Introduction Of Notch Research Articles

“Notch sensitivity and heat treatment effect on the fatigue behaviour of AlSi10Mg aluminium alloy processed by additive manufacturing”

This paper studies the fatigue behaviour of smooth and notched specimens made from AlSi10Mg aluminium alloy via LPBF additive manufacturing. Three material conditions were addressed: as-built, stress relief, and hot isostatic pressing. Heat treatments were conducted at a temperature to avoid Al-Si network rupture, resulting in an increased fatigue strength of both the smooth and notched specimens. This beneficial effect of the heat treatments was attributed to the homogenization of residual stresses through the specimen depth. In addition, the introduction of notches had a detrimental effect on fatigue life. Two fatigue life prediction models were successfully applied. The first one accounts for both the initiation and propagation periods using the SWT parameter and the FITNET FFS procedure, while the second one is based on a calibrated curve relating the SWT parameter and the number of cycles to failure generated from smooth specimens. Fatigue crack propagation from subsurface defects had a primary role on fatigue life of the tested alloy.

New approach to low-cycle fatigue lifetime prediction for deep-rectangular notched components with finite residual thickness: Experiment and simulation

The introduction of notches in engineering components often has detrimental effects on fatigue behavior. Current research on finite residual thickness is extremely limited, especially when dealing with more complex geometric shapes of notches. In this study, the low-cycle fatigue (LCF) life of cylindrical components with deep-rectangular notches were predicted based on the theory of critical distance (TCD) and the total stress field (TSF) method. The results indicated that the presence of stress concentration near the notch accelerated the initiation and propagation of cracks. Furthermore, finite element method (FEM) was conducted, revealing the need to comprehensively consider the stress distribution across the residual thickness zone (RTZ) for notched specimens. Through numerical method improvement and geometric modeling optimizations, the accuracy of fatigue lifetime prediction has been refined to within a margin of ± 1.5. Comparative simulations on notched specimens with various ratio of notch depth to residual thickness were conducted, characterizing the fatigue process zone (FPZ) near the notch root under LCF loading for Q345R steel, indicating that characteristic material parameter d* exhibits minimal fluctuations with changes in the notch size, while the corresponding local stress levels display a logarithmic upward trend, substantiating that fatigue lifetime decreases with larger notch sizes.

The atomistic mechanism of notch sensitivity on the deformation mode in metallic glasses

In previous studies, the influence of flaws on macro-scale and nano-scale metallic glasses (MGs) has always been a topic of great interest, with important applications in engineering. Moreover, through experiments and simulations, many researchers draw contradictory conclusions of the notch sensitivity, including the notch strengthening, weakening, and insensitivity in different MGs. In order to better understand its atomic mechanism, classical molecular dynamics simulations have been performed on the nano-scale notched MGs in the present work to investigate the deformation modes under the uniaxial tension. According to the results, after setting notches, the MG samples exhibit a significant change from the shear to necking failure, which indicates a notch strengthening phenomenon. At the same time, the evolution of atomic structures suggests that the introduction of notches will increase the degree of shear localization and further disturb the structural order of MGs. The atomic displacement, which is different from shear strain, can also be used as an index to visually describe the deformation behavior of MGs and shows the high notch sensitivity.

Measurement of load distribution in a cylindrical roller bearing with an instrumented housing: Finite element validation and experimental study

The load distribution between the rolling elements and raceway is crucial in performance evaluation of rolling element bearings. An experimental method is proposed to determine the load distribution by measuring the strain response at the bearing surface with a notched housing. Finite element analysis shows that the introduction of notches does not affect the load distribution. An experimental system was developed to investigate the load distribution in a cylindrical roller bearing. The experimental static load distribution agrees well with the theoretical calculation. The dynamic load at specific position of load zone reflects the manufacture difference among rollers and dynamic balance of distributing loads. The proposed method provides a possible way for real time load distribution measurement of cylindrical roller bearings.

Notched terahertz Bowtie metamaterials with strongly enhanced near-field and narrowed resonance linewidth.

Enhanced near-field and quality factor of resonance are key issues in plasmonic structures. Here, we demonstrate a kind of notched bowtie metamaterials in the terahertz (THz) regime with narrow linewidth and extremely enhanced near field. The notched bowtie is a variation of common bowtie structure created by introducing symmetric notches on the two sides of the triangular metallic structure. Benefiting from the introduction of notches, the modulation depth of transmittance spectra and near-field enhancement of the notched bowtie arrays were strongly enhanced due to the increase of the structure-derived equivalent inductance. The results demonstrated that near-field enhancement can be increased to above 4000. In addition, the designed structure possesses a narrowed resonance linewidth, and thus an improved quality factor, which could be a promising platform for THz sensing and other potential applications of THz metamaterials.

Determination of the critical stress intensity factor (KIC) of compacted pharmaceutical powders by the double torsion method.

The critical stress intensity factor KIC has been determined for compacts prepared at different pressures from both Avicel PH101 and sorbitol "Instant', by means of a double torsion method. This method avoids the need for displacement measurement and the introduction of notch into the specimens, both of which present problems with pharmaceutical materials. Measurements of fracture loads for such specimens were reproducible. The values of KIC derived for both materials were found to increase linearly with increase in compaction pressure and linearly with decrease in specimen porosity. Extrapolation of the latter relationship to zero porosity gave values of 1.81 and 0.69 MN m-3/2 for the KIC of Avicel PH101 and sorbitol "Instant', respectively.

A study on introduction of notch into thin-walled polygonal shell member to control plastic buckling behaviour in axial collapse

Focusing upon finding an optimum shape of crash box, which is one of the most important part of an automobile body to absorb impact energy at the time of a collision, for ensuring large energy absorption, the effect of introducing notch into a crash box on controlling plastic buckling behaviour was examined by three-dimensional finite element analyses. The influences of notch shape and arrangement on the deformation mode of a polygonal crash box was numerically examined and an optimum range of the dimensions of notch was quantitatively determined for ensuring stable buckling deformation. As a result, a fundamental scheme to optimise the shape and arrangement of the notches to ensure large energy absorption was proposed, which is applicable to a crash box with optional cross-sectional shape.

Issues in Recording Exchange Coupled Composite Media

Exchange coupled composite (ECC) media exhibits a lower switching field than conventional perpendicular media at the same level of thermal stability, and thus is able to achieve higher areal density. The inhomogeneity of ECC media is predicted to enhance the thermal attempt frequency: this increases both writability and adjacent track erasure (ATE). The adverse change in ATE is, however, countered by the angular dependence of the ECC media switching field. This angular dependence is further exploited with a head design featuring a larger pole width than track width and the introduction of notches in the down track direction. This reduces the effect of head skew and increases the write field. An optimized head is found to be consistent with terabit/in2 recording

Influence of aspect-ratio on the mixing and acoustic characteristics of plain and modified elliptic slot jets

This paper presents the results of an experimental program that was conducted to examine the effect of aspect-ratio on the flow development and the related acoustic properties of jets issuing from elliptic-slots. The aspect-ratios investigated are 2:1, 3:1 and 4:1. Fully expanded cases show a decrease in shear layer growth with increasing aspect-ratio resulting in a downstream shift in axis-switching location. Further the small aspect-ratio jet shows a dominance of large-scale structures close to slot exit relative to 3:1 and 4:1 jets. In the underexpanded condition the shock-structure development shows appreciable changes with aspect-ratio. At the end of first cell, oblique shock cross-over point in 2:1 jet is gradually replaced by a normal shock in 3:1 and 4:1 jets. The frequency content of jet noise also shows a corresponding increase in amplitude of fundamental screech frequency with increase in aspect-ratio. Introduction of notches along the minor-axis sides further modifies the shock development process which significantly alters the screech amplitudes for notched 3:1 and 4:1 jets indicating the weakening of the feedback process.

The effect of geometry on the properties of a dense alumina—carbon/epoxy laminate

This is a study of the effects of geometry on the properties of a laminate made of dense, thin alumina plates alternating with carbon/epoxy (C/E) prepreg. An advantage of this system is the elimination of the large flaws occurring in fiber-reinforced ceramic matrix composites which are responsible for the low stresses at first matrix cracking. Previous studies have been restricted to small specimens of simple geometry. In this study attention has been directed to the influences of size. the introduction of notches and a geometry in which a large specimen is formed from a mosaic of small elements. The loss of stiffness with increase of the applied strain is compared to the predictions of a simple one-dimensional, elastic—plastic shear lag theory. Although this model does not account for the branching phenomena observed in experiment, there is good agreement with experiment, suggesting that branching has only a second order influence on mechanical properties.