• Journal of Welding and Joining
• /
• v.32 no.1
• /
• pp.61-65
• /
• 2014

The purpose of this study is to evaluate the applicability of the element stress to establish S-N design curve for the welded lap joint with thin plates below 2mm thickness. In order to do it, the extensive fatigue tests of the welded lap joints with INVAR alloy were performed. With the results, the deign S-N curves for the lap-weld were established by using the reference stresses such as the nominal stress range at the weld throat area, hot spot stress range and element stress range, and compared with regard to the standard deviation. The standard deviation of S-N curves with element stress range was less than that of S-N curves with other reference stresses. In addition, FEA results show the amount of the element stress is less sensitive to mesh size. Based on the results, it can be concluded that the element stress is to be used as the reference stress for the design S-N curves of the welded lap joint.

• Proceedings of the KSME Conference
• /
• 2001.11a
• /
• pp.80-86
• /
• 2001

An engineering estimation equation for the crack opening displacement (COD) is proposed for a complex cracked pipe, based on the reference stress approach. To define the reference stress, a simple plastic limit load analysis for the complex cracked pipe subjected to combined bending and tension is performed considering the crack closure effect in the compressive-stressed region. Comparison with ten published test data and the results from existing method shows that the present method not only reduces non-conservatism associated with the existing method, but also provides consistent and overall satisfactory results.

• Journal of Aerospace System Engineering
• /
• v.9 no.4
• /
• pp.31-36
• /
• 2015

The fatigue analysis for cutout panel used for the weight reduction of aircraft has been conventionally performed through the open hole concept using the reference stress and stress concentration factor (Kt). However, in the actual structure cases, the goal of weight reduction might be less meaningful due to the conservative approach induced by the difficulties of extracting the confident reference stress from FE-Analysis in the complicated loading behavior. Therefore a new approach is proposed in order to secure the effectiveness of weight reduction and validate the confidence of the analysis results using the interaction of max-min principal stress at the critical location of open hole edge line.

• Proceedings of the KSME Conference
• /
• 2007.05a
• /
• pp.1824-1829
• /
• 2007

In the present paper, limit pressures for axial surface cracked pipe are proposed, and a reference stress based J estimation method is also provided based on the proposed limit pressure solutions. Employed cracks are assumed to be constant-depth, internal surface cracks, and wide ranges of variables are considered.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.1
• /
• pp.139-146
• /
• 2002

This paper provides validations of the reference stress based J and $C^{*}$ estimations, proposed in Part I, for inner, circumferential surface cracked pipes under internal pressure and global bending against detailed 3-D elastic-plastic and elastic-creep FE results. For this purpose, actual tensile properties of two typical stainless steels (TP304 and TP316) are used for elastic-plastic FE analyses and two realistic creep laws are used for elastic-creep FE analyses. For a total of twenty cases considered in this paper, agreements between the proposed reference stress based J and $C^{*}$ estimations and the FE results are excellent. More important aspect of the proposed estimations is that they can be used to estimate J and $C^{*}$ not only at the deepest point of the surface crack but also at an arbitrary point along the crack front.front.

• Proceedings of the KSME Conference
• /
• 2001.06a
• /
• pp.310-315
• /
• 2001

This paper provides validations of the reference stress based J and $C^*$ estimations, proposed in Part I, for inner, circumferential surface cracked pipes under internal pressure and global bending against detailed 3-D elastic-plastic and elastic-creep FE results. For this purpose, actual tensile properties of two typical stainless steels (TP304 and TP316) are used for elastic-plastic FE analyses and two realistic creep laws are used for elastic-creep FE analyses. For a total of twenty cases considered in this paper, agreements between the proposed reference stress based J and $C^*$ estimations and the FE results are excellent. More important aspect of the proposed estimations is that they can be used to estimate J and $C^*$ not only at the deepest point of the surface crack but also at an arbitrary point along the crack front.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.26 no.10
• /
• pp.2122-2129
• /
• 2002

Creep damage using a reference stress(RS) was analyzed for type 316LN stainless steel. The generalized K-R equation was reconstructed into the RS equation using a critical stress value $\sigma$. The RS equation was derived from the critical stress in failure time $t_f$ instead of material damage parameter $\omega$, which indicates the critical condition of collapse or approach to gross instability of materials during creep. For obtaining the reference stress, a series of creep tests and tensile tests were conducted with at 55$0^{\circ}C$ and $600^{\circ}C$. The stress-time data obtained from creep tests were applied to the RS equations to characterize the creep damage of type 316LN stainless steel. The value of creep constant r with stress levels was about 18 at 55$0^{\circ}C$ and 21 at $600^{\circ}C$. This value was almost similar with r = 24 in the K-R equation, which was obtained by using damage parameter $\omega$. Relationship plots of creep failure strain and life fraction $(t_f /t_r)$ were also obtained with different λ values. The RS equation was therefore more convenient than the generalized K-R equation, because the measuring process to quantify the damage parameter $\omega$ such as voids or micro cracks in crept materials was omitted. The RS method can be easily used by designers and plant operator as a creep design tool.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.28 no.3
• /
• pp.311-317
• /
• 2004

This paper proposes engineering estimation equations for the maximum deflection of a cylinder subject to bending under elastic-plastic and elastic-creep conditions. Being based on the reference stress approach, the proposed equations are simple to use and can accommodate general tensile and creep behaviours. Validation against detailed 3-D FE results using actual stress-strain data and realistic creep-deformation data shows excellent agreement, which provides confidence in the use of the proposed equation. Based on the proposed equations, together with information on in-service inspection data, discussion is given how to estimate future time-dependent and time-independent deflection of the CANDU pressure tube. Thus the present result would be valuable information for integrity assessment of the CANDU pressure tube.

• Steel and Composite Structures
• /
• v.19 no.1
• /
• pp.131-152
• /
• 2015

Easy detection and evaluation of defect in the tube structure is a continuous problem and remains a significant demand in tube inspection technologies. This study is aimed to automate defect detection using the pattern recognition approach based on the classification of high frequency stress wave signals. The stress wave signals from vibrational impact excitation on several tube conditions were captured to identify the defect in ASTM A179 seamless steel tubes. The variation in stress wave propagation was captured by a high frequency sensor. Stress wave signals from four tubes with artificial defects of different depths and one reference tube were classified using the autoregressive (AR) algorithm. The results were demonstrated using a dendrogram. The preliminary research revealed the natural arrangement of stress wave signals were grouped into two clusters. The stress wave signals from the healthy tube were grouped together in one cluster and the signals from the defective tubes were classified in another cluster. This approach was effective in separating different stress wave signals and allowed quicker and easier defect identification and interpretation in steel tubes.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.27 no.7
• /
• pp.1170-1178
• /
• 2003

This paper provides approximate J estimates for off-centred, circumferential through-wall cracks in cylinders under bending and under combined tension and bending. The proposed method is based on the reference stress approach, where the dependence of elastic and plastic influence functions of J on the cylinder/crack geometry, the off-centred angle and strain hardening is minimised through the use of a proper normalising load. Based on published limited FE results for off-centred, circumferential through-wall cracks under bending, such normalising load is found, based on which the reference stress based J estimates are proposed for more general cases, such as for a different cylinder geometry and for combined loading. Comparison of the estimated J with extensive FE J results shows overall good agreements for different crack/cylinder geometries and for combined tension and bending, which provides sufficient confidence in the use of the proposed method to fracture mechanics analyses of off-centred circumferential cracks. Furthermore, the proposed method is simple to use, giving significant merits in practice.