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<p>ISO 22889:2013 specifies methods for determining the resistance to stable crack extension in terms of crack opening displacement, <i>δ</i><sub>5</sub>, and critical crack tip opening angle, <i>ψ</i><sub>c</sub>, for homogeneous metallic materials by the quasistatic loading of cracked specimens that exhibit low constraint to plastic deformation. Compact and middle-cracked tension specimens are notched, precracked by fatigue, and tested under slowly increasing displacement.</p>
<p>ISO 22889:2013 describes methods covering tests on specimens not satisfying requirements for size-insensitive fracture properties; namely, compact specimens and middle-cracked tension specimens in relatively thin gauges.</p>
<p>Methods are given for determining the crack extension resistance curve (R-curve). Point values of fracture toughness for compact specimens are determined according to ISO 12135. Methods for determining point values of fracture toughness for the middle-cracked tension specimen are given.</p>
<p>Crack extension resistance is determined using either the multiple-specimen or single-specimen method. The multiple-specimen method requires that each of several nominally identical specimens be loaded to a specified level of displacement. The extent of ductile crack extension is marked and the specimens are then broken open to allow measurement of crack extension. Single-specimen methods based on either unloading compliance or potential drop techniques can be used to measure crack extension, provided they meet specified accuracy requirements. Recommendations for single-specimen techniques are described in ISO 12135. Using either technique, the objective is to determine a sufficient number of data points to adequately describe the crack extension resistance behaviour of a material.</p>
<p>The measurement of <i>δ</i><sub>5</sub> is relatively simple and well established. The <i>δ</i><sub>5</sub> results are expressed in terms of a resistance curve, which has been shown to be unique within specified limits of crack extension. Beyond those limits, <i>δ</i><sub>5</sub> R-curves for compact specimens show a strong specimen dependency on specimen width, whereas the <i>δ</i><sub>5</sub> R-curves for middle-cracked tension specimens show a weak dependency.</p>
<p>CTOA is more difficult to determine experimentally. The critical CTOA is expressed in terms of a constant value achieved after a certain amount of crack extension. The CTOA concept has been shown to apply to very large amounts of crack extension and can be applied beyond the current limits of <i>δ</i><sub>5</sub> applications.</p>
<p>Both measures of crack extension resistance are suitable for structural assessment. The <i>δ</i><sub>5</sub> concept is well established and can be applied to structural integrity problems by means of simple crack driving force formulae from existing assessment procedures.</p>
<p>The CTOA concept is generally more accurate. Its structural application requires numerical methods, i.e. finite element analysis.</p>
<p>Investigations have shown a very close relation between the concept of constant CTOA and a unique R-curve for both compact and middle-cracked tension specimens up to maximum load. Further study is required to establish analytical or numerical relationships between the <i>δ</i><sub>5</sub> R-curve and the critical CTOA values.</p>
Reģistrācijas numurs (WIID)
60890
Darbības sfēra
<p>ISO 22889:2013 specifies methods for determining the resistance to stable crack extension in terms of crack opening displacement, <i>δ</i><sub>5</sub>, and critical crack tip opening angle, <i>ψ</i><sub>c</sub>, for homogeneous metallic materials by the quasistatic loading of cracked specimens that exhibit low constraint to plastic deformation. Compact and middle-cracked tension specimens are notched, precracked by fatigue, and tested under slowly increasing displacement.</p>
<p>ISO 22889:2013 describes methods covering tests on specimens not satisfying requirements for size-insensitive fracture properties; namely, compact specimens and middle-cracked tension specimens in relatively thin gauges.</p>
<p>Methods are given for determining the crack extension resistance curve (R-curve). Point values of fracture toughness for compact specimens are determined according to ISO 12135. Methods for determining point values of fracture toughness for the middle-cracked tension specimen are given.</p>
<p>Crack extension resistance is determined using either the multiple-specimen or single-specimen method. The multiple-specimen method requires that each of several nominally identical specimens be loaded to a specified level of displacement. The extent of ductile crack extension is marked and the specimens are then broken open to allow measurement of crack extension. Single-specimen methods based on either unloading compliance or potential drop techniques can be used to measure crack extension, provided they meet specified accuracy requirements. Recommendations for single-specimen techniques are described in ISO 12135. Using either technique, the objective is to determine a sufficient number of data points to adequately describe the crack extension resistance behaviour of a material.</p>
<p>The measurement of <i>δ</i><sub>5</sub> is relatively simple and well established. The <i>δ</i><sub>5</sub> results are expressed in terms of a resistance curve, which has been shown to be unique within specified limits of crack extension. Beyond those limits, <i>δ</i><sub>5</sub> R-curves for compact specimens show a strong specimen dependency on specimen width, whereas the <i>δ</i><sub>5</sub> R-curves for middle-cracked tension specimens show a weak dependency.</p>
<p>CTOA is more difficult to determine experimentally. The critical CTOA is expressed in terms of a constant value achieved after a certain amount of crack extension. The CTOA concept has been shown to apply to very large amounts of crack extension and can be applied beyond the current limits of <i>δ</i><sub>5</sub> applications.</p>
<p>Both measures of crack extension resistance are suitable for structural assessment. The <i>δ</i><sub>5</sub> concept is well established and can be applied to structural integrity problems by means of simple crack driving force formulae from existing assessment procedures.</p>
<p>The CTOA concept is generally more accurate. Its structural application requires numerical methods, i.e. finite element analysis.</p>
<p>Investigations have shown a very close relation between the concept of constant CTOA and a unique R-curve for both compact and middle-cracked tension specimens up to maximum load. Further study is required to establish analytical or numerical relationships between the <i>δ</i><sub>5</sub> R-curve and the critical CTOA values.</p>
