Bending Of Samples Research Articles

Investigating fracture toughness of graphene epoxy nanocomposites using single edge notched bending specimens

Abstract The purpose of this study was to examine the fracture toughness of epoxy-based graphene nanocomposites. The single edge notched bending (SENB) samples with precrack tips were created by either tapping or sliding methods. For the tapping method, a single tap was conducted on a razor blade such a crack with a length of 2 mm was instantly propagated. For the sliding method, a razor blade was slid forward and backward into the samples, and a crack was generated with the blade edge. The SENB samples with graphene loadings (0.15 and 0.3 wt%) were subjected to three-point bending tests to evaluate fracture toughness. Results indicated that the graphene loading did not considerably affect the fracture toughness of the samples with tapping-induced precrack tips. However, the fracture toughness of the samples with sliding-induced precrack tips decreased as the graphene loading increased. For the 0.3 wt% graphene nanocomposites, the fracture toughness levels of the samples with sliding- and tapping-induced precrack tips were equal. In order to explicate the experimental results, the plastic zone sizes around the crack tip were evaluated using finite element analysis. For the sharp precrack tips (tapping method), the plastic zone was comparatively small (brittle behavior); hence, the effect of graphene on the inception of crack extension was minimal. Nevertheless, for blunt crack tips (sliding method), the plastic zone was larger and the size decreased as graphene loading increased; thus, the fracture behavior measured from the sliding method was dramatically influenced by the graphene loading.

The Blue Stain Attack and Its Effect on The Mechanical Properties of Five Light-Colour Woods

The processing of light-color wood often has problems due to blue stain, which can reduce the quality and economic value of the wood. This research aimed to evaluate the intensity of blue stain attack on five light-color woods and the effect on their mechanical properties. Pine, rubber, jabon, sengon, and gmelina logs with an average diameter of 30 cm were turned into 3 cm thickness disc samples for staining fungal test; 2 cm × 2 cm × 30 cm and 3 cm × 3 cm × 6 cm samples for bending and hardness tests respectively. All the samples were exposed to the environment above ground on a rack for six weeks. The results showed that the highest intensity of blue stain attack was found in pine wood (84%), followed by rubber wood (80%), jabon wood (65%), sengon wood (36%), and gmelina wood (27%). The mechanical properties (modulus of elasticity, modulus of rupture, and hardness) of all wood-attacked blue stains did not significantly differ from their control samples.

Unusual Spreading of Strain Neutral Layer in AZ31 Magnesium Alloy Sheet during Bending.

In this work, we reported an unusual phenomenon of strain neutral layer (SNL) spreading in an as-rolled AZ31B magnesium alloy sheet during V-bending. The SNL on the middle symmetrical surface perpendicular to the transverse direction (TD) of the sheet extended to the compression region and was accompanied by a mound-like feature. However, the SNL on the side surface perpendicular to the TD was distributed with a parallel band feature. The underlying mechanism was revealed by the finite element (FE) analysis. The results indicate that the three-dimensional compressive stresses in the compression region of the bending samples were responsible for the above phenomenon. Moreover, the area of the SNL in the middle position gradually decreased as the bending test progressed. The findings in this study provide some new insights into the bending deformation behavior of magnesium alloy.

Mixed‐mode I/II fracture properties and failure characteristics of microwave‐irradiated basalt: An experimental study

AbstractThe notched semicircular bending samples with different microwave irradiations were subjected to 3‐point bending fracture tests under mixed‐mode I/II loading to investigate the effects of microwave irradiation on the fracture characteristics of basalt. Influences of the irradiation duration on the temperature, P‐wave velocity, and mixed‐mode I/II fracture characteristics under 2 kW power were studied. The acoustic emission device was utilized to monitor the acoustic emission signals during the destruction process. The P‐wave velocity and equivalent fracture toughness are weakened by microwave irradiation, but the ductility of basalt is enhanced by microwave irradiation. The microscopic characteristics of the treated basalts were observed by scanning electron microscope. Microwave irradiation aggravated the creation and propagation of microcracks and pores. The study of the influence of microwave irradiation on mixed‐mode I/II fracture characteristics of rock provides effective theoretical support for microwave‐assisted rock fragmentation.

Bending test and simulation of carbon fiber aluminum honeycomb sandwich structure

According to the bending moment characteristics of carbon fiber aluminum honeycomb sandwich structure for the solar wing in use, this paper simulates and analyzes the large-scale bending samples and tests the bending samples at room temperature, 150 °C, and -150°C. The test results show that the bending performance is not different between low-temperature environment and room temperature environment, but the stiffness and strength at high temperature are reduced by 54.9% and 50%, respectively, compared with room temperature. Compared with the room temperature test results, the simulation results are about 10%, which can roughly reflect the bending performance characteristics of sandwich structures.

Effect of surface roughness on strain distribution during bending

The limited formability of ultra-high strength steels (UHSS) poses some challenges for the bending process in the form of strain localisation, surface defects and pseudo-polygonal “nut-like” shape of the bend. Bendability is well known to be affected by surface quality, and especially shot blasting. Therefore, in this study, the effect of surface roughness on bendability of UHSS grade is investigated with 3-point bending tests, utilising Digital Image Correlation (DIC) for measuring the strain distributions on the outer curvature. Investigated bending samples of 4 mm thick commercial martensitic were tested in different surface conditions: As-rolled (with scale), “lightly” shot blasted (SB I), “roughly” shot blasted (SB II), dry electropolished (As-rolled P) and a combination of “rough” shot blasting and dry electropolishing (SB II P). Shot blasting increased the surface roughness and subsurface hardness. Utilizing a commercial dry electropolishing process reduced the surface roughness, although this also had major effect on the hardness. Bending results showed that coarser surface roughness decreased the bending capacity, i.e. reduced maximum bending angle and critical strain. A strong correlation between surface roughness (with Rv: the maximum valley depth below the mean surface) and critical bending angle was found, likewise with the subsurface hardness and critical bending angle.

Void Formation and Crack Propagation in a Cr–Mn–N Metastable Austenitic Stainless Steel During Bending

Microstructure evolution via deformation‐induced martensitic transformation, void formation, and crack propagation is investigated in a metastable austenitic Cr–Mn–N stainless steel for up to 90° bending using a combination of electron backscattering diffraction and parent grain reconstruction. Stress–strain heterogeneity and stress triaxiality studied using finite‐element analysis reveal that the inner and outer radii are in approximately uniaxial compressive and tensile stress states, respectively, with the outer radius showing higher values for von Mises and principal stresses and equivalent strain. Voids are observed at both austenite/α′‐martensite and α′/α′‐martensite interfaces. Parent grain reconstruction applied to the 90° bending sample reveal that the cracks at α′/α′‐martensite interfaces tend to propagate predominantly along intergranular parent austenite grain boundaries. It is also found that both intragranular and intergranular cracks in parent austenite tend to propagate between α′‐martensite child–child grains comprising the same crystallographic packets. This is the first study of its kind to comprehensively show this phenomenon. A representative example of intergranular crack propagation within a ‖normal direction (ND)‐oriented parent austenite grain is also demonstrated.

P-Type PVA/MWCNT-Sb2Te3 Composites for Application in Different Types of Flexible Thermoelectric Generators in Combination with n-Type PVA/MWCNT-Bi2Se3 Composites

This work is devoted to the fabrication of p-type polyvinyl alcohol (PVA)-based flexible thermoelectric composites using multiwall carbon nanotubes-antimony telluride (MWCNT-Sb2Te3) hybrid filler, the study of the thermoelectrical and mechanical properties of these composites, and the application of these composites in two types (planar and radial) of thermoelectric generators (TEG) in combination with the previously reported PVA/MWCNT-Bi2Se3 flexible thermoelectric composites. While the power factors of PVA/MWCNT-Sb2Te3 and PVA/MWCNT-Bi2Se3 composites with 15 wt.% filler were found to be similar, the PVA/MWCNT-Sb2Te3 composite with 25 wt.% filler showed a ~2 times higher power factor in comparison with the PVA/MWCNT-Bi2Se3 composites with 30 wt.% filler, which is attributed to its reduced electrical resistivity. In addition, developed PVA/MWCNT-Sb2Te3 composites showed a superior mechanical, electrical, and thermoelectric stability during 100 consequent bending cycles down to a 3 mm radius, with insignificant fluctuations of the resistance within 0.01% of the initial resistance value of the not bent sample. Demonstrated for the first time, 2-leg TEGs composed from p-type PVA/MWCNT-Sb2Te3 and n-type PVA/MWCNT-Bi2Se3 composites showed a stable performance under different external loads and showed their potential for applications involving low temperature gradients and power requirements in the range of nW.

Degradation response of mode I and mode III fracture resistance of sandstone under wetting–drying cycles with an acidic solution

The edge notched disk bend samples were adopted to investigate the degradation response of mode I and mode III fracture resistance of green sandstone under wetting–drying cycles in an acidic solution. Meanwhile, the degradation damage mechanism was clarified by observing the variations of the microstructures of the rock. The results indicated that the mode I and mode III fracture resistance reduced with increasing wetting–drying cycle times, which were decreased respectively by 34.3% and 36.8% after undergoing 10 cycles. Fracture toughness ratio KIIIC/KIC was slightly reduced with increasing cycle times, and the degradation damage on mode I fracture resistance was less than that of mode III. The major reason for the decrease in fracture resistance was the irreversible physical–chemical damage accumulation and the changes in microstructure characteristics during cyclic wetting–drying procedure.

Production of compression and flexural test samples in 3D printer with PLA polymeric biomaterial and bone compression with appropriate properties

In this study, it is planned to design and develop a structure close to the real bone strength properties by using PLA (polylactic acid) material. 3D printers have started to take place in our daily lives with today's developing technology and are preferred because of their ease of production and low cost. It has been determined that the PLA biomaterial can be used as a bone substitute in the body. The samples produced have different filling ratios and different internal structures. In the study, the effects of changes in the internal structure on the mechanical properties were investigated. Bone geometry is considered as an important factor among the parameters affecting biomechanical properties. In order to determine the mechanical properties of PLA filament material, bending and compression samples were prepared as 3 pieces for each test. The aim of this study is to determine whether it can be used as bone in the body by measuring the mechanical properties of biocompatible PLA polymer material. In the current work, the quality of the 3d printer and the material used in production directly affects the mechanical properties. In bones in the human body, trabecular bone has 80% porosity and cortical bone 10% infill. In this study, it was tried to obtain structures with properties close to real bone strength by using test specimens with different infill rates. It has been determined from the obtained data that PLA polymer material can be developed and meet the mechanical values in bone.

Using the Stress Concentration Factor in Determining the Fracture Toughness

This paper offers the use of stress concentration factor in determining the critical fracture stress and fracture toughness of polymeric composite materials at various crack length ratios. The stress intensity factor has been turned into a function of the stress concentration factor derived from the maximum stress occurring at the notch tip and the tip stress generated by the force applied to the sample. This conversion allowed the use of a fixed theoretical radius (1.2732 mm) instead of the actual radius of the notch or crack. On the edge cracked three-point bending and tensile samples, the specified method detects the three point bending fracture stresses with a maximum error rate of 1.2%. This study also establishes a relationship between the clamped end and the pin-loaded tensile specimens and states that the underlying mechanism of the stress intensity factor of the clamped end tensile specimen is based on the normalization of the stress intensity factor of the pin-loaded conditions with the geometric correction factor.

The influence of constraint on fracture toughness: Comparing theoretical [formula omitted] shifts in master curve analyses with experimental data

Quantifying the relationship between crack tip constraint and fracture toughness is key to improving the structural integrity assessment of critical infrastructure. The role of in-plane and out-of-plane constraint on fracture toughness requires greater understanding, particularly for low strength materials where test data are limited. In this work a structural steel, grade S275, is assessed both experimentally and via computational methods to investigate the role of constraint on fracture toughness. Single edge notch bend (SENB) samples, tested under three point bend conditions, at temperatures within the ductile-to-brittle transition range (+20 °C to −70 °C) are presented. Both standard (B=W, B=0.5W) and non-standard (B=0.75W, B=0.25W) bend test geometries are assessed. Here it is shown that the in-plane and out-of-plane constraint parameters are interdependent. Out-of-plane (thickness) constraint trends which are generally accepted to occur under high in-plane conditions are not present when the in-plane constraint is reduced. The amount of ductile tearing incurred during fracture toughness testing is typically greater when both in-plane and out-of-plane constraint is reduced. Thin samples are shown to be more ductile than thicker samples for equivalent in-plane conditions. These findings are relevant to pressurised components operating at low temperatures.

Fracture behavior of Hastelloy X elaborated by laser powder bed fusion: Influence of microstructure and building direction

Laser Power Bed Fusion (LPBF) results in complex meso and microstructures, which significantly change the fracture mechanisms of Hastelloy X superalloys. This article aims to investigate the role played by original crack orientation (perpendicular or co-linear to sample lasing planes) on the fracture toughness values of LPBF HX. Single notched three-point bending samples were manufactured vertically (V) or horizontally (H) to estimate the fracture toughness for these two original crack directions. The highest value (about 1360 kJ/m²) is computed in V specimens with an original crack parallel to the lasing plane whereas a value of 1042 kJ/m² is estimated in H specimens with the second crack orientation. Compared to the values obtained in cast specimens, the fracture toughness of LPBF specimens is virtually 5–6 times higher. A non-self-similar cracking is specific to V specimens revealing a more tortuous crack path than in H specimens with self-similar cracking. In both cases, ductile failure is driven by both transgranular and intergranular modes. Nevertheless, the strong morphological texture contributes to promote intragranular fracture mode in V specimens which requires more energy than the one dissipated by an intergranular failure associated to H samples. Consequently, the fracture toughness is significantly higher in V specimens. • Fracture tests were conducted on Hastelloy X specimens elaborated by Laser Power Bed Fusion with two build directions. • In H specimens, intergranular fracture is dominant due to the grain boundaries aligned with the initial notch. • In V specimens, transgranular fracture occurs along with grain boundaries perpendicular to the initial notch. • The morphological texture is responsible for the fracture toughness anisotropy.

Experimental analysis of fluid‐assisted injection molding of pipe fittings with different angles by short‐shot method

AbstractBased on the self‐assisted injection experimental platform, experimental studies on gas‐assisted injection molding (GAIM), and water‐assisted injection molding (WAIM) of 2 curved pipe fittings by adopting short‐shot method were carried out. UDF model was constructed for numerical simulation analysis. The influence rules of auxiliary medium and bending angle on the terminal morphology, inner wall surface quality at bending angle, medial and lateral residual wall thickness, variation range, and residual wall thickness deviation rate of short‐shot fluid assisted injection molding (SSFAIM) bending samples were compared. Meanwhile, the influence mechanism was investigated. The following experimental findings were obtained. SSFAIM had secondary penetration, while water produced multiple penetrations. There are multiple vacuum shrinkage pores in the unpenetrated area at the end of the SSWAIM sample, as well as serious shrinkage depressions on the surface. The shape of the penetration front of water is arc‐shaped with many penetration holes. The shape of the penetration front of the gas at the end of the SSGAIM sample is “pointy.” Compared with the SSWAIM sample, the residual wall thickness of SSGAIM has a narrow distribution range when the bending angle is 0°. With the increase of the bending angle, the “foaming” phenomenon of the inner wall surface quality at the bending angle of the SSGAIM sample becomes less and less obvious. Moreover, the deviation of the inner and outer residual wall thickness of SSGAIM is more obvious than that of SSWAIM due to the increase of bending angle.

Measurement of Irreversible External-Compressive Strain at RT and Enhancing Strain Tolerance at RT on MgB2 Multifilament Wire

The strain tolerance of magnesium dioboride (MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) wire should be enhanced at room temperature for fabricating MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> coils by using the react and wind method. The irreversible external-compressive strain of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> filaments was measured by evaluating the critical current degradation of bent sample wires. From the results, MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> filaments can accept -1.77% strain, and the pre-compressive strain should be -0.88% at room temperature to minimize its reversible bending radius. A stainless-steel reinforced 18-filament MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> wire was fabricated and its strain tolerance was evaluated through bending and tensile tests at room temperature. The irreversible strain of this wire is 0.60%, and this wire seems to be suitable for the react and wind method. The filling factor of MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> of this wire is 17%, so this wire has both suitable strain tolerance for the react and wind method and higher engineering current density.

Effect of real-time high temperature and loading rate on mode I fracture toughness of granite

An in-depth understanding of the effect of real-time high temperature and loading rate on the fracture toughness of rocks is highly important for understanding the fracture mechanism of Hot Dry Rock (HDR). Three-point bending tests on notched semi-circular bending (NSCB) samples at the real-time temperatures (25, 100, 200, 300, 400 and 500 ℃) and different loading rates (0.1, 0.01 and 0.001 mm/min) were performed to characterize the temperature and rate dependence of the mode I fracture toughness. Besides, the characteristic of the fracture surface morphology was investigated by scanning electron microscope (SEM) and crack deviation distance analysis. Results show that the temperature has a significant effect on the development of intergranular and transgranular cracks. The fracture toughness and peak load are similarly influenced by temperature (i.e., they both decrease with increasing temperature). At the loading rates of 0.1 mm/min and 0.01 mm/min, from 25 to 400 °C, the fracture toughness decreases slightly with decreasing loading rates. However, at a loading rate of 0.001 mm/min, the fracture toughness values above 200 °C are very similar, and the fracture toughness does not strictly follow the law of decreasing with decreasing loading rate. Especially at 500 °C, fracture toughness and loading rate are negatively correlated. Our study also indicates that the effect of loading rate on macroscopic crack propagation path at real-time high temperature is not obvious. This study could provide an important basis for evaluating the safety and stability of geothermal engineering.

Effect of Heat Treatment on Ductility and Precipitation Size of Additively Manufactured AlSi10Mg

Laser powder bed fusion (LPBF) is a promising technology to manufacture complex components. Aluminium (Al) alloys are extensively implemented in automotive and aerospace applications for their exceptional strength and stiffness to weight ratios. AlSi10Mg is a precipitation strengthened alloy. Due to the high cooling rate during the LPBF process, a fine microstructure in as-built samples is expected, increasing strength and hardness values. However, the ductility of as-built AlSi10Mg alloys is limited. Heat treatment allows control of microstructure influencing the mechanical properties and ductility. In this study, AlSi10Mg samples with a relative density &gt;99.5% were manufactured with LPBF. Surface roughness values of 10.86 µm were achieved. Tensile and three-point bending samples were printed for analysis. Since load conditions of lattice structures in compression are much more complex compared to that of volume samples, increasing tensile ductility is not sufficient to determine the suitability of lattice structures for applications where high deformations are required. Therefore, lattice structures for compression testing were manufactured and individually heat treated to achieve a ductility of at least 20%. The precipitation size was found to increase depending on heat treatment from 0.44 µm up to 2.25 µm, giving insight on deformation behavior.

EFFECT OF MACHINING ON IMPACT TOUGHNESS VALUE OF RAIL SAMPLES DT350 FROM STEEL GRADE 76ХФ

It is known that the value of impact toughness is sensitive to the geometric accuracy of manufacturing, the quality of the surface and concentrator of samples for impact bending. These parameters have a particularly strong influence on samples made of high-carbon materials. At present, the main regulatory document for the manufacture of samples for impact bending is GOST 9454‒78, which does not regulate the method of applying concentrators. Currently, methods of drawing, milling and electroerosion processing are used to apply the concentrator. The issue of the influence of processing methods on the magnitude of impact strength, in particular rail steel, has not been fully studied. To study the effect of electroerosion processing on impact toughness value we made specimens of P65 rail of DT350 category from 76ХФ steel of current EVRAZ ZSMK production using CNC milling machine and electroerosion processing. It has been established that the decrease in the values of impact strength of samples made using electroerosive machining was due to martensite released during local melting of the metal and non-ferrous metals (Cu and Zn) released during processing. During the operation of the electroerosion processing machine, an uneven surface was formed when the arc locally knocked out “holes”, which serve as additional stress concentrators during impact bending tests. The application of the concentrator by a milling machine leads to the formation of a deformed layer up to 80 µm deep, which is not a stress concentrator and does not reduce the impact strength of the rail steel. As part of a further study, it is planned to investigate the effect of the application of the concentrator by the pulling method on the value of the impact toughness.

Analysis of tensile strength and fracture toughness of ZrB2–SiC ceramic from three-point bending samples with edge cracks

ZrB2–SiC ceramic is one of most promising high temperature resistant materials in the field of thermal protection, and its strength and toughness are two key mechanical indicators which determine its application prospects. How to conveniently and accurately obtain its strength and toughness is of great value for engineering applications. In this paper, the tensile strength and fracture toughness of the ZrB2–SiC ceramic were obtained according to the boundary effect model (BEM) from a series of three-point bending tests of ZrB2–SiC ceramic samples. Then, the BEM method and normal distribution methodology were employed for analysis of strength and toughness of ZrB2–SiC ceramic. Results show that there exists a linear relationship between maximum loads Pmax and effective area Ae, and the slope of the straight line passing through the coordinate origin is the tensile strength ft. The tensile strength ft and fracture toughness KIC of ZrB2–SiC ceramic can be predicted simply from a set of three-point bending tests according to the BEM method. Similarly, the maximum loads Pmax for three-point bending samples can also be predicted and determined when the ft, KIC and average grain size are available. Results indicate that the grain sizes, ft and KIC of the ZrB2–SiC ceramic follow the law of normal distribution. Satisfactory results of the predicted ft and KIC between the upper and lower bounds with 95% reliability can be achieved based on BEM method.

Multiple scattering of channeled and non-channeled positively charged particles in bent monocrystalline silicon

We present the results of an experimental study of multiple scattering of positively charged high-energy particles in bent samples of monocrystalline silicon. This work confirms the recently discovered effect of a strong reduction in the rms multiple scattering angle of particles channeled in the silicon (111) plane. The effect is observed in the plane orthogonal to the bending plane. We show in detail the influence of angular constraints on the magnitude of the effect. Comparison of the multiple scattering process at different energies indicates a violation of the law of inverse proportionality of the rms angle of channeled particles with energy. By increasing the statistics, we have improved the results of multiple scattering measurements for particles moving, but not channeled, in silicon crystals.