Modeling of Pipe System Behavior With Circumferential Surface Crack for Secondary Stress Margin Assessment

2017 ◽  
Author(s):  
M. F. Uddin ◽  
F. W. Brust ◽  
G. M. Wilkowski ◽  
S. Kalyanam ◽  
J. Martin
Keyword(s):  
Stress Reduction ◽  
Evaluation Criteria ◽  
Reduction Factor ◽  
Material Behavior ◽  
Welding Residual Stress ◽  
Nonlinear Material ◽  
Loading Conditions ◽  
Secondary Stress ◽  
Pipe System ◽  
Reduction Factors

In flaw evaluation criteria, the design limits for the secondary stresses is frequently different than the primary stresses. The evaluation procedure for primary stresses are load-controlled based which is independent of pipe deformation. The evaluation procedures for secondary stresses are displacement controlled which are dependent on pipe deformation. Certain stress components such as thermal expansion, thermal striping, welding residual stress, misalignment/cold-springing, dynamic anchor motion are historically considered secondary stresses and their design limits are based on elastic stress analysis. In reality, there can be much more rotation/displacement of the pipe with nonlinear fracture behavior due to nonlinear material behavior and plasticity at the crack plane providing extra margins on the elastically calculated rotation values that come from uncracked-pipe design analyses. In assessing secondary stress margin, a secondary stress reduction factor is defined as the ratio of elastic-plastic moment to elastic moment. This is equivalent to another concept using a Plastic Reduction Factor (PRF) as well as the inverse of structural (or safety) factor (SF) in ASME Section XI flaw evaluation criteria for various service levels. In this work, the secondary stress reduction factor was determined for a representative pipe system with multiple crack sizes, crack locations, and loading conditions. Nonlinear finite element (FE) analyses of a whole uncracked-pipe system were performed using ABAQUS® under various loading combinations to determine the critical locations for cracks in the pipe system. Next, FE analyses of the cracked-pipe system were carried out using cracked-pipe element — a methodology developed by the authors. Cracked-pipe system analyses were conducted for two loading conditions — one producing contained plasticity or single-hinge system and the other producing larger plasticity in the pipe system. Several analyses were conducted for each loading conditions with a combination of two crack sizes at two key locations. Secondary stress reduction factors were then calculated for both loading conditions in the pipe system. Finally, the margin in secondary stress was assessed for the pipe system by comparing the secondary stress reduction factors with that for straight pipe sections (determined for experimental bend tests) as well as with the recommended equivalent PRF and the equivalent ASME secondary stress correction factors.

Development of Secondary Stress Weighting Factor and Plastic Reduction Factor From Moment-Rotation Curves of Surface Cracked Pipe Tests

2017 ◽  
Author(s):  
S. Pothana ◽  
G. Wilkowski ◽  
S. Kalyanam ◽  
Y. Hioe ◽  
G. Hattery ◽  
...  
Keyword(s):  
Lower Bound ◽  
Stress Analysis ◽  
Elastic Stress ◽  
Weighting Factor ◽  
Reduction Factor ◽  
Bending Moments ◽  
Secondary Stress ◽  
Pipe System ◽  
Bend Tests

In flaw evaluation criteria, the secondary stresses (displacement controlled) may have different design limits than primary stresses (load-controlled stress components). The design limits are based on elastic stress analysis. Traditionally the elastic design stresses are used in the flaw evaluation procedures. But realistically a flaw in the piping system can cause non-linear behavior due to the plasticity at the crack plane as well as in the adjacent uncracked-piping material. A Secondary Stress Weighting Factor (SSWF) was established which is the ratio of elastic-plastic moment to the elastic moment calculated through an elastic stress analysis. As long as the remote uncracked pipe stresses are below yield, the SSWF is 1.0, and if the uncracked pipe plastic stresses are above the yield stress, the SSWF reaches a limit which is called the Plastic Reduction Factor (PRF). Four-point-bend tests were conducted on pipes with varying circumferential surface-crack lengths and depths. The moment-rotation plots obtained from various pipe tests were used in the determination of PRF. A lower-bound limiting PRF can be calculated from a tensile test, but pipe systems are not uniformly loaded like a tensile specimen. The actual PRF value for a cracked pipe was shown to have a lower bound, which occurs when the test section of interest is at a uniform stress (such as the center region in a four-point pipe bend tests). When multiple plastic hinges develop in a pipe system (a “balanced system” by ASME Section III NB-3650 design rules), this gives a greater reduction to the elastically calculated stresses since there is more plasticity. It was found that the plastic reduction is less when most parts of the pipe system remains elastic, or if the crack is located in the high strength/ lower toughness pipe or welds, or if the pipe size is large enough that elastic-plastic conditions occur even for a higher toughness material. Interestingly, it was shown that the same system with different loading directions could exhibit different actual PRF values if the change in the loading direction changes how much of the pipe system experiences plastic stresses. For smaller cracks, where the bending moments are high, the actual PRF is controlled by plasticity of the uncracked pipe, which is much larger than the plasticity that occurs locally at the crack. However, for large cracks where the bending moments are lower (closer to design conditions), the plasticity at the crack is equally important to the smaller amount of plasticity in the uncracked pipe for the actual PRF. Hence the plasticity of both the uncracked pipe and at the cracked sections is important to include in the determination of actual PRF values.

Mitigating stress concentration through defense hole system for improvement in bearing strength of composite bolted joint, Part 1: Numerical analysis

2017 ◽  
Vol 51 (26) ◽  
pp. 3685-3699 ◽  
Author(s):  
AR Othman ◽  
Khudhayer J Jadee ◽  
M-Z Ismadi
Keyword(s):  
Numerical Analysis ◽  
Stress Concentration ◽  
Stress Reduction ◽  
Progressive Failure ◽  
Material Behavior ◽  
Bolted Joints ◽  
Nonlinear Material ◽  
Bolted Joint ◽  
Failure Model ◽  
Bearing Strength

The use of defense hole system allows the flow of the stresses to be redistributed by introducing auxiliary holes in the low stress area near the main hole. However, the question remains on the optimal configuration of the defense hole system for effective stress mitigation at the bolt-hole region and, hence, increasing the bearing capacity of particular composite bolted joints. This study presents the influence of defense hole system geometrical design on the stress reduction in a single-bolt, double-lap composite bolted joint. The nonlinear material behavior of the joint was simulated using ANSYS through a progressive failure model, considering the circumferential and radial stresses at bearing, shear-out, and net tension regions of the bolt-hole. It was found that the stress has been reduced between 2.3% and 6.1% for the narrow laminates over a range of E/ D ratios (1–5) with the benefits of the defense hole was clearly marked at DS = 2 D and DHD = 0.75 D. In contrast, for those of wider laminates, the stress reduction ranged from 1.9% to remarkably 18.6%.

Rock Failure Under Dynamic Loading Conditions

1963 ◽  
Vol 3 (01) ◽  
pp. 1-8 ◽  
Author(s):  
N.T. Burdine
Keyword(s):  
The State ◽  
Cumulative Damage ◽  
Material Behavior ◽  
Particle Orientation ◽  
Loading Conditions ◽  
Hooke’S Law ◽  
Rock Samples ◽  
Cyclic Stresses ◽  
Hooke's Law ◽  
Failure Theories

BURDINE, N.T., SOCONY MOBIL OIL CO., INC., DALLAS, TEX Abstract The present investigation is concerned with the cumulative damage to rock samples when exposed to cyclic stresses under various loading conditions. Information on the response of rocks to repetitive deformational forces is an essential prerequisite to an understanding of the fundamentals of drilling. Using a laboratory designed and constructed dynamic-stress apparatus, preliminary data were obtained on cylindrical rock samples. The experiments consist of measuring the number of cycles to failure for a given axial load ( static plus dynamic). Data were obtained for various confining and pore pressures, pore fluids (air and water), frequencies of stress application and loading procedures. The results are related to failure theories and dynamic fatigue properties of other materials. Introduction In most conventional and new drilling processes, repetitive forces are applied to the bottom of the borehole. Furthermore, in hard-rock drilling the number of applications of the forces to a particular section of rock may become excessively large. The present investigation is concerned with the cumulative damage to rocks when exposed to cyclic stresses under various loading conditions. It is believed that the experiments will lead to a better understanding of the mechanical response of rocks to particular deformational forces and to a more efficient drillingprocedure.Thepresent investigation is the initial part of a general study of the behavior of inelastic materials under static and dynamic conditions, including both theoretical and experimental studies. SURVEY OF FAILURE THEORIES OF MATERIALS Few, even phenomenological, theories on rock deformation have been established because the state of knowledge of flow, fracture and strength of rocks is largely empirical. Most of the theories that do exist were originally formulated for other materials. HOOKE'S LAW The state of stress in continuous media is completely determined by the stress tensor and the state of deformation by the strain tensor . In the linear theory of elasticity the generalized Hooke's law is ..........................(1) where the coefficients are the components of the elasticity tensor. For homogeneous and isotropic conditions the number of independent coefficients reduce to two, and Eq. 1 becomes ..................(2) in which and are Lame's constants; is the kronecker delta; and is the dilation. This simplified version of Hooke's law has been used quite extensively in geophysical research where most of the information about the mechanical properties of the earth have been obtained. However, it has only limited application in rock fatigue studies. MATERIAL BEHAVIOR Many solids obey Hooke's law at small stresses, but for higher stresses a hysteretic effect occurs due to temporary or permanent residual deformation of the solid (inelastic deformation). Such deviations in mechanical behavior exist in varying degrees in different classes of materials. Most elastic materials have a microscopic heterogeneity due either to random distribution of anisotropic particles, or due to some preferred particle orientation, or both. Other materials are quite grossly heterogeneous. And the method of formation, particularly in rocks, oftentimes creates residual stress concentrations which have complicated states of imperfect equilibrium. Also, the thermal effects resulting from structural behavior give rise to nonuniform temperature distributions and the degradation of mechanical energy. When such bodies are exposed to certain large loading conditions, the inelastic behavior is intensified so strongly that the deformation, normally brittle, becomes ductile. SPEJ P. 1^

scholarly journals Improved parallel magnetic resonance imaging reconstruction with multiple variable density sampling

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jinhua Sheng ◽  
Yuchen Shi ◽  
Qiao Zhang
Keyword(s):  
Magnetic Resonance Imaging ◽  
Variable Density ◽  
Reduction Factor ◽  
Resonance Imaging ◽  
Parallel Magnetic Resonance Imaging ◽  
Multiple Variable ◽  
Space Data ◽  
Sampling Pattern ◽  
Undersampled Data ◽  
Reduction Factors

AbstractGeneralized auto-calibrating partially parallel acquisitions (GRAPPA) and other parallel Magnetic Resonance Imaging (pMRI) methods restore the unacquired data in k-space by linearly calculating the undersampled data around the missing points. In order to obtain the weight of the linear calculation, a small number of auto-calibration signal (ACS) lines need to be sampled at the center of the k-space. Therefore, the sampling pattern used in this type of method is to full sample data in the middle area and undersample in the outer k-space with nominal reduction factors. In this paper, we propose a novel reconstruction method with a multiple variable density sampling (MVDS) that is different from traditional sampling patterns. Our method can significantly improve the image quality using multiple reduction factors with fewer ACS lines. Specifically, the traditional sampling pattern only uses a single reduction factor to uniformly undersample data in the region outside the ACS, but we use multiple reduction factors. When sampling the k-space data, we keep the ACS lines unchanged, use a smaller reduction factor for undersampling data near the ACS lines and a larger reduction factor for the outermost part of k-space. The error is lower after reconstruction of this region by undersampled data with a smaller reduction factor. The experimental results show that with the same amount of data sampled, using NL-GRAPPA to reconstruct the k-space data sampled by our method can result in lower noise and fewer artifacts than traditional methods. In particular, our method is extremely effective when the number of ACS lines is small.

Structural Response and Remaining Life of Damaged Composites

2015 ◽  
Vol 813-814 ◽  
pp. 106-110
Author(s):  
Dalbir Singh ◽  
C. Ganesan ◽  
A. Rajaraman
Keyword(s):  
Hybrid Approach ◽  
Experimental Studies ◽  
Structural Response ◽  
Material Behavior ◽  
Experimental Results ◽  
Life Assessment ◽  
Nonlinear Material ◽  
Remaining Life ◽  
Design Effectiveness ◽  
Remaining Life Assessment

Composites are being used in variety of applications ranging from defense and aircraft structures, where usage is profuse, to vehicle structures and even for repair and rehabilitation. Most of these composites are made of different laminates glued together with matrix for binding and now-a-days fibers of different types are embedded in a composite matrix. The characterizations of material properties of composites are mostly experimental with analytical modeling used to simulate the system behavior. But many times, the composites develop damage or distress in the form of cracking while they are in service and this adds a different dimension as one has to evaluate the response with the damage so that its performance during its remaining life is satisfactory. This is the objective of the present study where a hybrid approach using experimental results on damaged specimens and then analytical finite element are used to evaluate response. This will considerably help in remaining life assessment-RLA- for composites with damage so that design effectiveness with damage could be assessed. This investigation has been carried out on a typical composite with carbon fiber reinforcements, manufactured by IPCL Baroda (India) with trade name INDCARF-30. Experimental studies were conducted on undamaged and damaged specimens to simulate normal continuous loading and discontinuous loading-and-unloading states in actual systems. Based on the experimental results, material characterization inputs are taken and analytical studies were carried out using ANSYS to assess the response under linear and nonlinear material behavior to find the stiffness decay. Using stiffness decay RLA was computed and curves are given to bring the influence of type of damage and load at which damage had occurred.

Analysis of Thermal Stresses and Residual Stress Changes in Railroad Wheels Caused by Severe Drag Braking

1977 ◽  
Vol 99 (1) ◽  
pp. 18-23 ◽  
Author(s):  
M. R. Johnson ◽  
R. E. Welch ◽  
K. S. Yeung
Keyword(s):  
Residual Stress ◽  
Stress Field ◽  
Yield Point ◽  
Thermal Stresses ◽  
Material Behavior ◽  
Nonlinear Material ◽  
Residual Stress Field ◽  
Thermal Stress Field ◽  
Stress Changes ◽  
Railroad Wheels

A finite-element computer program, which takes into consideration nonlinear material behavior after the yield point has been exceeded, has been used to analyze the thermal stresses in railroad freight car wheels subjected to severe drag brake heating. The analysis has been used with typical wheel material properties and wheel configurations to determine the thermal stress field and the extent of regions in the wheel where the yield point is exceeded. The resulting changes in the residual stress field after the wheel has cooled to ambient temperature have also been calculated. It is shown that severe drag braking can lead to the development of residual circumferential tensile stresses in the rim and radial compressive stresses in the plate near both the hub and rim fillets.

Response surface method strategies coupled with NLFEA for structural reliability analysis of prestressed bridges

2021 ◽  
Author(s):  
Silvia J. Sarmiento Nova ◽  
Jaime Gonzalez-Libreros ◽  
Gabriel Sas ◽  
Rafael A. Sanabria Díaz ◽  
Maria C. A. Texeira da Silva ◽  
...  
Keyword(s):  
Reliability Analysis ◽  
Response Surface ◽  
Response Surface Method ◽  
Structural Reliability ◽  
Limit State ◽  
Material Behavior ◽  
Nonlinear Material ◽  
State Function ◽  
Surface Method ◽  
Highly Nonlinear

<p>The Response Surface Method (RSM) has become an essential tool to solve structural reliability problems due to its accuracy, efficacy, and facility for coupling with Nonlinear Finite Element Analysis (NLFEA). In this paper, some strategies to improve the RSM efficacy without compromising its accuracy are tested. Initially, each strategy is implemented to assess the safety level of a highly nonlinear explicit limit state function. The strategy with the best results is then identified and used to carry out a reliability analysis of a prestressed concrete bridge, considering the nonlinear material behavior through NLFEA simulation. The calculated value of &#120573; is compared with the target value established in Eurocode for ULS. The results showed how RSM can be a practical methodology and how the improvements presented can reduce the computational cost of a traditional RSM giving a good alternative to simulation methods such as Monte Carlo.</p>

scholarly journals Finite Element Software for Rubber Products Design

2018 ◽  
Vol 3 (1) ◽  
pp. 13-20
Author(s):  
Dávid Huri
Keyword(s):  
Finite Element ◽  
Complex Analysis ◽  
Large Deformations ◽  
Material Behavior ◽  
Nonlinear Material ◽  
Material Models ◽  
Finite Element Software ◽  
Highly Nonlinear ◽  
Wide Range ◽  
Different Types

Automotive rubber products are subjected to large deformations during working conditions, they often contact with other parts and they show highly nonlinear material behavior. Using finite element software for complex analysis of rubber parts can be a good way, although it has to contain special modules. Different types of rubber materials require the curve fitting possibility and the wide range choice of the material models. It is also important to be able to describe the viscoelastic property and the hysteresis. The remeshing possibility can be a useful tool for large deformation and the working circumstances require the contact and self contact ability as well. This article compares some types of the finite element software available on the market based on the above mentioned features.

scholarly journals Meshless Radial Point Interpolation Method for Hyperelastic Materials

10.29007/r7sp ◽  
2020 ◽  
Author(s):  
Trong Khiem Bui ◽  
Vu Tuong Nguyen ◽  
Thanh Nha Nguyen ◽  
Tich Thien Truong
Keyword(s):  
Large Deformation ◽  
Interpolation Method ◽  
Biological Tissues ◽  
Material Behavior ◽  
Nonlinear Material ◽  
Radial Point Interpolation Method ◽  
Hyperelastic Materials ◽  
Radial Point Interpolation ◽  
Point Interpolation Method ◽  
Point Interpolation

Hyperelastic materials are special types of material that tends to behavior elastically when they are subjected to very large strains. These materials show not only the nonlinear material behavior but also the large deformation and stress-strain relationship is derived from a strain energy density function. Hyperelastic materials are widely used in many applications such as biological tissues, polymeric foams, and moreover. Neo - Hookean is a material model for hyperelastic solid which contains only two material parameters: bulk modulus and shear modulus. In the field of numerical analysis, the radial point interpolation method (RPIM) is a well-known meshfree method based on Garlekin's weak form. With the property of “free of mesh”, the RPIM approach shows its advantage for large deformation problems. In this study, a meshless radial point interpolation method is applied to demonstrate the elastic response of rubber-like materials based on the Mooney- Rivlin model. The obtained results are compared with the reference solutions given by other methods to verify the accuracy of the proposed method.

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