Propagation Rate Research Articles

Experimental investigation of bending fatigue behaviors for T-shaped welded joint

A fatigue test was conducted on a T-shaped welded joint under three-point bending conditions. Prior to the test, the geometry of the weld toe on both sides of the specimen was observed and measured. The locations of Fiber Bragg Gratings (FBG) strain gauges were determined based on the weld toe’s geometric features. During the experiment, a 2-level load spectrum block of cyclic loading was applied, resulting in distinct beach marks on the fatigue fracture surface. The stress-time history of the weld toe’s geometric features was monitored. After the test, the fatigue fracture was observed and measured, the influence of the crack path on the crack propagation rate was analyzed, and the influence of the crack propagation pattern on the stress evolution in the nearby area was studied. The experimental results show that the multiple cracks initiation positions have strong relationship with the characteristic points of weld toe morphology. Based on the Linear Elastic Fracture Mechanics (LEFM) theory and the concept of varying remote stress, four crack propagation simulation patterns were constructed and carried out. The results show that the varying remote stress has an more important influence on life prediction of welded joints, while the threshold mainly affect the life prediction of the early stage.

Comparative investigation of fatigue properties between additively and conventionally manufactured Invar 36 alloy

The mechanical properties of ASTM F1684 (Invar 36) alloy manufactured via laser beam powder-bed-fusion (PBF-LB) technique are strongly influenced by the non-equilibrium solidification microstructure. Due to the complexity of printed microstructure, e.g., the presence of melted pools, nano-precipitates, and high-density dislocations, it is very challenging to disentangle the specific mechanisms responsible for the fatigue properties. Here, a comparative investigation of the fatigue properties between PBF-LB and conventionally manufactured (CM) samples was conducted. Dedicated characterizations, including electron channeling contrast imaging (ECCI), and high-angular resolution EBSD (HR-EBSD), were performed. The mid-cycle (104–105 cycles) fatigue behaviors of both samples are comparable, while the fatigue resistance of PBF-LB sample becomes inferior at high-cycle range (≥106 cycles). This disparity can be ascribed to the competing effect between crack nucleation and propagation. PBF-LB samples are more susceptible to fatigue crack initiation due to the printed macro-defects. Whereas, the homogeneous plastic deformation and the grain fragmentation, both triggered by the ultrafine cellular structure, efficiently mitigate crack propagation rates. Based on these findings, the current understanding of the underlying mechanisms governing the fatigue performance of PBF-LB Invar 36 alloy is deepened, emphasizing the significant advantages of non-equilibrium solidification microstructure in retarding fatigue crack propagation.

Role of Molecular Water Layer State on Freezing Front Propagation Rate and Mode Studied with Thermal Imaging.

In this work, we study the relationship between the molecular water layer (MWL) and frost freezing onset and propagation. The progression of frost has been reported to be governed by various localized icing phenomena, including interdroplet ice bridging, dry zones, and frost halos. Reports studying the state of water on surfaces have revealed the presence of a thin nanometer water layer on a range of surfaces. Regardless of further investigations that show environmental humidity, temperature, and surface energy to affect the thickness of the MWL on surfaces, the influence of the MWL on frost nucleation and propagation has not yet been previously addressed in the literature. To study the effect of the MWL on surface freezing events, a range of surface-functionalized glass substrates were prepared. In situ monitoring of freezing events with thermal imaging allowed studying the effect of surface chemistry and environmental relative humidity (RH) on the thickness and continuity of the MWL. We argue that the observed icing nucleation and propagation kinetics are directly related to the presence and continuity of the MWL, which can be manipulated by controlling the environmental humidity and surface chemistry.

Study on crack resistance of basalt fiber reinforced asphalt mixture modified by titanate coupling agent based on digital image correlation

Basalt fiber is widely used in pavement engineering for its strong mechanical properties, while its smooth surface can cause it to slip within the asphalt mixture, weakening the overall structure. In addressing this issue, this study explores the application of a titanate coupling agent (TCA) for surface treatment of the fibers. The aim was to enhance the interfacial adhesion between the fiber and the asphalt, consequently improving the crack resistance of the fiber-asphalt mixture. This study delves into the modification mechanism and chemical grafting process of TCA, employing scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Furthermore, digital image correlation (DIC) was utilized to dynamically monitor the semicircular bending test (SCB) specimens under full loading conditions, facilitating a comprehensive evaluation of the damage evolution process. Through comparative analyses of load-displacement profiles, full-field strain, displacement, and crack development, alongside the characterization of the fracture process zone (FPZ), a multi-scale quantitative assessment was conducted on the cracking characteristics of the asphalt mixtures. Throughout the damage evolution process, the toughening and crack-blocking effects of the modified fibers were extensively evaluated. Concurrently, SEM was employed to observe the fiber distribution and microscopic morphology of the fracture surface, shedding light on the mechanism of action of TBF (Treated basalt fiber) from a microscopic perspective. The augmentation of TBFAM (Treated basalt fiber Asphalt Mixture) is systematically elucidated, demonstrating that, in comparison with the other two asphalt mixtures, TBFAM exhibits prolonged microcrack formation time and a slower rate of crack propagation. The strain at the crack initiation point increased by 1.45 %, with a concurrent 2.49 % increase in the high strain area, indicative of its superior crack resistance. TCA facilitates the generation of a biomimetic coating via chemical grafting, thereby enhancing the surface structure of basalt fibers and fortifying the fiber-asphalt interface bonding ability. The favorable surface structure of TBF fosters a three-dimensional network within the asphalt mixture system, offering functionalities such as bridging, adsorption, toughening, and crack prevention. This impedes crack development and further bolsters the stability of TBFAM.

Thermal fatigue behavior of the ZGH451 Ni-based superalloy fabricated by direct energy deposition in the temperature range of 900–1100 °C

In this study, a novel Ni-based superalloy, ZGH451, has been fabricated using direct energy deposition (DED). The thermal fatigue resistance of ZGH451 is systematically evaluated at 900, 1000, and 1100 °C, primarily focusing on the crack initiation and propagation behaviors. The results indicate that higher peak temperatures lead to earlier initiation and more rapid propagation of cracks. Cracks are initiated at the defects and grain boundaries in the vicinity of the notch, and different crack propagation mechanisms (γ' phase slip shearing, γ' phase distortion shearing, and γ' phase rafting shearing at 900, 1000, and 1100 °C, respectively) are the main reason for the different cracks propagation behaviors under the three temperatures. The main crack propagation paths are oriented at approximately 45° with respect to the build direction, suggesting activation of the {111}<110> slip system. Additionally, oxidation reduces the matrix strength and passivates the crack tips, leading to varying rates of crack propagation. At elevated temperatures, the synergistic effects of thermal stress and oxidative erosion are found to be the primary damage mechanisms of thermal fatigue. Overall, the proposed ZGH451 superalloy demonstrates exceptional thermal fatigue resistance, providing a crucial experimental reference for thermal fatigue in additively manufactured superalloys.

Nimodipine inhibits spreading depolarization, ischemic injury, and neuroinflammation in mouse live brain slice preparations

Nimodipine is used to prevent delayed ischemic deficit in patients with aneurysmal subarachnoid hemorrhage (aSAH). Spreading depolarization (SD) is recognized as a factor in the pathomechanism of aSAH and other acute brain injuries. Although nimodipine is primarily known as a cerebral vasodilator, it may have a more complex mechanism of action due to the expression of its target, the L-type voltage-gated calcium channels (LVGCCs) in various cells in neural tissue. This study was designed to investigate the direct effect of nimodipine on SD, ischemic tissue injury, and neuroinflammation. SD in control or nimodipine-treated live mouse brain slices was induced under physiological conditions using electrical stimulation, or by subjecting the slices to hypo-osmotic stress or mild oxygen-glucose deprivation (mOGD). SD was recorded applying local field potential recording or intrinsic optical signal imaging. Histological analysis was used to estimate tissue injury, the number of reactive astrocytes, and the degree of microglia activation. Nimodipine did not prevent SD occurrence in mOGD, but it did reduce the rate of SD propagation and the cortical area affected by SD. In contrast, nimodipine blocked SD occurrence in hypo-osmotic stress, but had no effect on SD propagation. Furthermore, nimodipine prevented ischemic injury associated with SD in mOGD. Nimodipine also exhibited anti-inflammatory effects in mOGD by reducing reactive astrogliosis and microglial activation. The results demonstrate that nimodipine directly inhibits SD, independent of nimodipine's vascular effects. Therefore, the use of nimodipine may be extended to treat acute brain injuries where SD plays a central role in injury progression.

To overcome the unconventional polymerization behavior of single-site symmetrical metallocene catalyst in the presence of borate

The β-H transfer of a propagating chain shows an unconventional polymerization behavior with single-site catalysts. In this work, we seek to address these challenges in the presence of different alkylaluminum cocatalysts. Adjusting the amount and type of cocatalyst in the polymerization process can affect molecular weight distribution (MWD) and chain ends formed via β-H transfer. The cocatalyst's elevated triethylelaluminum (TEA) by more than 50 % resulted in a drop in isoprene (IP) concentration, Mw, and activity, while pure TEA exhibited a smaller [C*]/[Zr] % than both pure Triisobutylaluminum (TIBA) and TIBA/TEA mixture. These results indicate that the type of alkylaluminum and its varying ratio affect the activation of metallocene catalysts. Secondly, this study also includes chain termination and transfer reactions and how comonomers participate in overcoming these issues. For this complicated process, we additionally performed the quench-labeling metal-polymer bonds technique (quantitative experiments (catalyst's active site)) leading to building a kinetic model that plays a significant role in mechanistic studies. The quantitative of active sites results indicate that the lower propagation rate constant (kp) was increased by nearly 20 % with TEA (25 %), and continuously increased with the TEA amount, meaning that TEA is a noticeable essential component in the cocatalyst for higher kp. The higher kpE and kpIP with TIBA might be associated with faster propagation and lower chain transfer reactions to Al−iBu and active centers and faster re-initiation of Al−iBu. The active center and 3,4 connections of IP are increased with increased TEA, meaning that the active site based on Al−Et bonds is facilitating more coordinated-to-IP through 3,4 connections. Finally, to clarify the impact of cocatalysts on MWD, a detailed theoretical splitting of the corresponding GPC was conducted. However, compared to PE MWD, TEA decreases the MWD of the polymers and becomes narrow. It is evident that introducing IP as a comonomer and TEA as a combined cocatalyst significantly reduces the chain transfer reaction that occurs during PE.

Numerical investigation of forced convective MHD tangent hyperbolic nanofluid flow with heat source/sink across a permeable wedge

The combined effect of wedge angle and melting energy transfer on the tangent hyperbolic magnetohydrodynamics nanofluid flow across a permeable wedge is numerically evaluated. Electronic gadgets produce an excessive amount of heat while in operation, so tangent hyperbolic nanofluid (THNF) is frequently used to cool them. THNF has the potential to dissipate heat more efficiently, thereby lowering the possibility of excessive heat and malfunctioning components. The effects of thermal radiation and heat source/sink are also examined on the flow of THNF. The flow has been formulated in the form of PDEs, which are numerically computed through the MATLAB solver BVP4c. The numerical results of BVP4c are relatively compared to the published work for validity purposes. It has been detected that the results are accurate and reliable. Furthermore, from the graphical results, it has been perceived that the rising impact of the Weissenberg number accelerates the velocity and thermal profile. The effect of the power-law index parameter drops the fluid temperature, but enhances the velocity curve. The variation in the wedge angle boosts the shearing stress and energy propagation rate, whereas the increment of Wi declines both the energy transfer rate and skin friction.

Turbulent partially cracked ammonia/air premixed spherical flames

The combustion of ammonia requires, for most energy conversion systems, a combustion promoter such as hydrogen to guarantee the start-up, stability and combustion efficiency. Partially cracked ammonia (PCA) can provide sufficient hydrogen concentrations to enhance the burning velocity in comparison with pure ammonia. However, little work exists on the use of PCA blends operating under relevant turbulent conditions. To that end the outwardly propagating spherical flame configuration was employed to determine the laminar and turbulent flame propagation characteristics of PCA (NH3/(H2+N2)) and corresponding binary (NH3/H2) mixtures across various turbulent combustion regimes. First, PCA and ammonia-hydrogen blends exhibit similar flame propagation rates under various turbulent intensities, even for the laminar case. The highest turbulent burning velocity was observed at leanest conditions, as opposed to laminar flames which exhibited highest flame speed at conditions above stoichiometry. Under rich conditions, no substantial flame enhancement due to turbulence was measured irrespective of the hydrogen content. This lack of flame enhancement under turbulent conditions is attributed to the effect of preferential diffusion with good agreement observed with trends in measured Markstein numbers. The normalized turbulent flame speed is dominated by the enhanced molecular diffusivity afforded by the presence of hydrogen up to 15 % enrichment, prior to decreasing upon further hydrogen addition under lean and stoichiometric conditions. This ‘bending’ phenomenon may be the contribution of several factors including; the transitioning between combustion regimes associated with low Damköhler numbers (Da) and flame thickening; merging of flamelets due to the presence of ammonia enhancing wrinkling; and combined changes in laminar burning velocity and preferential diffusional behavior. Furthermore, good agreement for turbulent flame speed is observed with a correlation that includes the influence of turbulent stretch (Ka) and non-equidiffusion (Le), with the agreement reducing with decreasing chemical to turbulent time scale ratios (Da << 1).

Experimental investigation on the combustion characteristics of electrolyte jets containing flame retardant tris (2-chloroethyl) phosphate

Abstract It is critical to well understand the combustion characteristics of the electrolytes inside lithium-ion batteries for safety concerns, particularly the electrolyte jet flames after thermal runaway. An electrolyte jet fire setup is developed in this study to investigate the combustion characteristics of electrolyte jets with the flame-retardant additive tris (2-chloroethyl) phosphate (TCEP) under high-temperature circumstances. Jet and ignition delay times and flammability are defined to characterize the flame-retardant effects. The fundamental parameters of self-extinguishing time and propagation rate are also measured for a comprehensive comparison. The experimental results show that the propagation of electrolyte flame at ambient temperature can be entirely stopped with 40 wt % of TCEP additives and 50 wt % can make the electrolyte nonflammable. Owing to the high boiling temperature and vaporization enthalpy of TCEP, more heat is required for the decomposition of electrolytes and TCEP mixtures, resulting in lower decomposition reaction rates and heat release rates. Thus, both the jet delay times and the ignition delay times significantly increase with the TCEP additives. Moreover, analyses on the spectrum of electrolyte jet flame reveal that the suppressing effects of TCEP on the combustion of electrolyte jets are operated by scavenging the OH radical and heat release.

Influence of rolling defects on fatigue crack initiation of leaf spring

ABSTRACT Leaf springs, as vital suspension components in trucks, endure various forces such as torsion, compression, tension and impact, rendering them highly susceptible to fatigue and fracture risks, thereby posing a significant threat to vehicle safety. During the production process of leaf springs, surface decarburisation can easily occur, leading to the formation of numerous surface rolling defects. These defects exert varying influences on the initiation of fatigue crack. This study investigates the influence of various forms of rolling defects caused by decarburisation on fatigue crack initiation in 50CrMnMoNbAT leaf spring through experimental and numerical analysis of fatigue fracture behaviour. The results indicate that fracture locations in the leaf springs are predominantly concentrated approximately 297 mm and 698 mm from the ends. Furthermore, the occurrence of surface decarburisation during the rolling process engenders a significant number of surface rolling defects. Surface defects in leaf springs can be categorised into three forms: Parallel defect, Parcel defect and Occlusal defect. In terms of defect propagation rate, rolling defects on the concave surface are most prone to initiate fatigue cracks, with Occlusal defects exhibiting the highest likelihood of developing internal cracks and the fastest crack propagation rate.

Latent heat storage bio‐composites from egg‐shell/PE/PEG as feasible eco‐friendly building materials

AbstractIntegrating phase change materials (PCMs), which store thermal energy as latent heat, into renewable energy production is an efficient way to harness solar energy. Thereby, the aim of this work is to develop convenient and efficient method to prepare a bio‐composite phase change materials (BCPCMs) that are eco‐friendly and cheap. The polyethylene glycol (PEG) with large latent heat was used as PCM, eggshell powder (ES) as an energy storage material (bio‐energy resources/bio‐waste is converted into useful energy storage material), the low‐density polyethylene (PE) performed as the supporting material and powder graphite (G) was the additives for improving the thermal conductivity. According to thermal gravimetric analysis (TGA), the use of ES and G improved the thermal stability of BCPCM. On the other hand, the results of the differential calorimetric analysis (DSC) showed that BCPCM6 with the addition of 5 wt% of graphite filler in the mixture PEG/PE/ES (70/20/5 wt%) provides excellent thermal stability and high energy storage density per unit mass. In light of its high latent heat storage capacity of 120.1 J/g as well as its ability to prevent PEG exudation, BCPCM ensures higher thermal conductivity and shape stability during phase transition than ordinary PCM. Significant enhancement in melting‐solidification time shows an improvement in Thermal Energy Storage (TES) response time to the demand by adding ES and G respectively to the PCM. Based on the obtained results, the BCPCM as a potential candidate for an application in buildings of hot and dry climates.Highlights Shape‐stabilized BCPCMs were prepared by blending and impregnating method. The BCPCM combines a high storage capacity and high heat propagation rate. BCPCM6 provides excellent thermal stability and high energy storage density. Enhancement in melting‐solidification time by adding ES and G to the PCM. BCPCM as a candidate for an application in buildings of hot and dry climates.

Torsional fatigue behaviour and damage mechanisms of martensitic spring steel in the HCF regime

This study investigates the fatigue behaviour and damage mechanisms of the martensitic spring steel SAE 9254, with emphasis on short crack propagation. Shear stress-controlled torsional fatigue tests are performed at stress ratio R = -1 and test frequency f = 79 Hz using structure-sensitive measurement techniques to detect the relevant damage mechanisms. An in-situ torsional fatigue testing device is applied for shear-controlled fatigue tests at two amplitudes of the torsion angle using R = –1 and f = 5 Hz, and the microstructural-dependent short crack propagation path is documented by means of confocal laser microscopy and electron backscattering analysis. It is found that the early development of fatigue damage is characterised by the formation of slip bands, which serve as crack initiation sites. In this process, crack initiation occurs preferentially at or near prior austenite grain boundaries. Furthermore, prior austenite grain boundaries were identified as obstacles for the propagation of short cracks, because of the change of the crystallographic orientation leading to an oscillating propagation rate of short cracks. The short crack density ρCD, which is an important parameter for fatigue damage, is rapidly growing with increasing shear stress amplitude ΔτT/2 and reveals a stress type specific behaviour.

A compact tri-notched flexible UWB antenna based on an inkjet-printable and plasma-activated silver nano ink

The rapid development of ultrawideband (UWB) communication systems has resulted in increasing performance requirements for the antenna system. In addition to a wide bandwidth, fast propagation rates and compact dimensions, flexibility, wearability or portability are also desirable for UWB antennas, as are excellent notch characteristics. Although progress has been made in the development of flexible/wearable antennas desired notch properties are still rather limited. Moreover, most presently available flexible UWB antennas are fabricated using environmentally not attractive subtractive etching-based processes. The usage of facile additive sustainably inkjet printing processes also utilizing low temperature plasma-activated conductive inks is rarely reported. In addition, the currently used tri-notched flexible UWB antenna designs have a relatively large footprint, which poses difficulties when integrated into miniaturized and compact communication devices. In this work, a silver nano ink is used to fabricate the antenna via inkjet printing and an efficient plasma sintering procedure. For the targeted UWB applications miniaturized tri-notched flexible antenna is realized on a flexible polyethylene terephthalate (PET) substrate with a compact size of 17.6 mm × 16 mm × 0.12 mm. The antenna operates in the UWB frequency band (2.9–10.61 GHz), and can shield interferences from WiMAX (3.3–3.6 GHz), WLAN (5.150–5.825 GHz) and X-uplink (7.9–8.4 GHz) bands, as well as exhibits a certain of bendability. Three nested "C" slots of different sizes were adopted to achieve notch features. The simulation and test results demonstrate that the proposed antenna can generate signal radiation in the desired UWB frequency band while retaining the desired notch properties and having acceptable SAR values on-body, making it a viable candidate for usage in flexible or wearable communication transmission devices. The research provides a facile and highly efficient method for fabricating flexible/wearable UWB antennas, that is, the effective combination of inkjet printing processing, flexible substrates, low temperature-activated conductive ink and antenna structure design.

Tensile and Fatigue Strength, Fatigue Crack Propagation Rate, and Fracture Behavior of CaO-Added AM30 Alloy

Tensile and Fatigue Strength, Fatigue Crack Propagation Rate, and Fracture Behavior of CaO-Added AM30 Alloy

Crystal plasticity modeling of grain boundary softening and fatigue in U75V pearlite steel under low strain conditions: A study of cyclic rolling contact fatigue

Grain boundaries (GBs) exhibit fatigue-induced softening under low strain conditions, making them the weakest and most vulnerable regions within the material. This phenomenon significantly influences plastic deformation, plastic strengthening, and the initiation and propagation of microcracks, leading to material fatigue failure. This investigation presents a comprehensive model for the rolling contact fatigue (RCF) damage mechanism of U75V railway steel. Leveraging data from Electron Backscatter Diffraction (EBSD) and employing the Crystal Plasticity Finite Element Method (CPFEM), intragranular mechanical responses are elucidated. A modified bilinear Traction Separation Law (TSL) Cohesive Zone Model (CZM) is developed to capture the impact of GBs fatigue. Integrating this CZM with CPFEM, mechanical properties, scalar stiffness degradation (SDEG), fatigue damage factors, and crack evolution patterns are analyzed to explore the effects of grain morphology, orientation, GB angle, and area on GB fatigue damage and crack initiation. Results indicate a significant increase in GBs damage with increasing GBs angle or decreasing GBs area, highlighting the potential for reducing RCF damage through deliberate grain morphology design. Additionally, GBs are found to impede crack propagation, suggesting that grain refinement can mitigate crack propagation rates. This study enhances our understanding of intergranular fracture, mechanical responses, and microstructure evolution in U75V rail steel under cyclic rolling contact loading, offering novel methodologies for investigating metallic materials' deformation behavior concerning GB fatigue.

Improving fatigue resistance of ultrafine bainitic steel by exploiting segregation-induced bands

An ultrafine bainitic steel was designed with segregation-induced martensitic/austenitic (MA) bands. The steel comprises almost 21 % retained austenite (RA); the rest is mainly bainitic ferrite and a small fraction of martensite. The steel exhibits room temperature (RT) yield strength of ∼914 MPa, ultimate tensile strength of ∼1969 MPa, and total elongation to failure of ∼11.5 %. Low cycle fatigue (LCF) behavior was investigated under a fully reversed strain-controlled waveform at RT, with a loading-axis parallel to the MA bands. LCF stress response reveals initial cyclic hardening followed by softening or saturation, depending on the applied strain amplitude. This is attributed to the interplay of strengthening mechanisms, which include RA transforming to martensite and dislocation multiplication/interactions and the softening effects of dislocation annihilation and crack formation/propagation. Damage studies reveal a mixed fracture mode, displaying brittle striations, secondary cracks, quasi-cleavage facets, and dimples. The secondary cracks mainly appear to originate from the main crack and propagate predominantly along the matrix-bands interphase regions or within MA bands. Additionally, surface-initiated cracks along their propagation path were deflected and branched around the interphase regions. This tortuosity reduces the crack propagation rate. Overall, the significant work hardening capability of the steel, along with its banded microstructure, contributes to its superior fatigue resistance compared to non-banded bainitic steels reported in the literature.

Propagation rate transients in J-controlled fatigue characterization of adhesives

Fatigue analyses of adhesively bonded composite laminates were conducted to investigate discrepancies in experimentally measured rates of crack propagation in double cantilever beam specimens subjected to increasing or decreasing load histories. A cohesive fatigue damage model that accounts for the quasi-static traction-separation response and bridging was used in a finite element model of the test to identify transient effects caused by the evolution of the process zone in the adhesive, as well as the long-range, low-intensity bridging induced by the knit supporting carrier inside the adhesive. In addition to the quasi-static cohesive properties, the fatigue model requires two parameters that were obtained by fitting the rates of propagation at two experimental data points. The results indicate that the analyses accurately reproduce transient and steady-state rates of propagation observed in the experimental results, as well as the threshold of propagation. Transient rates of propagation consistently exceed those in steady state, which underscores the need to understand transients and account for them in fatigue characterization. The results also highlight that a Paris curve for steady-state propagation can be obtained most quickly using a decreasing load function, but that this curve is an unconservative bound to the rates of propagation. A lateral shift in the Paris curve is proposed for a conservative characterization that removes the effect of bridging and other R-curve effects.

Using the Lagrange Interpolation Polynomial Method to calculate the prevalence of coronavirus disease 2019 (COVID-19) in Turkey

The goal of this paper is to look into a numerical approximation for the spread of the coronavirus disease 2019 (COVID-19) in Turkey. From March 11th to November 30th, all data is examined one by one for this purpose. The Lagrange interpolation method does not require evenly spaced x values. On the other hand, it is usually preferable to look for the closest value in the table and then use the lowest-order interpolation that is consistent with the functional form of the data. Using this method, a function for monthly and general data on the number of COVID-19 disease deaths and cases infected with the disease is obtained. Matlab programming is used to obtain Lagrange interpolation polynomials. Simulations for month by month and general data are obtained using Lagrange interpolation polynomial. The rate of spread of disease and death numbers is obtained by taking the first derivative of this function. Monthly and general tables are constructed for this propagation rate data. Peak point of the disease and different change values ​​are determined from the information in these simulations. The rates of death and spread of the disease by months are compared. As a result of this comparison, it can be seen in which months the rate of spread of disease and death increases and decreases. Monthly increase and decrease values ​​can be seen from the Figure 3-Figure 6. For example, a relative decrease can be observed in April and May

Analysis of cracking failure of gast iron brake disc

To investigate the causes of crack initiation and propagation in brake discs, a comprehensive analysis of surface cracks was conducted using macroscopic observation, metallographic observation, scanning electron microscopy, and microhardness testing. The results revealed that the internal structure of the brake disc material consists mainly of pearlite and a small amount of ferrite. Near the friction surface, the internal structure undergoes grain refinement and the formation of a small amount of granular pearlite, with a microhardness range of 350 ∼ 410 HV. Based on metallographic observations, it is evident that there are loose defects within the brake disc. When the brake disc is subjected to external loads and thermal stress, stress concentration occurs around these defects, initiating cracks and their outward propagation, thereby accelerating the crack propagation rate. The crack growth exhibits a combination of transgranular and intergranular characteristics. Analysis of the crack width in the brake disc reveals that the width of the radial primary cracks is approximately three times that of the micro-cracks, and the depth of the micro-cracks is relatively shallow, with a maximum depth of 4 mm. In contrast, the primary crack extends to a depth of 9 mm. This implies that the failure of the brake disc is associated with the extension and deepening of cracks.