Bottom Of Notch Research Articles

Prediction on aeroengine blade foreign object damage validated by air gun tests

Aeroengine in service was prone to ingest foreign objects, leading to foreign object damage (FOD) and failure accidents of the blades. In this paper, laboratory FOD tests were firstly conducted on TC4 and AM355 steel simulated airfoil specimens impacted by 3 mm diameter projectile at a speed of 350 m/s, and numerically reproduced using Johnson-Cook (J-C) model with failure criterion. A penetrating-type notch (P-notch) with severe material loss was observed, and a good agreement between experiments and finite element (FE) predictions could be found for both notch morphology and size. The influence of impact velocity on FOD and the FOD-induced residual stress were investigated by the proposed FE model. High tensile stress was observed along the notch edge, while the bottom of notch was mainly dominated by compressive stress. Finally, a FE model of aeroengine blade considering the initial centrifugal force was developed, and the influences of FOD to compressor blade on its modal properties were discussed. Compared to the normal blade, the damage induced a deviation in frequency within 1 %.

Analysis on damage evolution and corrosion fatigue performance of high-strength steel wire for bridge cable: Experiments and numerical simulation

Corrosion fatigue (CF) failure is one of the typical failure modes of high-strength steel wires for bridge cables because the cables are subjected to the long-term cyclic loads and exposed to the heavy polluted environment at the same time. In this paper, the damage evolution process and CF performance were investigated, and the service life was predicted for steel wire with machine-cut notch via experiments and numerical simulation. Firstly, a novel experimental device was constructed to apply fatigue load and corrosive medium on multiple specimens simultaneously. With the constructed device, two groups of experiments were conducted to analysis the fatigue performance and CF performance of surface notched wire specimens, and the fatigue life and CF life of steel wire were obtained under fatigue load and the coupling effect of corrosive medium and fatigue load (CCF) respectively. Additionally, in order to study the fatigue damage evolution process and CF damage evolution process of surface notched steel wire under fatigue load and CCF respectively, a fatigue damage constitutive equation and a CF damage constitutive equation were proposed respectively according to continuum damage mechanics, and experimental data were used to determine the value of each parameter in these two equations. With the proposed model, damage evolution process in steel wire was simulated under fatigue loads and CCF respectively. The effect of corrosive medium on wire life was discussed. The results show that the fatigue life and CF life of surface notched wire obtained from simulation are consistent well with the experimental results, which shows that the simulation method can achieve the expected goal, and has high reliability in predicting the fatigue life and CF life, and simulating the fatigue damage evolution and CF damage evolution of surface notched wire. For the fatigue damage evolution process and CF damage evolution process, damage evolves gradually, and the damage evolution rate gradually increases. There are more and more damage elements at the bottom of machine-cut notch, and some elements inside the steel wire are also damaged. Comparing the damage distribution of steel wire subjected to fatigue load only and CCF, it can be found that corrosive medium will cause the damaged elements to appear earlier. Under the same stress range, the fatigue life and CF life of steel wire with machine-cut notch are significantly different, but the fatigue damage evolution rate and CF damage evolution rate are similar. It can be concluded that the difference in service life is mainly due to the corrosive medium that causes the damaged elements near the surface notch appear earlier, especially under higher stress ranges.

Influence of microstructure on fatigue property of ultra high-strength steels

Ultra-high-strength steels (with tensile strength higher than 980 MPa) are widely used in automobile manufacturing owing to their lightweight that contributes to fuel efficiency. The fatigue strength of ultra-high-strength steels with a notch tends to decrease, which is known as the effect of notch sensitivity. In this study, 4-point bending fatigue tests were performed to examine the fatigue strength and notch sensitivity of four steels; namely 590 MPa class steel, 980 MPa class martensitic steel, 980 MPa class bainitic steel, and 980 MPa class precipitation hardening steel plates with three different stress concentration factors. The results indicate that the fatigue strength and notch sensitivity of 980 MPa class steel specimens were higher than those of 590 MPa class steel specimens. The notch sensitivities of tested plate specimens were lower than those reported for cylindrical specimens of bainitic ultra-high-strength steels. Fatigue crack observation revealed that the cracks initiated in 590 MPa class steel, 980 MPa class bainitic, and martensitic steel propagated southward from the lowest bottom of notch. Although similar initial crack propagation pattern was detected in precipitation hardening steel, the crack changed direction when it reached the central part of the specimen.

PREVENTION OF ROUND TIMBER LATERAL CRACKING IN WOODEN HOUSE CONSTRUCTION

The article is devoted to the most widespread defect of regularized round timbers in wooden house construction, i.e. their lateral cracking in the process of further use of buildings and structures. A method is proposed to cut lateral saw kerfs in the round timber surface upon timber rounding, which almost completely excludes appearance of cracks on exposed surfaces. Saw kerfs are cut in the exterior surfaces of round timber on the opposite side of the simultaneously manufactured technological notch. According to the results of theoretical and experimental studies, it was ascertained that the saw kerf is the main factor which excludes appearance of lateral cracking in regularized round timber. Taking into account the technological notch, the optimal depth of a saw kerf should not be more than 35% of the round timber cross-section radius. The absence of visible lateral macro-cracks on exposed surfaces of round timber will improve the appearance of a building and prolong its service life. Macro-cracks appear at the bottom of the technological notch and at the bottom of the saw kerf which serve as stress concentrators. Such stresses occurring due to the hygroscopic moisture gradient along the round timber cross-section radius and anisotropy of wood shrinkage in points with stress concentrators can exceed the limit values upon extension in the tangential direction, wherefore macro-cracks will form in the areas with stress concentrators. According to estimates, additional energy consumption for making a lateral saw kerf will be 1–2%.

Oscillatory transformative domain wall inner structure of the depinning domain wall around a notched ferromagnetic wire

We have investigated the domain wall (DW) depinning behavior around the symmetric notches in ferromagnetic nanowires by means of a micromagnetic simulation. We observed that the depinning field decreases as the size of the notch increases. The change in the ratio of the height to the length of the bottom of the triangular notch is also considered, and a relatively insensitive variation of the depinning field is observed with for ratios greater than 2. When the depinning field strength is varied, the DW internal structure is found to change during the depinning process. At a lower depinning field ( 4 mT), the DW is depinned with a transformation of the inner structure with an antivortex soon after the DW has escaped from the notch due to the Walker breakdown phenomenon. Very interestingly, with any external field, the depinned DW with antivortex inner structure is observed to move back to the original notch position. This is explainable because the notch acts as an attractive pinning potential for the DW.

Improvement of fatigue limit by shot peening for high‐tensile strength steel containing a crack in the stress concentration zone

PurposeThe purpose of this paper is to investigate the effect of shot peening (SP) on the fatigue limit of high‐tensile‐strength steel containing a crack in the stress concentration zone.Design/methodology/approachAn artificial semi‐circular slit was introduced into the bottom of notch, and SP was performed. Bending fatigue tests were then carried out.FindingsFirst, the fatigue limits of specimens containing a slit of 0.2 or 0.3 mm in depth were improved up to approximately twice their original values. Second, in the case of shot‐peened specimens with a crack of 0.2 mm in depth, the fractures occurred from outside the slit. Moreover, the specimens recovered to fatigue limits up to those of non‐slit specimens. Finally, the effect of stress concentration (Kt=1.9) on the slit size could be rendered harmless by SP was not found in the fatigue test.Originality/valueThere are very few examples of evaluations of the fatigue limit of materials containing crack‐like surface defects after SP has been performed in the stress concentration zone. The study elucidated the effect of SP on the fatigue limit in such materials, compared with that of a smooth zone.

Study on Machining of Cracking Notches for Automotive Connecting Rod Using WEDM

In order to resolve the problem of connecting rod notches machining, a new process of WEDM (Wire Electric Discharge Machine) has been presented, and it is greatly possible that expensive laser process can be replaced by WEDM in virtue of its unique advantages. Firstly, process parameters of notch have been analyzed, and project of machining notch using WEDM has been introduced, including measures to achieve good-quality notch. The relationship between cutting speed and power supply parameters has been investigated, and it is discovered that micro-crackle on bottom of notch are greatly effect to fracture splitting process, also new idea of active controlling micro-crackle has been presented. Finally, fracture splitting machining has been carried out. The cost and entrance standard of fracture splitting process are greatly dropped owing to new breakthrough of machining notch using WEDM.

Experimental and numerical study of stress–strain state of pressurised cylindrical shells with external defects

Work presents the experimental technique with using of strain gauges for determining of strain distribution near longitudinal external defects of semielliptical shape in pressurised cylindrical shells and an appropriate procedure of numerical calculation based on a finite element method (FEM) for assessment of strain state near such defects. Numerical assessment of elastic stress distribution at bottom of external semielliptical notch in pressurised cylindrical shell is in a good agreement with the data received on the base of different analytical models. Here, the FEM results and data based on Glinka-Newport model are the most close for maximal stress. A comparison an experimental and calculation results showed on their acceptable coincidence and this fact gives the ground for using the numerical calculations instead labour-intensive and expensive experimental tests.

Stress Concentrations of a Hollow Circular Cylinder with a Semicircular Notch under Internal Pressure.

This paper deals with the stress concentration problem of a hollow circular thick walled elastic cylinder with a semicircular groove under internal pressure. A method of solution is presented for the problem by applying Green's functions for axisymmetric body force problems of a thick plate. The Green's functions are defined as solutions for a thick plate subjected to axisymmetric body forces acting along a circle in the interior of the plate. A principle of the method of solution is to imagine a hollow cylinder with a notch and to distribute axisymmetric body forces in the thick plate so as to satisfy the boundary conditions of the hollow cylinder. The problem is formulated by an intergral equation with unknown functions of body forces. Stress concentrations at the notch are investigated by numerical calculations and stress distributions near the notch and form factors are shown. The maximum stress appears at the bottom of notch or the inner boundary of smallest cross section depending on the inner radius of cylinder and the notch radius.

123 半円切欠きみぞをもつ厚肉円筒の内圧による応力集中(GS-1 構造解析・応力解析(1))

This paper deals with the stress concentration problem of a hollow circular thick walled elastic cylinder with a semicircular groove under internal pressure. A method of solution is presented for the problem by applying Green's functions for axisymmetric body force problems of a thick plate. The Green's functions are defined as solutions for a thick plate subjected to axisymmetric body forces acting along a circle in the interior of the plate. A principle of the method of solution is to imagine a hollow cylinder with a notch and to distribute axisymmetric body forces in the thick plate so as to satisfy the boundary conditions of the hollow cylinder. The problem is formulated by an intergral equation with unknown functions of body forces. Stress concentrations at the notch are investigated by numerical calculations and stress distributions near the notch and form factors are shown. The maximum stress appears at the bottom of notch or the inner boundary of smallest cross section depending on the inner radius of cylinder and the notch radius.

Fatigue Strength of Notched Specimen by Super Rapid Induction Heating and Quenching.

It seems to be possible to heat treat the gears having higher fatigue strength with lower distortion by applying newly developed super rapid induction heating and quenching (SRIHQ) technology. In this previous research, rotating bending fatigue properties of S 45 C tempered martensite structure plane specimens heat treated by SRIHQ having shallower hardened layer and higher compressive residual stress were studied, and it was observed that the fatigue strength was not improved due to the fatigue cracks initiation just beneath the shallow hardened layer. In the present research, rotating bending fatigue properties of same specimens with notch (α=2.3) heat treated by SRIHQ were studied. As a result, on the contrary of previous work, much higher fatigue strength was obtained in spite of shallow hardened layer. The compressive residual stress formed at the bottom of notch is extremely high (2000 MPa) due to the effect of stress concentration.

溶融亜鉛めっき槽用鋼板溶接材料の実機槽への適用に関する研究

This study was carried out to select suitable welding methods and welding consumables used for constructing a galvanizing bath. In this report, these were selected in terms of the elevated temperature strength, the susceptibility of liquid metal embrittlement and corrosion resistance in liquid zinc.The base metal used was a carbon steel specialized for a galvanizing bath. The shielded metal arc (SMA) and gas shield arc weldings (GMA) were used with a covered electrode (E1) and solid and flux cored wires (F1, F2 and F3).The elevated temperature strength of all deposited metals were measured at the temperature range from room temperature to 600°C.Moreover, the notched bar tensile (NBT) test, where the bottom of notch was coated by liquid zinc, was performed at the temperature of 480°C to know the susceptibility of liquid metal embrittlement. Corrosion resistance was measured at the temperature of 450°C in molten zinc of practical bath.Strength at the elevated temperature of deposited metals by GMA welding was higher than that by SMA welding. The susceptibilities of liquid metal embrittlement of deposited metals became high in the order of E1, F3, F1 and F2. The susceptibilities of F1 and F3 were almost corresponded with that of the base metal. The susceptibility of liquid metal embrittlement at liquid zinc increased with an increase in the term of C+Si+Mn. Moreover, corrosion resistances of F1 and F2 in liquid zinc were higher than those of the base metal, E1 and F3. When the value of C+Si+Mn exceeds 1.7%, corrosion resistance of weld metal decreases.The solid wire, F3 was. selected as a candidate of welding consumable used for constructing a galvanizing bath from the present results.

Mixed Boundary Value Problem with Two Displacement Boundaries for Thin Plate Bending.

Solution of the mixed boundary value problem for thin plate bending with two external force and two displacement boundaries is derived. General solution is derived using a rational mapping and complex stress functions. A semi-infinite plate with two displacemen constraints within a semi-elliptic notch under uniform bending is considered as an application. Stress distributions, stress intensity of debonding at the tip of the displacement constraint, stress concentration factors at the bottom of the semi-elliptic notch, and stress intensity factors when the semi-elliptic notch is changed into an edge crack are calculated. Besides, a general solution for one external force boundary and one displacement boundary is also derived.

Vertical laryngeal size and the lowest tone in the evaluation of the average fundamental frequency (F0) of Finnish speakers

This study tested in Finnish speakers (N=90) two methods that could be used as an aid in the evaluation of habitual speaking pitch. 1) The vertical size of the larynx was measured through percutaneous palpation as the distance between the lower border of the cricoid cartilage and the bottom of the thyroid notch. 2) The difference (in semitones, st) between the lowest tone the subjects could produce in soft voice and the average fundamental frequency (F0) in text reading was calculated. The vertical laryngeal size did not correlate with the average F0. For those speakers evaluated as using ?optimum? pitch, the difference between the lowest tone and the average F0 was about 6 st for the males and 5 st for the females. The difference correlated with the perceptual evaluation of pitch (p<0.05).

Impulsive torsion of semi-infinite body with circular rod. (Analysis of generalized dynamic stress intensity factor)

To discuss the initiation of crack in the material, it will be important to get the knowledge about the singular stress at the bottom of the sharp notch. In this paper, dynamic singular stress field is discussed on the periphery of the periphery of the function part of the semi-infinite rod fixed on the surface of the semi-infinite body. It is assumed that the one dimensional torsional stress wave travels down the rod and arrived at the junction. Stresses on the rod and the semi-infinite body are analyzed based on the dynamic theory of elasticity and Laplace transformation method. An integral equation is solved numerically in the transformed domain. Stresses near the function and the generalized stress intensity factor are calculated from the above results by using the numerical inversion of the Laplace transformation.

Analytic approximations for degenerate accumulation layers in semiconductors, with applications to barrier lowering in isotype heterojunctions

The Joyce-Dixon approximation for the Fermi energy in a degenerate semiconductor is used to obtain rapidly converging series expansions for both the potential and the electric field for degenerate accumulation layers in semiconductors, as functions of the electron concentration. The expressions are valid for electron concentrations up to about 20 times the effective density of states. The approximation is applied to Schottky barriers on degenerate semiconductors, where it leads to an increase in the value of the Gummel-Scharfetter correction in the C-V relation for Schottky barriers. A detailed quantitative treatment is given for the barrier lowering in abrupt n-N heterojunctions with increased reverse bias. Both barrier lowering and reverse bias are given as closed-form parametric expressions, with the electron concentration at the bottom of the heterojunction notch as the independent variable.

Efficacy of preoperative laryngogram for localization of the ventricle at the anterior commissure.

AbstractThe localization of the ventricle exactly above the anterior commissure of the vocal cords is important in performing supraglottic laryngectomy. The lateral projections of pre‐operative laryngograms are examined and the following two dimensions are measured on the film: (1) distance between the bottom of the thyroid notch and the inferior border of the thyroid cartilage and (2) distance between the anterior part of the ventricle and the inferior border. The ratio of these two distances is obtained and is designated as distance ratio (DR). The DR is similarly calculated from the actual measurements of the laryngeal specimens and is compared with the DR based on the laryngograms. Differences between these two DR's are nonsignificant (0.5 &lt;p &lt;0.6). Also, there is a high degree of relationship between these two DR's (P &lt;0.001). Thus, the DR based on the laryngogram is an accurate index to determine the level of the ventricle just above the anterior commissure in performing a transection of the thyroid cartilage. When the thyroid cartilage is exposed completely during surgery a measurement between the bottom of the thyroid notch and the inferior border is made. Actual distance between the inferior border and the anterior part of the ventricle can be calculated by the DR obtained from the preoperative laryngogram. This method ensures that neither anterior commissure nor pre‐epiglottic space is violated when the thyroid cartilage is transected.

Effect of Mean Stress on Fatigue Crack Initiation and Propagation : From Different Configurations of Notch

In previous papers, the effect of a mean stress on a fatigue crack initiation and its propagation from a circular hole was estimated. It is well known that a crack initiated at a bottom of a dull notch have a large propagating rate. Therefore, a degree of the effect of the mean stress on the fatigue crack initiation and its propagating rate may be affected by sharpness of the notch.A fatigue test was additionally made with specimens containing two kinds of shapes of the notch and it is discussed how the degree of the effect of the mean stress on them is affected by sharpness of the notch and the following onclusions are obtained : (1) The mean stress does not affect the crack initiation at every shape of the notch. A life to the crack initiation at the circular hole or two slits is determined only by an alternating stress at the point inner e0 from the bottom of the each notch without regard to the shape of notch. e0 corresponds to a mean size of a ferrite patch of S35C steel used in this experiment.(2) The degree of the mean stress on the fatigue crack propagating rate decreases with sharpening of the notch and this can be explained by the behaviour of the crack propagation previously reported by the authors.

Change in Surface States and Incipient Fatigue Cracks in Electro-Polished Low Carbon Steel (Plain and Notched Specimens) under Rotating Bending Stress

Using electro-polished low carbon steel specimens, the change in surface states and the incipient fatigue cracks of plain and notched specimens subjected to rotating bending stress were investigated. The main results obtained are as follows. (1) When the limit stress for macro-crack initiation σw1 is repeated, the amount of slip bands appearing at the root of notch is nearly equal, not only after 107 cycles but also at every cycle ratio, even if the maximum stress ασw1 at the bottom of notch is different in various radii of the notches. (2) In the specimens with various radii of the notches, the limit stress for slip bands initiation σws is almost proportional to the stress σw1, that is, σwsb(0.85∼0.9)σw1. (3) The incipient fatigue cracks, which appear on plain specimens after 107 cycles of the stress σw1, can hardly sustain the tensile stress statically and dynamically.

衝撃疲労における&lt;I&gt;S&lt;/I&gt;-&lt;I&gt;N&lt;/I&gt;曲線（疲労割れの発生と進展について）

Usually, U(energy)-N curves are used to study the impact fatigue, so we cannot compare the results with other impact fatigue data or non-impact fatigue data. So we tried to show a few example of S(stress)-N curves of the impact fatigue, based on the results of our previous experiments in which the relation between impact stresses and impact energy were studied. And we carried out the experiments on the stand-point of the formation and the propagation of fatigue cracks, and whether the stresses applied are tensile, compressive or tensile-compressive stresses alternately is very important to study fatigue phenomena. We used Matsumura’s impact fatigue testing machine and notched test pieces (annealed 0.2% and 0.3% carbon steels). We can compare the fatigue data under two different conditions. From S-N curves for impact fatigue (S is stress at the bottom of notch), N0 (number of blows at which the fatigue crack begins to propagate) is the largest for the Case C, and the smallest for the Case T-C. (Case C means that the stresses at the bottom of the notches are compressive stress, Case T means tensile stresses, and Case T-C means tensile and compressive stresses alternately). For the Case C, the relation between l (length of fatigue cracks) and N (number of blows), and V (velocity of propagation of cracks) and I are as follows. l=K logN/N_0 V=0.4343 K/N K is constant and means tangent of l−logN curves. We applied the above formula to the results of the Cases T and T-C approximately, and compared K and V for each case. K in the Cases T and T-C were almost the same, and K in the Case C was smaller. V in the Case T-C was the largest and in the Case C was the smallest.