bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two-Dimensional Geometrically Nonlinear Finite Element Formulation for Analysis of Straight Pipes
Authors: Attia Saher , Mohareb Magdi , Martens Michael , Yoosef Ghodsi Nader , Li Yong , Adeeb Samer 
Published: October 2020

Abstract
The paper presents a new and simple geometrically nonlinear finite element formulation to simulate the structural response of straight pipes under in-plane loading and/or internal pressure. The formulation employs the Green-Lagrange strain tensor to capture finite deformation-small strain effects. Additionally, the First Piola-Kirchhoff stress tensor and Saint Venant-Kirchhoff constitutive model are adopted within the principle of virtual work framework in conjunction with a total Lagrangian approach. The formulation is applied for a cantilever beam under three loading conditions. Results are in good agreement with shell models in ABAQUS. Although the solution is based on a single element, the formulation provides reasonable displacement and stress predictions.
Examination of the Transferability of CTOA From Small-Scale DWTT to Full-Scale Pipe Geometries Using a Cohesive Zone Model
Authors: Bassindale Chris , Wang Xin , Tyson William R. , Xu Su 
Published: October 2020

Abstract
In this work, the cohesive zone model (CZM) was used to examine the transferability of the crack tip opening angle (CTOA) from small-scale to full-scale geometries. The pipe steel STPG370 was modeled. A drop-weight tear test (DWTT) model and pipe model were studied using the finite element code ABAQUS 2017x. The cohesive zone model was used to simulate crack propagation in 3D. The CZM parameters were calibrated based on matching the surface CTOA measured from a DWTT finite element model to the surface CTOA measured from the experimental DWTT specimen. The mid-thickness CTOA of the DWTT model was in good agreement with the experimental value determined from E3039 and the University of Tokyo group’s load-displacement data. The CZM parameters were then applied to the pipe model. The internal pressure distribution and decay during the pipe fracture process was modeled using the experimental data and implemented through a user-subroutine (VDLOAD). The mid-thickness CTOA from the DWTT model was similar to the mid-thickness CTOA from the pipe model. The average surface CTOA of the pipe model was in good agreement with the average experimental value. The results give confidence in the transferability of the CTOA between small-scale specimens and full-scale pipe.
Frequency Dependency of Beam Collapse due to Vibration Loads
Authors: Sasaki Ryunosuke , Ichimiya Masakazu , Lyu Jinqi , Kasahara Naoto 
Published: October 2020

Abstract
Since the accident at the Fukushima Daiichi power plant, in addition to “design to prevent accidents”, “mitigating the severe accident” has come to be emphasized. Thus, it is necessary to evaluate the actual failure mode under beyond design basis events (BDBEs). In this study, authors focus on the failure mode of piping in nuclear power plants under excessive earthquakes. The piping design of nuclear power plants has been conservative assuming that seismic load acts as load-controlled and the collapse happens by maximum acceleration. However, the test conducted by Electric Power Research Institute (EPRI) confirmed that when excessive vibration load was applied to the piping with the elbow, ratchet deformation occurred with time and eventually collapsed. Unfortunately, this failure mechanism is not clear, so it is highly important to consider the actual failure mode, namely ratchet deformation leading to collapse. Authors tried to clarify the mechanism of ratchet deformation by experiments and analyses of inputting acceleration to a beam simulating piping. According to these results, it is identified that ratchet deformation is likely to occur when the vibration load whose frequency is lower than resonance frequency is applied, and is difficult to occur on the higher frequency area. Hereafter, the ratio of the frequency of vibration load to the natural frequency of beams is referred as “frequency ratio”. In this study, half-cycle vibration load was applied to the beam, and the frequency dependence of the collapse phenomenon was investigated.
Acoustic Emission Monitoring During Fatigue Crack Growth in Standard C(T) and Miniature Single Edge Notch Tension Specimens
Authors: Prakash Raghu V. , Mukhopadhyay Chandan K. , Pokharkar Prathmesh , Thomas Manuel 
Published: October 2020

Abstract
The fatigue crack growth rate studies in a structural alloy has been carried out using ASTM E-647 standard compact tension (C(T)) specimens and miniature single edge notch tension specimens (SEN(T)) at two different stress ratios of 0.1 and 0.7. Standard C(T) specimen had a dimension of 63.5 × 61 × 8 mm thickness while the miniature SEN(T) specimen had a size of 20 mm effective length × 10 mm wide and 0.7 mm thickness. A starter notch of 0.5 mm was cut using wire EDM process to initiate fatigue crack growth in miniature SEN(T) specimen. A special fixture was designed for testing the miniature SEN(T) specimen.
During the fatigue crack growth experiments, Acoustic Emission (AE) activity was monitored on-line using AE sensors from Physical Acoustics, Mistras Group, USA. For the experiments on standard C(T) specimens, a standard probe (R15A) of 15 mm diameter was used, while for small size compact tension specimen, a Nano30 AE probe was used. The crack growth was monitored by visual methods as well as by compliance technique. The cumulative counts and absolute energy information obtained during fatigue crack growth testing was used to correlate the crack growth rate with acoustic emission activity. Empirical fit of data was used to obtain cross-correlation between crack growth rate and AE parameters for both the specimen geometries. The study suggested that suitable selection and placement of sensors is essential to obtain good results using AE sensor technique.
Correlation Analysis Between Time-Dependent Creep Crack-Tip Stress and Constraint Effect on Creep Crack Initiation Time
Authors: Lee Seung-Ho , Jung Hyun-Woo , Kim Yun-Jae , Nikbin Kamran , Ainsworth Robert A. 
Published: October 2020

Abstract
In this study, to qualify the constraint effect on creep crack initiation, the correlation analysis between proposed constraint parameter Q’ using time-dependent creep crack-tip stress and creep crack initiation time variable Ai was performed. Ai implies the influence of constraint effect on creep crack initiation. The procedure to calculate the Ai and the Q’-parameter was presented. To evaluate various status of constraint effect, creep crack growth tests for twenty-one compact tension specimens of Type 316H stainless steel at 550°C were investigated. The results of correlation analysis explain the reason for the different initiation time at the same C* level in respect of constraint effect.
Fatigue Life Prediction of Notched Specimen Based on Stress Gradient
Authors: Takanashi Masahiro 
Published: October 2020

Abstract
Many failure accidents have indicated fatigue as the primary cause for the failure of a machine or structure. In general, the origin of failure is a structural discontinuous part such as a welded joint or a notched member that causes stress concentration. While designing such a component, a finite element analysis (FEA) has to be conducted, and the peak stress has to be compared with a design fatigue curve obtained from small-sized specimens to evaluate whether the component satisfies the design life. However, it is known that a fatigue life prediction at a stress concentration part based on a peak stress always provides an excessively conservative estimation. This is due to the stress gradient of the component. This paper discusses the stress-gradient approach to eliminate the conservatism and rationalize a fatigue design. Using literature test data, the relationship between the stress gradient calculated using FEA, and the fatigue strength reduction ratio was determined. Later, a fatigue test was conducted on a notched specimen of low-alloy steel to verify the stress-gradient approach, and the fatigue life of the notched specimen was predicted considering the stress gradient at the notch root. The predicted fatigue life agreed well with the experimental results.
Comparison of Stress Intensity Factor Coefficients for Plates and Cylinders Under Membrane Stress
Authors: Lee Darrell R. , Cipolla Russell C. , Liu Michael C. 
Published: October 2020

Abstract
Until the 2000 Edition of API-579 [1], the geometries (Ri/t, a/ℓ, a/t in cylinders or spheres) for which a complete set of stress intensity factor influence coefficients (Gi) existed was limited. To bridge that gap, many analysts have used the G0 and G1 coefficients for flat plate geometries to represent axial or circumferential flaws in cylinders. Because the cylindrical geometry contains additional stiffness effects due to curvature, it was generally assumed that the plate geometry (Ri/t = ∞) will be bounding and therefore conservative [2].
Since 2007, extensive sets of Gi coefficient have been published for plates, cylinders and spheres based on finite element models. These coefficients for cylinders have been curve fit and are available in Appendix A of the ASME Boiler and Pressure Vessel Code, Section XI [3]. This paper compares the G0 coefficients at the deepest point of semi-elliptical flaws from a plate to those for an OD and ID circumferential flaw in a cylinder to confirm the conservatism of the G0 coefficients from a plate geometry.
Damage to Oil Tanks Caused by Severe Strong Ground Motion due to the 2018 Hokkaido, Japan Iburi-Tobu Earthquake (Mw6.6)
Authors: Hatayama Ken , Nishi Haruki , Hayashi Masahiko , Tokutake Koya 
Published: October 2020

Abstract
Damage and influences to oil tanks caused by severe strong ground motion due to a large earthquake (Mw6.6) that occurred in the district of Iburi-tobu, Hokkaido, Japan on September 6, 2018 are reported in this paper. In the vicinity of the seismic source region, two large-scale crude-oil storage bases are located. The neighboring two bases had in total 86 large oil storage tanks with a capacity of 115,000 m3. The oil storage bases were hit by strong ground motion with peak ground accelerations of 590 to 1,570 cm/s2 and with peak ground velocities of 50 to 80 cm/s. Shell plates of a small bunker A tank with a capacity of 306 m3 suffered diamond buckling and elephant-foot buckling. No large oil storage tanks lost their function of oil storage despite of the severe strong ground motion. However, most of them splashed oil from the gap between the floating roof and the shell plate, and many of them had damage to their pontoons, gauge poles, guide poles, rolling ladders, liquid-level meters, and shoulders of foundation. One of the 115,000-m3-in-capacity tanks was equipped with a displacement gauge system to measure uplift of the bottom of the shell plate from the shoulder of tank foundation. The system recorded a maximum uplift of 4.4 cm. This is the world’s first record of uplift of a large tank caused by a natural earthquake.
Hydrogen Embrittlement Evaluation of Different Heats of AISI 8630 Steel in Subsea Applications
Authors: Li Xiaoji , Thodla Ramgopal , Alves Fabio , Castro Mario , Venkatesh Anand 
Published: October 2020

Abstract
AISI 8630 steel used in subsea applications is subject to hydrogen embrittlement from externally applied cathodic protection. In this work, susceptibility variation on three grades of 8630 steel of different yield strength (YS), 100 ksi, 110 ksi and 120 ksi, were evaluated in terms of fracture toughness. Two different testing methods, slow rising displacement and incremental step loading testing, were used to generate J-R curves and determine the fracture toughness. The tests were performed at 40°F in air and simulated sea water (3.5 wt.% NaCl) with applied CP of −1050 mV SCE.
The normalized fracture toughness values are discussed in this work. In all three grades, regardless of the test methods, the environmental toughness under CP conditions were significantly lower than the in-air values indicating that they are susceptible to hydrogen embrittlement. Effect of YS on the hydrogen embrittlement was also observed. The incremental step loading technique showed that Jth and the J-R curve slope decreased as the YS increases. The rising displacement method also clearly showed the lowest toughness and the flattest J-R curve slope in the highest strength grade (120ksi) despite showing similar performance between the 100ksi and 110ksi grades. The true stress-true strain analysis showed different strain hardening behavior among the three grades that may suggest the strain hardening plays a role in influencing the hydrogen embrittlement behavior among the grades. Overall, slight variation could be observed in the results from the two test methods which, however, did not appear to be biased against each other in determining lower bounds of the results.
Mechanical Properties of Ion-Irradiated Stainless Steel Determined by Nanoindentation Tests and Finite Element Analyses
Authors: Sim Jae Min , Chang Yoon-Suk , Kong Byeong Seo , Jang Changheui 
Published: October 2020

Abstract
While austenitic stainless steels (ASSs) have been widely adopted for reactor vessel internals because of their excellent material properties, diverse ageing-related degradation may occur due to high temperature, corrosive and neutron radiation environments during operation. In particular, since the change of mechanical properties is a major concern in long-term operation but it is difficult to prepare and handle standard specimens influenced by neutrons, most of experimental researches for enhanced understanding of the radiation effects have been focused on high-energetic ion-irradiation and tests of small specimens.
In this study, systematic finite element analyses were carried out to quantify changing mechanical properties based on both virgin and ion-irradiated nanoindentation test data of typical ASS material. First of all, numerical analysis was carried out to obtain unirradiated material constitutive parameters by using trial set along the miniature specimen and comparing test data, and then indentation stress-strain (ISS) curve was derived. Subsequently, ISS was converted into uniaxial stress-strain response taking into account simple correlation. Finally, with regard to the irradiated material, similar analytical procedures were established. 304 SS was irradiated with 2 MeV proton and radioactivity is being measured. Comparison between analysis result and experimental one will be carried out, of which details and key findings will be discussed.
Validation of the Incremental Step Loading Technique Application to Small Punch Tests in Aggressive Environments in X80 Steel
Authors: Arroyo B. , Andrea L. , González P. , Álvarez J. A. , Cicero S. , Fernández A. , Lacalle R. 
Published: October 2020

Abstract
The Small punch test, which consists on punching a small plane specimen up to failure, is a technique to be taken into account for the estimation of mechanical properties when there is shortage of material. In recent works it has been applied to the estimation of mechanical properties steels in aggressive environments.
In aggressive environments, tests under a constant load are usually employed for the threshold stress determination, but this a slow and sometimes inaccurate technique. The standard ASTM F1624 solves these issues; it consists on applying steps of constant loads subsequently increased up to the specimen’s failure. In a previous work, it was indicated how to implement this technique for Small Punch testing of steels in hydrogen embrittlement scenarios, adapting the steps duration. This proposal allows to obtain a threshold load by using at least 3 specimens in a total time of around a week.
In the present work, the incremental step loading technique from ASTM F1624 standard is applied to the Small Punch test in order to estimate tensile threshold stress of a X80 high strength steel in hydrogen embrittlement environments by cathodic polarization in an acid electrolyte. Regular standard tests on cylindrical tensile specimens were carried out following the ASTM F1624 standard, in order to validate the methodology proposed.
Fatigue Life Estimation Using Frequency Domain Technique and Probabilistic Linear Cumulative Damage Model
Authors: Pascualinotto Junior Vagner , Burgos Diego Felipe Sarzosa 
Published: October 2020

Abstract
Engineering critical structures, such as pressure vessels and pipelines, are designed to withstand a variety of in-service loading specific to their intended application. Random vibration excitation is observed in most of the structural component applications in the offshore, aerospace, and nuclear industry. Likewise, fatigue life estimation for such components is fundamental to verify the design robustness assuring structural integrity throughout service. The linear damage accumulation model (Palmgren-Miner rule) is still largely used for damage assessment on fatigue estimations, even though, its limitations are well-known. The fact that fatigue behavior of materials exposed to cyclic loading is a random phenomenon at any scale of description, at a specimen scale, for example, fatigue initiation sites, inclusions, defects, and trans-granular crack propagation are hardly predicted, indicates that a probabilistic characterization of the material behavior is needed. In this work, the methodology was applied to a Titanium alloy structural component. Low alloyed titanium alloys have no tendency to corrosion cracking in high-temperature high-pressure water containing impurities of chloride and oxygen found in a steam generator of nuclear power plants. The inherent uncertainties of the fatigue life and fatigue strength of the material are characterized using the random fatigue limit (RFL) statistic method. Furthermore, a frequency domain technique is used to determine the response power spectrum density (PSD) function of a structural component subjected to a random vibration profile excitation. The fatigue life of the component is then estimated through a probabilistic linear damage cumulative model.
Numerical Simulation of the Assembly Process of Bolted Flange Joints Used in Rotating Machinery
Authors: Zhu Linbo , Bouzid Abdel-Hakim , Hong Jun , Shi Zhenming 
Published: October 2020

Abstract
Bolted joints are widely used to connect structural components in rotating machinery. However, the initial tightening of the bolts is a delicate operation because it is extremely difficult to achieve the target load and uniformity due to elastic interaction. The scatter in the bolt preload has a major impact on the concentricity and consequently the dynamic behavior of rotating machinery. The risk of failure due to vibration and fatigue under service loading becomes an issue. This paper treats the effect of elastic interaction on the eccentricity during the tightening of bolted joints of rotating machinery using finite element (FE) method. In this regard, a two-component bolted flange joint of a high pressure compressor (HPC) of an aero-engine is investigated. The component surface tolerances measured by Rotary Precision Instruments (RPI) are taken into account in the numerical simulation. A method is proposed to calculate the concentricity of components obtained from the radial runout data based on the Least Square method (LSM). The scatter in bolt preload under different interference fit, surfaces tolerance, initial preload, and tightening sequence are evaluated. Furthermore, the influence of these structures and tightening sequence parameters on the concentricity are investigated. The validity of the finite element analysis is supported by experimental tests conducted on scaled specimens of HPC. This study can provide guidance and enhance the dynamic performance of bolted joints for rotating machinery.
Elastic-Plastic Analogy for Examination of Softening Response for Strip Yield Models
Authors: Metzger Don , Reinhardt Wolf 
Published: October 2020

Abstract
The manner in which the spread of inelastic deformation of a softening cohesive zone affects the load capacity is examined. The analysis makes use of an elastic-plastic analogy to the strip yield model applied to pure bending. The example of pure bending is one case where inelastic deformation contributes to enhancing the load capacity. The analytical solution to the elastic-plastic case is developed for zero hardening (baseline for strip yield case for which analytical solution is known) as well as for a range of linear softening rates. Evaluation of the results shows that the maximu m bending load capacity is always reached before the stress at the surface becomes zero.
Evaluation of High Temperature Material Models for High Temperature Advanced Reactor Component Analysis
Authors: Casagranda A. , Pitts S. A. , Spencer B. W. , Chakraborty A. , Messner M. C. , Capolungo L. 
Published: October 2020

Abstract
The high temperature environments in proposed advanced reactor designs pose unique challenges for the integrity of structural components. Capabilities to model metals in this environment are being developed in Grizzly, a finite element-based structural simulation code developed at Idaho National Laboratory. To represent the constitutive behavior of metals at high temperatures, Grizzly offers two distinctly different approaches.
The first is to use phenomenological engineering models with a unified representation of creep and plasticity. These models are provided through a library developed at Argonne National Laboratory. These models represent the effects of multiple important phenomena on the aspects of the material response important to engineering analysis and are calibrated to engineering-scale material data. The second modeling approach is being developed at Los Alamos National Laboratory and is based on mesoscale models that directly account for the effects of material texture. These models directly represent the underlying physical phenomena that affect the engineering-scale material response. Through the use of data analytics, reduced order models based on the mesoscale models have been developed. These models can be efficiently used in engineering calculations, while faithfully representing the behavior of the high fidelity mesocale models. This paper provides brief summaries of both modeling approaches, and demonstrates their application on a common set of bench-mark problems to assess their applicability to component-level simulations.
Development of “Material Specific” Creep Continuum Damage Mechanics-Based Constitutive Equations
Authors: Vega Ricardo , Cano Jaime A. , Stewart Calvin M. 
Published: October 2020

Abstract
The objective of this study is to introduce a method for creating “material specific” creep continuum damage mechanics-based constitutive models. Herein, material specific is defined as a constitutive model based on the mechanism-informed minimum creep strain rate (MCSR) equations found in deformation mechanism maps and calibrated to available material data. The material specific models are created by finding the best MCSR model for a dataset. Once the best MCSR model is found, the Monkman Grant inverse relationship between the MCSR and rupture time is employed to derive a rupture equation. The equations are substituted into continuum damage mechanics-based creep strain rate and damage evolution equations to furnish predictions of creep deformation and damage. Material specific modeling allows for the derivation of creep constitutive models that can better the material behavior specific to the available data of a material. The material specific framework is also advantageous since it has a systematic framework that moves from finding the best MCSR model, to rupture time, to damage evolution and, creep strain rate. Data for Alloy P91 was evaluated and a material specific constitutive model derived. The material specific model was able to accurately predict the MCSR, creep deformation, damage, and rupture of alloy P91.