Trans RINA, Vol 153, Part A4, Intl J Maritime Eng, Oct-Dec 2011
direction of the principal stresses was examined with the aim of stress vector presentation.
The stress concentration factor, SCF is commonly defined as the ratio of the hot-spot stress,
hot spot the normal stress, i.e.: n SCF
hot spot n
(1)
The stress concentration factor measures the increase of stress concentration in a particular spot and is used for fatigue life estimation based on S-N curve approach.
Figure 4 – Hot spots 5
The stress concentration factor at the hot spot 1 is 1.73 and at the hot spot 2 is 1.67. The stress concentration factor at the hot spot 3 location has rather high value for the hogging loading condition and for the local load case 2 i.e. SCF=2.69. This is the highest stress concentration factor concerning all the cases.
The stress concentration factor at the hot spot 4 location is 1.89. This may be compared directly to the stress concentration factor of 1.67 for the hot spot 2, as this is the same spot on both spot-weld and all-weld models. The SCF for the 5th and 6th location are 1.32 and 1.48 respectively.
4. FATIGUE DAMAGE Figure 5 – Hot spot 6, all-weld model
The hot spot 5 is shown in Figure 4. The high stress concentration is located at the edge of the small side weld that connects the supporting
plate with the
trapezoid longitudinal. Figure 5 presents the hot spot 6 in detail.
3. HOTSPOT STRESS ANALYSIS
The aim of the hotspot stress analysis is to evaluate the stresses at the structural detail weld toe. The International Institute of Welding [6] presented the extrapolation procedure following advances in research on that topic and gives recommendation on how to effectively apply for the hotspot extrapolation procedure.
The hot spot principal stresses are determined by direct computation using finite element analysis. The mesh refinement of the local finite element model is sufficient and with element lengths near high stress zones equal to the plate thickness. A linear extrapolation is employed in hot spot stress calculations.
As 20-node solid finite elements are used, nodal stresses were available directly from the solver results. The
The trapezoid longitudinal of concern is located below the car deck and it is subjected to both lateral and axial load. The lateral load is provoked by the truck breaking load and has the magnitude of 48.75 kN for the vehicle under consideration. The truck breaking load is induced due to the breaking of car on the position of parking on the deck.
It is considered that the wave induced stresses in the welded joints studied may be described as a Gaussian process with zero mean value. In that case the stress amplitude distribution follows the Rayleigh distribution for any short sea state. The long-term stress distribution is defined based on Rayleigh short sea-state induced stress distributions and are quantified as a function of the probability of occurrence of any sea state of reference. The probability density function for the sea state conditions may differ and different distributions may be adjusted.
The linear model assumption is generally adequate, but in severe seas, the response may not be linear and a nonlinear analysis should be conducted.
The combination of wave induced load with the loads due to cargo operation (low and high frequency loads) is applied in this work. It is observed that the duration of the impulse force in the case of the cargo operation is rather small.
A-234 ©2011: The Royal Institution of Naval Architects and
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