Method and system for evaluating air hole defects in ship welding structure

Abstract

The invention provides a method and system for evaluating air hole defects in a ship welding structure, and the method comprises the steps: obtaining the feature information of the air hole defects in an actual ship welding structure; according to an actual ship welding structure, constructing a three-dimensional welding structure model comprising pore defects; calculating a fatigue stress range of the pore defect; according to the fatigue stress range and the material performance parameters of the ship welding structure, the crack propagation behavior of the pore defect is calculated through a crack propagation model; generating a failure evaluation curve according to the material performance parameters; based on the crack propagation behavior, calculating evaluation parameters under different cycle times; and comparing the evaluation parameters under different cycle times with the failure evaluation curve, and judging the influence of the pore defect on the structural safety in combination with the designed life.

Description

Technical Field

[0001] This invention relates to the field of ship structural safety assessment, and more specifically, to a method and system for assessing porosity defects in ship welded structures. Background Technology

[0002] In the shipbuilding industry, in pursuit of lightweight structures, high-strength steel is increasingly widely used in ship construction due to its advantages such as light weight, high strength, and ease of processing. Currently, high-strength steel hull components are generally connected by welding, and welding processes and technologies are constantly being updated and iterated. However, due to differences in welding processes and the inherent inhomogeneity of the material, defects inevitably appear in the weld joint area, with porosity being a typical defect. When ships navigate in complex sea conditions, they are subjected to repeated irregular alternating loads, making the ship structure prone to fatigue failure. Weld joints and weld toe areas, due to stress concentration and microstructural changes, are often considered the source of fatigue crack initiation. When fatigue cracks appear in this area, the presence of initial defects such as porosity significantly exacerbates this process, becoming a key factor in crack propagation and ultimately leading to fatigue fracture and loss of load-bearing capacity.

[0003] Currently, the main method for fatigue assessment of ship structures is the fatigue cumulative damage calculation method based on the Palmgren-Miner linear cumulative damage criterion, which predicts the entire service life of the ship structure. This method is mainly applicable to structures without cracks at the macroscopic level and cannot predict the fatigue life of structures with cracks, thus having certain limitations. Research on fracture mechanics methods for predicting fatigue life and assessing structural safety of structures with defects can more accurately predict their fatigue life and reduce fatigue failures due to initial defects during the ship's operational period. For this method, international standards such as BS7910 have established systematic evaluation frameworks. However, these standards mainly consider surface cracks or penetrating cracks, especially focusing on structures such as pipeline steel and pressure vessels. A systematic evaluation method has not yet been developed for common internal defects such as porosity in ship structure welding, leading to uncertainty in the evaluation results.

[0004] Therefore, a dedicated assessment method and system are urgently needed to address the fatigue safety issues related to embedded defects containing porosity in welded ship structures. This is crucial not only for accurately predicting structural lifespan and ensuring safe ship operation, but also for providing a theoretical basis for structural design and compensating for the shortcomings of current standards and specifications in this area. Summary of the Invention

[0005] In view of the lack of systematic assessment of porosity defects in welded structures in the prior art, this application provides a method and system for assessing porosity defects in ship welded structures to make up for the deficiencies of existing standards and provide a reliable basis for ship design.

[0006] To achieve the above and other related objectives, the present invention provides a method for evaluating porosity defects in welded structures of ships, comprising: To obtain characteristic information of porosity defects in actual ship welded structures; Based on the actual ship welding structure, a three-dimensional welding structure model including the porosity defect is constructed; Calculate the fatigue stress range of the porosity defect; Based on the fatigue stress range and the material property parameters of the ship welded structure, the crack propagation behavior of the porosity defect is calculated using a crack propagation model. Based on the material performance parameters, a failure assessment curve is generated; Based on the crack propagation behavior, the evaluation parameters are calculated for different number of cycles. The evaluation parameters at different cycle counts are compared with the failure evaluation curves, and the impact of the porosity defects on structural safety is determined in conjunction with the design life.

[0007] Optionally, the characteristic information of the porosity defect includes: the location, number, and size of the porosity defect.

[0008] Optionally, the material performance parameters include: the material's elastic modulus, yield strength, tensile strength, and stress-strain.

[0009] Optionally, the crack propagation model is the Paris model, and its formula is: ;in, Let be the crack propagation rate, ΔK be the stress intensity factor amplitude, and C and m be material constants.

[0010] Optionally, based on the material performance parameters, generating a failure assessment curve includes: A coordinate system is established with the plastic instability coefficient Lr as the abscissa and the fracture coefficient Kr as the ordinate; Based on the material performance parameters, the coordinates of each point on the failure assessment curve are calculated using a formula. The formula for calculating the failure assessment curve is: ; And determine the cutoff limit Lr,max of the abscissa of the failure assessment curve as: ; Where E is the elastic modulus of the material, εref is the strain value of the material, σY and ReH are the yield strength of the material, and Rm is the tensile strength of the material.

[0011] Optionally, based on the crack propagation behavior, the evaluation parameters for different number of cycles are calculated as follows: for each cycle number predicted by the crack propagation behavior: Ni and its corresponding crack size ai: Based on the current crack size ai: calculate the reference stress σref and stress intensity factor KI; According to the formula Calculate the plastic instability coefficient; According to the formula Calculate the fracture coefficient; Where Kmat is the fracture toughness of the material, and ρ is the plasticity trimming factor.

[0012] Optionally, the evaluation parameters at different cycle numbers are compared with the failure evaluation curve, and combined with the design life, the impact of the porosity defect on structural safety is determined, including: If the evaluation points (Lr, Kr) corresponding to all cycles are located within the region of the failure evaluation curve, then the porosity defect is deemed acceptable. If all evaluation points are located in or outside the failure evaluation curve, then the porosity defect is determined to be non-compliant with safety requirements. If some evaluation points are located on the failure evaluation curve and the rest are located inside the curve, it is determined to be a critical state. Calculate the number of cycles nL required for the critical defect to extend to failure. If nL is greater than 3 times the design life n0, it is determined to be acceptable; otherwise, it is determined to be unacceptable.

[0013] This application also provides a system for assessing porosity defects in welded structures of ships, including: The data acquisition module is used to acquire characteristic information about porosity defects; The stress analysis module is used to construct a three-dimensional finite element model and calculate the fatigue stress range. The crack prediction module is used to calculate the crack propagation behavior of porosity defects. The evaluation curve module is used to generate failure evaluation curves based on material performance parameters. The safety assessment module is used to calculate assessment parameters, perform comparisons, and output safety assessment results.

[0014] As described above, the method and system for evaluating porosity defects in ship welded structures provided by the present invention have at least the following beneficial technical effects: The porosity defect assessment method for welded structures in ships provided in this embodiment effectively fills the gap in the existing field of porosity defect assessment for welded structures in ships. By integrating non-destructive testing, localized refined finite element analysis, crack propagation dynamics prediction, and failure assessment curves, a quantitative and dynamic safety assessment process specifically for ship structures has been established. This method can accurately simulate the entire process of crack initiation and propagation of porosity under service loads, and uses failure assessment curves combined with design life to make a triple accurate judgment (safe, critical, unsafe). This completely changes the situation of high uncertainty and reliance on experience in the assessment of such defects by traditional methods. Under the premise of ensuring the safety and reliability of the ship structure throughout its entire life cycle, it can avoid unnecessary structural repairs or material waste caused by overly conservative judgments, and provides a scientific basis and key technical support for ship design, construction process optimization, and in-service safety management. Attached Figure Description

[0015] Figure 1 The flowchart shown is a method for assessing porosity defects in a ship welded structure, as an example.

[0016] Figure 2 The diagram shows a single pore defect.

[0017] Figure 3 The diagram shows a structure with multiple pore defects coplanar in the thickness direction of the plate.

[0018] Figure 4 The diagram shows a structure with multiple pore defects coplanar in the width direction of the plate.

[0019] Figure 5 The diagram shows a structure with multiple pore defects coplanar in both the thickness and width directions of the plate.

[0020] Figure 6 The flowchart shown is for steps S4-S7 provided in Embodiment 1.

[0021] Figure 7 The diagram shown is a schematic of the failure assessment curve provided in Example 1. Detailed Implementation

[0022] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0023] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Although the illustrations only show components related to the present invention and are not drawn according to the actual number, shape and size of the components, the shape, quantity, positional relationship and proportion of each component can be arbitrarily changed under the premise of realizing the technical solution of this invention, and the layout of the components may also be more complex.

[0024] Example 1 This embodiment provides a method and system for assessing porosity defects in welded structures of ships, such as... Figure 1 As shown, the method for assessing porosity defects in the welded structure of a ship in this embodiment includes: S1: Obtain characteristic information of porosity defects in actual ship welded structures; S2: Based on the actual ship welding structure, construct a three-dimensional welding structure model including the porosity defect; S3: Calculate the fatigue stress range of the porosity defect; S4: Based on the fatigue stress range and the material property parameters of the ship welded structure, calculate the crack propagation behavior of the porosity defect using a crack propagation model; S5: Generate a failure assessment curve based on the material performance parameters; S6: Based on the crack propagation behavior, calculate the evaluation parameters for different number of cycles; S7: Compare the evaluation parameters with the failure evaluation curve, and in conjunction with the design life, determine the impact of the porosity defect on structural safety.

[0025] Specifically, step S1: Obtain characteristic information of porosity defects within the actual ship welded structure. The characteristic information of porosity defects includes: the location, quantity, and size of the porosity defects.

[0026] Optionally, non-destructive testing methods, including ultrasonic testing or radiographic testing, are employed. The information obtained includes the depth and location of porosity defects, the number of pores, their distribution location, and their approximate shape. Specifically, this also includes generating a defect report that clearly records the precise location (based on the weld coordinate system) of each pore found within the target weld area and its total number.

[0027] Specifically, the size of the defect is determined based on the defect report. The number of defects is categorized into two groups: single defects and multiple defects.

[0028] For a single pore defect, such as Figure 2 The diagram shown is a schematic of a single pore defect, with the pore length 2c and pore height 2a measured. For multiple pore defects, in addition to measuring the size of each individual pore, it is also necessary to perform equivalent processing based on their relative positions and orientations in space. Generally, the determination of the length and height parameters of multiple pores is related to the orientation of the pores, specifically divided into three types: coplanar in the direction of plate thickness, coplanar in the direction of plate width, and coplanar in both the direction of plate thickness and plate width.

[0029] like Figure 3 The diagram shows a structure with multiple porosity defects coplanar along the plate thickness direction; the equivalent porosity length is the sum of the lengths of individual pores plus the spacing, and the equivalent height is the height of a single pore. Specifically, as shown... Figure 3 As shown: the pore length is 2c = max(2C1, 2C2), and the pore height is 2a = 2a1 + S + 2a2, where S is the distance between two pores along the thickness direction. like Figure 4 The diagram shows a structure with multiple porosity defects coplanar along the width of the plate; the equivalent porosity length is the length of a single porosity, and the equivalent height is the sum of the heights of a single porosity plus the spacing. Specifically, as shown... Figure 4 As shown: the length of the pore is 2c = 2c1 + S + 2c2, where S is the distance between two pores along the width direction, and the height of the pore is 2a = max(2a1, 2a2). like Figure 5 The diagram shows a structure with multiple porosity defects coplanar in both the thickness and width directions of the plate; the equivalent pore length and height are the superposition of the pore size and spacing in their respective directions. Specifically, as shown... Figure 5 As shown, the pore length is 2c = 2c1 + S + 2c2, S1 is the distance between the two pores along the width direction, the pore height is 2a = 2a1 + S + 2a2, and S2 is the distance between the two pores along the thickness direction. Specifically, such as Figure 3 , 4 As shown in Figure 5, it is also necessary to measure the shortest distance P from the surface to the porosity defect and the cross-sectional thickness B where the porosity defect is located. These parameters together define the relative position of the defect in the thickness direction of the plate.

[0030] Specifically, S2: Based on the actual ship welding structure, construct a three-dimensional welding structure model including the porosity defect.

[0031] Specifically, it includes S21: Determining the model range, which extends by two strong frame distances along the longitudinal, lateral, and vertical directions of the location of the pore defect; and S22: Geometric modeling.

[0032] S21: Determine the model scope: Generally, the model range is large enough to ensure that the stress results calculated at the defect location are not affected by artificially set boundary conditions, i.e., to eliminate boundary effects. Specifically, with the porosity defect location determined in S1 as the center, the model range is extended by two strong frame distances along the longitudinal (i.e., the hull length direction), transverse (i.e., the hull width direction), and vertical (i.e., the hull height / plate thickness direction) directions of the defect location.

[0033] S22: Geometric Modeling Within the defined model scope, based on the ship structural design drawings, precise three-dimensional geometric entities, including hull plates, decks, and skeletons (such as longitudinal bones and ribs), are created. Subsequently, based on the feature information obtained from S1, three-dimensional geometric bodies matching the actual size and shape of pores are created at the corresponding locations in the weld area to represent defects.

[0034] Optionally, mesh generation can be performed during geometric modeling to ensure computational accuracy.

[0035] Specifically, a high-density mesh is applied to the area surrounding the porosity defects. Since the edge of the pore is the area of ​​most severe stress concentration, a sufficiently fine mesh is necessary to capture the gradient of this "hot spot stress".

[0036] Specifically, S3: Calculate the fatigue stress range of the porosity defect; Specifically, the fatigue stress range at the defect location is calculated using the finite element method. The main steps of the finite element calculation include: S31. Based on the three-dimensional welded structure model obtained in S2, select the load case for finite element calculation: Specifically, to comprehensively assess the worst-case scenarios the ship may encounter during operation, eight typical operating conditions under full load and ballast conditions were selected. These conditions combine different wave loads (such as camber and sagging), kinetic inertial loads, etc., covering the main alternating stress states that the structure may bear. The hot spot stress method was used to perform fatigue calculations on the structure at the defect location. This method can effectively eliminate the sensitivity of mesh size and capture the stress concentration effects caused by macroscopic structural geometry (including the defects themselves).

[0037] Specifically, the loads and boundary conditions of the above eight working conditions are applied to the three-dimensional welded structure model of S2, and linear static solutions are performed to obtain the stress distribution cloud map of the model under each working condition.

[0038] S32: Extract hot spot stress and calculate fatigue stress range: Specifically, this includes stress extraction, finding the maximum stress range, and calculating the fatigue stress range (Δσ).

[0039] Stress extraction: From the calculation results of each set of working conditions, extract the stress in the region with the most severe stress concentration at the edge of the porosity defect. Typically, this involves reading the stress distribution along a path through the hot spot. The extracted stress distribution is then interpolated using linear extrapolation to accurately determine the hot spot stress value at the root of the porosity defect.

[0040] Finding the maximum stress range: Combine and analyze the calculation results of all eight working conditions. For each potential danger point at the edge of the pore, find its maximum stress value (σmax) and minimum stress value (σmin) in all working conditions.

[0041] Calculate the fatigue stress range (Δσ): Using the formula Δσ = σmax - σmin, calculate the maximum stress fluctuation range experienced by this point throughout the entire load history. This Δσ is the most critical load input parameter in subsequent crack propagation analysis.

[0042] like Figure 6 The diagram shows a flowchart of steps S4-S7 provided in this embodiment; specifically, S4: based on the fatigue stress range and the material property parameters of the ship welded structure, the crack propagation behavior of the porosity defect is calculated using a crack propagation model; Specifically, it includes: S41: Determine the input parameters of the calculation model; S42: Predict crack propagation based on fracture mechanics; S43: Perform iterative calculation of crack propagation.

[0043] S41 defines the input parameters for the computational model. These input parameters include: initial defect size, material mechanical properties, crack propagation material constants, load spectrum, and fracture toughness constants. Initial defect size: Based on the characteristic information of the porosity defect obtained in S1, it is equivalent to the initial defect size. For a single pore, the initial crack size is length 2c and height 2a; for multiple pores, the selection is made according to the content shown in step S1. Material mechanical property parameters include the material's elastic modulus (E), yield strength (σy), and tensile strength (σuts). Crack propagation material constants: These are the parameters C and m in the Paris formula, obtained through fatigue crack propagation tests. Load spectrum: Based on the fatigue stress range (Δσ) and its corresponding number of cycles calculated in S3. To simplify the calculation, a constant amplitude load is often used for conservative evaluation, assuming that all stress cycles are within the maximum stress range Δσ. Fracture toughness constant: The fracture toughness (Kmat) of the material, used to determine whether the crack will propagate unstably.

[0044] S42: Crack propagation prediction based on linear elastic fracture mechanics; Specifically, the prediction model uses the Paris model formula for calculation, which is as follows: ;in, ΔK is the crack propagation rate, representing the increment of crack size with each stress cycle; ΔK is the stress intensity factor amplitude, which is the driving force for crack propagation. The value of ΔK is related to the current crack size 'a' and the fatigue stress range Δσ, and is calculated using the following formula: , where Y is the geometric correction factor; C and m are material constants.

[0045] S43: Performing crack propagation iterative calculations includes: Initialization: Set the initial crack size a=a0 as the starting point, a0=f(2c,2a), set the initial number of cycles N=0, and set the cycle increment ΔN.

[0046] Iterative loop steps: Step 1, Calculate the current driving force: Step 2: Calculate the current expansion rate. Step 3: Calculate the current crack increment: Step 4: Update state variables: ai = ai-1 + Δai; Ni = Ni-1 + ΔNi. Step 5: Store and judge: Store the current data point (Ni, ai); judge whether the loop should continue (e.g., whether the crack size ai exceeds the critical value, or whether the number of iterations has reached the upper limit). If the conditions are not met, return to step 1 and start the next iteration.

[0047] Specifically, this embodiment uses two cycles as an example for detailed explanation: Initial state: initial crack size a0; First cycle, calculate the stress intensity factor amplitude. Substituting ΔK1 into the Paris formula: Calculate the current crack propagation rate ; Calculate crack increment: Update the crack size to a1 = a0 + Δa1. Second loop: Crack size a1, calculate the stress intensity factor amplitude. Substituting ΔK2 into the Paris formula, the current crack propagation rate is calculated. ; Calculate crack increment: The crack size is updated to a2 = a1 + Δa2.

[0048] Specifically, update the crack size and accumulate the number of iterations; use the updated crack size as the current size and repeat step S43.

[0049] Through the above iterative calculations, a curve showing the evolution of crack size *a* as a function of the number of cycles *N* (the *aN* curve) is finally obtained, along with the current crack size *a* corresponding to different number of cycles *N*. This characterizes the crack propagation behavior of porosity defects and provides time-varying defect state input for the next step of safety assessment.

[0050] Specifically, S5: Generate a failure assessment curve based on the material performance parameters; like Figure 7 The diagram shown is a schematic of the failure assessment curve provided in this embodiment; a two-dimensional rectangular coordinate system is established with the plastic instability coefficient Lr as the abscissa and the fracture coefficient Kr as the ordinate. Based on the material performance parameters, the coordinates of each point on the failure assessment curve are calculated using a formula. The formula for calculating the failure assessment curve is: ; And determine the cutoff limit Lr,max of the abscissa of the failure assessment curve as: ; Where E is the elastic modulus of the material, εref is the strain value of the material, σY and ReH are the yield strength of the material, and Rm is the tensile strength of the material.

[0051] Specifically, S6: Based on the crack propagation behavior, calculate the evaluation parameters for different number of cycles; Specifically, based on the crack propagation behavior obtained from S4, the steps for calculating and evaluating parameters for different cycle numbers Ni and their corresponding crack sizes ai are as follows: S61: Calculate the reference stress σref and stress intensity factor KI based on the current crack size ai; Specifically, the reference stress σref is calculated as an equivalent net cross-sectional stress based on the current crack size ai and the applied load. It reflects the average stress level on the remaining ligament section of the structure in the presence of a crack. Its calculation follows a standard method, typically expressed as a function of the applied load P and the crack size ai: σref = f(P, ai); Specifically, the stress intensity factor KI is calculated, characterizing the intensity of the elastic stress field at the crack tip. Its calculation formula is typically: , where Y is a correction factor that depends on the structural geometry, crack shape, and loading method.

[0052] S62: Calculate the evaluation parameters Lr and Kr for the current evaluation point; According to the formula Calculate the plastic instability coefficient Lr; According to the formula Calculate the fracture coefficient Kr; Where ReH is the yield strength of the material, Kmat is the fracture toughness of the material, and ρ is the plasticity trimming factor, which is usually taken as 0.2 or 0.25.

[0053] S63: Output and Iteration; The (Lr, Kr) calculated at the current cycle number Ni is used as an evaluation point.

[0054] Specifically, S7: Compare the evaluation parameters with the failure evaluation curve at different cycle counts, and in conjunction with the design life, determine the impact of the porosity defect on structural safety. For example... Figure 7 As shown, the failure evaluation curve provided in this embodiment is displayed.

[0055] Specifically, the evaluation point obtained after each cycle is compared with the relative position of the failure evaluation curve. If the evaluation point is located on or above the curve, the cycle stops; otherwise, the cycle continues. Usually, the maximum number of cycles is set to 100 times the design life, and the design life is represented as n0. 1. If the evaluation points (Lr, Kr) corresponding to all cycle counts are located within the region of the failure evaluation curve, meaning the driving force Kr at the crack tip is always lower than the material's fracture resistance (curve definition), and the overall stress level Lr of the structure is always lower than its plastic instability limit (curve definition), then the porosity defect is safe throughout the entire design life n0 of the structure and will not lead to fatigue fracture or plastic collapse. Therefore, the defect is deemed acceptable. The structure at this location requires no repair or reinforcement and can be safely put into use.

[0056] 2. If all evaluation points are located in or outside the failure evaluation curve, the porosity defect is deemed to fail to meet safety requirements; such porosity defect poses an unacceptable risk to structural safety. In this case, remedial measures must be taken, such as: returning to step S2 and modifying the local structural design (e.g., increasing plate thickness, optimizing geometry) to reduce stress; or reducing the initial defect size through process improvements, and then re-evaluating until the safety requirements are met.

[0057] 3. If some evaluation points lie on the failure assessment curve, while the rest lie inside the curve (i.e., some points lie on the failure assessment curve), it indicates that the structure is in a critical state. To ensure the safety and reliability of the structure under defective conditions, a more accurate life assessment is needed.

[0058] First, calculate the number of cycles nL required for the critical defect to propagate to failure: find the number of cycles nL corresponding to the first intersection of the evaluation point and the failure evaluation curve (i.e., reaching the critical state) on the crack propagation curve (aN curve); second, set a safety threshold, and this application introduces a safety margin of 3; when nL > 3 times the design life 3n0, it means that even considering sufficient safety margin, the time required for the defect to propagate to a dangerous state is much longer than the service life of the structure, and the risk is extremely low, so it is judged to be acceptable; when nL ≤ 3n0, it is considered that the safety margin is insufficient, the risk is unacceptable, and it is judged to be unsatisfactory, and the design needs to be modified according to the above-mentioned unsafe state handling method.

[0059] The porosity defect assessment method for welded structures in ships provided in this embodiment effectively fills the gap in the existing field of porosity defect assessment for welded structures in ships. By integrating non-destructive testing, localized refined finite element analysis, crack propagation dynamics prediction, and failure assessment curves, a quantitative and dynamic safety assessment process specifically for ship structures has been established. This method can accurately simulate the entire process of crack initiation and propagation of porosity under service loads, and uses failure assessment curves combined with design life to make a triple accurate judgment (safe, critical, unsafe). This improves the situation where traditional methods have high uncertainty and rely on experience in assessing such defects. Under the premise of ensuring the safety and reliability of the ship structure throughout its entire life cycle, it can avoid unnecessary structural repairs or material waste caused by overly conservative judgments, and provides a scientific basis and key technical support for ship design, construction process optimization, and in-service safety management.

[0060] Example 2 This embodiment also provides a porosity defect assessment system for ship welded structures, specifically including: a data acquisition module for acquiring characteristic information of porosity defects; a stress analysis module for constructing a three-dimensional finite element model and calculating the fatigue stress range; a crack prediction module for calculating the crack propagation behavior of porosity defects; an evaluation curve module for generating a failure evaluation curve based on material performance parameters; and a safety judgment module for calculating evaluation parameters, comparing them, and outputting the safety judgment result.

[0061] Specifically, the data acquisition module, as the system's data input port, is responsible for collecting initial information related to defects and structures. Its specific functions include: receiving and processing raw data from non-destructive testing equipment (such as ultrasonic flaw detectors and radiographic testing equipment); accurately analyzing and recording the characteristic information of porosity defects, including but not limited to: the three-dimensional location coordinates and number of defects, as well as key dimensional parameters (such as pore length 2c, height 2a, the shortest distance P from the surface to the defect, and cross-sectional thickness B). When multiple pores exist, it can automatically perform equivalent processing according to preset rules. Simultaneously, this module is also used to input basic design parameters such as the structure's design life n0.

[0062] The stress analysis module is responsible for performing detailed mechanical simulation analysis. Based on the information provided by the data acquisition module, it automatically or assisted the user in constructing a locally refined three-dimensional finite element model containing accurate porosity geometry. The module has a built-in library of typical ship load conditions (such as eight sets of full load / ballast conditions) and can perform batch calculations using the hot spot stress method. Finally, it automatically extracts and interpolates the most dangerous fatigue stress range Δσ at the porosity defect.

[0063] The crack prediction module enables dynamic prediction of defect evolution behavior. It incorporates a crack propagation model library, defaulting to and preferentially using the Paris model as the computational engine. It receives Δσ from the stress analysis module and material constants C and m from the data acquisition module, and performs crack propagation simulation through a cyclic iterative algorithm. Ultimately, the module outputs a curve depicting the relationship between crack size a and the number of cycles N (the aN curve), comprehensively describing the crack propagation behavior of porosity defects throughout their entire lifecycle.

[0064] The assessment curve module is responsible for establishing the absolute benchmark for safety assessment. Based on the input material property parameters (elastic modulus E, yield strength σy, tensile strength σuts, and stress-strain data), the module automatically calculates and plots a standard failure assessment curve according to internationally accepted formulas. The module automatically calculates and identifies the curve's horizontal cutoff limit Lrmax, fully defining the safety boundary.

[0065] The safety assessment module performs the final safety assessment. It reads the results from the crack prediction module and, for each predicted cycle number Ni and crack size ai, automatically calculates the corresponding evaluation parameters: the plastic instability coefficient Lr and the fracture coefficient Kr. The module automatically compares all these evaluation points (Lr, Kr) with the failure assessment curve provided by the curve generation module. Based on preset judgment rules that combine the design life n0 and the safety factor, the module automatically outputs the final safety assessment conclusion: acceptable, critical, acceptable, or does not meet the requirements, and can generate a detailed assessment report as needed.

[0066] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for evaluating porosity defects in welded structures of ships, characterized in that, include: To obtain characteristic information of porosity defects in actual ship welded structures; Based on the actual ship welding structure, a three-dimensional welding structure model including the porosity defect is constructed; Calculate the fatigue stress range of the porosity defect; Based on the fatigue stress range and the material property parameters of the ship welded structure, the crack propagation behavior of the porosity defect is calculated using a crack propagation model. Based on the material performance parameters, a failure assessment curve is generated; Based on the crack propagation behavior, the evaluation parameters are calculated for different number of cycles. The evaluation parameters at different cycle counts are compared with the failure evaluation curves, and the impact of the porosity defects on structural safety is determined in conjunction with the design life.

2. The method for evaluating porosity defects in ship welded structures according to claim 1, characterized in that, The characteristic information of the porosity defect includes: the location, number, and size of the porosity defect.

3. The method for evaluating porosity defects in ship welded structures according to claim 1, characterized in that, The material performance parameters include: the material's elastic modulus, yield strength, tensile strength, and stress-strain.

4. The method for evaluating porosity defects in ship welded structures according to claim 1, characterized in that, The crack propagation model is the Paris model, and its formula is: ;in, Let be the crack propagation rate, ΔK be the stress intensity factor amplitude, and C and m be material constants.

5. The method and system for assessing porosity defects in ship welded structures according to claim 1, characterized in that, Based on the aforementioned material performance parameters, failure assessment curves are generated, including: A coordinate system is established with the plastic instability coefficient Lr as the abscissa and the fracture coefficient Kr as the ordinate; Based on the material performance parameters, the coordinates of each point on the failure assessment curve are calculated using a formula. The formula for calculating the failure assessment curve is: ； And determine the cutoff limit Lr,max of the abscissa of the failure assessment curve as: ； Where E is the elastic modulus of the material, εref is the strain value of the material, σY and ReH are the yield strength of the material, and Rm is the tensile strength of the material.

6. The method for evaluating porosity defects in ship welded structures according to claim 1, characterized in that, Based on the crack propagation behavior, the evaluation parameters for different cycle numbers are calculated as follows: for each cycle number predicted by the crack propagation behavior: Ni and its corresponding crack size ai: Based on the current crack size ai: calculate the reference stress σref and stress intensity factor KI; According to the formula Calculate the plastic instability coefficient; According to the formula Calculate the fracture coefficient; Where Kmat is the fracture toughness of the material, and ρ is the plasticity trimming factor.

7. The method for evaluating porosity defects in ship welded structures according to claim 1, characterized in that, By comparing the evaluation parameters with failure evaluation curves at different cycle numbers and in conjunction with the design life, the impact of the porosity defect on structural safety is determined, including: If the evaluation points (Lr, Kr) corresponding to all cycles are located within the region of the failure evaluation curve, then the porosity defect is deemed acceptable. If all evaluation points are located in or outside the failure evaluation curve, then the porosity defect is determined to be non-compliant with safety requirements. If some evaluation points are located on the failure evaluation curve and the rest are located inside the curve, it is determined to be a critical state. Calculate the number of cycles nL required for the critical defect to extend to failure. If nL is greater than 3 times the design life n0, it is determined to be acceptable; otherwise, it is determined to be unacceptable.

8. A system for assessing porosity defects in welded structures of ships, characterized in that, include: The data acquisition module is used to acquire characteristic information about porosity defects; The stress analysis module is used to construct a three-dimensional finite element model and calculate the fatigue stress range. The crack prediction module is used to calculate the crack propagation behavior of porosity defects. The evaluation curve module is used to generate failure evaluation curves based on material performance parameters. The safety assessment module is used to calculate assessment parameters, perform comparisons, and output safety assessment results.

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