Strength Of Sheets Research Articles

Research on the thickness effect and micro-fracture mechanism of graphite sheets with layered structures

Size effect refers to alterations in material properties as their size varies, garnering significant attention as a cutting-edge issue. Graphite sheets, known for their exceptional thermal and electrical conductivity, the thickness effect on their mechanical properties is a notable gap in research. In this paper, the tensile strength, damage rate, and micro-fracture mechanism of graphite sheets with different thicknesses were studied through uniaxial tensile, digital image correlation (DIC) tests, and scanning electron microscope (SEM). The results reveal a significant thickness effect on the tensile strength of graphite sheets: thinner graphite sheets exhibit higher tensile strength and greater resistance to tensile fracture. Additionally, the thickness effect on the tensile strength was elucidated through the modified Weibull scaling law and Bažant size effect law. The thickness effect on the damage rate was revealed through strain evolution measured by DIC and the damage model. Thicker graphite sheets exhibit a more accelerated damage rate. It is noteworthy that the different fracture modes of layered structures are a crucial factor affecting the thickness effect of graphite sheets. Thinner graphite sheets exhibit more layers of stepped-like fracture, longer crack length, and a higher critical energy release rate. This study provides valuable insights for choosing the appropriate thickness of graphite sheets in practical applications and has the potential to enhance the safety performance of devices employing graphite sheets.

Vorticity dynamics at partial-slip boundaries

In this paper we discuss the dynamics of vorticity at partial-slip boundaries. We consider the total vector circulation, which includes both the total vorticity of the fluid and the slip velocity at the boundary (the interface vortex sheet). The generation of vector circulation is an inviscid process, which does not depend on either viscosity or the slip length at the boundary. Vector circulation is generated by the inviscid relative acceleration between the fluid and the solid, due to either tangential pressure gradients or tangential acceleration of the partial-slip wall. While the slip length does not affect the creation of vector circulation, it governs how vector circulation is distributed between the total vorticity of the fluid and the interface vortex sheet. Specifically, the partial-slip boundary condition prescribes the ratio between boundary vorticity and the strength of the interface vortex sheet, and the viscous boundary flux transfers vector circulation between the interface vortex sheet and the fluid interior to maintain this condition. The interaction between a vortex ring and a partial-slip wall is examined to highlight various aspects of this formulation. For the head-on collision, the quantity of vector circulation diffused into the fluid as secondary vorticity increases as the slip length is decreased, resulting in a stronger secondary vortex and increased rebound of the vortex ring. For the oblique interaction, the extent to which the vortex ring connects to the boundary increases as the slip length is increased.

Influence of Femtosecond Laser Surface Modification on Tensile Properties of Titanium Alloy.

Titanium alloy components often experience damage from impact loads during usage, which makes improving the mechanical properties of TC4 titanium alloys crucial. This paper investigates the influence of laser scanning irradiation on the tensile properties of thin titanium alloy sheets. Results indicate that the tensile strength of thin titanium alloy sheets exhibits a trend of initial increase followed by a decrease. Different levels of enhancement are observed in the elongation at break of a cross-section. Optimal improvement in the elongation at break is achieved when the laser fluence is around 8 J/cm2, while the maximum increase in tensile strength occurs at approximately 10 J/cm2. Using femtosecond laser surface irradiation, this study compares the maximum enhancement in the tensile strength of titanium alloy base materials, which is approximately 8.54%, and the maximum increase in elongation at break, which reaches 25.61%. In addition, the results verify that cracks in tensile fractures of TC4 start from the middle, while laser-induced fracture cracks occur from both ends.

Prediction of the Bond Strength of Externally Bonded FRP Sheets Applied to Concrete via Grooves Technique Using Artificial Neural Networks

The present study aims to fill a gap in the literature on the estimation of the bond strength of fiber reinforced polymer sheets bonded to concrete, via the externally bonded reinforcement on grooves (EBROG) technique, employing the curve-fitting on existing datasets in the literature and the methodology of Artificial Neural Networks (ANNs). Therefore, a dataset of 39 experimental results derived from EBROG technique is collected from the literature. A mathematical equation for the bond strength of FRP sheets applied on concrete via the EBROG technique was suggested using curve-fitting and general regression. The proposed mathematical equation is compared and validated with experimental results. The developed ANN model was constructed after testing diverse hidden layers and neurons to find the optimal predictions. The validation of the model is carried out using the experimental results and a statistical analysis is applied to assess the proposed mathematical equation and the proposed ANN model. Furthermore, a parametric study using the ANN model was also performed to investigate the influence of various factors on the bond strength of FRP sheets bonded to concrete. The parametric study proves that the bond strength increases with increasing the tensile stiffness per width, the FRP sheet width, and the concrete compressive strength; however, the effect of the Groove’s width and depth is found to be not monotonous.

Fatigue strength of steel–aluminum alloy dissimilar lap joints fabricated by dimple spot welding for automotive application

AbstractRecently, a new dissimilar mechanical joining method, dimple spot welding (DSW), has been developed for joining steel sheets and aluminum alloys. In this study, tensile shear tests and fatigue tests were conducted on four types of dissimilar lap joints, with two types of steel sheets and two types of Al alloys joined by DSW. Both the tensile shear strength and fatigue strength of DSW joints were found equal to or greater than those of a self‐piercing riveting (SPR) joint. In all four types of DSW joints, fatigue cracks were initiated from the Al alloy and were associated with fretting induced by repeated contact and friction. A finite element analysis showed that the tangential stress was mainly governed by the friction coefficient and also affected by the steel sheet strength. Higher‐strength steel led to lower tangential stress, resulting in a longer fatigue life for the DSW joint.

Microstructural regulation and mechanical behavior of asymmetrically extruded high-content TC4p reinforced AZ31 composite

Asymmetric extrusion (AE) is frequently used to weaken the texture of magnesium (Mg) alloys to improve their mechanical properties. In this paper, to explore the influence of asymmetric extrusion on the microstructure and mechanical properties of Mg matrix composites (MMCs), we synthesized TC4/AZ31 composite sheets via ball milling coupled with sintering and then various extrusions (including conventional extrusion (CE), transverse-directional AE (TDE), and normal-directional AE (NDE)). The differences in microstructure and performance among the three processed samples were compared and analyzed using SEM, XRD, EBSD characterization and tensile testing. The results showed that the asymmetrically extruded samples achieved better mechanical properties compared to their CE counterparts. It found that the grain refinement was relatively significant and texture evolution was dispersed in AE samples compared to the CE ones, which was attributed to the TC4 particle (TC4p) disturbance and extra asymmetric shear of matrix flow. Three different macro-textures were obtained in various extruded processes, and the micro-texture of each sample changed in diverse regions. Based on grain orientation spread (GOS) analysis, the introduction of TC4p resulted in dynamic recrystallization (DRX) and particle-stimulated nucleation (PSN) effects during the AE process at 350 °C. The mechanisms of the combination of ductility and strength in the AE-processed sheets were related to the finer grains, high Schmid factor (SF), evenly distributed dislocations and scattered texture. This work can also provide the feasibility and prospects of applying asymmetric extrusion to MMCs.

Observation of Micro Fatigue Cracks at GMA Welded Joint of Thin Steel Sheet, Effect of the Strength of Steel Sheets and Wires on Residual Stress of Thin Steel Sheet Lap-fillet GMA Weld Joint

Observation of Micro Fatigue Cracks at GMA Welded Joint of Thin Steel Sheet, Effect of the Strength of Steel Sheets and Wires on Residual Stress of Thin Steel Sheet Lap-fillet GMA Weld Joint

Improvement in Fatigue Strength of Non-oriented Electrical Steel Sheet by Low Energy Laser Peening

Improvement in Fatigue Strength of Non-oriented Electrical Steel Sheet by Low Energy Laser Peening

A Continuously Derivable Uniaxial Tensile Stress-Strain Model of Cold-Formed Circular Steels

Promoting prefabricated steel structures is considered one of the crucial approaches to meeting the objectives of “carbon peak” and “carbon neutrality” in the construction industry. Due to insufficient practical experience and incomplete fine engineering techniques in civil construction, the sustainable development of prefabricated building systems in China faces many challenges. Taking steel components as an example, the design process of tubular columns does not pay enough attention to the influence of the cold-working effect on material mechanical properties, and the constitutive relationship of cold-formed steels is not clear, which will cause an engineering economic burden and may affect the judgment of catastrophic problems. To serve the refined design and meet the intelligent construction technology using the computer platform, a modified Menegotto-Pinto model using a continuously derivable function is proposed in the paper. The proposed model can successfully describe the complete stress-strain curve of cold-formed circular mild steels as long as the basic mechanical parameters of the parent material are determined. Taking into account the influence of the strength and thickness of the parent steel sheets, as well as the internal bending radius r, on the cold-rolling effect, the model can also flexibly track the elastic-plastic nonlinearity of the cold-formed materials. In addition, the research shows that the cold-rolling effect will weaken with the increase of the yield strength fsy,0 of the parent steels and r/t ratio, and may disappear when fsy,0 reaches 1748 MPa or the r/t ratio is approximately 60, which can be used as economic indicators during the design process.

Preparation, Microstructure, and Mechanical Properties of Aluminum Matrix Composite by Accumulating Roll Bonding Method

The ARB (Accumulative Roll Bonding) method is greatly watched as a new severe plastic deformation process that uses only a conventional general rolling machine. The ARB method is a preparation method of ultra-fine-grained, high-strength thin metal and alloy sheets by repeated rolling. The purpose of this study was to clarify the effectiveness of the ARB method as a metal matrix composite manufacturing process. At first, alumina particles and short carbon fibers were used as dispersoids, and pure aluminum was used as the thin plate. Then, the dispersoids were deposited on a pure aluminum plate to 2 vol.% dispersoids. Six of these aluminum sheets were stacked to form a multi-layer composite sheet, which was then cold rolled at a rolling reduction of 67%. After rolling, the sheet composites were cut in half, overlapped, and rolled again. The composites were obtained by repeating this process. When the repetition exceeded 6 times, the dispersoids tended to disperse in the aluminum matrix. In addition, uniform dispersion progressed through further repeat rolling. By repeated rolling, the tensile strength of the composite sheets was greatly improved. In addition, the tensile strength of the composites was higher than that of the ARB-processed monolithic aluminum sheet. The improvement in strength was caused by the refinement of aluminum grains rather than the particle dispersion.

Investigation on shear and fatigue performance of CFRP/aluminum alloy single-lap adhesive joint

The size parameter is quite significant for the performance of adhesive joint. In order to investigate the effect of size parameters on the mechanical property and failure behavior of CFRP/aluminum alloy single-lap adhesive joint, T300 CFRP laminate and AA5182 aluminum alloy sheet were bonded by Sika Power 497 structural adhesive under different size parameters. The quasi-static shear test and fatigue test were implemented, and the failure behavior and failure mechanism were analyzed. Results showed that the increase of aluminum alloy sheet thickness or bonding area length could effectively improve the bonding strength of adhesive joint, when the strength of the aluminum alloy sheet or the adhesive layer was insufficient. The shear failure modes of adhesive joint mainly included adhesive failure, base material failure and mixed failure. The fatigue failure modes of adhesive joint were mainly adhesive cohesion failure and adhesive adhesion failure. At low stress levels, the aluminum alloy sheet might fracture. In addition, this work can provide a scientific guidance for the engineering application of adhesive bonding technology.

Effects of weaving parameters on the properties of completely biological tissue-engineered vascular grafts

Tissue-engineered vascular grafts (TEVGs) made of human textiles have been recently introduced and offer remarkable biocompatibility as well as tunable mechanical properties. The approach combines the use of cell-assembled extracellular matrix (CAM) threads, produced by cultured cells in vitro, with weaving, a versatile assembly method that gives fine control over graft properties. Herein, we investigated how production parameters can modify the geometrical and mechanical properties of TEVGs to better match that of native blood vessels in order to provide long-term patency. Our goals were to decrease the mechanical strength and the luminal surface profile of our first generation of woven TEVGs, while maintaining low transmural permeability and good suture retention strength. Different TEVGs were produced by varying CAM sheet strength as well as weaving parameters such as warp count, weft ribbons width, and weft tension. An optimized design reduced the burst pressure by 35%, wall thickness by 38% and increased compliance by 269%. The improved TEVG had properties closer to that of native blood vessels, with a burst pressure of 3492 mmHg, a wall thickness of 0.69 mm, and a compliance of 4.8%/100 mmHg, while keeping excellent suture retention strength (4.7 N) and low transmural permeability (24 ml·min−1·cm−2). Moreover, the new design reduced the luminal surface profile by 48% and utilized 47% less CAM. With a comparable design, the use of decellularized CAM threads, instead of devitalized ones, led to TEVGs with much more permeable walls and higher burst pressure. The next step is to implant this optimized graft in an allogeneic sheep model of arteriovenous shunt to assess its in vivo remodeling and performance.

Effect of the Homogenization Process on Titanium Oxide-Reinforced Nanocellulose Composite Membranes

Indonesian pineapple production can reach 200 tons per day; however, pineapples generate a significant amount of waste. Pineapple peel waste can be used to make membranes. Composite membranes containing TiO2 have dense properties, low porosity, and increase the mechanical strength of the cellulose sheet. This research uses various ultrasonic homogenizers to homogenize the distribution of nanocellulose and TiO2 (50% and 100% power with 30, 60, and 90 minutes). The casting method is used to shape the membrane. The SEM test shows that the higher the power used and the longer the sonication time, the less agglomeration of about 1.63%/ cm2 and a thickness of 16.56 µm. Identification of X-ray diffraction (XRD) results shows that sonication treatment for too long causes the peak at an angle of 25o to disappear. The analysis revealed no new peaks in the diagram pictures that were found using Fourier Transform Infrared Spectroscopy (FTIR) to analyze the functional groups, but it is known that changes occur in the O-H bonds of cellulose and C=C. The 50% sample with a power of 60 minutes had the lowest roughness value of 1.008 µm. Furthermore, as the power and time on the sample are increased, the roughness increases.

Recovery of sheet formability of cold-rolled pure titanium by cryogenic-deformation treatment

The sheet formability of cold-rolled pure titanium (Ti) was remarkably recovered after being slightly rolled at 77 K, i.e., subjected to cryogenic-deformation treatment (CDT). This recovery occurred because CDT increased the thinning capability of the cold-rolled pure Ti, thereby suppressing cracking by restraining local strain concentration during subsequent sheet forming. The thinning capability was high because CDT formed twins, and slip in their orientations was favorable to accommodate thinning deformation. In addition, twinning during deformation contributed to high thinning capability. The twinning was possible because during deformation, the preformed twins by CDT acted as twin nuclei, enabling growth-dominant twinning without requiring a substantial activation stress for twin nucleation. CDT also increased the strength of cold-rolled pure Ti by twinning-induced grain refinement and dislocation accumulation. These abilities of CDT are noteworthy because sheet formability and strength are typically mutually exclusive. Thus, CDT achieved a superior combination of sheet formability and strength, which cannot be achieved by cold rolling alone, overcoming the trade-off between these two properties in pure Ti.

Kraft pulp viscosity as a predictor of paper strength: Its uses and abuses

For bleached kraft pulps, two factors govern paper strength: the individual fiber strength, and the bond strength that adheres the individual fibers together in the paper matrix. Inherent fiber strength is related to the length of the carbohydrate polymers, also known as the degree of polymerization (DP). Average DP (DP) is inferred by performing pulp viscosity measurements. Under certain circumstances during kraft pulping and bleaching, the average polymer lengths can be shortened, resulting in lower pulp viscosity, and may indicate fiber damage. Fiber damage typically manifests itself as a reduction in tear strength for well-bonded handsheets. This paper will review the literature on how pulp viscosity can predict paper/fiber strength and how it can be used as a diagnostic tool. It can be a means to monitor pulp quality during pulping and bleaching, as well as to alert when such operations approach a critical threshold. However, viscosity losses must be carefully and judiciously analyzed. Like most diagnostic tools, viscosity measurements can be misused and abused, which can lead to incorrect inferences about intrinsic fiber strength. This review will also cover these misuses. The overall goal is to provide the papermaker a better understanding of what pulp viscosity is, how it correlates to potential sheet strength, and what its limitations are. It will be illustrated that when pulp viscosity drops below a critical value, it will indicate an appreciable deterioration in the paper’s tear and tensile strength.

Precipitation/recovery kinetics and mechanical properties in rapidly solidified AA6005 AlMgSi sheets via thin strip casting: Effects of casting cooling rate and thermomechanical processing route

Rapidly solidified AA6005 Al-Mg-Si sheets produced via a novel Thin Strip (TS) casting route were characterized and compared with conventional Direct Chill (DC) counterparts for the evolution of microstructure (i.e., precipitation/recovery kinetics) and mechanical properties at various thermo-mechanical tempers. To get to 1 mm final gauge, the DC ingot was homogenized, hot and cold rolled, whereas the TS casting was only cold rolled. After solutionizing (the T4 temper), the final-gauge DC and TS sheets exhibited a similar aging response upon the T6 temper. However, upon artificial aging without solutionizing, termed TSH temper, the as-rolled TS sheets showed a better age hardening kinetics, as manifested in a larger volume fraction of precipitates (primarily β' in this case) and a higher yield strength than the DC sheets (285.1 ± 5.1 MPa vs. 195.2 ± 2.2 MPa, respectively). This was attributed to the higher cooling rates the as-rolled TS sheets experienced during casting; thereby a higher Mg/Si supersaturation in the matrix due to rapid solidification. The TS sheet with the TSH temper exhibited a comparable yield strength to that of the T6 temper, though at a reduced ductility (5.5 ± 0.6% vs. 11.8 ± 0.3% elongation, respectively). Despite with a reduced volume fraction of the hardening precipitates (as compared with the T6 temper), the yield strength of the TS sheet at the TSH temper was compensated for by a considerable amount of remaining cold work from the prior cold rolling stage. Finally, a yield strengths model for the TS-TSH material was developed.

Structure changes of ethanol–water modified oat flour and the influence on the processing qualities of oat noodles

The oat dough lacks viscoelasticity and hinders its utilization in noodles. In this study, oat flour was modified by ethanol–water treatment, the changes in starch structure and properties during modification, and the influence of modified oat flour on the processing qualities of noodles containing 50% oat flour was investigated. The granular cold–water swelling starch (GCWS) was prepared during the modification, and the A–type starch crystal transformed to the V–type. No endothermic peaks were observed in the DSC thermograms. Modified oat flour has an advantage over oat flour in that it has higher cold water viscosity. As the modified oat flour content rose from 0% to 10%, the tensile strength of dough sheet increased from 345.57 g to 367.19 g, the transverse relaxation time (T2) of water molecules increased. Water absorption of cooked oat noodles rose from 125.18% to 129.32%, with a reduction in cooking loss from 10.12% to 8.97%. The shear force, which indicates the hardness of cooked oat noodles, showed a decline of from 210.83 g to 190.02 g. The mentioned results indicated the ethanol–water treatment prepared GCWS, and that improves the processing quality of dough sheets via the increase of its tensile strength.

Effect of Hemicellulose on the Wet Tensile Strength of Kozo Paper.

Kozo paper, usu-mino-gami, is frequently used as the first back lining paper of hanging scrolls in order to support the main paper with a painting or a work of calligraphy on it. To dye it an appropriate color, paper is often treated with an alkali mordant solution. However, current kozo paper products have received such comments from conservators that wet tensile strength is weak and hard to handle. Therefore, improving the wet tensile strength of kozo paper is required. In previous papers, the effect of the sheet forming method, cooking condition, and parenchyma cell content between fibers on the wet tensile strength of kozo paper has been investigated. In this paper, the effect of glucuronoxylan, the main component of hardwood hemicellulose on the wet tensile strength of kozo paper was investigated. The wet tensile strength of kozo paper, when made in different cooking conditions, was evaluated using the Finch device. Glucuronoxylan content in fiber was analyzed using GC-FID. According to the results, it has been proved that glucuronoxylan content (with a xylan to glucan molar ratio of 4.43% to 5.16%) itself contributes to the wet tensile strength of the kozo sheet. Therefore, to increase the wet tensile strength of kozo paper, it is recommended to cook under milder conditions, thus retaining a higher amount of glucuronoxylan in the pulp.

Natural rubber composites with high strength, modulus, water-resistance, and thermal stability, prepared with cellulose nanofibrils and sodium methacrylate

Natural rubber (NR) composite sheets consisting of TEMPO-oxidized cellulose nanofibrils (TEMPO–CNFs) and sodium methacrylate (mAANa) were prepared. An aqueous mixture of NR latex, TEMPO–CNFs, and mAANa was oven-dried; the dried material was kneaded to prepare cross-linked composite sheets. The NR/TEMPO–CNF/mAANa (100/20/11.2 by mass) sheets exhibited high tensile strengths of ∼23 MPa, whereas the tensile strengths of the neat NR sheets were ∼5 MPa. Scanning electron microscopy observations indicate that the TEMPO–CNFs formed fewer aggregates in the composite sheet containing mAANa than in the mAANa-free sheets. Thermomechanical tests indicate that the NR/TEMPO–CNF/mAANa sheets had higher storage moduli over the entire range from −100°C to 200°C than the neat NR sheet. The NR/TEMPO–CNF/mAANa composite sheets exhibited hysteresis loss and permanent deformation behaviors, similar to or better than those of NR/carbon black composite sheets. Thus, the NR/TEMPO–CNF/mAANa composite sheets can be used in a similar manner as those consisting of all-carbon neutral components.

PROCESSING AND CHARACTERIZATION OF MICRO AND NANOCELLULOSE FIBRES PRODUCED BY A LAB VALLEY BEATER (LVB) AND A SUPER MASSCOLLOIDER (SMC)

Cellulose nanofibers, known for their high aspect ratio (>150), are difficult to process and characterize due to a variety of reasons, including lower diameters. In this work, cellulose micro and nanofibers produced by a Lab Valley Beater (LVB) and a Super Masscolloider (SMC) were characterized using optical microscopy and SEM. The thermal degradation behavior was analyzed using thermogravimetric analysis and solar radiation tests. With decreasing clearance between two grinders, SMC refining resulted in fibres with smaller diameter (400 nm to 8 μm) and a marginal increase in the number of fines was noted. LVB refining resulted in fibres with shorter length (500 μm), but a significant increase in the number of fines, contributing to higher tensile strength. The tensile strength of SMC sheets was 10-fold lower and severe ductile fracture was observed when compared to LVB refining. However, a 30 °C increase in thermal stability was found for fibres produced by SMC compared to LVB refining. This could be due to lesser heterogeneity in fibre morphology (reduced packing density), lack of surface fibrillation (reduced mechanical interlocking) and altered cellulose-lignin interaction for SMC refined fibres. Hence, it can be recommended to use blends of LVB and SMC refined fibres to make sheets for applications involving higher temperatures (250 °C) and higher tensile strengths (25 MPa), but the sheets need to be fabricated using the cast evaporation technique by maintaining the water bath temperature at 95-98 °C. The dust capturing ability of SMC sheets was tested using a dust sampler and it was found that sheet SMC_0.01 can capture PM2.5 dust particles, i.e. a weight increase of 7% was noticed in 6 h.