besides that, the shear lips ratio decreases as the loading rates increases. A high loading rate and specimen thickness resulted in low plasticity behaviour because the stress states are in plane strain conditions where the formation of shear lips is minimum. From the three-point bending test, a good agreement of data gains from the dependency of shear lips ratio on specimen thickness and loading rates. Overall, aluminium 6061 is fractured in a ductile manner with significant shear lips formation.

Method for calculating local bearing capacity of concrete under bond stress from reinforcement in straight anchor section

A pull-out test is performed on 30 concrete specimens to determine the effect of bond stress on the local bearing capacity. The parameters include the dimensions of the headed bars, strength grade of the concrete, embedded length of the reinforcement, and diameter of the reinforcement. The dimensions of the headed bars are 50 mm × 50 mm × 20 mm and 60 mm × 60 mm × 20 mm, and the strength grades of concrete are C30, C40, and C50. The diameters of the reinforcement are 25 mm and 32 mm and its embedded length is divided into five types in the test. The local bearing capacities of 30 concrete specimens are obtained, and three failure modes are observed in specimens. The different modes of failure primarily depend on the combined action of the shell structure and wedge of the concrete. The pull-out test results indicate that the local bearing capacity of concrete under headed bars increases with an increase in the embedded length of reinforcement and the strength grade of concrete, with an almost linear relationship. In addition, the local bearing capacity decreases with an increase in the relative protective-layer thickness of the concrete specimens. Finally, a calculation method is proposed for the local bearing capacity of concrete under the action of bond stress from the reinforcement in a straight anchor section. The calculations considered the relative embedded length and the relative protective layer thickness of concrete as independent variables and the ratio of the local bearing capacity of concrete to the bearing capacity of concrete under the headed bars as a dependent variable. This calculation method provides a theoretical basis for standard revision and engineering applications.

Investigation of the Scale Factor Impact on the Results of Acoustic Emission Monitoring of the Steel Specimens Tension Process

The research is devoted to steel structure diagnostics by the acoustic emission (AE) method. The existing regulatory documents for AE diagnostics of metals and alloys do not take into account some critical factors, among which one is the scale factor should be highlighted. As a result, this can lead to an unreliable assessment of the danger degree of defects in structures when using standard AE diagnostic criteria. This paper presents a quantitative assessment of the scale factor impact on the AE data during the static tension test of steel specimens to failure. Experimental studies were carried out on flat specimens of various thicknesses with a side notch made of high-quality alloyed steel 30 KhGSA. It was established that AE data changed (rise in the AE signals amplitudes and AE activity) within the increase of specimen thickness. Growth in the recorded AE signals cumulative energy was registered with a greater specimen thickness. Partial correlation dependences of the mean count frequency and cumulative energy of AE signals on the specimen thickness were obtained. It was shown that such an effect occurred due to both a general increase in the deformed metal volume and greater strain intensity during the tension of thick specimens. The obtained dependences may contribute to the development of AE diagnostics of metallic materials which is invariant to the scale factor impact.

The Effect of Different Nanomaterials Additions in Clay-Based Composites on Electromagnetic Transmission.

In this study, clay composites were subjected to electromagnetic transmission testing at frequencies in the region of non-ionizing radiation. Specimens were made with partial substitution of clay with different admixtures by mass. Admixtures used were Fly Ash, four different particle sizes and phases of Titanium Dioxide (TiO2), Zinc Ferrite (ZnFe2O4), Maghemite (γ-Fe2O3) and Antimony Tin Oxide (ATO). The additives were thoroughly (chemically, structurally, morphologically) characterized. The replacement percentage was 5 wt.%. Electromagnetic transmission assessment included S21 transmission coefficient measurements for samples with different additives. The lowest transmission was reported for the clay specimens with ATO and Titanium Dioxide, especially at higher frequencies. A decrease in the transmission parameter with increasing specimen thickness was also confirmed.

Temperature and test specimen thickness (TST) effect on tensile and fracture behavior of AA2050-T84 alloy

AA2050-T84 is a third-generation Al-Li alloy used for primary structures of the modern transport aircraft wing. Temperature variation is common during flights, and the effect of temperature on the damage tolerance behavior of Al-Li alloys is significant. In the present work, the effect of temperature on tensile and fracture toughness of the AA2050-T84 alloy was tested experimentally. Further, the effect of Test Specimen Thickness (TST) on crack behavior is studied numerically using constraints variation. The Compact Tension (C(T)) specimen was used for linear elastic fracture analysis with variation in thickness to width ratio (B/W) as 0.1, 0.5, and 1. T11 and T33 constraint parameters were used to measure the effect of TST at −20 °C, 24 °C, and 200 °C. Increase in specimen thickness for constant stress intensity factor (KI) resulted in the decrease of T11. However, the T33 increased with an increase in specimen thickness for all temperatures considered. At −20 °C and 24 °C temperatures, the T11 variation was almost identical at all thicknesses. However, a decrease in T11 around 8% was witnessed at 200 °C compared to room temperature. The temperature effect on the T33 variation was steady and marginal. The temperature and TST effect on AA2050-T84 alloy was significant, and the present investigation results are crucial for aircraft design engineers.

A Test Method for Acoustic Emission Properties of Natural Cellulose Fiber-Reinforced Composites

To test the acoustic performance of fiber-reinforced composites for replacing wood, an acoustic vibration test method is developed. For evaluation of the test method, composites are manufactured using hemp and ramie embedded in epoxy, through vacuum-assisted resin infusion molding. The effects of the most important factors, i.e., impulse, relative humidity (RH), and specimen thickness, on the acoustic vibration response of the composites are systematically studied. The magnitudes of the impulses, represented by different masses of the dropping balls, seem to have little influence on the shapes of the acoustic vibration curves, although the intensity of the spectra increases as the impulse increases. The RH influences the spectrum shape significantly due to variation in the Young’s modulus and density of the material upon absorption of moisture. The specimen thickness also greatly affects the testing results. The specific dynamic modulus, acoustic radiation damping coefficient, and acoustic impedance change a little as the impulse magnitude and RH change, but decrease substantially as the specimen thickness increases. The specific dynamic modulus can be linearly correlated with the flexural modulus of a material.

Effect of Light-Sources and Thicknesses of Composite Onlays on Micro-Hardness of Luting Composites.

The aim of this study was to compare three different light-curing-units (LCUs) and determine their effectiveness in the adhesive cementation of indirect composite restorations when a light-curing resin cement is used. Two resin composites were selected: Enamel Plus HRI (Micerium) and AURA (SDI). Three thicknesses (3 mm, 4 mm and 5 mm) were produced and applied as overlays and underlays for each resin composite. A standardized composite layer was placed between underlay and overlay surfaces. Light curing of the resin-based luting composites was attained through the overlay filters using LCUs for different exposure times. All specimens were allocated to experimental groups according to the overlay thickness, curing unit and curing time. Vickers Hardness (VH) notches were carried out on each specimen. Data were statistically evaluated. The curing unit, curing time and overlay thickness were significant factors capable of influencing VH values. The results showed significantly decreased VH values with increasing specimen thickness (p < 0.05). Significant differences in VH values were found amongst the LCUs for the various exposure times (p < 0.05). According to the results, a time of cure shorter than 80 s (with a conventional quartz–tungsten–halogen LCU) or shorter than 40 s (with a high-power light-emitting diode (LED) LCU) is not recommended. The only subgroup achieving clinically acceptable VH values after a short 20 s curing time included the 3 mm-thick overlays made out of the AURA composite, when the high-power LED LCU unit was used (VH 51.0). Composite thickness has an intense effect on polymerization. In clinical practice, light-cured resin cements may result in insufficient polymerization for high thickness and inadequate times. High-intensity curing lights can attain the sufficient polymerization of resin cements through overlays in a significantly shorter time than conventional halogen light.

Quasi Static and Fatigue Properties of Long Carbon Fiber Reinforced Polyamide

In this experimental work, the quasi static and fatigue properties of a 40 wt.% long carbon fiber reinforced partially aromatic polyamide (Grivory GCL-4H) were investigated. For this purpose, microstructural parameter variations in the form of different thicknesses and different removal directions from injection-molded plates were evaluated. Mechanical properties decreased by increasing misalignment away from the melt flow direction. By changing the specimen thickness, no change in the general fiber distribution pattern transversal and normal to the axis of melt flow was observed. It has shown that with increasing specimen thickness the quasi static properties along the melt flow direction decreased and vice versa resulting in superior properties normal to the melt flow axis. At around 5 mm, an intersection suggests quasi-isotropic behavior. In addition, the fatigue strength of the material was significantly higher in the flow direction than normal to the flow direction. No change in fatigue life was observed while changing specimen thickness. The Basquin equation seems to describe the effect of stress amplitude on the fatigue strength of this composite. Scanning electron microscopy was used to investigate fracture surfaces of tested specimens. Results show that mechanical properties and morphological structures depend highly on fiber orientation.

Three-Dimensional Stress Intensity Factor Correction Method Based on Thickness Size Effect

This paper presents the fatigue crack growth test of 7N01 aluminum alloy specimens with different thicknesses under three-point bending. Moreover, the effect of specimen thickness on the fatigue crack growth life was analyzed. The influence mechanism of the thickness size effect on the stress intensity factor was explored. A three-dimensional stress intensity factor calculation model based on the thickness size effect was proposed by combining the finite element method and the interaction integral method. The results show that the fatigue crack growth life of 7N01 aluminum alloy decreases with the increase of specimen thickness. The numerical solutions of the stress intensity factor (the proposed model) are higher than the analytical solutions (the traditional formula) in the steady-state crack growth stage. The difference between numerical solutions and analytical solutions increases with the increase of crack growth length and specimen thickness. Compared with the analytical solutions, the relationship curve between crack length “a” and cycle number “N” from the numerical solutions is closer to the experimental data. This result proves that the proposed calculation model can correct the stress intensity factor with the thickness size effect.

Live Processing of Momentum-Resolved STEM Data for First Moment Imaging and Ptychography

A reformulated implementation of single-sideband ptychography enables analysis and display of live detector data streams in 4D scanning transmission electron microscopy (STEM) using the LiberTEM open-source platform. This is combined with live first moment and further virtual STEM detector analysis. Processing of both real experimental and simulated data shows the characteristics of this method when data are processed progressively, as opposed to the usual offline processing of a complete data set. In particular, the single-sideband method is compared with other techniques such as the enhanced ptychographic engine in order to ascertain its capability for structural imaging at increased specimen thickness. Qualitatively interpretable live results are obtained also if the sample is moved, or magnification is changed during the analysis. This allows live optimization of instrument as well as specimen parameters during the analysis. The methodology is especially expected to improve contrast- and dose-efficient in situ imaging of weakly scattering specimens, where fast live feedback during the experiment is required.

4D-STEM at interfaces to GaN: Centre-of-mass approach & NBED-disc detection

4D-scanning transmission electron microscopy (4D-STEM) can be used to measure electric fields such as atomic fields or polarization-induced electric fields in crystal heterostructures. The paper focuses on effects occurring in 4D-STEM at interfaces, where two model systems are used: an AlN/GaN nanowire superlattice as well as a GaN/vacuum interface. Two different methods are applied: First, we employ the centre-of mass (COM) technique which uses the average momentum transfer evaluated from the intensity distribution in the diffraction pattern. Second, we measure the shift of the undiffracted disc (disc-detection method) in nano-beam electron diffraction (NBED). Both methods are applied to experimental and simulated 4D-STEM data sets. We find for both techniques distinct variations in the momentum transfer at interfaces between materials: In both model systems, peaks occur at the interfaces and we investigate possible sources and routes of interpretation. In case of the AlN/GaN superlattice, the COM and disc-detection methods are used to measure internal polarization-induced electric fields and we observed a reduction of the measured fields with increasing specimen thickness.

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.

Indentation Measurement in Thin Plates under Bending Using 3D Digital Image Correlation

In the current paper, a novel experimental methodology to characterize the contact behavior on thin plates under bending is presented. The method is based on the experimental measurement of the indentation observed during contact experiments. Tests were conducted using aluminum thin plates and a steel sphere to evaluate the effect of thickness and bending during contact. For this purpose, a non-contact optical technique, 3D Digital Image Correlation (3D-DIC), has been employed to measure the out-of-plane displacements experienced at the rear face of the specimens (opposite where the contact is occurring). An indirect measurement of the experimental contact law is obtained for different plate thicknesses (2 mm, 3 mm, 4 mm, 5 mm and 6 mm) as the contact load increases. An energy balance performed during contact experiments made it possible to evaluate and quantify the applied energy to generate bending and contact deformation. When the specimen thickness increases from 2 mm to 6 mm, contact deformation reaches higher values from the total applied energy. In addition, it is also possible to evaluate the portion of the elastically recovered energy for contact and bending deformation during the unloading. It has been observed that thicker specimens show a lower elastic energy recovery due to bending and a higher elastic energy recovery due to contact. Results clearly show how the ratio between absorbed and applied energy changes as the specimen thickness increases, highlighting the relevance of the proposed method for the characterization of contact behavior in thin plates.