Plastizität und Bruchmechanik - Technische Fakultät
Plastizität und Bruchmechanik - Technische Fakultät
Plastizität und Bruchmechanik - Technische Fakultät
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ASTM E 399:<br />
<strong>Bruchmechanik</strong><br />
Standard Test Method for Linear-Elastic Plane-Strain Fracture Toughness<br />
K Ic of Metallic Materials<br />
Significance and Use<br />
‣ Characterizes the resistance of a material to fracture in a neutral environment in the<br />
presence of a sharp crack <strong>und</strong>er essentially linear-elastic stress and severe tensile<br />
constraint, such that (1) the state of stress near the crack front approaches tritensile<br />
plane strain, and (2) the crack-tip plastic zone is small compared to the crack size,<br />
specimen thickness, and ligament ahead of the crack;<br />
‣ Is believed to represent a lower limiting value of fracture toughness;<br />
‣ May be used to estimate the relation between failure stress and crack size for a material<br />
in service wherein the conditions of high constraint described above would be expected;<br />
‣ Only if the dimensions of the product are sufficient to provide specimens of the size<br />
required for valid K Ic determination.<br />
Specimen Size, Configuration and Preparation<br />
‣ Specimen size<br />
Ligament ( W a)<br />
2<br />
⎛<br />
Ic<br />
2.5 K ⎞<br />
− ≥ ⎜ ⎟<br />
σ<br />
YS<br />
⎝<br />
⎠<br />
where σ YS is the 0.2 % offset yield strength<br />
Meeting this requirement cannot be assured in advance. Thus, specimen dimensions<br />
shall be conservatively selected for the first test in a series.<br />
‣ Specimen configurations<br />
• SE(B): Single-edge-notched and fatigue precracked beam loaded in three-point<br />
bending; support span S = 4 W, thickness B = W/2, W = width;<br />
• C(T): Compact specimen, single-edge-notched and fatigue precracked plate<br />
loaded in tension; thickness B = W/2;<br />
• DC(T): Disk-shaped compact specimen, single-edge-notched and fatigue<br />
precracked disc segment loaded in tension; thickness B = W/2;<br />
• A(T): Arc-shaped tension specimen, single-edge-notched and fatigue<br />
precracked ring segment loaded in tension; radius ratio r 1<br />
r 2<br />
unspecified;<br />
• A(B): Arc-shaped bend specimen, single-edge-notched and fatigue precracked<br />
ring segment loaded in bending; radius ratio r 1<br />
r 2<br />
= 0.6 ÷ 1.0 for S/W = 4 and<br />
r1 r<br />
2<br />
= 0.4 ÷ 1.0 for S/W = 3;<br />
‣ Specimen preparation<br />
Fatigue precracking from starter notch; crack size (total size of crack starter plus fatigue<br />
crack) 0.45 W ÷ 0.55 W<br />
Calculation and Interpretation<br />
Determination of force P Q by a 5% offset secant in the force-displacement record; if<br />
P P ≤ proceed to calculate K Q<br />
max Q<br />
1.1<br />
fracture-toughness, Wolfgang Brocks, 23-Nov-11, - 2 -
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