Katsuyuki Tokimasa

Fatigue-creep life prediction of 214Cr—1Mo steel by inelastic analysis

Abstract This paper covers the second part of the Benchmark Project by the Subcommittee on the Inelastic Analysis and Life Prediction of High Temperature Materials, JSMS, concerning the life prediction methods under fatigue—creep interaction by taking into account the plasticity—creep interaction described by the constitutive models treated in the first part. By specifying a normalized and tempered 2 1 4 Cr —1 Mo steel at 600°C, uniaxial fatigue—creep tests under six patterns of strain waves are performed. Adopting eight types of life estimation methods, two kinds of life prediction procedures are examined: one is a normal way based on an experimentally obtained stress—strain hysteresis loop; and the other is a way of employing the calculated stress—strain hysteresis loop by use of ten types of constitutive models. Predicted lives of the material are compared with observed failure lives, and discussions on the evaluation of the methods are included.

A new high-temperature creep-fatigue damage rule based on the strain range partitioning concept

Abstract A new life prediction model based on the strain range partitioned crack growth rate equations is presented which can evaluate the material damage and the residual life under variable creep-fatigue strainings. Two-step sequential creep-fatigue straining tests such as High-Low and Low-High tests were conducted on Mod. 9Cr-1Mo steel and type 316LC stainless steel in order to examine the validity of the proposed model. It was found that the proposed model can be more successfully applied to the creep-fatigue life prediction under variable strainings than the conventional life prediction methods.

High Temperature Fatigue Properties and Life Prediction of SUS304 Stainless Steel under Variable Straining

ABSTRACT In order to examine the applicability of the proposed fatigue life prediction model under variable straining, PP type High-Low and Low-High tests were conducted for the as solution-treated SUS304 at 700, 800°C and for the thermally aged SUS304 at 700°C in air. It was found that the experimental results for the as solution-treated material at 800°C and for the aged material at 700°C were well explained by the proposed model. On the other hand, in the case of the as solution-treated material at 700°C the deviation from the proposed model was observed in some testing condition. By comparing the cyclic hardening behavior under each testing condition, it was supposed that the discrepancy from the proposed model prediction was caused by the influence of the cyclic hardening during the primary straining on the inelastic strain range of the secondary straining.

Environmental effects on the crack growth properties of alloy 600

Abstract Double U-bend tests are usually applied for estimation of stress corrosion cracking in nickel alloys in pressurized water reactor environments. The test environment is often selected to be severe by the addition of an NaOH concentration higher than that of the actual plant environment. In this study the effects of NaOH concentration on the crack growth properties of Alloy 600 were identified by crack growth tests under a high stress ratio. The crack growth curves of mill-annealed Alloy 600 and thermally treated Alloy 600 were determined in various environments between All-Volatile Treatment water and a 40% NaOH solution. The crack growth rates and fracture surfaces are discussed in terms of the effects of environment and heat treatment.

High Temperature Strength. Prediction of Crack Initiation Life of Converter Shell Based on Stress Analysis.

In order to clarify effective measures to extend a life of converter shell in a steel production plant, the thermal fatigue crack initiation life was predicted by the strain range partitioning method.A three-dimensional FEM model of the converter which is composed of a shell and bricks was established. An inelastic strain of the shell caused by a thermal cycle during operation was evaluated by an elastic-plastic-creep analysis. Since the thermal expansion of bricks is partly absorbed by a gap between bricks, the inelastic strain of the shell is affected by the gap size. Therefore, in the FEM model the hyperelastic element was used in order to describe the deformation behavior of bricks and gaps, and the stress analysis was conducted taking the gap size into consideration.Based on the analytical results and creep-fatigue properties of a shell material, the crack initiation life of the shell was predicted. The relationship between the shell life and cooling conditions at the outer surface of the shell and the relationship between the shell life and the gap size were examined. The following results were obtained.(1) The predicted shell life corresponded well with that in the actual converter.(2) It is possible to extend the shell life by decreasing the maximum shell temperature which can be attained by increasing the film coefficient of cooling at the outer suface of the shell.(3) It is also possible to extend the shell life by increasing the gap size. Futhermore, the larger the gap size is, the decrease of shell temperature becomes more effective for the shell life extention.

High Temperature Fatigue Properties of Type 316LC Steel under Variable Straining.

1 緒 言 高温でのクリープ疲労余寿命評価 を精度良く行 うため には材料の変動ひずみ条件下におけるクリープ疲労特性 を明らかにする必要があること,お よびこのような変動 ひずみ条件下のクリープ疲労特性をもとに任意の波形下 の寿命を一貫 した考え方で評価できる可能性があること を著者 らはこれまでの一連の報告1)~7)に より明らかにしてき た.す なわち,Mod.9Cr-1Mo鋼 を供試材 として各種 のクリープ疲労ひずみ波形下においてひずみ範囲あるい はひずみ波形が変動する二段二重変動ひずみ試験を行い, この試験結果を予測 しうる寿命評価モデルを提案 した. さらに,SUS304鋼 溶体化処理材および時効材 を用い てひずみ波形がPP型 でひずみ範囲が変動す る二段二 重変動ひずみ試験を行い,1次 波の繰返 し加工硬化が2 次波の疲労寿命に及ぼす影響が小さい場合には提案 した 寿命評価モデルがSUS304鋼 について も適用で きるこ とを示 した. この寿命評価モデルの特徴はひずみ範囲分割概念に基 つく巨視き裂進展則6)を用いて平滑丸棒試験片の微小き裂 進展曲線を記述することと各波形モー ドに固有の初期き 裂長さと最絡き裂長 さの存在を仮定することにあ り,平 滑丸棒試験片のクリープ疲労特性,CCT試 験片の巨視 き裂進展特性および平滑丸棒試験片の二段二重変動ひず みクリープ疲労特性に基づいて任意の負荷条件下におけ る仮想的な平滑丸棒試験片の微小 き裂進展曲線を推定 し うることにある7). このような寿命評価モデルの妥当性を明らかにするた めには,さ らに他の材料への適用性について検討 し,そ の一般性を検証するとともに,提 案モデルに より推定さ .れる微小き裂進展挙動 と実際の微小 き裂進展挙動の比較 を行い,両 者が対応 していることを確認する必要があ る. 以上の観点か ら本報では316LC鋼 を用いてひずみ波 形がPP型 でひずみ範囲が変動する二段二重変動 ひず み試験 を行い,提 案モデルの316LC鋼 への適用性を明 らかにするとともに,平 滑丸棒試験片における微小 き裂 進展挙動の観察を行い,提 案モデルによる推定結果 との 対応について検討 した.

Strain range partitioning analysis of high temperature creep fatigue cracks.

The strain range partitioning analysis of creep-fatigue cracks is conducted for the normalized and tempered 21/4 Cr-1 Mo steel at 550°C and for SUS 304 stainless steel at 700°C, assuming that creep-fatigue life relations can be simply obtained by integrating creep-fatigue growth rate equations. For Δeij straining, crack growth rate equations in air and vacuum are respectively given by (1/a) (da/dN)ij=ln(af/a0)ij(Δeij/Aij)1/mij and (1/a)(da/dN)ij=ln(af/a0)ij(Δeij/αijDi)2, where respective partitioned strain versus life relations are given by Δeij=AijNij-mij and Δeij=αijDiNij-0.5, and (af/a0)ij is the ratio of final half crack length to initial one. For (ΣΔeij) straining, it is assumed that the crack growth rate is given by Σ(da/dN)ij.It is shown based on air data that ln(af/a0)pp=8.3, ln(af/a0)pc=10.3, ln(af/a0)cp=2.6 and ln(af/a0)cc=4.0 for 21/4 Cr-1 Mo steel, and that ln(af/a0)pp=13.7, ln(af/a0)pc=5.5, ln(af/a0)cp=5.4 and ln(af/a0)cc=5.2 for SUS 304 steel.Furthermore, (a0)ij and (af)ij of very small size are evaluated on the basis of the obtained values of (af/a0)ij. It is suggested that four types of inelastic strain range, Δeij, are new and useful parameters that will help us to evaluate the crack initiation life, the remaining life and the material damage in future.