{"id":21250,"date":"2022-07-23T16:07:37","date_gmt":"2022-07-23T08:07:37","guid":{"rendered":"https:\/\/www.meetyoucarbide.com\/?p=21250"},"modified":"2022-07-27T11:24:16","modified_gmt":"2022-07-27T03:24:16","slug":"august-wohlers-experiment-statics-showing-you-how-the-4-elements-impact-on-fatigue-crack","status":"publish","type":"post","link":"https:\/\/www.meetyoucarbide.com\/vi\/august-wohlers-thu-nghiem-tinh-hien-thi-ban-cach-4-yeu-to-tac-dong-tren-su-met-moi-crack\/","title":{"rendered":"Th\u00ed nghi\u1ec7m c\u1ee7a August W\u00f6hler cho b\u1ea1n th\u1ea5y c\u00e1ch 4 y\u1ebfu t\u1ed1 t\u00e1c \u0111\u1ed9ng \u0111\u1ebfn v\u1ebft n\u1ee9t m\u1ec7t m\u1ecfi"},"content":{"rendered":"

Fatigue cracks are generally the result of periodic plastic deformation in local areas. Fatigue is defined as “failure under repeated load or other types of load conditions, and this load level is not sufficient to cause failure when applied only once.” This plastic deformation occurs not because of the theoretical stress on the ideal component, but because the component surface can not be actually detected.<\/a><\/a><\/a><\/a><\/a><\/a><\/p>

August W\u00f6hler l\u00e0 ng\u01b0\u1eddi ti\u00ean phong trong nghi\u00ean c\u1ee9u v\u1ec1 s\u1ef1 m\u1ec7t m\u1ecfi v\u00e0 \u0111\u01b0a ra m\u1ed9t ph\u01b0\u01a1ng ph\u00e1p th\u1ef1c nghi\u1ec7m. T\u1eeb n\u0103m 1852 \u0111\u1ebfn n\u0103m 1870, w \u00f6 hler \u0111\u00e3 nghi\u00ean c\u1ee9u s\u1ef1 h\u01b0 h\u1ecfng d\u1ea7n d\u1ea7n c\u1ee7a c\u00e1c tr\u1ee5c \u0111\u01b0\u1eddng s\u1eaft. \u00d4ng \u0111\u00e3 ch\u1ebf t\u1ea1o gi\u01b0\u1eddng th\u1eed nh\u01b0 trong H\u00ecnh 1. Gi\u01b0\u1eddng th\u1eed n\u00e0y cho ph\u00e9p quay v\u00e0 u\u1ed1n hai tr\u1ee5c \u0111\u01b0\u1eddng s\u1eaft c\u00f9ng m\u1ed9t l\u00fac. W \u00f6 hler v\u1ebd bi\u1ec3u \u0111\u1ed3 m\u1ed1i quan h\u1ec7 gi\u1eefa \u1ee9ng su\u1ea5t danh ngh\u0129a v\u00e0 s\u1ed1 chu k\u1ef3 d\u1eabn \u0111\u1ebfn h\u01b0 h\u1ecfng, sau n\u00e0y \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 bi\u1ec3u \u0111\u1ed3 SN. M\u1ed7i \u0111\u01b0\u1eddng cong v\u1eabn \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 \u0111\u01b0\u1eddng aw \u00f6 hler. Ph\u01b0\u01a1ng ph\u00e1p Sn v\u1eabn l\u00e0 ph\u01b0\u01a1ng ph\u00e1p \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng r\u1ed9ng r\u00e3i nh\u1ea5t hi\u1ec7n nay. M\u1ed9t v\u00ed d\u1ee5 \u0111i\u1ec3n h\u00ecnh c\u1ee7a \u0111\u01b0\u1eddng cong n\u00e0y \u0111\u01b0\u1ee3c th\u1ec3 hi\u1ec7n trong H\u00ecnh 1.<\/p>

<\/a><\/p>

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H\u00ecnh 1 th\u1eed nghi\u1ec7m m\u1ecfi khi u\u1ed1n khi quay c\u1ee7a W \u00f6 hler<\/figcaption><\/figure>

<\/a><\/p>

Several effects can be observed through the w \u00f6 hler line. First, we note that the SN curve below the transition point (about 1000 cycles) is invalid because the nominal stress here is elastoplastic. We will show later that fatigue is caused by the release of plastic shear strain energy. Therefore, there is no linear relationship between stress and strain before fracture, and it cannot be used. Between the transition point and the fatigue limit (about 107 cycles), the Sn based analysis is valid. Above the fatigue limit, the slope of the curve decreases sharply, so this region is often referred to as the “infinite life” region. But this is not the case. For example, aluminum alloy will not have infinite life, and even steel will not have infinite life under variable amplitude load.<\/a><\/p>

V\u1edbi s\u1ef1 xu\u1ea5t hi\u1ec7n c\u1ee7a c\u00f4ng ngh\u1ec7 khu\u1ebfch \u0111\u1ea1i hi\u1ec7n \u0111\u1ea1i, ng\u01b0\u1eddi ta c\u00f3 th\u1ec3 nghi\u00ean c\u1ee9u c\u00e1c v\u1ebft n\u1ee9t m\u1ecfi m\u1ed9t c\u00e1ch chi ti\u1ebft h\u01a1n. B\u00e2y gi\u1edd ch\u00fang ta bi\u1ebft r\u1eb1ng s\u1ef1 xu\u1ea5t hi\u1ec7n v\u00e0 lan truy\u1ec1n c\u1ee7a v\u1ebft n\u1ee9t m\u1ecfi c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c chia th\u00e0nh hai giai \u0111o\u1ea1n. Trong giai \u0111o\u1ea1n \u0111\u1ea7u, v\u1ebft n\u1ee9t truy\u1ec1n theo m\u1ed9t g\u00f3c kho\u1ea3ng 45 \u0111\u1ed9 so v\u1edbi t\u1ea3i tr\u1ecdng t\u00e1c d\u1ee5ng (d\u1ecdc theo \u0111\u01b0\u1eddng \u1ee9ng su\u1ea5t c\u1eaft l\u1edbn nh\u1ea5t). Sau khi v\u01b0\u1ee3t qua hai ho\u1eb7c ba ranh gi\u1edbi h\u1ea1t, h\u01b0\u1edbng c\u1ee7a n\u00f3 thay \u0111\u1ed5i v\u00e0 m\u1edf r\u1ed9ng d\u1ecdc theo h\u01b0\u1edbng kho\u1ea3ng 90 \u0111\u1ed9 so v\u1edbi t\u1ea3i tr\u1ecdng t\u00e1c d\u1ee5ng. Hai giai \u0111o\u1ea1n n\u00e0y \u0111\u01b0\u1ee3c g\u1ecdi l\u00e0 n\u1ee9t giai \u0111o\u1ea1n I v\u00e0 n\u1ee9t giai \u0111o\u1ea1n II, nh\u01b0 trong H\u00ecnh 2.<\/a><\/a><\/a><\/a><\/p>

\"\"
H\u00ecnh 2 S\u01a1 \u0111\u1ed3 s\u1ef1 ph\u00e1t tri\u1ec3n c\u1ee7a v\u1ebft n\u1ee9t \u1edf giai \u0111o\u1ea1n I v\u00e0 giai \u0111o\u1ea1n II<\/figcaption><\/figure>

If we observe a stage I crack at high magnification, we can see that the alternating stress will lead to the formation of a continuous slip band along the maximum shear plane. These slip bands slide back and forth, much like a deck of cards, resulting in uneven surfaces. The concave surface finally forms a “budding” crack, as shown in Figure 3. In phase I, the crack will expand in this mode until it meets the grain boundary and will stop temporarily. When enough energy is applied to the adjacent crystals, then the process will continue.<\/p>

<\/a><\/p>

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H\u00ecnh 3 S\u01a1 \u0111\u1ed3 c\u1ee7a d\u1ea3i tr\u01b0\u1ee3t li\u00ean t\u1ee5c<\/figcaption><\/figure>

<\/a><\/a><\/a><\/a><\/a><\/a><\/p>

Sau khi v\u01b0\u1ee3t qua hai ho\u1eb7c ba ranh gi\u1edbi h\u1ea1t, h\u01b0\u1edbng lan truy\u1ec1n v\u1ebft n\u1ee9t l\u00fac n\u00e0y chuy\u1ec3n sang ch\u1ebf \u0111\u1ed9 pha II. \u1ede giai \u0111o\u1ea1n n\u00e0y, c\u00e1c t\u00ednh ch\u1ea5t v\u1eadt l\u00fd c\u1ee7a s\u1ef1 lan truy\u1ec1n v\u1ebft n\u1ee9t \u0111\u00e3 thay \u0111\u1ed5i. B\u1ea3n th\u00e2n v\u1ebft n\u1ee9t t\u1ea1o th\u00e0nh v\u1eadt c\u1ea3n v\u0129 m\u00f4 \u0111\u1ed1i v\u1edbi d\u00f2ng \u1ee9ng su\u1ea5t, l\u00e0m cho \u1ee9ng su\u1ea5t d\u1ebbo t\u1eadp trung cao \u1edf \u0111\u1ea7u v\u1ebft n\u1ee9t. Nh\u01b0 trong H\u00ecnh 4. C\u1ea7n l\u01b0u \u00fd r\u1eb1ng kh\u00f4ng ph\u1ea3i t\u1ea5t c\u1ea3 c\u00e1c v\u1ebft n\u1ee9t \u1edf giai \u0111o\u1ea1n I s\u1ebd ph\u00e1t tri\u1ec3n sang giai \u0111o\u1ea1n II.<\/a><\/p>

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H\u00ecnh 4<\/figcaption><\/figure>

In order to understand the propagation mechanism of stage II, we need to consider the situation of crack tip cross-section during the stress cycle. As shown in Figure 5. The fatigue cycle begins when the nominal stress is at point “a”. As the stress intensity increases and passes through point “B”, we notice that the crack tip opens, resulting in local plastic shear deformation, and the crack extends to point “C” in the original metal. When the tensile stress decreases through the “d” point, we observe that the crack tip closes, but the permanent plastic deformation leaves a unique serration, the so-called “cut line”. When the whole cycle ends at the “e” point, we observe that the crack has now increased the “Da” length and formed additional section lines. It is now understood that the range of crack growth is proportional to the range of applied elastic-plastic crack tip strain. A larger cycle range can form a larger Da.<\/a><\/p>

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H\u00ecnh 5 S\u01a1 \u0111\u1ed3 s\u1ef1 lan truy\u1ec1n v\u1ebft n\u1ee9t trong giai \u0111o\u1ea1n II<\/figcaption><\/figure>

<\/p>

C\u00e1c y\u1ebfu t\u1ed1 \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn t\u1ed1c \u0111\u1ed9 ph\u00e1t tri\u1ec3n v\u1ebft n\u1ee9t m\u1ecfi<\/h2>

\u1ea2nh h\u01b0\u1edfng c\u1ee7a c\u00e1c th\u00f4ng s\u1ed1 sau \u0111\u1ebfn t\u1ed1c \u0111\u1ed9 ph\u00e1t tri\u1ec3n v\u1ebft n\u1ee9t m\u1ecfi \u0111\u01b0\u1ee3c nghi\u00ean c\u1ee9u v\u00e0 gi\u1ea3i th\u00edch v\u1ec1 m\u1eb7t kh\u00e1i ni\u1ec7m:<\/p>

1 Gi\u1ea3m c\u0103ng th\u1eb3ng<\/h3>

From the diagram, we can see that a certain “amount” of shear stress is released during the periodic change of the strength of the nominal stress. And the larger the range of stress changes, the greater the energy released. Through the SN curve shown in Figure 1, we can see that the fatigue life decreases exponentially with the increase of the stress cycle range.<\/a><\/p>

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H\u00ecnh 6 \u1ee9ng su\u1ea5t v\u00e0 bi\u1ebfn d\u1ea1ng \u0111\u00e0n h\u1ed3i d\u1ecdc theo b\u1ec1 m\u1eb7t tr\u01b0\u1ee3t v\u00e0 \u1edf g\u1ed1c c\u1ee7a v\u1ebft n\u1ee9t<\/figcaption><\/figure>

<\/a><\/p>

2 c\u0103ng th\u1eb3ng trung b\u00ecnh<\/h3>

\u1ee8ng su\u1ea5t trung b\u00ecnh (\u1ee9ng su\u1ea5t d\u01b0) c\u0169ng l\u00e0 m\u1ed9t y\u1ebfu t\u1ed1 \u1ea3nh h\u01b0\u1edfng \u0111\u1ebfn t\u1ef7 l\u1ec7 h\u01b0 h\u1ecfng do m\u1ecfi. V\u1ec1 m\u1eb7t kh\u00e1i ni\u1ec7m, n\u1ebfu \u1ee9ng su\u1ea5t gi\u00e3n n\u1edf \u0111\u01b0\u1ee3c \u00e1p d\u1ee5ng cho v\u1ebft n\u1ee9t giai \u0111o\u1ea1n II, v\u1ebft n\u1ee9t s\u1ebd b\u1ecb \u00e9p m\u1edf ra, do \u0111\u00f3, b\u1ea5t k\u1ef3 chu k\u1ef3 \u1ee9ng su\u1ea5t n\u00e0o s\u1ebd c\u00f3 \u1ea3nh h\u01b0\u1edfng \u0111\u00e1ng k\u1ec3 h\u01a1n. Ng\u01b0\u1ee3c l\u1ea1i, n\u1ebfu \u00e1p d\u1ee5ng \u1ee9ng su\u1ea5t n\u00e9n trung b\u00ecnh, v\u1ebft n\u1ee9t s\u1ebd bu\u1ed9c ph\u1ea3i \u0111\u00f3ng l\u1ea1i, v\u00e0 b\u1ea5t k\u1ef3 chu tr\u00ecnh \u1ee9ng su\u1ea5t n\u00e0o c\u0169ng c\u1ea7n ph\u1ea3i v\u01b0\u1ee3t qua \u1ee9ng su\u1ea5t n\u00e9n tr\u01b0\u1edbc th\u00ec v\u1ebft n\u1ee9t m\u1edbi c\u00f3 th\u1ec3 ti\u1ebfp t\u1ee5c m\u1edf r\u1ed9ng. C\u00e1c kh\u00e1i ni\u1ec7m t\u01b0\u01a1ng t\u1ef1 c\u0169ng \u00e1p d\u1ee5ng cho c\u00e1c v\u1ebft n\u1ee9t \u1edf giai \u0111o\u1ea1n I.<\/p>

3 b\u1ec1 m\u1eb7t ho\u00e0n thi\u1ec7n<\/h3>

B\u1edfi v\u00ec v\u1ebft n\u1ee9t m\u1ecfi th\u01b0\u1eddng xu\u1ea5t hi\u1ec7n \u0111\u1ea7u ti\u00ean tr\u00ean b\u1ec1 m\u1eb7t c\u1ee7a c\u00e1c c\u1ea5u ki\u1ec7n c\u00f3 khuy\u1ebft t\u1eadt, ch\u1ea5t l\u01b0\u1ee3ng c\u1ee7a b\u1ec1 m\u1eb7t s\u1ebd \u1ea3nh h\u01b0\u1edfng nghi\u00eam tr\u1ecdng \u0111\u1ebfn x\u00e1c su\u1ea5t xu\u1ea5t hi\u1ec7n v\u1ebft n\u1ee9t. M\u1eb7c d\u00f9 h\u1ea7u h\u1ebft c\u00e1c m\u1eabu th\u1eed nghi\u1ec7m v\u1eadt li\u1ec7u \u0111\u1ec1u c\u00f3 l\u1edbp ho\u00e0n thi\u1ec7n b\u1eb1ng g\u01b0\u01a1ng, v\u00ec v\u1eady ch\u00fang c\u0169ng s\u1ebd \u0111\u1ea1t \u0111\u01b0\u1ee3c tu\u1ed5i th\u1ecd m\u1ecfi t\u1ed1t nh\u1ea5t. Trong th\u1ef1c t\u1ebf, h\u1ea7u h\u1ebft c\u00e1c th\u00e0nh ph\u1ea7n kh\u00f4ng th\u1ec3 \u0111\u01b0\u1ee3c so s\u00e1nh v\u1edbi c\u00e1c m\u1eabu, v\u00ec v\u1eady ch\u00fang ta c\u1ea7n ph\u1ea3i s\u1eeda \u0111\u1ed5i c\u00e1c \u0111\u1eb7c t\u00ednh m\u1ecfi. L\u1edbp ho\u00e0n thi\u1ec7n b\u1ec1 m\u1eb7t c\u00f3 \u1ea3nh h\u01b0\u1edfng l\u1edbn h\u01a1n \u0111\u1ebfn s\u1ef1 m\u1ecfi c\u1ee7a c\u00e1c th\u00e0nh ph\u1ea7n ch\u1ecbu chu k\u1ef3 \u1ee9ng su\u1ea5t bi\u00ean \u0111\u1ed9 th\u1ea5p.<\/p>

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H\u00ecnh 7 Gi\u1ea3n \u0111\u1ed3 v\u1ec1 \u1ea3nh h\u01b0\u1edfng c\u1ee7a tr\u00ecnh t\u1ef1 chu k\u1ef3 \u1ea3nh h\u01b0\u1edfng c\u1ee7a \u0111\u1ed9 ho\u00e0n thi\u1ec7n b\u1ec1 m\u1eb7t c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c bi\u1ec3u th\u1ecb b\u1eb1ng c\u00e1ch m\u00f4 h\u00ecnh h\u00f3a, ngh\u0129a l\u00e0 nh\u00e2n \u0111\u01b0\u1eddng cong SN v\u1edbi tham s\u1ed1 hi\u1ec7u ch\u1ec9nh b\u1ec1 m\u1eb7t \u1edf gi\u1edbi h\u1ea1n m\u1ecfi.<\/figcaption><\/figure>

4 x\u1eed l\u00fd b\u1ec1 m\u1eb7t<\/h3>

X\u1eed l\u00fd b\u1ec1 m\u1eb7t c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c s\u1eed d\u1ee5ng \u0111\u1ec3 t\u0103ng c\u01b0\u1eddng kh\u1ea3 n\u0103ng ch\u1ed1ng m\u1ecfi c\u1ee7a c\u00e1c b\u1ed9 ph\u1eadn. M\u1ee5c \u0111\u00edch c\u1ee7a x\u1eed l\u00fd b\u1ec1 m\u1eb7t l\u00e0 h\u00ecnh th\u00e0nh \u1ee9ng su\u1ea5t n\u00e9n d\u01b0 tr\u00ean b\u1ec1 m\u1eb7t. Theo chu k\u1ef3 bi\u00ean \u0111\u1ed9 th\u1ea5p, \u1ee9ng su\u1ea5t tr\u00ean b\u1ec1 m\u1eb7t r\u00f5 r\u00e0ng l\u00e0 th\u1ea5p, v\u00e0 th\u1eadm ch\u00ed duy tr\u00ec tr\u1ea1ng th\u00e1i n\u00e9n. Do \u0111\u00f3, cu\u1ed9c s\u1ed1ng m\u1ec7t m\u1ecfi c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c k\u00e9o d\u00e0i \u0111\u00e1ng k\u1ec3. Tuy nhi\u00ean, nh\u01b0 ch\u00fang t\u00f4i \u0111\u00e3 ch\u1ec9 ra, t\u00ecnh hu\u1ed1ng n\u00e0y ch\u1ec9 \u0111\u00fang \u0111\u1ed1i v\u1edbi c\u00e1c th\u00e0nh ph\u1ea7n ch\u1ecbu chu k\u1ef3 \u1ee9ng su\u1ea5t bi\u00ean \u0111\u1ed9 th\u1ea5p. N\u1ebfu \u00e1p d\u1ee5ng chu k\u1ef3 bi\u00ean \u0111\u1ed9 cao, qu\u00e1 tr\u00ecnh n\u00e9n tr\u01b0\u1edbc s\u1ebd b\u1ecb v\u01b0\u1ee3t qua b\u1edfi chu k\u1ef3 bi\u00ean \u0111\u1ed9 cao v\u00e0 c\u00e1c \u01b0u \u0111i\u1ec3m c\u1ee7a n\u00f3 s\u1ebd b\u1ecb m\u1ea5t \u0111i. C\u0169ng nh\u01b0 ch\u1ea5t l\u01b0\u1ee3ng b\u1ec1 m\u1eb7t, t\u00e1c \u0111\u1ed9ng c\u1ee7a vi\u1ec7c x\u1eed l\u00fd b\u1ec1 m\u1eb7t c\u00f3 th\u1ec3 \u0111\u01b0\u1ee3c th\u1ec3 hi\u1ec7n b\u1eb1ng c\u00e1ch m\u00f4 h\u00ecnh h\u00f3a.<\/p><\/div>","protected":false},"excerpt":{"rendered":"

Fatigue cracks are generally the result of periodic plastic deformation in local areas. Fatigue is defined as “failure under repeated load or other types of load conditions, and this load level is not sufficient to cause failure when applied only once.” This plastic deformation occurs not because of the theoretical stress on the ideal component, but…<\/p>","protected":false},"author":2,"featured_media":21253,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[79],"tags":[],"class_list":["post-21250","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-materials-weekly"],"jetpack_featured_media_url":"https:\/\/www.meetyoucarbide.com\/wp-content\/uploads\/2022\/07\/\u56fe\u72472.png","jetpack_sharing_enabled":true,"_links":{"self":[{"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/posts\/21250","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/comments?post=21250"}],"version-history":[{"count":0,"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/posts\/21250\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/media\/21253"}],"wp:attachment":[{"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/media?parent=21250"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/categories?post=21250"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.meetyoucarbide.com\/vi\/wp-json\/wp\/v2\/tags?post=21250"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}