M9
Joints & Connections

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17:35
conference time (CEST, Berlin)
Efficient Stress Linearization in FEA Continuum Models for Weld Fatigue Assessment
26/10/2021 17:35 conference time (CEST, Berlin)
Room: M
N. Fried, W. Vonach (CAE Simulation & Solutions Maschinenbau Ingenieurdienstleistungen GmbH, AUT)
N. Fried, W. Vonach (CAE Simulation & Solutions Maschinenbau Ingenieurdienstleistungen GmbH, AUT)
The strength assessment of welded structures is often conducted using FEA models with 3D continuum elements, especially when castings are involved. The accuracy of the corresponding displacement and stress fields is clearly superior to the one that can be obtained with shell element models. However, continuum element models exhibit a major disadvantage regarding the assessment of the stresses: The FE stress results at the weld root cannot be used directly for an assessment because they are strongly influenced by geometric singularities. The assessment of welds, on the other hand, relies primarily on equivalent linearized stresses across the weld section. Therefore, it is necessary to linearize the nonlinear FE stress fields. At a previous NAFEMS conference we have presented a first corresponding method, which is based on strain sensor elements. Unfortunately, the applicability of this method suffers from some geometric restrictions, and a more general solution is necessary. In this contribution, a fundamentally different and much more general postprocessing method is presented for calculating linearized stress fields in arbitrary sections of a continuum FE model. This method is based on the nodal forces of the FE elements adjacent to this section. From these forces an equivalent linearized stress field is calculated in a separate chain of bi-linear elements along the longitudinal direction of the section (weld). The corresponding algorithm was designed specifically for taking into account those nodal forces along the boundaries that arise from stress singularities. The problem is solved iteratively so that the linearized stress field equilibriates the FE element nodal forces. The calculated linearized stresses can be used directly for weld fatigue assessment (e.g., according to IIW). The proposed method has been implemented in the stress assessment software LIMIT along with an efficient workflow. The results are very encouraging and initiate further development of this method towards automated R1 notch stress assessment of welds.
Finite Element Analysis, Postprocessing, Durability & Fatigue, Weld, Engineering Simulation
17:55
conference time (CEST, Berlin)
Optimization of Development Process of Barge Modules Through Advanced Numerical Simulation
26/10/2021 17:55 conference time (CEST, Berlin)
Room: M
H. Bastien (CREAFORM, CAN); B. Leclerc (Ocean, CAN)
H. Bastien (CREAFORM, CAN); B. Leclerc (Ocean, CAN)
The use of advanced numerical simulations in the mechanical characterization of a new design of modular barge system allows to optimize both development process and final design. The case study presented herein illustrates how non-linear analyses on a detailed Finite Element Model of a Modular Barge System allowed to simplify its design and certification processes in comparison with a more traditional and conservative analytical approach or in comparison with an iterative and costly approach relying on extensive physical tests. Detailed Finite Element Analyses (FEA) allowed to efficiently size the structure of the module, identifying the limiting elements. Finite Element discretization allows to virtually assess effect of any loading on the whole design, taking into account the local effect of particular features; with more precision than if a less discretized and more analytical approach is taken. Welded connections have been identified as critical within the modular unit; detailed FEA allowed to represent precisely the geometry of each joint and study the impact of specific aspects such as weld bead penetration. Finite element representation could then be correlated on smaller scales tests, more accessible and more efficient. Connections between independent modular units have been identified as critical and potentially affecting the capacity of the system. Global to local detailed modeling allowed to design and assess the strength of an innovative connection system, easily useable on-site. The use of non-linear analysis allows to take into account the progressive application of loading and non-linear effects such as the evolution of stiffness matrix and material properties. Precise Stress distribution generated by non-linear analysis allows an efficient mass saving by pinpointing areas where mass is not used efficiently. In this case, buckling of main structural elements have been identified as limiting the capacity of a single unit. Detailed non-linear analyses allowed to simulate the behaviour of the unit and showed its collapsing due to buckling at the critical load level. Based on the detailed model of a single unit, multiple units assemblies in different configurations were analyzed to document the maximum resistant shear load and the maximum resistant moment sustainable by each connection configuration and each unit. Numerical Modelling can also save time and money as it can surrogate to a physical prototype within the establishment and acceptance of load rating of the design by standards regulators. The rating established allows the use of the modular units in future designs of barges without extensive structural investigations. The detailed non-linear analyses showing the collapsing behaviour of the connection at a critical load level and establishing the capacity of the system has been accepted by Lloyd’s Register in lieu of physical testing. Finite Element Modelling reduced the need for mechanical testing and prototyping, allowing multiple iterations to be carried out numerically; and thus, saved a great amount of time in the design process. Moreover, it allowed the rating of the system without the full-scale test. Equivalent physical testing would have required important resources in terms of both time and material, due to the size of the units and the load levels to be generated. The implications of such physical testing might have compromised the feasibility of the overall design process. This paper illustrates the use of advanced finite element analysis in the load rating of a new modular barge system design. Different design steps showcasing the use of advance non-linear analyses are presented. It emphasizes on how the advanced analyses allowed to reduce time and budget dedicated to development process and how the final design is optimized by this approach.
Barge, Finite Element, Non-linear Analysis, optimization, numerical simulation
18:15
conference time (CEST, Berlin)
Thread Analysis for Downhole Applications; From Mechanics to Numerical Simulation
26/10/2021 18:15 conference time (CEST, Berlin)
Room: M
S. Pirayeh Gar, A. Zhong (Halliburton Carrollton Technology Center, USA)
S. Pirayeh Gar, A. Zhong (Halliburton Carrollton Technology Center, USA)
Thread analysis is a critical structural analysis for downhole applications in the oil and gas industry, where strength and sealing performance of the thread connection is evaluated under the design load envelope. The first step of thread analysis is to reasonably model the initial make-up-torque to account for the pre-stressing effects caused by the torque-induced axial force at the bearing surfaces. This modelling is typically done by calculating and introducing an interference fit in 2D axisymmetric simulations. The well-known power-screw equation, which estimates the torque-induced axial forces on the thread bearing surface, is commonly used to find the axial force at the bearing surface. The initial interference is then determined by calculating the axial deformation of the threaded connection. However, interference calculations become challenging if the thread design and geometry are not conventional, such as threads with two nose-to-shoulder bearing surfaces (double-shoulder), where the power-screw equation is no longer applicable. The goal of this paper is to establish a general method to numerically calculate the interference fit applicable to both single-shoulder and double-shoulder threads using 2D axisymmetric models. The fundamental difference between make-up-torque mechanisms of single-shoulder and double-shoulder threads is highlighted and the application of power-screw equation is extended using classical mechanics to establish the torque-axial force relationship for double-shoulder threads through a new equation. Full 3D simulations followed by 2D axisymmetric finite element analyses are conducted to better understand the mechanics of the problem and verify the torque-axial force relationship. The analysis results confirm the substantial difference in mechanics of the single-shoulder and double-shoulder threads and the way torque-induced axial force is distributed. Finite element analyses reveal the high fidelity of the proposed methodology, where the results of 3D and 2D simulations as well as the predictions of the proposed equation come into good agreement. The results of this study can substantially improve the make-up torque simulation method using 2D axisymmetric models.
Thread Analysis, Make-up Torque, Power Screw Equation, Interference Fit, Finite Element Analysis
18:35
conference time (CEST, Berlin)
Is Bolt Loosening Based on Advanced Pretension Functionality Predictable?
26/10/2021 18:35 conference time (CEST, Berlin)
Room: M
M. Klein (INTES GmbH, DEU)
M. Klein (INTES GmbH, DEU)
In mechanical engineering, bolts are frequently used as standard fastening elements, which have to fulfil important mechanical functions like strength and safety. In Finite Element (FE) analysis, there exist a great number of possibilities to model bolts dependent on their importance for the desired analysis and on the focus on global or local structural behavior. When it comes to local stress and strength, there is a clear trend to apply solid models for the bolts, where all parameters are like the real bolt including pretension but the thread is not detailed. Fasteners can be mission critical, i.e. if bolts lose pretension during operation, the structure will fail. In many cases it is not necessary to make an absolute statement as to whether the screw will loosen or not. It is sufficient to state whether the tendency to loosen screws is increasing or decreasing. With this knowledge, the assembly can be improved through simulation. It was assumed that a detailed modeling of the thread is necessary in order to obtain this knowledge. But the more details are increasing the computation time drastically, which makes this approach not usable for multi body designs. So, simplified bolt models with advanced pretension functionality are needed, which gives reliable indication for bolt loosening. This leads to the main question: Is an advanced pretension functionality for model without thread sufficient to evaluate the tendency of loosening? An advanced contact with thread system on cylindrical model is shown. The accuracy of the contact directions and the contact forces in the thread area is significantly increased through the use of screw parameters and thread coordinate system. At the same time, the modeling effort and the computing time are kept low. The screw connection of a rim is shown as an example. Different rim geometries are compared to check the predictability of the new approach.
FEA, FEM, contact anaysis, bolt loosening, srew, pretension, thread
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