Bending Of Samples Research Articles

Non-planar additive manufacturing of pre-impregnated continuous fiber reinforced composites using a three-axis printer

Non-planar additive manufacturing (AM) demonstrates great potential in enhancing interlayer bonding force and surface smoothness of parts, offering a more flexible design and manufacturing approach for continuous fiber composites to fully exploit material capabilities. This study developed a three-axis printer utilizing an adjustable fiber printing head that can achieve non-planar slicing (NPS) AM of pre-impregnated continuous fibers. The research delves into the influence of deposition inclined angle on the surface roughness of printed samples, enabling the design and printing of NPS samples using continuous carbon fiber (CF), glass fiber (GF), and hybrid fiber composites. The investigation also assesses bending failure morphologies of the printed parts and validates the efficacy of the NPS method through the fabrication of the double-sinusoidal curved surface structure and spherical surface grid structure. The results indicated that maintaining a deposition inclined angle below 15° is crucial to ensure surface accuracy in continuous fiber printed parts. Curved surface bending samples printed with NPS method exhibit substantial enhancements in bending performance and surface accuracy compared to those produced using planar slicing (PS). The NPS-CF sample achieves a remarkable increase of over 170% in maximum bending force and a 63% reduction in surface roughness compared to the PS-CF sample.

The influence of temperatures on the mechanical properties and fracture behavior of rocks under mixed mode I/II loading

A comprehensive understanding of the fracture behavior of pre-heated rocks under to mixed mode I/II loading is crucial for deep underground engineering. The effect of high temperature on the fracture process zone (FPZ) and fracture toughness of rocks was experimentally investigated using semi-circular bend (SCB) samples. Surface displacement and associated strain field under loading were captured using digital image correlation. The results showed that the mechanical properties of SCB samples gradually decreased with increasing temperature. Rocks exposed at temperature exceeding 600 °C demonstrated a significant reduction in peak load, generalized stiffness, fracture toughness, and absorbed energy. Moreover, the load–displacement curves and macroscopic fracture characteristics of pre-heated SCB samples revealed a transition from brittleness to ductility with increasing temperature under mixed mode I/II loading. Both the length and width, as well as the crack tip opening displacement of the FPZ, increased with rising temperature. At lower temperatures (25 ∼ 400 °C), the ratio of FPZ length to width typically ranged between 2 and 3. While, at elevated temperature (600 ∼ 1000 °C), this ratio expanded to between 3 and 4. The initiation of thermally induced cracks in rocks will accelerate damage evolution under mixed mode I/II loading, as indicated by the development of the maximum principal strain with displacement. Scanning electron microscopy and polarization microscopy images of the microscopic fracture morphology in pre-heated rocks illustrated isolated and dispersed microcracks appeared at lower temperatures, whereas at elevated temperatures, intricate microcrack networks and broken grains were observed.

Fatigue and delamination of 6061 aluminum cold spray on a similar wrought substrate

Fatigue crack growth and fracture of a thick 6061 aluminum cold spray coating on 6061-T6 aluminum substrate were studied through in-situ observation of fatigue crack growth through the coating to the interface in notched four-point bend samples. Mode I cracking was observed through the coating before delamination at the substrate. Crack tip strain fields during the delamination event were plotted with DIC. Interfacial steady-state strain energy release rates were measured using the bimaterial four-point bend solutions by Charalambides. The interfacial crack primarily spread cleanly along the coating/substrate interface, with a post-fracture surface morphology containing a wavy structure with an amplitude on the same order of magnitude as the cold spray particle diameters. The in-situ video of crack propagation and coating-substrate delamination provides lessons for improving the coating-substrate interfacial toughness and thus expands use cases for structural cold spray applications

Experimental and meshless numerical simulation on the crack propagation processes of marble SCB specimens

In order to correctly understand the rock multi-fissure interactions and crack propagation laws, three-point bending fracture tests of the marble semi-circular bend samples (SCB samples) are carried out, and the crack propagation processes are simulated by the Smoothed Particle Hydrodynamics (SPH) method. Results show that: Cracks initiate from the guide fissure tip and propagate vertically in the SCB sample with no obstacle fissures; The overlap positions of crack1 and the obstacle fissure are biased towards the lower left end of the obstacle fissure with the increase of the inclination angle α; With the increase of the eccentric distance d, the overlap positions of crack1 and the obstacle fissure are biased towards the upper right end of the obstacle fissure; The peak load of the samples decreases with the increase of inclination angle α, while increases with the increase of eccentric distance d. The “failure coefficient” η is introduced into the conventional SPH momentum equations, which can simulate the multi-fissure propagations of the SCB samples. The simulation results are consistent with the experimental results, and the mechanisms of the crack propagation morphologies between the guide fissure and the obstacle fissure are discussed. The research results can provide some references for correctly understanding the crack propagation mechanisms of multi-fissure rock masses and the applications of the SPH method into simulating rock multi-fissure interactions.

An approach for identifying the deformation-induced strain from tensile tests and x-ray diffraction measurements

ABSTRACT Non-uniform plastic deformation and phase transformation introduce residual stress (RS) in a material. The present study focuses on the influence of tensile strain on RS development in 304L austenitic stainless steel, wherein strain-induced martensite (SIM) transformation influences deformation behaviour. Room temperature tensile tests were interrupted at various tensile strains between the material yield and ultimate tensile strength at 5.21 × 10−4 and 1.3 × 10−2 s−1 strain rates. Microstructural characterisation of as-received and deformed samples by electron backscatter diffraction provides evidence of SIM formation and shear bands. Analysis of tensile flow and work hardening behaviour is discussed in correlation to the microstructural and dislocation density variations. In addition, RS in the austenite and martensite phases was measured using the x-ray diffraction method, and the RS balance that occurs between the longitudinal and transverse components and the two phases after tensile deformation is presented. It is shown that a combined analysis of RS and x-ray diffraction peak width could be utilised to find the deformation level in tensile fractured, press brake bent, and roll bent samples.

Experimental and theoretical investigation of the influence of post-curing on mixed mode fracture properties of 3d-printed polymer samples

This study explores the mechanical properties and fracture characteristics of additively manufactured acrylonitrile butadiene styrene specimens, focusing on the impact of raster angle and post-process heat treatment. To this end, a large number of tensile and semi-circular bending samples with three distinct raster angles of 0/90°, 22/ − 68°, and 45/ − 45° were prepared and exposed to four types of heat treatments with different temperature and pressure conditions. Simultaneously, theoretical models of maximum tangential stress (MTS) and generalized MTS (GMTS) were developed to estimate the onset of specimen fracture under mixed-mode in-plane loading conditions. Recognizing the non-linear behavior within the stress–strain curve of tensile test samples, particularly in the annealed samples, an effort was undertaken to transform the original ductile material into a virtual brittle material through the application of the equivalent material concept (EMC). This approach serves the dual purpose of bypassing intricate and tedious elastoplastic analysis, while concurrently enhancing the precision of the GMTS criterion. The experimental findings have revealed that while the annealing process has a minimal effect on the yield strength, it considerably enhances energy absorption capacity, increases fracture toughness, and reduces the anisotropy. Additionally, the combined EMC-GMTS criterion has demonstrated its capability to predict the failure of the additively manufactured parts with an acceptable level of accuracy.

Tensile Strength and Mode I Fracture Toughness of Polymer Concretes Enhanced with Glass Fibers and Metal Chips.

This study experimentally investigates the influence of metal chips and glass fibers on the mode I fracture toughness, energy absorption, and tensile strength of polymer concretes (PCs) manufactured by waste aggregates. A substantial portion of the materials employed in manufacturing and enhancing the tested polymer concrete are sourced from waste material. To achieve this, semi-circular bend (SCB) samples were fabricated, both with and without a central crack, to analyze the strength and fracture behavior of the composite specimens. The specimens incorporated varying weight percentages comprising 50 wt% coarse mineral aggregate, 25 wt% fine mineral aggregate, and 25 wt% epoxy resin. Metal chips and glass fibers were introduced at 2, 4, and 8 wt% of the PC material to enhance its mechanical response. Subsequently, the specimens underwent 3-point bending tests to obtain tensile strength, mode I fracture toughness, and energy absorption up to failure. The findings revealed that adding 4% brass chips along with 4% glass fibers significantly enhanced energy absorption (by a factor of 3.8). However, using 4% glass fibers alone improved it even more (by a factor of 10.5). According to the results, glass fibers have a greater impact than brass chips. Introducing 8% glass fibers enhanced the fracture energy by 92%. However, in unfilled samples, aggregate fracture and separation hindered crack propagation, and filled samples presented added barriers, resulting in multiple-site cracking.

Experimental exploration of fracture behavior (pure mode III) in eco-friendly steel fiber-reinforced self-compacting concrete with waste tempered glass as coarse aggregates

To aid in the creation of sustainable structures, scientists have utilized waste materials found in the environment to serve as alternatives for traditional resources in the construction sector. They have undertaken extensive investigations pertaining to this matter. In this particular study, tempered glass as waste glass coarse aggregate (WGCA) was substituted for natural coarse aggregate (NCA) at varying proportions of 15%, 30%, and 45% in the formulation of eco-friendly self-compacting concrete (SCC), combined with hooked-end steel fibers (SFs) at various volumes. The study assessed concrete’s flowability, permeability, compressive strength, and fracture parameters at 28 and 56 days. A total of 240 edge-notched disc bending samples (ENDB) and 60 cubic samples (150 × 150 mm) were tested to assess fracture resilience and compressive strength, respectively. The results showed that increasing SF and WGCA content reduced slump flow diameter and blockage ratio, particularly at higher levels. The solidified characteristics of all specimens incorporating SF and WGCA displayed heightened attributes when contrasted with the reference sample. Among the entire array of specimens, WG15SF0.5 and WG30SF0.5 exhibited the most superior performance, demonstrating an average percentage elevation of 20.29 and 27.63 in both compressive strength and fracture toughness assessments across the different curing periods. SF had the most significant impact on post-cracking behavior by enhancing load-bearing capacity through a bridging fiber mechanism. Through a comparison of the influence of SFs and WGCA on the fracture toughness of pure mode III, it was observed that the inclusion of SF in samples with a 30% replacement of WGCA resulted in an average increase of approximately 15.48% and 11.1% in this mode at the ages of 28 and 56 days, respectively, compared to the control sample.

Laboratory Investigations on Fracture Toughness of Self-compacting Concrete Containing Recycled Materials

This article investigates the fracture toughness in self-compacting concrete containing different percentages of recycled concrete materials using edge-notched disc bend (ENDB) samples. For this reason, 0, 25, 50, 75 and 100 percent of recycled aggregate were used instead of natural aggregate in the mixing designs. To obtain the fracture toughness, ENDB samples were used under loading of mixed mode I/III and pure modes I and III. Cubic samples were also used to obtain compressive strength. The results show that the compressive strength of the samples has a direct relationship with the fracture toughness and the reverse ratio with the percentage of recycled concrete materials. Also, samples containing 25% recycled materials have the highest compressive strength and fracture toughness. Furthermore, as the recycled percentage of the samples increases, the performance of samples against shear forces and compressive strength is reduced. Keywords: Fracture toughness, Mixed mode I/III, Recycled materials, Self-compacting concrete, ENDB sample

Influence of Aging on the Flexural Strength of PLA and PLA-X 3D-Printed Materials.

The three-point bending test is a valuable method for evaluating the mechanical properties of 3D-printed biomaterials, which can be used in various applications. The use of 3D printing in specimen preparation enables precise control over material composition and microstructure, facilitating the investigation of different printing parameters and advanced materials. The traditional approach to analyzing the mechanical properties of a material using a three-point bending test has the disadvantage that it provides only global information about the material's behavior. This means that it does not provide detailed insight into the local strain distribution within the material. However, the 2D Digital Image Correlation (DIC) method offers additional insight, especially in terms of strain localization. DIC is an optical technique that measures full-field displacements and strains on the surface of a sample. PLA and enhanced PLA-X material were utilized to create three-point bending samples. The aim of this paper was to analyze and compare the influence of aging on the mechanical properties of PLA and enhanced PLA-X materials using three-point bending coupled with the DIC method. The results showed statistically significant differences between the PLA and PLA-X, for both the new and aged materials. The aged PLA samples had the highest average value of maximal force around 68 N, which was an increase of 8.8% compared to the new PLA samples. On the other hand, the aged PLA-X material had an increase of 7.7% in the average maximal force compared to the new PLA-X samples. When comparing the two materials, the PLA samples had higher maximal force values, 6.2% for the new samples, and 7.3% for the aged samples. The DIC results showed that both the new PLA and PLA-X samples endured higher strain values at Points 1 and 2 than the aged ones, except for the aged PLA-X sample at Point 2, where the new sample had higher strain values. However, for the first 5 min of the experiment, both materials exhibited identical behavior, after which point significant differences started to occur for both materials, as well as at Points 1 and 2. A more profound comprehension of the biomechanical characteristics of both PLA and PLA-X material is essential to enhance the knowledge for potential biomedical applications. The DIC method was found to be a powerful tool for analyzing the deformation and failure behavior of samples and for complementing the traditional approach to material testing.

Significant improvement of bending properties for WE43 magnesium alloys under the coupling effects of weak basal texture and high deformation temperature

Significant improvement of bending properties (approximately 64.7%) for WE43 magnesium alloy was realized by weakening the basal texture and raising the deformation temperature. The mechanisms for such improvement were investigated in detail by combining the experiment and finite element model. The results concluded that the coupling effects of weak basal texture and high deformation temperature was the key reason producing the above improvement of bending properties. Specially, the TD sample with weak basal texture was more conducive to activating basal slip than the RD sample, resulting in its higher strain hardenability and consequently more significant bending properties. Based on weak basal texture, raising the deformation temperature could further improve the bending properties. This improvement mechanism was attributed to the abundant activations of non-basal slip instead of basal slip, which could increase the independent slip systems and efficiently delay the development of the strong basal texture. Moreover, the occurrence of partial DRV and DRX relieved the stress concentrations by consuming the dislocations, further improving the bending properties. The activations of these deformation mechanisms matching the corresponding bending stress states caused the crystal rotation and the texture variety in the bending samples. Basal slip activation aligned the (0002) basal planes parallel to tensile stress in the outer region or perpendicular to compressive stress in the inner region. Additionally, prismatic slip activation induced crystal rotation around the c-axis, developing <10-10>//LD texture in the outer region but <10-10>⊥LD texture in the inner region.

Effect of Nozzle Diameter on Tensile and Fracture Behavior of FDM-PLA Samples

Fused Deposition Modeling (FDM) technique is a subcategory of additive manufacturing processes that works by extruding a fine polymeric filament on the heated bed. The current research paper surveys the influence of nozzle diameter as a manufacturing parameter on the mechanical properties and mode I fracture behavior of the FDM-PLA samples. Four different nozzle diameters of 0.4, 0.6, 0.8, and 1 mm with two raster configurations of 0/90° and 45/-45° were considered for printing the dog-bone and Semi-Circular Bending (SCB) samples. Also, to evaluate the fracture resistance of FDM-PLA pre-cracked samples, the critical value of J-integral (Jc) was used and calculated through a finite element analysis. The obtained results indicated that the raster angle of 45/-45° resulted in higher mechanical properties compared to 0/90° one, also, the 1 mm nozzle diameter presented a better performance from a mechanical property point of view. The SCB sample printed through the 1 mm nozzle diameter and 45/-45° raster orientation had the highest value of Jc (10400 J/m2). Besides, the crack extension paths were monitored and discussed comprehensively.

4D Printing of Commercial based Conductive Polylactic Acid: Strength and Resistance Properties

Four-dimensional (4D) printing technology is an innovative concept integrating conventional 3D printing additive manufacturing (AM) and smart materials programed to change properties or shape over time in response to environmental stimuli. This study aims to characterize the strength and electrical resistance of a commercial electrically conductive polylactic acid (PLA) with carbon black (CB) particles printed by fused filament fabrication (FFF) technique to evaluate the development feasibility of two sensor prototypes: (1) a load-cell sensor, and (2) a temperature sensor. Experiments were performed to study the orientation and raster angle–dependent mechanical and electrical performance of a PLA-CB conductive polymer manufactured by AM-FFF technology. A good agreement was observed between the data received from the manufacturer and the experimental density of the conductive AM-FFF PLA-CB three-point bending samples. The mechanical properties of 3D-printed PLA-CB were characterized based on three-point bending flexural test. Two build orientations (flat and upright) and three raster patterns (0°/90°, +45°/-45°, and concentric) were printed to check the optimal mechanical properties for electrical conductivity; six samples were printed for each one of the six configurations. The three-point bending flexural test results of the examined 36 specimens demonstrated that the samples printed in the concentric and +45°/-45° raster patterns exhibit the best mechanical properties, with the highest flexural strength and flexural modulus of elasticity in the flat orientation. Nevertheless, the concentric pattern has an advantage over the +45°/-45° pattern due to higher density and homogeneity. To examine the electrical resistance of the PLA-CB material another 12 specimens were printed and divided into four groups, each with different lengths. The electrical intrinsic resistivity was calculated from the geometry of the specimens and the measured resistance, with an average value of 13.2 [Ω·cm]. To check the production feasibility of a load-cell sensor prototype the effect of load on electrical conductivity was examined, however no effect of load on resistance was discovered. To prove the production feasibility of a sensor prototype for temperature measurements a preliminary device was designed and the effect of increasing and decreasing the temperature between 24 and 42°C on electrical resistance was examined. Based on the experimental results a calibration function was built linking between the temperature and the material’s resistance.

Pure modes I and II fracture behavior of Modified-Hot mix asphalt (HMA) under Long-Term aging condition

Top-down crack (TDC) as one of the pavement distresses, has a significant contribution to the quality of pavement service. Low-temperature top-down crack, which are subcategories of low-temperature crack (LTC) is representative of the cracks located on the pavement's surface and are directly affected by different environmental conditions such as temperature, air (oxygen), and light. Therefore, in the pavement body, this type of crack is more affected by long-term aging (LTA) than other cracks. To make sustainable mixtures, this research, it was tried to assess the long- and short-term fracture performance of hot mix asphalt (HMA) and HMA reinforced with different percentages of hospital waste pyrolysis carbon black (HWPCB) and hospital waste pyrolysis hydrocarbon (HWPHC) under mode I and II. The symmetrical specimen SCB and modified specimen SCB-2 geometries are utilized to simulate pavement crack behavior under tensile (opening) deformation and shear (sliding) deformations, respectively. For simulating the cracking behavior of semi-circular bending (SCB) samples in the laboratory with the pavement cracking behavior under the LTA process, an LTA condition, which was equivalent to a 12-year failure, was applied. Then, the long- and short-term fracture performance of the samples was examined using different fracture indices at temperatures of −15 °C. The results revealed that adding HWPCB and HWPHC to the HMA sample improved the fracture energy (GIIF and GIF) and fracture toughness (KIIC and KIC) of the HMA mixture under modes II and I (at −15 °C). Also, the improvement of the fracture stiffness and reduction of fracture brittleness of HMA specimens reinforced with HWPCB and HWPHC was concluded in long- and short-term conditions at the studied temperature (under modes II and I). From an operational point of view, the HMA mixtures reinforced with lower percentages of HWPCB and HWPHC are recommended for use in areas with an average temperature of about −15 °C and medium-heavy vehicle volumes. Also, the HMA mixtures reinforced with higher percentages of HWPCB and HWPHC are recommended for use in areas with medium temperatures and medium-heavy vehicle volumes. Moreover, the mixture containing both additives (HWPCB + HWPHC) is recommended for areas with medium temperature and high heavy vehicle volumes.

INVESTIGATION OF CARBON-ALUMINUM COMPOSITE WITH A BARRIER COATING ON CARBON FIBERS

Barrier SiO2 coatings on the surface of carbon fibers were deposited by the sol-gel solutions (dip coating) based on tertraethoxysilane Si(C2H5O)4. The average thickness of the barrier SiO2 coating on carbon fibers is 127 ± 30 nm. Carbon-aluminum composites were obtained by a type of liquid-phase infiltration — by the shell molding process. The components of the composite were placed in a steel hermetic shell, then after the shell evacuate and heat until the aluminum melts, the fibers were infiltrated by the melt under the external pressure, followed by cooling. Composites with SiO2 coating and without coating on carbon fibers were obtained. After extracting the composite from the metal shell, the structure, phase composition, and mechanical properties of the samples were studied. Studies of the structure of composites showed that the interfiber space is filled with aluminum melt, without porosity and macroscopic defects. The study of the phase composition of the composite reinforced with uncoated carbon fibers showed that aluminum carbide peaks are observed at the angles 2θ = 41°, 67°, 74°. Quantitative analysis carried out by the Rietveld method revealed that the amount of aluminum carbide in the composite is 12.0 ± 1.3 %. The deposition of a barrier SiO2 coating on carbon fibers leads to a decrease in the intensity of the main peaks of aluminum carbide, while the amount of Al4C3 decreases by 4 times, to 3.0 %. An analysis of the fracture surface of the samples after mechanical testing revealed that the fracture of the composite reinforced with uncoated carbon fibers is almost flat. No protrusions and relief are observed on the fracture surface. The fracture surface of a composite reinforced with coated carbon fibers has a relief surface, and separately sticking out fibers are observed. Mechanical tests of samples for three-point bending showed that the barrier coating on the fibers increases the strength to 520 ± 50 MPa, the strength of the uncoated composite is 350 ± 8 MPa. Barrier SiO2 coating applied to the surface of carbon fibers prevents the formation of aluminum carbide and fiber degradation in the carbon-aluminum composite.

The effect of induced precipitations and pre-twins on the bending neutral layer migration behaviors of AZ80 Mg alloy sheet

To explore the effect of the precipitated phase particles and twins on the microstructure evolution and neutral layer evolution during bending, {10–12} tensile twins were introduced along the transverse direction (TD) on AZ80 Mg alloy sheets at room temperature. Then pre-compressed samples were aged to induce more precipitations. The reverse tensile tests were carried out at room temperature, and the three-point bending deformation was carried out at 100 °C. After aging treatment, precipitations increased. The results showed that twin crystals can promote precipitation formation. And the YS (yield strength) values of the pre-twinned aged samples were significantly larger than that before aging. During the bending process on the pre-compressed samples, the outside of the sample was dominated by the detwinning behaviors, while the inside region was dominated mainly by twinning. For pre-compressed bending samples, the k values were smaller than the initial bending sample. The tension and compression asymmetry in its inner and outer regions was weaker than that of the original bending sample. The existence of precipitations hindered the detwinning behaviors in outside the pre-twinning aged bending samples, and the twinning in inner region was restrained as well so that the inner and outer tension asymmetry decreased. The k values were smaller than that of the unaged samples, which was beneficial to weaken the bending springback of Mg alloy sheets.

Low temperature cracking behavior of modified asphalt mixture under modes I and III

The study of the short- and long-term cracking behavior of asphalt pavement under tensile and tear deformations, and the production of sustainable mixtures using recycled additives, were the two main goals of this study. For this purpose, two types of additives, namely pyrolysis carbon black (PCB) and pyrolysis hydrocarbon (PHC), which were made from hospital waste recycling as a result of the COVID-19 pandemic, were used to study the fracture behaviour of asphalt mixture under modes I and III (at −15 °C). For simulating the actual pavement conditions with the Edge Notched Disc Bend (ENDB) samples, 0 and 3 freeze–thaw damage (FTD) cycles were applied to mixtures. Laboratory findings indicated that the addition of 6, 12, and 18 % PCB, 1.25, 2, and 2.75 % PHC, and 18 % PCB + 2.75 % PHC into the asphalt mixtures resulted in an increase in the total fracture energy of mixtures at −15 °C by increasing the GIfpre-peak and GIIIfpre-peak as well as increasing the fracture toughness, for both FTD cycles. Also, the results of brittleness indices revealed that using 18 % PCB + 2.75 % PHC in the asphalt mixture had more flexible behaviour than the mixture containing PCB (due to a higher average brittleness index) and more brittle behaviour than the mixture containing PHC (due to a lower average brittleness index) under mode I. While the mixtures containing PCB, PHC, and 18 %PCB + 2.75 %PHC were more flexible under mode III. Finally, the mixture containing 18 % PCB + 2.75 % PHC had the best fracture performance under mode I. It increased the asphalt mixture's fracture energy and toughness respectively under 3 FTD cycles by 62 and 54 %, in comparison with the unmodified mixture and without applying FTD cycles. Also, it was indicated that the modified mixture with 18 %PCB + 2.75 %PHC can compensate for 97 % of the fracture energy decrease due to the influence of FTD cycle (under mode III), while in terms of the fracture toughness index, a 12 % increase was obtained.

The effect of aging heat treatment on the formability and microstructure of the AA6063 tube in the rotary draw bending process

This research delves into the impact of aging heat treatment on both the formability and microstructural characteristics of 6063 aluminum tubes when subjected to the rotary draw bending (RDB) procedure. To ascertain a heat treatment regimen that can yield desirable hardness and formability for the bending process, the tube was subjected to T3, T6, and annealing heat treatment cycles under diverse conditions and subsequently the tube's bendability was evaluated. The findings indicate that as temperature and dissolution time are raised, there is a corresponding rise in the extent of elliptical deformation, consequently resulting in higher hardness values. The research outcomes suggest that elevating both temperature and dissolution time leads to a more pronounced elliptical shape in the bent sample. For instance, when subjected to heat treatment at 530 °C and 545 °C for 60 min, the samples exhibited respective increases in ellipticity of 5.30 % and 4.34 % compared to those treated for just 30 min. Additionally, higher internal pressure led to a reduction in the degree of elliptical deformation, notably a decrease of 9.85 % observed at a pressure of 20 bar. Moreover, the hardness of samples subjected to the T3 cycle exhibited an upward trend with increasing both temperature and duration of heat treatment. To elaborate, the hardness measurements were conducted at three distinct temperatures (530 °C, 545 °C, and 560 °C) and four different durations (30, 45, 60, and 75 min). The sample subjected to a 75-minute heat treatment at 560 °C exhibited the highest recorded hardness value, measuring at 62.55 HV. In summary, the results indicate that aging heat treatment can enhance the formability of 6063 aluminum tubes during the RDB process. Furthermore, it is noteworthy that temperature and internal pressure serve as crucial parameters to control in order to mitigate elliptical deformation and enhance hardness.

Ultrahigh-temperature mechanical behavior and failure mechanisms of SiCf/SiC composites

SiCf/SiC composites are potential candidates in the aerospace fields for application as high-temperature structural components. Their mechanical properties and failure behaviors at ultra-high temperatures (above 1473 K) are important to obtain systematically. This work performed the in-plane compressive, bending, and interlaminar shear tests at 1573 K and 1773 K in an inert atmosphere. The results showed dramatically that the in-plane compressive and interlaminar shear strengths increased with the temperature increment from 1573 K to 1773 K. In contrast, a reduction in flexural strength was noticeable. To reveal the failure mechanisms, fracture surface microstructures of these SiCf/SiC samples were characterized. It was found that the fiber surfaces for the samples tested at 1773K were rougher than the samples tested at 1573K. It meant that, with the temperature increasing, the fiber-matrix interfaces enhanced, which resulted in increasing compressive and interlaminar strengths. For the bending tests, serious delamination occurred when the temperature increased to 1773K, which induced the flexural strength reduction. The numerical simulations of bending samples were developed to reveal the mechanism of strength degradation as the temperature elevated.

Prediction model and measurement of fracture parameters in eco-friendly coarse copper slag-SFRSCC based on semi-circular bending test

This research has used 16 concrete mix designs containing 0.1, 0.3, and 0.5% steel fiber (SF), and 20, 30, 40, 50, and 60% copper slag (CS) to examine their fresh and hardened characteristics, and study their microstructural features with the help of scanning electron microscope (SEM) images. In addition, it has tried to evaluate the fracture characteristics of semi-circular bending (SCB) samples under loading modes I, I/II, II/I, and II. According to the results, increasing CS will improve the fresh concrete properties and reduce the negative SF effects on its performance. At 60% (fixed) CS, using 0.1% SF reduces the compressive strength by 10.08%, and applying 0.5% SF increases it by 17.24%, compared to the control sample. Increasing SF and CS improves the tensile strength of all concretes in the 14.02–86.02% range, compared to the control design. SEM images show that up to 30% replacement, the WCS-steel fiber reinforced self-compacting concrete (SFRSCC) microstructure is homogeneous, integrated and dense, and the fracture toughness and energy are higher under, respectively, pure loading modes II and I than other modes. Fracture toughness of concretes with the highest SF and CS volumes, compared to plain concrete, has increased 1.45, 1.61, 1.67, and 1.36 times under loading modes I, I/II, II/I, and II, respectively. Compared to ANN, using ALK to estimate the fracture features reduces the need for training data by 36.53%, and R2 (correlation coefficient) reduces by 0.91 and 1.52% for estimating the fracture energy and fracture toughness, respectively. Using ANN and ALK can provide a robust prediction model to estimate the fracture energy parameters of the CS-FRSCCs (R2 ≥ 0.970).