Engineering Stress-strain Curve: Part One

概要:

The engineering tension test is widely used to provide basic design information on the strength of materials and as an acceptance test for the specification of materials. In the tension test a specimen is subjected to a continually increasing uniaxial tensile force while simultaneous observations are made of the elongation of the specimen.

The shape and magnitude of the stress-strain curve of a metal will depend on its composition, heat treatment, prior history of plastic deformation, and the strain rate, temperature, and state of stress imposed during the testing. The parameters, which are used to describe the stress-strain curve of a metal, are the tensile strength, yield strength or yield point, percent elongation, and reduction of area. The first two are strength parameters; the last two indicate ductility.

An example of the engineering stress-strain curve for a typical engineering alloy is shown in Figure 1. From it some very important properties can be determined. The elastic modulus, the yield strength, the ultimate tensile strength, and the fracture strain are all clearly exhibited in an accurately constructed stress strain curve.


Figure 1: An example of the engineering stress strain curve for a typical engineering alloy

The elastic modulus, E (Young’s modulus) is the slope of the elastic portion of the curve (the steep, linear region) because E is the proportionality constant relating stress and strain during elastic deformation: σ = Eε.

The 0.2% offset yield strength is the stress value, σ0.2%YS of the intersection of a line (called the offset) constructed parallel to the elastic portion of the curve but offset to the right by a strain of 0.002. It represents the onset of plastic deformation.

The ultimate tensile strength is the engineering stress value or σuts, at the maximum of the engineering stress-strain curve. It represents the maximum load, for that original area, that the sample can sustain without undergoing the instability of necking, which will lead inexorably to fracture.

The fracture strain is the engineering strain value at which fracture occurred.

At the outset, though, a clear distinction must be made between a true stress-true strain curve and an engineering stress-engineering strain curve. The difference is shown in Figure 2, which are plotted, on the same axes, the stress-strain curve and engineering stress-strain curve for the same material. The difference is also evident in the definitions of true stress-true strain and engineering stress-engineering strain.


Figure 2: Comparison of engineering and true stress-strain curves

The engineering stress is the load borne by the sample divided by a constant, the original area. The true stress is the load borne by the sample divided by a variable the instantaneous area. Note that the true stress always rises in the plastic, whereas the engineering stress rises and then falls after going through a maximum.

The maximum represents a significant difference between the engineering stress-strain curve and the true stress-strain curve. In the engineering stress-strain curve, this point indicates the beginning of necking. The ultimate tensile strength is the maximum load measured in the tension test divided by the original area.

ナレッジベース検索

検索したい語句を入力:

検索方法

全文一致
キーワード

前方一致
要約

この記事は連載記事として掲載されております。詳細を見るには下記のリンクをクリックして下さい。

Total Materia Extended Range(拡張版)には数千種の金属合金塑性域、熱処理、加工温度等における計算に必要な応力‐歪み曲線が収録されております。さまざまな歪み速度に応じた真応力、エンジニアリング応力曲線も表示されます。

簡単でしかも数秒以内でデータベースの応力‐歪み曲線を探せます。

検索対象の材料を入力して下さい。材料入力のフィールドで国/規格を指定し検索を絞る事ができます。


対象材料を選んでから応力‐歪み曲線のリンクをクリックするとデータが御覧になれます。御覧になれる応力‐歪みデータの数はリンクわきのカッコ内に表示されております。


Total Materiaデータベースの応力‐歪み曲線は規格それぞれに中立的なものでサブグループのどれが適切なリンクをクリックしてデータを見て下さい。


他の加工温度に対する応力‐歪み曲線をみることができます。

まず、決められた温度範囲内で新たな温度を’ 温度入力’ のフィールドに入力するだけで構いません。

次に計算ボタンをクリックすると新しい曲線が表示され表の数字が入力された温度に応じて表示されます。 250°Cにて入力した場合の例を御覧下さい。


Total Materiaデータベースをあなたにテスト評価を頂くために15万人以上の方が登録されている無料お試しコミュニティ-へ御招待致します。