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

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 vertically 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

ダイ41ジ ナンキョク チイキ カンソクタイ キショウ ブモン ホウコク 2000

この報告は,第41次南極地域観測隊気象部門が,2000年2月1日から2001年1月31日まで,昭和基地において行った気象観測結果をまとめたものである.観測方法,測器,統計方法等は,第40次隊とほぼ同様である. 越冬期間中,特記される気象現象として,次のものが挙げられる.1) 地上気象観測において,3月には好天が継続し,月平均気温の低い方,月最低気温の低い方,月間日照時間の多い方等の,また,10月には曇天が持続し,月平均雲量の多い方,月間日照時間の少ない方のそれぞれの極値の更新があった.2) 高層気象観測では,9月,10月の50hPaより上の領域で30年平均値に比べて強い西風偏差が現れた.3) オゾン全量観測において,昨年に引き続き大規模なオゾンホールを観測した.オゾンホールの消滅は12月1日で,オゾンホールが継続して大規模に発達している1992年以降では94年に次ぎ2番目に早かった.4) エアロゾルゾンデ観測において,春季南極上空で形成されるオゾンホールの重要要因となっていると思われる極成層圏雲(PSCs)の雲粒子の分布状況を観測した.This report is a collection of results on meteorological observations performed by the 41st Japanese Antarctic Research Expedition from February 1, 2000 through January 31, 2001 at Syowa Station. The measuring instruments and means of compiling statistics were almost the same as those used on the 40th Expedition. Remarkable weather phenomena during the wintering period are as follows.1) In surface weather observations, fine weather continued in March, the minimum monthly mean temperature, monthly lowest temperature, and maximum duration of monthly sunshine were recorded. On the other hand, cloudy weather continued in October, the maximum monthly mean cloud amount and the minimum duration of monthly sunshine were recorded.2) In upper air observations, heavy westerly wind blew above 50hPa compared to a normal year, in September and October.3) The large-scale ozone hole was observed, as in the previous year. The ozone hole disappeared on December 1; the recovery of the total amount of ozone was secondary earliest in the last 9 years.4) In observations using aerosol sondes, we observed variations of polar stratospheric clouds (PSCs), which are thought to be the most important cause of ozone holes formed in the springtime Antarctic lower stratosphere