Study of the Bimetallic Joint CuCrZr/316L(N)

In this work, a study of the cases of destruction of the CuCrZr / 316L (N) bimetallic joint (BMJ) obtained by diffusion welding under conditions of hot isostatic pressing (HIP) was carried out. The identified defects are cracks propagating in the BMJ zone in the corner zone of the mock-ups of the heat-sink elements (HE). The analysis of the causes of destruction of the BMJ was carried out and the factors leading to the weakening of the BMJ zone are analyzed. The analysis of the thermal and stress-strain state of the HE mock-up during the manufacturing process was carried out. The study of the elements of the HE mock-up were carried out by methods of non-destructive testing (ultrasonic testing (UT)) and destructive testing (metallography; fractography; energy-dispersive X-ray spectroscopy; tensile tests). The inclusion of brittle phases in the zone of the BMJ was revealed and an assumption was made about the chemical composition of these phases. It was revealed that this line of brittle phases is a crack propagation zone in all cases of destruction of the BMJ in the HE mock-ups. The temperature range is revealed at which the effect of "ductility failure" of the CuCrZr is observed during the tensile testing of the samples.

Effect of deep tempering on microstructure and mechanical properties of G13Cr4Mo4Ni4V steel

By means of the post heat treatment of deep tempering on the aviation bearing steel G13Cr4Mo4Ni4V after quenching and high-temperature tempering, the effect of the treatment on microstructure and mechanical properties of the steel was studied. Results show that, the deep tempering promotes the precipitation of carbides along the boundaries and on the bodies of martensite blocks. In this process, the block martensite structure is decomposed and refined. After three or more times of deep tempering treatments, the hardness of the steel is slightly improved due to the carbide precipitation on the boundaries and bodies of the martensite blocks and the growth of carbides. After 5 times of deep tempering treatments, the impact toughness and the elongation of the samples are slightly reduced, while the tensile strength is increased. The area of the crack propagation zone on the rotating-bending fatigue fracture increases, while that of the transient fracture zone decreases. The ultimate strength of the rotating-bending fatigue is increased from 560 MPa to 660 MPa, with the increased extent of 17.8%, which results from the decomposition and refinement of martensite blocks.

Dynamice fracture in a semicristalline polymer: an analysis of the fracture surface

The fracture behaviour of a specific material, a semi-crystalline biobased polymer, was here studied. Dynamic fracture tests on strip band specimens were carried out. Fracture surfaces were observed at different scales by optical and electron microscopy to describe cracking scenarios. Crack initiation, propagation and arrest zones were described. Three distinct zones are highlighted in the initiation and propagation zone: a zone with conical markings, a mist zone and a hackle zone. The conical mark zone shows a variation in the size and density of the conical marks along the propagation path. This is synonymous with local speed variation. Microcracks at the origin of the conical marks in the initiation zone seem to develop from the nucleus of the spherulites. In the propagation zone with complex roughness, the direction of the microcracks and their cracking planes are highly variable. Their propagation directions are disturbed by the heterogeneities of the material. They branch or bifurcate at the level of the spherulites. In the arrest zone, the microcracks developed upstream continue to propagate in different directions. The surface created is increasingly smoother as the energy release rate decreases. It is shown that the local velocity of the crack varies in contrast to the macroscopic speed.

Fatigue Properties and Fracture Characteristics of the Aluminum Alloys for High-Speed Train Carbody

The fatigue tests on two types of domestic aluminum alloys were conducted and the P-S-N curves of both aluminum alloys were obtained. The microscopic characteristics at the fatigue fracture surface were observed with scanning electron microscopy. The results show that the tensile strength of A7 is 376MPa, while the tensile strength of A6 is 311MPa. The fatigue strength of A7 is 75MPa at 107 circles, and it is just a little higher than that of A6, which is 71.57MPa. The fatigue cracks initiated from or near the surface of the specimen. The fatigue fracture can be divided into three parts, namely, the initiation zone, the propagation zone and the sudden fracture zone. Typical characteristics could be observed on fracture surface.A6 has better plasticity than A7.

Corrosion Properties of Friction Stir Welded 2024 Aluminum Alloys

The corrosion properties of friction stir welded 2024 aluminum alloys are studied in this paper. The results show that after 50 hours corrosion in 3.5% NaCl solution, the strength limit, Yield strength and elongations decreased compared to non-corrosion specimen, but not much. All fracture initiated at surface or sub-surface flaws at advancing side. Larger propagation zone is seen in corrosion specimen compared to non-corrosion.

Investigation on Fatigue Damage of the Al5Zn2Mg High Strength Aluminum Alloy

The fatigue fracture and the microstructure of Al5Zn2Mg high strength aluminum alloy were observed by OM, SEM and TEM, and the low cycle fatigue properties were tested and analyzed. The results of experimentation show that the low cycle fatigue life of Al5Zn2Mg high strength aluminum alloy is 9.28×104 cycle in R=0.1, f=8Hz, and σmax=0.75σb. The tensile strength is 444MPa. The fatigue fracture is composed of the initiation zone, the propagation zone, and the sudden fracture zone, which is characteristic of a mixed-type fatigue fracture. The fatigue crack initiates in the surface of Al5Zn2Mg aluminum alloy sample, while there is no fatigue striation in fatigue crack propagation zone. The η′(MgZn2) transitional strengthening phases are precipitated in Al5Zn2Mg aluminum alloy, and mostly distributed in grain boundary. The diameter of η′ strengthening phase is fine, about is 10nm. There is none precipitated zone in width nearby the grain boundary

Quantitative Analysis on Fatigue Fracture of Spray Formed GH738 Alloy

Low-cycle fatigue (LCF) fracture of the spray formed GH738 alloy was investigated under total strain controlled mode at 650°C. Basic theory for evaluating fatigue lives by fatigue striations has been introduced. The crack length a and the crack propagation rate da/dN were measured and the curve of da/dN in crack propagation zone was obtained with Paris formula and tabulation trapezoidal formula, respectively. The size and symmetry of rapid fracture zone of fatigue were also studied. The results showed that the relationship of a and N was linear with tabulation trapezoidal formula, and the da/dN and a was conic with Paris formula. At last, quantitative analysis of fatigue fracture was also discussed.

Using the Mass Ratio to Induce Band Gaps in a 1D Array of Nonlinearly Coupled Oscillators

A one dimensional system of nonlinearly coupled magnetic oscillators has been studied. After deriving the equations of motion for each oscillator, the system is linearized about a stable equilibrium and studied using an assumed solution form for a traveling wave. Wave propagation and attenuation regions are predicted by reducing the system of equations to a standard eigenvalue problem. Through evaluating these equations across the entire irreducible Brillouin zone, it is determined that when the masses of each oscillator are identical, the entire frequency range of the system is a propagation zone. By varying the masses comprising a unit cell, band gaps are observed. It is shown that the mass ratio can be used to guide both the size and location of these band gaps. Numerical simulations are performed to support our analytical findings.

Safety and utility of supplemental depth electrodes for localizing the ictal onset zone in pediatric neocortical epilepsy

Object Depth electrodes provide a better sampling of sulci and regions of cortex that lie tangential to the plane of subdural electrodes. The aim of this study was to evaluate the utility of supplemental depth electrodes in the surgical treatment of pediatric patients with neocortical epilepsy. Methods Cases involving 12 consecutive pediatric patients (mean age [SD] 10.9 ± 4.4 years) were reviewed. Focal resective surgery (in 9 cases) or functional hemispherectomy (in 3 cases) was performed after intracranial monitoring. The mean total number of electrodes was 118 ± 29; the mean numbers of grid, strip, and depth electrodes were 95 ± 27, 10 ± 6, and 13 ± 5, respectively The most common pathological condition was focal cortical dysplasia. Results In 4 cases, depth electrodes demonstrated the ictal onset zone in an area not easily accessible by grids or strips (in the basal temporal region in 3 cases and the upper opercular region in 1 case). In 3 of these 4 cases, the ictal onset zone was defined exclusively by the depth electrodes. In each of these 3 cases, the surface electrodes (on grids or strips) demonstrated early propagation but not ictal onset. In 9 cases, the depth electrodes also demonstrated the early propagation zone. The information about the ictal onset zone and the early propagation zone helped to provide additional information that affected the extent (in 7 cases) or depth (in 3 cases) of the resection. The proportion of the electrodes involved in resection relative to the total number of implanted electrodes was low (mean ± SD, 0.26 ± 0.09). Nine patients (75.0%) became seizure free (Engel class IA outcome) after surgery (mean duration of follow-up 25.7 ± 4.29 months). There were no surgical complications related to intracranial electroencephalography monitoring. Conclusions Most patients (75.0%) became seizure free after extensive monitoring and more limited resection of seizure-onset regions. Supplemental depth electrodes contribute to improved outcome by providing information about the ictal onset zone that is not accessible by grid or strip electrodes in some cases. The supplemental depth electrodes conferred an extra dimension of depth to the analysis, which allowed for successful outcome with more limited resection.

The correlation of electrical charge with strain on stressed rock samples

Laboratory experiments on rock samples have shown electric signal emissions when the samples are subjected to temporal stress increase especially when the samples approach failure. These electric signals are attributed to the generation and propagation of microcracks that guide the sample to mechanical failure. In this work the temporal evolution of electric charge release is studied for marble samples subjected to stress at a constant rate up to fracture and it is correlated to the respective recordings of the yielded strain. The results exhibit a systematic linear correlation between electric charge and deformation, with a constant proportionality factor independent of stress rate magnitude. This linear correlation, which is in accordance with the Moving Charged Dislocations (MCD) model, exists from the instant that the marble samples are driven to the non-linear region of mechanical behaviour due to the applied stress, and more precisely to the Crack Propagation Zone (CPZ) up to the pre-failure phase.