Fracture Surfaces Of Samples Research Articles

Deformation Mechanisms and Fracture of Ni-Based Metallic Glasses

Abstract The cracking of materials and fracture surface is of great practical and academic importance. Over the last few years the development of the fractography of crystalline alloys resulted in a useful tool for the prediction or failure analysis. Many attempts have been made to observe cracks using optical microscopy, X-ray topography and transmission electron microscopy (TEM). Of these techniques, the resolution of optical microscopy and X-ray topography is too poor. By contrast, the resolution of TEM is high enough for detailed information to be obtained. However, in order to apply TEM observations, a thin foil specimen must be prepared, and it is usually extremely difficult to prepare such a specimen from a pre-selected region containing a crack. In the present work, deformation mechanisms fracture surfaces of Ni-based metallic glass samples have been studied by specially designed experiments. In order to study the deformation mechanisms and fracture the Ni-based metallic glasses have been investigated in the tensile test. The structure and fracture surfaces after the decohesion process in tensile tests were observed using transmission electron microscope (TEM) and scanning electron microscope (SEM), respectively. The studies of structure were performed on thin foils. Moreover the investigated tape was subjected to a banding test. Then, the tape was straightened and the thin foil from the area of maximum strain was prepared. This thin foil sample was deformed before the TEM investigation to obtain local tears.

Effect of laser shock peening on the compressive deformation and plastic behavior of Zr-based bulk metallic glass

The compressive deformation and the plastic behavior of Zr35Ti30Cu8.25Be26.75 bulk metallic glass (BMG) in as-cast and laser peened state were investigated. It was found that as-cast sample displayed brittle fracture with an limited plastic strain of 0.22% and the fracture was mainly localized on one single shear band. For laser peened sample, an apparent plastic strain of 1.48% could be observed in the stress-strain curve, which was much greater than that of as-cast sample. Scanning electron microscope observations revealed that the normal fracture surfaces of both samples displayed a shear mode and consisted of vein-like structure. The relatively uniform distribution of multiple shear bands was observed on the side fracture surface of laser peened sample. Numerical simulation was performed to understand quantitatively the plasticity enhancement of laser peened sample. Under the effect of LSP induced residual stress, the laser peened sample exhibited a larger concentrated stress around the main shear stress plane which could promote the initiation of new shear bands. Besides, the increased free volume in main shear stress plane were beneficial for the generation of multiple shear bands which would probably improve the compressive plasticity of Zr-based BMG.

The nature of structural inhomogeneity in ceramics produced by zirconium nitridation

The morphology of transverse fracture surfaces of one-dimensional zirconium nitride samples prepared by heating zirconium in an argon gas atmosphere (at a pressure of 1.2 × 105 Pa) at a temperature of 1500°C for 4, 6, 11, 16, 21, and 60 min has been studied by scanning electron microscopy. The forming ZrN ceramics have been shown to have a bilayer structure, which results in markedly different fracture surface morphologies. The formation of polycrystalline layers differing in grain size is interpreted in terms of multiorientation ZrN endotaxy when a certain nitrogen concentration in the α-Zr-based solid solution is reached.

Effect of Local Crystallographic Texture on the Fissure Formation During Charpy Impact Testing of Low-Carbon Steel

The severity of the formation of fissures (also known as splitting or delamination) on the fracture surface of Charpy impact-tested samples of a low-carbon steel has been found to increase with the decrease in finish rolling temperature [1093 K to 923 K (820 °C to 650 °C)]. Combined scanning electron microscopy and electron back-scattered diffraction study revealed that crystallographic texture was the prime factor responsible for the fissure formation. Through-thickness texture band composed of cube [Normal Direction (ND)║〈001〉] and gamma [ND║〈111〉] orientations developed during the inter-critical rolling treatment. Strain incompatibility between these two texture bands causes fissure cracking on the main fracture plane. A new approach based on the angle between {001} planes of neighboring crystals has been employed in order to estimate the ‘effective grain size,’ which is used to determine the cleavage fracture stress on different planes of a sample. The severity of fissure formation was found to be directly related to the difference in cleavage fracture stress between the ‘main fracture plane’ and ‘fissure plane.’ Clustering of ferrite grains having cube texture promoted the fissure crack propagation along the transverse ‘fissure plane,’ by increasing the ‘effective grain size’ and decreasing the cleavage fracture stress on that plane.

The strengthening and toughening effects of a novel octa(propargyl propyl sulfide) POSS (OPPSP) on silicon-containing arylacetylene (PSA) resin

A novel octa(propargyl propyl sulfide) POSS (OPPSP) was synthesized by the thiol-halogen reaction between octa(mercaptopropyl) POSS (POSS-SH) and propargyl chloride under phase transfer catalysis. Furthermore, OPPSP was employed as a reinforcing agent to prepare a modified silicon-containing arylacetylene (OPPSP-PSA) resin. The resulting OPPSP-PSA thermoset with 10wt% of OPPSP exhibits 80.5% and 92.8% increment in flexural strength and impact fractured energy as compared to pristine PSA thermoset. Scanning Electron Microscope (SEM) and Energy Dispersive Spectrometer (EDS) are used to observe the dispersion of OPPSP in the fractured surfaces of samples. The results show that both the nano-dispersion of POSS cages and the POSS-enriched “particles” are possible mechanisms behind the improved mechanical properties.

Crystallization and mechanical properties of solid solutions between bismuth and antimony chalcogenides

Using scanning electron microscopy, we have studied how the conditions of preparation of granules of Sb2Te3–Bi2Te3 and Bi2Te3–Bi2Se3 solid solutions through melt solidification in a liquid influence their morphology, fractographs of fracture surfaces of samples prepared by hot-pressing the granules, and the contents of the major components in the samples. The granules are rounded (solidification in water and liquid nitrogen) or platelike (solidification in water under an excess pressure and in liquid-nitrogen-cooled ethanol) in shape. Fracture surfaces of hot-pressed samples prepared from granules comminuted in a ball mill have a uniform, fine microstructure, with faceted grains several microns in size. Characteristically, samples prepared from granules comminuted in a cutting mill have transgranular layered fractures, with layers up to hundreds of microns in thickness. The mechanical properties of the samples (ultimate strength and relative elongation) have been studied using compression tests at temperatures of 300 and 620 K. The samples experience brittle fracture. Their compression strength σc is 55 ± 12 MPa. With increasing temperature, σc varies only slightly, but at 620 K the samples become more plastic and their relative elongation eb increases by a factor of 2–4. The ultimate strength of hot-pressed samples prepared by uniaxial compression is 20% higher than that of samples prepared by biaxial compression.

Analysis on Fracture Toughness of the L415MS/N08825 Bimetallic Composite Pipe Welded Joint

Crack tip opening displacement (CTOD) tests were conducted on the weld and heat affected zone (HAZ) of L415MS/N08825 bimetallic composite pipe welded joint according to BS7448, ISO12135(2002) and ISO15653(2010) standards at room temperature. The fracture toughness of weld and HAZ were studied and analyzed. The fracture surface and inclusions were characterized using scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDS), respectively. The results showed that the average CTOD value of the weld was less than HAZ, CTOD values of HAZ exhibited larger discrete, which was mainly caused by Pop-in effect in P-V curve of HAZ samples. CTOD value of sample with Pop-in effect dropped several times than sample without Pop-in effect. The fracture surfaces of the weld and HAZ showed tough fracture to a certain extent, and the fracture surface of HAZ sample with Pop-in effect exhibited significant quasi-cleavage feature.

Evaluation and Identifying the Ductile Fracture Area of X70 Steel from DWTT Broken Specimens

Fracture surfaces of X70 steel DWTT broken samples are analyzed using statistical methods and fractal concepts. Besides of fractal geometry concept the new approach based on the normal vectors analysis is presented. The fracture surface is covered by a triangle net. For every triangle the normal vector is determined. Fractal dimension is significantly correlated to the angular deviation of neighboring normal vectors. The mean value of deviation angles and fractal dimension is lower for ductile than for brittle fracture areas. The k-means cluster analysis and multivariate probability distribution are applied to determine the local characteristics of the fracture surface. The fracture surface map of ductile fracture probability and k-means clusters highly corresponds to the real placement of ductile and brittle fracture area on fracture surface of the broken sample. Newly presented statistical methods applied on the fracture surface of DWTT broken samples are useful tools for objective evaluation of ductile fracture percentage.

Microstructural Characteristics with Various Finish Rolling Temperature and Low Temperature Toughness in Hot Rolled Nb–Ti Ferritic Steel

In order to investigate the effects of finish rolling temperature on the microstructural characteristics and fracture mechanism of Nb–Ti ferritic steel, the samples with various finish rolling temperature have been observed by optical microscopy, scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy. The results indicated that both ferrite grain size and volume fraction of (Nb,Ti)C precipitates decreased with the decreasing finish rolling temperature, but the size of (Nb,Ti)C precipitates changed little with the finish rolling temperature. All of these factors caused the yield strength, tensile strength and elongation remained similar. However, the low temperature toughness was significantly influenced by the finish rolling temperature. Based on the observation results of fracture surface of samples tested at −40°C, the fracture type of steels with finish rolling temperature of 940°C and 910°C was brittle, while the fracture of steel with finish rolling temperature of 880°C was ductile. At last, the crack initiation and propagation mechanism is elucidated in details. At −40°C, both intergranular cracks and transgranular cracks existed in the steels finish rolled at 940°C and 910°C, and only microvoides were observed in the steel finish rolled at 880°C with high toughness.

Effect of segregations on mechanical properties and crack propagation in spring steel

Considerable efforts have been made over the last decades to improve performance of spring steels, which would increase the service time of springs and also allow vehicles weight reduction. There are different possibilities of improving properties of spring steels, from modifying the chemical composition of steels to optimizing the deformation process and changing the heat treatment parameters. Another way of improving steel properties is through refining the microstructure and reducing amount of inclusions. Therefore, the focus of the current investigation was to determine the effect of more uniform and cleaner microstructure obtained through electro-slag remelting (ESR) of steel on the mechanical and dynamic properties of spring steel, with special focus on the resistance to fatigue crack propagation. Effect of the microstructure refinement was evaluated in terms of tensile strength, elongation, fracture and impact toughness, and fatigue resistance under bending and tensile loading. After the mechanical tests the fracture surfaces of samples were analyzed using scanning electron microscope (SEM) and the influence of microstructure properties on the crack propagation and crack propagation resistance was studied. Investigation was performed on hot rolled, soft annealed and vacuum heat treated 51CrV4 spring steel produced by conventional continuous casting and compared with steel additional refined through ESR. Results shows that elimination of segregations and microstructure refinement using additional ESR process gives some improvement in terms of better repeatability and reduced scattering, but on the other hand it has negative effect on crack propagation resistance and fatigue properties of the spring steel.

Sliding wear behavior of E-glass-epoxy/MWCNT composites: An experimental assessment

This investigation has evaluated the sliding wear properties of E-glass-epoxy/MWCNT (multiwalled carbon nanotube) composite and Epoxy/MWCNT composite. Four different reinforcements (0, 0.5,1 and 1.5 wt %) of MWCNTs are dispersed into an epoxy resin. Design of experiments (DOE) and Analysis of variance (ANOVA) are employed to understand the relationship between control factors (Percentage of reinforcement, Sliding distance, Sliding velocity and Normal load) and response measures (specific wear rate and friction coefficient). The control variables such as sliding distance (300, 600, 900 and 1200 m) and normal loads of 10, 15, 20 and 25 N and at sliding velocities of 1, 2, 3 and 4 m/s are chosen for this study. It is observed that that the specific wear rate and friction coefficient can be reduced by the addition of MWCNTs. Scanning electron microscopy (SEM) is used to observe the worn surfaces of the samples. Compared with neat epoxy, the composites with MWCNTs showed a lower mass loss, friction coefficient and wear rate and these parameters decreased with the increase of MWCNT percentage. Microscopic investigation of worn out sample fracture surface has revealed that fiber debonding happens when the stresses at the fiber matrix interface exceeds the interfacial strength, causing the fiber to debond from the matrix. The optimum control variables have been derived to reduce both wear and friction coefficient of composites.

Effects of Zr/Ti Ratio on the Electric-Induced Light Scattering Performances of PLZT Transparent Ceramics

Lead lanthanum zirconate titanate (PLZT) transparent ceramics have attracted more and more attentions for their unique electric-induced light scattering effects. The PLZT ceramics of 7.45 mole% lanthanum with different Zr/Ti ratios (Zr/Ti=68/32, 69/31, 70/30, 71/29, 72/28) were prepared by the hot-press sintering method. The X-ray diffraction patterns confirm that all the PLZT samples are perovskite structure without detected secondary phases. The SEM images of the fracture surfaces of the samples show that all the PLZT materials tend to fracture transgranularly, and exhibit fully dense and uniform microstructures. All the samples with different Zr/Ti ratios present typical relaxation ferroelectric phase transition characteristics with square shaped hysteresis loops. Noticeably, all the original PLZT samples show an excellent transparency in the wavelength range from visible to near-infrared, and they will become opaque after an appropriate electric field experienced. The opaque sample can also recover to the transparent state when an inverse compatible electric field acts on it. The contrast ratio of the sample increases firstly and then decreases when the Zr/Ti ratio increases from 68/32 to 72/28 (λ=632.8nm). The PLZT (7.45/70/30) material shows a maximum contrast ratio, which makes it promising to apply in optical modulators.

The effect of aging process on the microstructure and mechanical properties of a Cu–Be–Co–Ni alloy

Abstract The paper investigated the effect of two aging processes (i.e. normal aging and interrupted aging) on the microstructure and mechanical properties of a Cu–Be–Co–Ni alloy. The results of tensile and Kahn tear tests showed that the interrupted aging (IA) process could significantly improve the uniform elongation and plane stress fracture toughness with tiny decrease in ultimate tensile strength, when compared with the results from normal aging (NA) process. Under the scanning electron microscope, the fracture surface of samples treated by NA followed the intergranular fracture, while that of the samples treated by IA followed the transgranular fracture. The transmission electron microscope study revealed the differences between the microstructure of the alloy treated by NA and IA processes. After the NA process, the slender strip of γ′ precipitates aggregated at grain boundaries with a length of approximately 10 to 45 nm; the disk-shaped γ″ precipitates in the alloy treated by IA distributed homogenously throughout whole grains with a length of about 3 to 10 nm. The discussion of strengthening mechanisms demonstrated that the mechanism of precipitate shearing by dislocations made a contribution to the strengthening of the alloy treated by IA, while the Orowan mechanism was the dominant strengthening mechanism in the alloy treated by NA.

Dynamic Compressive Behavior and Damage Mechanism of Magnesium Alloy

The dynamic compression test was carried out for the AZ91 Magnesium alloy of as-cast and aging state with a split Hopkinson pressure bar, and the dynamic behavior has been investigated. Finally the fracture surface of samples at the different strain rates was analyzed by scanning electron microscope (SEM). The results show that compared with the as-cast AZ91, it is more impressible for the solid solution and age-treatment AZ91 at the similar strong strain rates, while the stress-strain curve has the duality of positive and negative effects as the variation of strain rate.

Influence of Intercritical Annealing Temperature on Mechanical Properties and Microstructure of 0.23%C Low Alloy Steel

The influence of intercritical annealing temperature on the microstructure and mechanical properties of an 0.23%C low alloy steel was undertaken in this work. The as-received steel was normalised and afterwards annealed in the (α+γ) region at 730OC, 750OC, 770OC and 790OC followed by quenching in hot water at about 50OC.Mechanical testing (tensile, impact and hardness) of the annealed samples were conducted at room temperature. The fracture surfaces of the impact test samples were examined using the scanning electron microscope (SEM). Micros structural evolution of the samples was also examined with an optical microscope. The results showed that all the evaluated mechanical properties were improved by intercritical annealing, with the samples treated at 790OC possessing the optimum combination of properties. The ultimate tensile strength (UTS), yield strength (YS), impact strength (IS), total elongation (TEL) and hardness of these samples improved by 2.7%, 13.7%, 19.7% and 31.05% respectively over the normalised sample. The microstructure photographs of the intercritically annealed samples revealed duplex structures of predominantly martensite in a ferrite matrix with little dispersions of either carbide or retained austenite, which is a typical characteristic of conventional dual phase steel.http://dx.doi.org/10.4314/njt.v34i3.11

Improvement on the properties of polylactic acid (PLA) using bamboo charcoal particles

Bamboo charcoal (BC) derived from bamboo plants is one kind of well recognized multi-functional materials which has been used in various applications such as medical, cosmetic, food processing and health-related products. In this paper, BC particle is used as reinforcement for polylactic acid (PLA) to enhance its mechanical, thermal and optical properties. The comparison on tensile, flexural and impact properties of BC particle reinforced PLA composites (BC/PLA composites) with the content ranging from 2.5 to 10 wt.% is conducted. Experimental results indicated that the maximum tensile strength, flexural strength and ductility index (DI) of BC/PLA composites increased by 43%, 99% and 52%, respectively as compared with those of neat PLA. This phenomenon was attributed to the uniform distribution of high aspect ratio and surface area of BC particles. Further increasing the BC content to 7.5 wt.% would decrease the glass transition temperature of BC/PLA composites. The mechanical properties of BC/PLA composites were reduced as compared with a neat PLA sample when they were exposed to compost degradation. However, less reduction in these properties was found when they were subject to UV irradiation. UV–Vis spectrometer analysis supported the results of UV irradiation. Fracture surfaces of tensile test samples with and without compost degradation or UV irradiation were analysed by using scanning electron microscopy (SEM). SEM images revealed that there was a good BC particle dispersion in the composites through extrusion and injection moulding processes if the particle content was below 7.5 wt.%.

Development of <i>Sansevieria trifasciata</i> - Carbon Fiber Reinforced Polymer Hybrid Nanocomposites

This paper presents studies on experimental values of tensile strength properties of hybrid nanocomposites were studied and compared with theoretical values. It was observed that, experimental strengths were fallen shorter than the theoretical values. Nanocomposites were fabricated by filling MMT nanoclay by weight ratio and reinforced with short sansevieria trifasciata (STF) and short carbon fibre (CF) by randomly orientation. Organically modified montmorillonite clay filled with different proportions viz.0, 1, 3 and 5 wt.% dispersed into the vinyester matrix modified system by hand lay-up technique. Natural fiber was treated by NaOH solution was brought significant performance. Tensile strength was found maximum when clay content was Clay 3wt%. In the fracture surfaces of samples were analysed by SEM analysis, in which it was observed that, increased clay viscosity played vital role in bringing the performance as the viscosity of the mixture made difficult to flow the resin. Thermal stability was significantly improved for the 5wt% sample due to the high content of silicate particles and carbon fibre content.

Development of <i>Sansevieria trifasciata</i> - Carbon Fiber Reinforced Polymer Hybrid Nanocomposites

This paper presents studies on experimental values of tensile strength properties of hybrid nanocomposites were studied and compared with theoretical values. It was observed that, experimental strengths were fallen shorter than the theoretical values. Nanocomposites were fabricated by filling MMT nanoclay by weight ratio and reinforced with short sansevieria trifasciata (STF) and short carbon fibre (CF) by randomly orientation. Organically modified montmorillonite clay filled with different proportions viz.0, 1, 3 and 5 wt.% dispersed into the vinyester matrix modified system by hand lay-up technique. Natural fiber was treated by NaOH solution was brought significant performance. Tensile strength was found maximum when clay content was Clay 3wt%. In the fracture surfaces of samples were analysed by SEM analysis, in which it was observed that, increased clay viscosity played vital role in bringing the performance as the viscosity of the mixture made difficult to flow the resin. Thermal stability was significantly improved for the 5wt% sample due to the high content of silicate particles and carbon fibre content.

Study on the Microstructure and Property for T-Joints of Al-Li Alloy Welded by Double Sided Synchronization Fiber Laser

In the experiment, the T-joints of 2060-T8/2099-T83 Aluminum-Lithium by double sided synchronization Fiber laser welding with thickness of 2 mm was studied aimed to know the microstructure, the distributions of micro-hardness, and the tensile strength of the T-joints. The results show that the microstructure is columnar fine grain zone, dendrite zone, and equiaxed crystal zone in turn from the weld fusion line to weld centre; the micro-hardness of the weld is lower than the micro-hardness of base metal, and softening phenomenon appears in the weld; The average circumferential tensile strength of T-joints is 423 MPa at room temperature, which reaches the strength of the base metal 82%, the average longitudinal tensile strength of T-joints is 449 MPa, which reaches the strength of the base metal 87%; The fracture of circumferential tensile samples initiates at the weld toe, and breaks in the weld centre or heat affected zone. The fracture of longitudinal tensile samples initiates at varying cross-section, there are dimples in the fracture surfaces of both circumferential tensile samples and longitudinal tensile samples, and the fracture is ductile.

Fabrication of natural rubber/epoxidized natural rubber/nanosilica nanocomposites and their physical characteristics

Epoxidized natural rubber (ENR) was initially prepared from an in situ performic acid epoxidation reaction with 46.09 mol% epoxide groups, and the curing characteristics of the ENR/natural rubber (NR) blend with different blend ratios of ENR were studied using a Monsanto moving die rheometer. The mechanical properties of the blends, such as the tensile strength, modulus at 300% elongation and elongation at break, were also examined. The tensile strength and 300% modulus decreased with increasing ENR content and the elongation at break increased steadily with increasing ENR content. In addition, the scorch time, cure time, maximum torque and torque difference decreased with increasing ENR content. Scanning electron microscopy (SEM) of the tensile fracture surfaces of the rubber blend samples revealed better compatibility between NR and ENR with lower ENR contents. Nanocomposites based on NR/ENR blends with two different ratios, 100/0 and 80/10, reinforced with 10 phr nanosilica were also prepared to examine the effects of ENR on the mechanical properties and morphology of the nanocomposites. SEM showed that ENR assists in the dispersion of nanosilica in the NR matrix, resulting in improved mechanical properties of the nanocomposite. Open image in new window