JP4956367B2 - Stiffeners and welded structures with excellent brittle crack propagation characteristics - Google Patents

Description

  The present invention relates to a stiffener used to reinforce a T-type welded structure composed of a vertical member and a horizontal member having a butt weld, and a welded structure using the stiffener, such as a ship, an offshore structure, The present invention relates to a welded structure such as a low-temperature tank, a line pipe, a civil engineering / building structure, and more particularly to a welded structure of a longitudinal member near the upper deck of a large container ship or a bulk carrier.

  As a mechanism for the occurrence of brittle fracture in large container ships and bulk carriers, brittle cracks generally propagate along welds starting from weld defects that occurred during butt welding performed on longitudinal members near the upper deck. However, when the crack length exceeds a certain limit, it is considered that brittle fracture occurs.

  For this reason, even if a brittle crack is generated in the welded portion, it is necessary to reliably stop the brittle crack so as not to cause brittle fracture. For this, it has been considered that there is no problem if a steel plate having a certain degree of arrestability is used for the longitudinal member and the upper deck.

  However, in particular, when a thick steel plate is used for the longitudinal member and the upper deck, a brittle crack generated at the welded portion of the longitudinal member reaches the upper deck without stopping, and the upper deck without further stopping. Recent research has shown that there is potential for progress.

  For this reason, development of the technique which stops reliably the brittle crack which generate | occur | produced in the welding part of the longitudinal member reliably was desired.

  In Patent Document 1, in a welded structure, an average equivalent-equivalent grain of 0.5 to 5 μm is formed on an aggregate disposed so as to intersect a butt weld, over a thickness region of 3 mm or more in a surface layer portion and a back layer portion. Using a steel plate having a diameter and having a (100) crystal plane X-ray plane strength ratio of 1.5 or more in a plane parallel to the plate thickness plane, at least in a region where the butt weld and the aggregate intersect, Disclosed is a welded structure in which a range having a width equal to or greater than the bead width of the butt weld and a length of 70% or more of the plate thickness from the front or back surface of the aggregate is disclosed. It is said that energy is absorbed by being introduced into the aggregate, and a brittle crack can be stopped as a crack arrester.

  However, there is a concern that partially changing the welding conditions as described above causes a reduction in work efficiency in a large-scale structure, and the economic efficiency is significantly deteriorated.

  On the other hand, in fracture mechanics, it is considered that a brittle crack stops when the value of the dynamic stress intensity factor Kd during which the brittle crack is progressing is equal to or less than the value of the inherent brittle crack propagation termination coefficient Kca. Yes. However, since it is difficult to calculate the value of Kd, it is possible to determine whether or not to stop by comparing static stress intensity factors (hereinafter referred to as “static stress intensity factors”) KT and Kca. Many.

  It is known that KT is determined not only by the stress intensity factor Kσ determined by the uniform tensile stress σ but also by the influence of reinforcement (arrester) and welding residual stress, as shown by the following formula (1) (non- Patent Document 1).

KT = Kσ + KA + Kr Equation (1)
Here, KA is the degree of influence of the arrester on the stress intensity factor (<0), and Kr is the degree of influence of the welding residual stress on the stress intensity factor.

  In the case of a large crack, | Kr | is negligibly small compared to | Kσ |, so KT takes into account Kσ determined by uniform stress and only the influence degree (KA) of the arrester. It can be approximated by Kσ + KA.

  Non-Patent Document 1 discloses an arrester effect obtained by arranging a stiffener 3 above a horizontal member 2 in a T-shaped welded joint as shown in FIG. Regarding the brittle crack growth suppression effect), the influence of the thickness ratio (t / tv) of the stiffener in the width direction B and the stiffener thickness on the vertical member is disclosed.

However, in order to reliably stop the progress of the brittle crack generated in the welded portion 4 of the vertical member 1, it is necessary to accurately determine the plate thickness t of the stiffener 3 and the mounting distance a from the horizontal member. However, including the non-patent document 1, there has been no method for determining these values simply and accurately. Therefore, it has been difficult to provide a stiffener that can reliably stop the development of a brittle crack without overdesigning.
Susumu Machida, Mitsuru Aoki, "Fundamental research on crack arresters (7th report): Prevention of long cracks and design of arresters", The Shipbuilding Society of Japan, Japan Society of Marine Science and Technology, June 1972, No. 131, p. 367-378 JP 2005-111501 A

  Therefore, the present invention provides a welded structure in which a vertical member formed by butt welding steel plates is welded to a horizontal member by T-type welding, and the development of a brittle crack generated in the welded portion of the vertical member without overdesign. It is an object of the present invention to provide a stiffener capable of reliably stopping the welding and a welded structure using the stiffener.

The invention according to claim 1 is a welded structure formed by T-welding either one of upper and lower ends of a vertical member formed by butt welding the left and right ends of a steel plate to a horizontal member. The stiffener is used by welding in parallel with the horizontal member so as to intersect the butt weld of the vertical member, and T-type welding of the butt weld of the vertical member is performed. The effective stress intensity factor Keff of the butt weld at the reached position when a brittle crack generated at the other end propagates through the butt weld and reaches the horizontal member through the stiffener The thickness t of the stiffener and the distance a of the stiffener from the horizontal member are adjusted such that the value of the stiffener is equal to or less than the value of the brittle crack propagation stop stress intensity factor Kca inherent to the material of the horizontal member. To become Wherein, an excellent stiffener to brittle crack propagation characteristics.

The invention according to claim 2 is a stiffener excellent in the brittle crack propagation characteristics according to claim 1, which satisfies the following formula.
Formula Keff = 980.665 [(9.10 × 10 ⁻⁴ × t−1.15) a + 563]
Here, the unit of Keff is N / mm ^1.5 , and the unit of t and a is mm.

  The invention according to claim 3 is the stiffener having excellent brittle crack propagation characteristics according to claim 2, which is used for the vertical member having a vertical length of 1.2 m or less.

The invention according to claim 4 is the stiffener having excellent brittle crack propagation characteristics according to claim 2 or 3, wherein the length L in the direction along the vertical member is 7.5 t or more.

The invention according to claim 5 is a stiffener having excellent brittle crack propagation characteristics according to claim 1, wherein the length L in the direction along the vertical member is less than 7.5 t and satisfies the following formula. is there.
Formula 2 Keff = (1.25-0.0328 * L / t) * 9.80665 [(9.10 * 10 < ^-4 > * a-1.15) t + 563]
Here, the unit of Keff is N / mm ^1.5 , and the units of L, t, and a are mm.

The invention according to claim 6 is a stiffener excellent in brittle crack propagation resistance according to claim 1, which satisfies the following formula, where B is the width in the direction perpendicular to the vertical member of the stiffener. .
Formula Keff = (B / 200) ^−0.117 × 9.80665 [(9.10 × 10 ⁻⁴ × a−1.15) t + 563]
Here, the unit of Keff is N / mm ^1.5 , and the unit of B, t, and a is mm.

  The invention according to claim 7 is a welded structure formed by T-welding at least one of upper and lower ends of a vertical member formed by butt welding the left and right ends of a steel plate to a horizontal member, the vertical member It is excellent in the brittle crack propagation characteristic characterized by welding the stiffener of any one of Claims 1-6 in parallel with the said horizontal member so that it may cross | intersect the butt welding part of this. A welded structure.

According to the present invention, when the brittle crack generated in the butt weld of the vertical member propagates through the butt weld and passes through the stiffener and reaches the horizontal member, the butt weld in the arrival position is effective. The thickness t of the stiffener and the distance a of the stiffener from the horizontal member are adjusted so that the value of the stress intensity factor Keff is equal to or less than the value of the brittle crack propagation stop stress intensity factor Kca of the horizontal member. By doing so, it has become possible to provide a stiffener that can reliably stop the development of a brittle crack generated in the welded portion of the vertical member without overdesigning, and a welded structure using the stiffener.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

Embodiment
As shown in FIG. 1, the welded structure according to the present invention is formed by T-welding a lower end portion of a vertical member 1 formed by butt welding the left and right end portions of a steel plate to a horizontal member 2. And in order to reinforce this welding structure, the stiffener 3 which concerns on this invention is welded in parallel with the horizontal member 2 so that the butt welding part 4 of the vertical member 1 may be crossed.

And the brittle crack which generate | occur | produced in the butt-welding part 4 of the vertical member 1 propagates through this butt-welding part 4, passes through the stiffener 3 and reaches the horizontal member 2, and the butt-welding at the reaching position. From the thickness t of the stiffener 3 and the horizontal member 2 of the stiffener 3 so that the value of the effective stress intensity factor Keff of the portion becomes equal to or less than the value of the brittle crack propagation stop stress intensity factor Kca specific to the material of the horizontal member 2. The distance a is adjusted.

  Here, the effective stress intensity factor Keff can be estimated by the following equation (2), for example.

Keff = 9.80665 [(9.10 × 10 ⁻⁴ × a−1.15) t + 563]...
Formula (2)
Here, the unit of t and a is mm, and the unit of Keff is N / mm ^1.5 .

  Hereinafter, the process of deriving the above equation (2) will be described.

  First, the welded structure shown in FIG. 1 was modeled, and an attempt was made to calculate a static stress intensity factor KT by numerical analysis using a finite element method.

  First, the vertical length (height) Wv = 700 mm of the vertical member 1, the thickness tv = 60 mm of the vertical member 1, the width Wh = 400 mm of the horizontal member 2, and the plate thickness th = 60 mm of the horizontal member 2 are constant. . Then, the plate thickness t of the stiffener 3 and the installation distance a of the stiffener 3 from the horizontal member are variously changed, and a uniform tensile stress 256 MPa is applied to the vertical member 1 in the horizontal direction. When a crack generated at the uppermost end of 4 (that is, the end not to be welded with T-type) propagates through the butt weld 4 and passes through the stiffener 3 and reaches the horizontal member 2 (see FIG. 2). However, the figure shows the case where no stiffener is installed.) The static stress intensity factor KT at the reached position was obtained by the above numerical analysis. The installation distance a of the stiffener 3 from the horizontal member 2 refers to the distance from the upper surface of the horizontal member 2 to the center position of the thickness of the stiffener 3 as shown in FIG.

  However, as described in Non-Patent Document 1, it is known that the idea of the linear fracture mechanics cannot be applied as it is to the propagation stop characteristics of long cracks. Therefore, the following correction equation for estimating the effective K value (referred to as “effective stress intensity factor” in this application) Keff of a long fissure from the static stress intensity factor KT shown in the same document The effective stress intensity factor Keff was obtained from the static stress intensity factor KT calculated by the above numerical analysis using the equation (3).

When KT ≦ 200, Keff = KT
When 200 <KT ≦ 1400 Keff = −2.78 × 10 ⁻⁴ (KT-1400) ² +600
When 1400 <KT, Keff = 600 (3)
However, the unit of KT and Keff is kgf / mm ² · √mm.

The relationship between Keff (kgf / mm ² · √mm) obtained as described above, the stiffener thickness t (mm), and the distance a (mm) from the horizontal member of the stiffener is summarized in FIG. It becomes like this.

  From the relationship between t and a and Keff shown in FIG. 3, it was found that the following relationship (2 ') is established as a simple equation.

Keff = (9.10 × 10 ⁻⁴ × a−1.15) t + 563 (2 ′)
However, the unit of Keff is kgf / mm ² · √mm, and the unit of t and a is mm.

By converting the Keff unit in the above formula (2 ′) to the SI unit, the following formula (2) is obtained. Note that 1 kgf / mm ² · √mm = 980.665 N / mm ^1.5 .
Keff = 980.665 [(9.10 × 10 ⁻⁴ × a−1.15) t + 563]
Reprinting ceremony (2)
However, the unit of Keff is N / mm ^1.5 and the unit of t and a is mm.

  That is, it can be said that the brittle crack is stopped when the value of Keff calculated by the simplified formula of the above formula (2) (or formula (2 ')) becomes equal to or less than the value of Kca.

  Therefore, by designing the stiffener 3 so that the thickness t and the installation distance a from the horizontal member 2 satisfy Kca> Keff, a brittle crack generated in the butt weld 4 of the vertical member 1 without overdesign. It is possible to provide the stiffener 3 that can reliably stop the progress of the above.

  And by using the welded structure which installed such a stiffener 3, the welded structure excellent in the brittle fracture resistance came to be provided at low cost.

By the way, from the above equation (2 ′), the reduction effect ΔKeff (kgf / mm ² · √mm) of the effective stress intensity factor Keff by the stiffener installation can be estimated as a function of t and a as in the following equation (4). .

ΔKeff = − (9.10 × 10 ⁻⁴ × a−1.15) t Equation (4)

Therefore, using the numerical analysis result obtained by the finite element method, the static stress intensity factor KT is similarly determined as the KT reduction effect ΔKT (kgf / mm ² · √mm) by the stiffener installation as expressed by the above equation (4). ), The following equation (5) is obtained as a function of t and a.

ΔKT = − (2.14 × 10 ⁻³ × a-3.41) t Equation (5)

Here, the thickness t of the stiffener 3 and the installation distance a from the horizontal member 2 are generally set in the range of t ≦ 100 mm and a ≧ 100 mm due to construction restrictions. Therefore, the practical maximum value of the KT reduction effect ΔKT by installing the stiffener 3 is obtained by substituting t = 100 mm and a = 100 mm into the above equation (5), and ΔKTmax = 320 (kgf / mm ² · √ mm).

However, when the KT after the stiffener 3 is set to exceed 1400 (kgf / mm ² · √mm), the Keff becomes constant at 600 (kgf / mm ² · √mm) as apparent from the above equation (3). The arrest effect by 3 installations cannot be obtained sufficiently. Therefore, when the KT before the stiffener 3 is KT> 1400 + ΔKT, the KT after the stiffener 3 is 1400 (kgf / mm ² · √mm) even if the KT is reduced by ΔKT due to the stiffener 3 being installed. Therefore, the arrest effect due to the installation of the stiffener 3 is reduced. As described above, since the practical maximum value ΔKTmax of the KT reduction effect ΔKT is estimated to be 320 (kgf / mm ² · √mm), the KT before the stiffener 3 is set is 1400 + ΔKTmax = 1720 (kgf / mm ² · If it exceeds √mm), the arrest effect due to the stiffener 3 is practically reduced.

  Therefore, when the stiffener 3 is not installed, the relationship between the length Wv of the vertical member and KT is obtained by numerical analysis by the finite element method, and is shown in FIG. From the figure, the relationship between Wv and KT can be approximated by the following equation (6).

  KT = 1.23 × Wv + 267 (6)

Substituting 1720 (kgf / mm ² · √mm) into the left side of the above equation (6) yields Wv = 1180 mm. Therefore, when Wv exceeds 1180 mm (≈1.2 m), KT when the stiffener 3 is not installed exceeds 1720 (kgf / mm ² · √mm), and the effect of installing the stiffener 3 is practically reduced. It will be. Therefore, in the case of a T-type welded structure like this embodiment in which no other member (for example, a horizontal member is also joined to the upper end) is joined to the upper end of the vertical member 1, It is desirable to use the stiffener 3 designed based on the above formula (2) for a length (height) Wv of 1.2 m or less.

  In the numerical analysis by the finite element method, the length of the stiffener 3 (length in the direction along the vertical member 1) L = 600 mm and its width (width in the direction perpendicular to the vertical member 1) B = 200 mm are fixed. The effective stress intensity factor Keff was estimated, and further, the effect of changing these parameters L and B on the estimated value of Keff was investigated.

  First, the width B = 200 mm of the stiffener 3, its plate thickness t = 60 mm, and the installation distance a = 240 mm from the horizontal member of the stiffener 3 are fixed, and the length L of the stiffener 3 is sequentially changed to increase the effective stress. The coefficient Keff was estimated and calculated. As a result, as shown in FIG. 5, when L / t is less than 7.5, Keff decreases almost linearly as L increases, but when L / t exceeds 7.5, Keff is substantially constant. It turned out to be value. And in the analysis performed by fixing the length L = 600 mm and the width B = 200 mm of the stiffener 3, since t was changed in the range of 40 to 80 mm (see FIG. 3), L / t was 10 It is in the range of ~ 15. Therefore, when L / t ≧ 7.5, the above formula (2) can be applied as it is.

  On the other hand, when L / t <7.5, as described above, Keff changes almost linearly as L / t increases. Therefore, it is necessary to use the following formula (7) in consideration of the influence of L / t. More preferred.

Keff = (1.25−0.0328 × L / t) × 9.80665 [(9.10 × 10 ⁻⁴ × a−1.15) t + 563] (7)
Here, the unit of Keff is N / mm ^1.5 , and the units of L, t, and a are mm.

  Next, the length L = 600 mm of the stiffener 3, its plate thickness t = 60 mm, and the installation distance a = 240 mm from the horizontal member of the stiffener 3 are fixed, and the width B of the stiffener 3 is sequentially changed to obtain effective stress. The estimation calculation of the expansion coefficient Keff was performed. As a result, as shown in FIG. 6, it was found that Keff decreases exponentially as B increases.

  Therefore, it is more preferable to use the following formula (8) in consideration of the influence of B for Keff.

Keff = (B / 200) ^−0.117 × 9.80665 [(9.10 × 10 ⁻⁴ × a−1.15) t + 563] (8)
Here, the unit of Keff is N / mm ^1.5 , and the unit of B, t, and a is mm.

(Modification)
In the above embodiment, the horizontal member 2 is T-welded to the lower end of the vertical member 1, but the horizontal member 2 is T-welded to the upper end of the vertical member 1 instead of the lower end of the vertical member 1. You may use what you did.

In the welded structure shown in FIG. 1, a steel plate having a Kca of −398 ° C. (kgf / mm ² · √mm) (≈3900 N / mm ^1.5 ) is used as a base material used for the vertical member 1. The optimum structure of the stiffener 3 was designed when a steel plate having a Kca of −10 ° C. and 510 (kgf / mm ² · √mm) (≈5000 N / mm ^1.5 ) was used.
This welded structure has a design requirement that a brittle crack does not enter the horizontal member 2 at −10 ° C.

First, considering the workability and the like, the stiffener 3 has a width B of 200 mm, a length L of 500 mm, and a plate thickness t of 60 mm. Next, the condition for stopping the brittle crack is that the Kca of the horizontal member 2 is 510 (kgf / mm ² · √mm). Therefore, by using the above equation (2 ′), the following equation (9) is obtained. It is expressed by the relationship of the inequality shown.

Kca = 510 (kgf / mm ² · √mm) ≧ Keff = (9.10 × 10 ⁻⁴ × a−1.15) × 60 + 563 (9)

Therefore, from the same equation, the distance a between the stiffener 3 and the horizontal plate 2 is
a ≦ {(510-563.) / 60. +1.15} / (9.10 × 10 ⁻⁴ ) = 290 mm
Within this range, it may be determined in consideration of workability and the like.

It is a perspective view which shows the structure of the stiffener which concerns on this invention, and a welding structure using the same. It is a deformation figure calculated by numerical analysis by the finite element method showing a state when a brittle crack generated in a butt weld of a vertical member reaches a horizontal member. It is a graph which shows the relationship between the thickness a of the stiffener t, the distance a from the horizontal member of the stiffener, and the effective stress intensity factor Keff. It is a graph which shows the relationship between the length Wv of the perpendicular | vertical direction of a perpendicular | vertical member, and the static stress intensity factor KT in the case where the stiffener is not installed. It is a graph which shows the relationship between ratio L / t of length L of the stiffener and thickness t, and effective stress intensity factor Keff (relative value). It is a graph which shows the relationship between the width | variety B (relative value) of a stiffener, and the effective stress intensity | strength coefficient Keff (relative value).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Vertical member 2 ... Horizontal member 3 ... Stiffener 4 ... Butt welding part

Claims (7)

In a welded structure formed by T-welding one of upper and lower ends of a vertical member formed by butt welding the left and right ends of a steel plate to a horizontal member, the vertical member is used to reinforce the welded structure. A stiffener used by welding in parallel with the horizontal member so as to intersect the butt weld of
When a brittle crack generated at the end of the butt weld of the vertical member that has not been T-shaped welded propagates through the butt weld and passes through the stiffener to reach the horizontal member. The thickness t of the stiffener is set so that the effective stress intensity factor Keff of the butt weld at the reaching position is not more than the value of the brittle crack propagation stopping stress intensity factor Kca inherent to the material of the horizontal member. A stiffener having excellent brittle crack propagation characteristics, wherein the distance a of the stiffener from the horizontal member is adjusted. The stiffener having excellent brittle crack propagation characteristics according to claim 1, which satisfies the following formula.
Formula Keff = 9.80665 [(9.10 × 10 ⁻⁴ × a−1.15) t + 563]
Here, the unit of Keff is N / mm ^1.5 , and the unit of t and a is mm.   The stiffener excellent in brittle crack propagation resistance according to claim 2, which is used for a vertical member having a vertical length of 1.2 m or less.   The stiffener excellent in brittle crack propagation characteristics according to claim 2 or 3, wherein a length L in a direction along the vertical member is 7.5 t or more. The stiffener excellent in brittle crack propagation resistance according to claim 1, wherein a length L in a direction along the vertical member is less than 7.5 t and satisfies the following formula.
Formula Keff = (1.25−0.0328 × L / t) × 9.80665 [(9.10 × 10 ⁻⁴ × a−1.15) t + 563]
Here, the unit of Keff is N / mm ^1.5 , and the units of L, t, and a are mm. The stiffener excellent in brittle crack propagation resistance according to claim 1, wherein the width of the stiffener in a direction perpendicular to the vertical member is B, and the following equation is satisfied.
Formula Keff = (B / 200) ^−0.117 × 9.80665 [(9.10 × 10 ⁻⁴ × a−1.15) t + 563]
Here, the unit of Keff is N / mm ^1.5 , and the unit of B, t, and a is mm. A welded structure formed by T-welding at least one of upper and lower ends of a vertical member formed by butt welding the left and right ends of a steel plate to a horizontal member so as to intersect the butt weld of the vertical member A welded structure excellent in brittle crack propagation characteristics, wherein the stiffener according to any one of claims 1 to 6 is welded in parallel with the horizontal member.

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