Tatsuro Morita

The 22rd and 23th Fatigue Design Short Courses for Beginners

1. はじめに 各種機械製品の破損事故の多くは,繰返し応力負荷に より発生する「疲労現象」を原因としています.そのた め,製品の設計および保守に携わる技術者にとって,疲 労破壊の防止や寿命予測は重要です.一方,近年の社会 的状況下では,疲労に係る知識および技術伝承は必ずし も容易ではありません. 以上を背景として,疲労部門委員会では2日に渡る「初 心者のための疲労設計講習会」を開催しています.以前 は毎年1回の開催でしたが,最近は受講希望者からのご 要望もあり,関東および関西両地区等で毎年2回以上開 催しています. 本講習会は,疲労に係る問題を抱えている技術者だけ でなく,若手研究者や工学系学生をも対象としています. 講習会では,事故事例の紹介から始まり,基礎知識全般 を習得してもらった後,実際の疲労設計法について説明 されます.各講習日の最後には,理解を深めてもらうた めに演習を実施しています.具体的な講義内容は下記の 通りです. 1. 疲労現象と事故事例 2. 疲労強度I:S-N曲線,切欠きの影響,寸法効果 3. 疲労強度II:平均応力および残留応力の影響,低 サイクル疲労 4. 疲労き裂進展:破壊力学の基礎,疲労き裂の進展 挙動および影響因子 5. 実働応力下の疲労:線形累積損傷則,ランダム荷重 6. 疲労強度設計I:疲労強度設計および疲労寿命設 計の概論,溶接構造物の設計規格 7. 疲労強度設計II:鉄道車軸および台車枠の設計法 8. 疲労強度設計III:原子力機器の設計指針 9. 演習 受講者には疲労部門委員会より修了証が発行されま す.また,本講習会の受講は日本材料学会技能検定・ 材料試験士 1級(疲労試験)の受験条件となっていま す. 2. 第22回講習会 第22回の講習会は,本年9月1日~ 2日に大阪工業大 学うめきたナレッジセンター(グランフロント大阪ナ レッジキャピタルタワー C9階)で開催されました.定 員40名のところ,受講者は40名と満杯でした.受講者 の皆さんは,熱心に講義を聞かれておりました(図1). また,講義の合間には多数の受講者が,講習内容だけで なく,個別の案件について講師の先生に質問されていま した. 3. 第23回講習会 第23回の講習会は,本年9月4日~ 5日に中央大学後 楽園キャンパスで開催されました.受講者は18名で, 全員が企業の方でした.このことからも本講習会が社会 的に必要とされていることがわかります.第23回の講 習会でも,講義の合間に多数の受講者が講師の先生に質 問されていました. 4. おわりに 初心者のための疲労設計講習会は,今後も引き続き開 催を予定しています.関西地区での次回講習会は,本学 会主催による「材料WEEK」が来年10月中旬に京都で 開催されるため,その期間中に実施される予定です.皆 様,是非参加してスキルアップを図って下さい.なお, 講習会で使用されているテキストは,「初心者のための 疲労設計法」(ISBN4-90138125-3)として発行されてい ます.社内勉強会や講義等にどうぞご活用下さい. 第 22回・23回初心者のための疲労設計講習会 † 森 田 辰 郎* 久 森 紀 之**

Hidden images on color honeycomb moiré patterns

This portfolio paper shows colorful honeycomb moiré patterns and the application of honeycomb moiré to hidden images. It is well known that fine regular line patterns are overlapped to generate coarse moiré fringes. In order to generate spotted moiré, the authors have employed honeycomb patterns constructed with tiny hexagons as shown in Fig. 1. The left image is a color honeycomb pattern with red, blue and white hexagons used for a base pattern and the right one is a monochrome pattern for a screen overlapped on the base pattern, screen on which white color expresses transparent area. If these images are overlapped without shift and rotation, we can see only red hexagons through the transparent part of the screen. However, by rotating the screen at an overlapping angle θ, a spotted moiré pattern, that is called honeycomb moiré in this paper, is generated and the spatial frequency periodically changes with the overlapping angle. Figures 2(a) and (b) show a uniform honeycomb moiré for θ = 2 deg and a deformed one using a B/W screen modulated with some image effect software. Moiré is used as a technique of hidden image(1), (2) and the honeycomb moiré is also effective for hiding target images. Since the spatial frequency of honeycomb moiré periodically changes every 60 deg by rotating an overlapping screen, we have only to angularly modulate the honeycomb pattern in the area of target image at 30 deg on a base pattern or a screen one, in order to embed the image on the pattern. The spatial frequencies of honeycomb moiré in the target area and in the background are the same to each other at the overlapping angle 15 deg, hence the border of the target image become invisible. Inversely, the target image is clearly visible at the overlapping angles 0 and 30 deg because the spatial frequency on the area of the target image is quite different from that on the background. Figures 2(c) and (d) are an example of hidden and appeared images for a Chinese character “ ” using color honeycomb moiré. In this case, the character is embedded in a base honeycomb pattern consisting of sky blue, green and white hexagons.

Consideration on Behavior of Fatigue Crack Propagation by Dislocation Dynamics Simulation

The influence of the loading history and stress ratio on the behavior of fatigue crack propagation was investigated through the computer simulation based upon the emission and movement of dislocations from the crack-tip. The result of the simulation showed that there is a power relation between the stress intensity range in the preceding cycles and the threshold value where the crack stops propagating. It was also found that the threshold value obtained by the simulation is closely connected with the stress ratio through the Walker relation. The existence of those relations was explained from the viewpoint that the above two parameters control not only the maximum stress intensity but also the crack opening stress intensity level which is determined by the degree of the shielding effect due to the residual dislocations. This idea was supported by the simulation result that the crack propagation rate was clearly related to the effective stress intensity range which was defined as the difference between the maximum stress intensity and the above crack opening stress intensity.

Fatigue Properties of Nitrided Pure Titanium in a Hydrochloric Environment.

A Study has been made to clarify the effect of gas-nitriding on the corrosion resistance and the fatigue properties of pure titanium in a hydrochloric environment. The results are summarized as follows : ( 1 ) most of the fatigue life of nitrided pure titanium is spent in the period of the destruction of the TiN layer associated with pit formation due to hydrochloric acid attack ; ( 2 ) the fatigue strength of annealed pure titanium is greatly reduced in a hydrochloric environment because a fatigue crack initiation along the grain boundary is promoted by hydrochloric acid attack.