Elastic Stress Analysis Research Articles

ANALYTICAL AND NUMERICAL INVESTIGATION OF ELASTIC STRESSES IN THERMOPLASTIC MATRIX COMPOSITE DISCS UNDER TEMPERATURE EFFECT

In this study, elastic stress analysis was performed on thermoplastic composite discs. The modulus of elasticity of thermoplastic composite discs is also different from each other. Our goal is to study elastic stretching. The field of application of primitive stresses caused by uneven temperature distribution in engineering is quite large. Under the parabolic temperature distribution of the disks, radial stresses formed on the inner and outer parts of the disks were calculated by assuming that the modulus of elasticity does not change with temperature at temperatures of 30 °C, 60 °C, 90 °C, 120 °C on the inner and outer surfaces of the disk. During the study, analytical and numerical analysis was performed using a computer program and mathematically modeled ANSYS programs. Both methods give similar results. In other words, the differences analytical and numerical results can be ignored. At the end of this study, it was determined that the radial and tangential stress values were higher at high temperatures than at low temperatures. It has been established that tangential stresses are much larger than radial stresses. The purpose of this article is to study the behavior of the thermal load on two different thermoplastic disks.

Failure Mode Determination of American Petroleum Institute 12F Shop-Welded Tanks With a New Roof-to-Shell Junction Detail

Abstract The American Petroleum Institute (API) 12F is the specification for vertical, aboveground shop-welded storage tanks published by the API. The nominal capacity for the twelve tank designs given in the current 13th edition of API 12F ranges from 90 bbl. (14.3 m3) to 1000 bbl. (159 m3). The minimum required component thickness and design pressure levels are also provided in the latest edition. This study is a part of a series research project sponsored by API that dedicates to ensure the safe operation of API 12 series storage tanks. In this study, the twelve API 12F tank designs presented in the latest edition are studied. The elastic stress analysis was conducted following the procedures presented in the ASME Boiler and Pressure Vessel Code 2019, Section VIII, Division 2 (ASME VIII-2). The stress levels at the top, bottom, and cleanout junctions subject to the design pressures are determined through finite element analysis (FEA). The bottom uplift subjected to design pressures are obtained, and the yielding pressure at the roof-shell and shell-bottom junctions are also determined. The specific gravity of the stored liquid is raised from 1.0 to 1.2 in this study. A new roof-shell attachment detail is proposed, and a 0.01 in. (0.254 mm) gap between the bottom shell course and the bottom plate is modeled to simulate the actual construction details. In addition, the flat-top rectangular cleanout presented in the current edition of API 12F is modeled. Moreover, various thickness combinations are considered to further investigate the effect due to different component thicknesses.

Structural Analysis on the Coil Spring of Motorcycle Suspension System

The motorcycle suspension system is one of the crucial components. It helps to support the motorcycle’s weight, isolate the vibration level caused by road imperfection, and keep the wheel in contact with the road surface. Therefore, the performance of suspension system needs to be enhanced to ensure the ride comfort and safety of riders. Coil spring is one of the essential parts of motorcycle suspension system. In this study, two different materials of coil spring are being focused include steel alloy and carbon fiber reinforced plastic (CFRP). The geometry of the coil spring is the existing design in the market. The static structural analyses are carried out to determine the directional deformation of y-axis, equivalent stress and equivalent elastic stress analysis of the corresponding coil spring material. The obtained results are discussed. It is found that the steel coil spring has better performance for the existing coil spring design. The directional deformation, equivalent stress and equivalent elastic strain of steel coil spring are considered at the lower side, which is 0.029357mm, 2003MPa and 0.010051mm/mm respectively. In this study, it is observed that the number of turns of coil spring should be increased to enhance the performance of CFRP coil spring.

Efficient elastic stress analysis method for piping system with wall-thinning and reinforcement

A piping system stress analysis need to be re-performed for structural integrity assessment after reinforcement of a pipe with significant wall thinning. For efficient stress analysis, a one-dimensional beam element for the wall-thinned pipe with reinforcement needs to be developed. To develop the beam element, this work presents analytical equations for elastic stiffness of the wall-thinned pipe with reinforcement are analytically derived for axial tension, bending and torsion. Comparison with finite element (FE) analysis results using detailed three-dimensional solid models for wall-thinned pipe with reinforcement shows good agreement. Implementation of the proposed solutions into commercial FE programs is explained.

Two-dimensional Mapping of Bulk Residual Stress Using Cut Mouth Opening Displacement

BackgroundPrior work described an approach for mapping the two-dimensional spatial distribution of biaxial residual stress in plate-like samples, the approach combining multiple slitting measurements with elastic stress analysis. Objective This paper extends the prior work by applying a new variation of the slitting method that uses measurements of cut mouth opening displacement (CMOD) rather than back-face strain (BFS). MethodsFirst, CMOD slitting is validated using an experiment where: BFS and CMOD are measured simultaneously on the same sample during incremental slitting; two residual stress profiles are computed, one from the BFS data and a second from the CMOD data; and the two residual stress profiles are compared. Following validation, multiple adjacent CMOD slitting measurements are used to construct two-dimensional maps of residual stress in plates cut from quenched aluminum. ResultsThe two residual stress versus depth profiles, each computed separately from BFS or CMOD data, are in agreement, with compression near the plate boundaries (-150 MPa) and tension near the plate center (100 MPa); differences between the two stress profiles have a maximum of 25 MPa and a RMS of 7.2 MPa. Repeated biaxial residual stress mapping measurements show the CMOD technique is repeatable, and complementary contour method measurements show the mappings are valid. Aspects of CMOD and BFS deformations during slitting are also described and show they are generally complementary but that CMOD slitting is favorable in narrow samples.

Study on mechanical stress of semicircular and rectangular channels in printed circuit heat exchangers

Recuperator and precooler are key components of supercritical CO2 Brayton cycle. One of promising candidates is printed circuit heat exchanger (PCHE) due to its high compactness and heat transfer performance. However, both of them operate at high pressure, which is a great challenge for their safety. Therefore, accurate and quick mechanical stress analysis is important for PCHE design. In this work, a simplified mechanical stress method based on homogenization method is proposed for PCHE. An optimized rectangular channel, which has the same mechanical characteristics with a semicircular channel is proposed. Then the PCHE numerical model is constructed, and the mechanical stress of PCHEs with semicircular and rectangular channels is examined by elastic stress analysis. The results show that the maximum stresses of the semicircular channel, simplified rectangular channel and optimized rectangular channel are 151.6 MPa, 253.0 MPa and 184.3 MPa, respectively. The mechanical characteristics of the optimized rectangular channel are close to the corresponding semicircular channel, which can improve the design accuracy and is benefit for the weight and volume reduction of PCHE.

3D elastic dental analysis by a local RBF collocation method

In this paper, the local radial basis function collocation method (LRBFCM) is presented to analyze 3D elastic problems of complex geometries. In particular, a real tooth domain built by cone beam computer tomography (CBCT) data is considered. The reconstruction process of a tooth shape, the choice of the local influence domain in the LRBFCM, as well as the treatments of the boundary conditions are detailed described in this paper. Linear elastic analyses of five different examples are carried out to validate the effectiveness of the proposed approach. The stress difference between a tooth with the dental caries and a healthy tooth is investigated and discussed by the 3D elastic deformation and stress analysis.

Secondary Stress Weighting Factor and Plastic Reduction Factor of Surface Cracked Pipes Under Bending

Abstract In piping design analysis, the secondary stresses (displacement controlled) may have different design limits than primary stresses (load-controlled stresses). The current design limits for secondary stresses are based on elastic stress analysis. But realistically, a flaw in the piping system can cause nonlinear behavior due to the plasticity at the crack plane as well as in the adjacent uncracked-piping material. Hence, the actual stresses in a cracked piping system, which are elastic-plastic, are different than the design stresses, which are elastically calculated. To assess margins in the secondary stresses calculated using elastic stress analysis in pipe flaw evaluation, two parameters are defined in this paper. The first one is the secondary stress weighting factor (SSWF) on total stress, which is defined as the ratio of actual elastic-plastic stresses in a system to the elastic design stress. An alternative approach to applying margins on secondary stresses is to use a reduction factor only on stresses above the yield stress called plastic reduction factor (PRF). In this paper, a methodology developed to determine these factors for circumferential surface-cracked TP304 stainless steel pipes subjected to bending loads at ambient temperature is described. Four-point-bend tests are conducted on pipes with varying circumferential surface-crack lengths and depths. The moments and rotations needed for the pipe failure for different crack sizes are determined and compared to elastically calculated moments and rotations to establish margins.

Fatigue of wire+arc additive manufactured Ti-6Al-4V in presence of process-induced porosity defects

Currently, additive manufactured titanium alloy Ti-6Al-4V predominantly fails from process-induced defects, when subjected to cyclic loading in the polished condition. These defects not only lead to premature failure, but also contribute to the significant dispersion of fatigue life commonly seen in metal additive manufacturing. In this work, we have studied the source of dispersion and the influence of pore size on fatigue life using samples from the standard processing route and samples with intentionally introduced porosity defects. According to the fracture surface study, contrary to the common belief, the source of dispersion is primarily the pore location, e.g. surface or embedded pore, rather than the pore size. In the case of embedded pores as the failure source, a threshold pore size of approximately 85 μm was observed, below which the wrought level fatigue performance was achieved. For surface pores above the threshold size, fatigue life was reduced by two orders of magnitude, but remained unchanged, even though crack initiating pore size increased roughly by a factor of four. This experimental observation was supported by local elastic stress analysis, which indicated that pores above a certain size could behave like micro-notches suggesting the popular Kitagawa-Takahashi diagrams should be presented with a horizontal asymptote for this alloy.

Improvement of structural characteristics of composite thin-walled beams using variable stiffness concept via curvilinear fiber placement

This study presents the use of variable stiffness concept via curvilinear fiber placement to achieve improved structural characteristics in composite thin-walled beams (TWBs). The TWB used in the study is constructed in circumferentially asymmetric stiffness (CAS) configuration. The variation of fiber angles along the span and the width of the TWB is included by defining two fiber path functions. A parametric study is performed to investigate the effects of different fiber paths on the structural performance metrics including frequency spacing, unit twist, and critical buckling load. For this purpose, a semi-analytical solution method is developed to conduct free vibration, deformation, and buckling analyses of the TWB with curvilinear fibers. The semi-analytical method is validated with several finite element (FE) analyses performed using ABAQUS. Elastic stress analyses of TWBs with selected fiber paths subjected to simplified distributed loading are also conducted using the FE method, and a ply failure criterion is applied to evaluate the strength of these TWBs. Overall results show that curvilinear fiber placement varied along the span leads to greater structural performance for a composite TWB than the straight fiber configuration.

Brittle fracture assessment of API 12F shop-welded tanks with a new roof-to-shell junction detail

Temporary production storage is largely needed in the oil and gas industry, thus, storage tanks that have the capability to sustain the normal operation condition are needed. The American Petroleum Institute (API) specification 12F provides twelve shop-welded tank designs that can accommodate storage and operational pressure needs of the facility requires temporary production storage. The nominal capacity of these twelve designs ranges from 90 bbl. (14.3 m3) to 1000 bbl. (158.99 m3). These API 12F tanks are typically fabricated in shop and transported to facilities of needs, they are relatively smaller than tank designs provided in API 12D, which is the specification of field-welded storage tanks for production liquids. The brittle fracture assessment is conducted following FAD technique adopted by API 579, with updated operational pressure in the API 12F standard published in 2019. The specific gravity of the stored liquid is assumed to be 1.2 and more component thickness combinations are under consideration in this study, thus, effects of internal pressure, hydrostatic pressure, and component thickness to brittle fracture behavior are investigated. The stresses at roof-shell joint (top junction), shell-bottom plate (bottom junction), and cleanout junction are obtained using finite element analysis approach. The top junction and bottom junction are studied under axisymmetric idealization; thus, the axisymmetric models are generated. The cleanout junction is studied by using sub-modeling technique. Stress classification is performed after performing elastic stress analysis, the results are then used to evaluate brittle fracture behavior with assuming operating at a location with one-day mean temperature of −55 °F (−48.3 °C). The report presents the results and discussion obtained from the brittle fracture assessment of the twelve API 12F tank designs.

Fatigue performance evaluation of plate and shell heat exchangers

Fatigue life of plate and shell heat exchangers has been determined by experiments. Tests occurred with the aid of a pneumatic-hydraulic setup in which plate pack samples were internally pressurized by water. The samples were exposed to cyclic pressure loads varying from ambient to service pressure in the range 1.0–1.4 MPa, typical operating pressure range of crude oil production sites. Stress determination was possible due to strain gauge measurements. A heterogeneous stress field occurs along the corrugated plate due to its complex geometry. The external welded region is the preferential failure location. An average stress-life curve has been provided with 50% failure probability in accordance to ISO-12107. Fatigue strength reduction factors at the critical welded locations were determined via elastic stress analysis as proposed by ASME procedure. PSHE useful life increases with decreasing spacing between plates.

The sensitivity of failure analysis of boiler tubes to the shape of elliptical external erosion flaws

Localized erosion is one of the most common failure mechanisms associated with boiler tubes, driven by impaction of the tube surface by fly ash, soot blowing steam, falling slag or other abrasive substances from the boiler’s combustion chamber. The tubes may experience significant localized reduction in their wall thickness, becoming susceptible to plastic collapse and bursting. The replacement of failed tubes is one of the leading causes of unplanned and forced boiler outages in process and power plants. In this study, geometric functions to enable the accurate modelling of boiler tubes with localized erosion flaws were developed from conceptualized models and finite element analyses were conducted on the modelled flawed tubes. The effect of geometry on the stress concentration in the tubes and on the failure pressure associated with the tubes was investigated. Linear elastic stress analysis is sensitive to the flaw geometry – for a representative problem stresses vary 38% as the flaw shape is varied. However, nonlinear elastic-plastic analysis shows significantly reduced sensitivity to flaw shape. The collapse pressure of the same representative problem now varies only 2.45% as the flaw shape is varied. This finding was demonstrated for various failure thresholds sourced from the literature, based either on plastic strain or Von Mises equivalent stress, which demonstrates that the failure of the tubes is insensitive to the specific choice of shape parameterization, as long as the minimum remaining wall thickness is matched. The outcome of these investigations gives further insight into the behaviour of tubes with localized external flaws while in service.

A modification on 3S criterion and simplified elastic-plastic ratcheting analysis in ASME VIII-2

Ratcheting is a common and important failure mode in pressure vessels. ASME VIII-2 2019 edition provides two kinds of ratcheting assessment methods——the elastic stress ratcheting assessment (paragraph 5.5.6) applied to the design by elastic stress analysis and the elastic-plastic ratcheting assessment (paragraph 5.5.7) applied to the design by elastic-plastic stress analysis. This paper focuses on the elastic stress ratcheting assessment, which includes again two methods——the elastic ratcheting analysis (paragraph 5.5.6.1), i.e. the 3S criterion, and the thermal stress ratcheting assessment (paragraph 5.5.6.3). This article reviews the development history of 3S criterion and discusses its applicable scope. The study found that the 3S criterion is not a complete elastic ratcheting assessment criterion, when the primary membrane stress range exceeds two-thirds of the cyclic yield stress, i.e. (2/3)Sy, the ratcheting assessment based on 3S criterion is unsafe for some situations. When the general primary membrane stress Pm and the local primary membrane stress PL, which allowable limit exceeds (2/3)Sy, are applied simultaneously, there is still the possibility of ratcheting failure in the structure even if the 3S criterion is met. As an extension of the 3S criterion, a complete and safe criterion on three-dimensional elastic ratcheting assessment is proposed in this paper. In order to avoid the inconvenience of partition assessment, a simplified thermal stress ratcheting assessment method based on double checking surfaces is proposed. It is a simple and conservative assessment method. Finally, elastic ratcheting analysis, thermal stress ratcheting assessment and simplified elastic-plastic analysis in ASME VIII-2 are integrated, a universal elastic stress ratcheting assessment is proposed.

Effective utilization of recycled fine aggregate powder as reinforcement particles in polyethylene composite

Effective waste concrete recycling is desirable from the viewpoints of environmental protection and extending the working lives of waste concrete final disposal sites. Recycled fine aggregate powders (RFAP) were obtained by milling waste concrete, and in this paper, we attempted to use RFAP as reinforcement particles in a polyethylene (PE) composite material. The PE powder and RFAP were blended together, and composites were fabricated using compression molding. Our results showed that the flexural strength and flexural modulus of the created composites improved with increased RFAP content. The RFAP dispersion state was honeycomb-like in the composite material, and from inspecting the specimen side view after three-point bending tests, it was apparent that crack propagation proceeded into the RFAP part of the composite, between PE particles. We then performed elastic stress analysis on the composites, in order to define the RFAP reinforcing behavior, using finite element analysis based on the homogenization method. As a result, it was revealed that the Mises stress decreased with increased RFAP content, confirming that there is a potential role for RFAP as reinforcement particles in PE-based composites.

Design Optimization of Pressure Vessel in Compliance With Elastic Stress Analysis Criteria for Plastic Collapse Using an Integrated Approach

Abstract The design and verification of pressure vessels is governed by the design codes specified by the ASME Boiler and Pressure Vessel Code (BPVC). Convention design satisfying the ASME BPVC code requirements would lead to a conservative design. This situation will to be solvable by modern structural optimization methods. The size optimization of pressure vessel complying with design-by-analysis requirements within the ASME Sec. VIII Division 2 specification is discussed in this paper. This is accomplished by an integrated approach in which the stress analysis is carried out by ANSYS. These results are used by an optimization code in matlab to perform design optimization. The integrated approach is fully automated and applied to the optimal design of a real pressure vessel. The results show that the material used by the pressure vessel can be minimized while satisfying the maximum stress specified in the BPVC.

The utility of laser scanning welds for improving fatigue assessment

Welded joints are a common source of fatigue failures. Traditional fatigue assessment approaches usually describe the weld with an idealized geometry defined by the weld flank angle and the weld toe radius. By doing so, the actual stress concentrations are not considered in such fatigue life predictions. 3D laser scanning technology offers an opportunity to more accurately represent the weld geometry, and accordingly perform fatigue assessment on more accurate representations of weld geometry. This manuscript explores the benefit of incorporating scanned weld geometries into linear elastic stress analysis for fatigue life prediction. Additionally, the capabilities to explain experimental scatter of six different fatigue indicator parameters have been quantified. Using experimental data from 28 tests across three geometries, a total of 60 deterministic and probabilistic fatigue models were assessed using both scanned and idealized weld geometries. The use of scanned weld geometries is found to substantially improve fatigue prediction when using local fatigue indicator parameters. However, if nonlocal fatigue indicator parameters are employed, the use of scanned weld geometries does not display a benefit. In total, the use of nonlocal fatigue indicator parameters with idealized weld geometry offer the greatest accuracy across the three cases examined. Thus, for linear elastic fatigue life assessment, the use of a nonlocal parameter in the fatigue life model is more motivated than utilizing 3D scanned weld geometry. Regardless of how the weld geometry is included, the signed von Mises equivalent stress led to the most reliable fatigue life predictions overall for the specimens considered in this work.

Simplified elastic-plastic analysis procedure for strain-based fatigue assessment of nuclear safety class 1 components under severe seismic loads

This paper proposes a simplified elastic-plastic analysis procedure using the penalty factors presented in the Code Case N-779 for strain-based fatigue assessment of nuclear safety class 1 components under severe seismic loads such as safety shutdown earthquake and beyond design-basis earthquake. First, a simplified elastic-plastic analysis procedure for strain-based fatigue assessment of nuclear safety class 1 components under the severe seismic loads was proposed based on the analysis result for the simplified elastic-plastic analysis procedure in the Code Case N-779 and the stress categories corresponding to normal operation and seismic loads. Second, total strain amplitude was calculated directly by performing finite element cyclic elastic-plastic seismic analysis for a hot leg nozzle in pressurizer surge line subject to combined loading including deadweight, pressure, seismic inertia load, and seismic anchor motion, as well as was derived indirectly by applying the proposed analysis procedure to the finite element elastic stress analysis result for each load. Third, strain-based fatigue assessment was implemented by applying the strain-based fatigue acceptance criteria in the ASME B&PV Code, Sec. III, Subsec. NB, Article NB-3200 and by using the total strain amplitude values calculated. Last, the total strain amplitude and the fatigue assessment result corresponding to the simplified elastic-plastic analysis were compared with those using the finite element elastic-plastic seismic analysis results. As a result of the comparison, it was identified that the proposed analysis procedure can derive reasonable and conservative results.

Numerical estimation of fretting fatigue life of bolted joints using continuum damage mechanics and SEAM Tool

For fretting fatigue, micro-slipping often causes initial micro-cracks in the contact surfaces, which gradually propagate and eventually result in fracture failure. However, it is difficult to directly observe and measure the crack initiation and propagation processes of single-lap bolted joints due to the obstacle of testing technique. Therefore, this article presents an elastic analysis–based method, in which the total fretting fatigue lifetime is divided into initiation life predicted by continuum damage mechanics and propagation life calculated by SEAM Tool in combination with Paris’s law. Since the initiation life model implicitly reflects the result of damage process, one can directly calculate the initiation life based on the elastic stress analysis. The predicted fretting fatigue life, initial crack location, and propagation path are in reasonable agreement with the fretting fatigue test and scanning electron microscope observation results. In addition, it is found that among the main factors affecting fretting fatigue of steel single-lap bolted joints, the initial life is affected by cyclic stress, friction coefficient, and tightening torque, and the propagation path is mainly influenced by tightening torque.

Elastic limit load resource when reaming holes in turbine rotor discs

The main topic of the article is the evaluation of load capacity by elastic stress analysis of impulse steam turbine rotors with bore drilled discs used for pressure equalization. Long-time operation of such turbines leads to fatigue fractures. The authors have analyzed stress distribution around the holes in turbine rotors in their nominal state and after reaming, which is the preferred method of removing fractures. Two approaches were used in analysis of bore drilled disc problem: continuous model and its mathematical solution and numerical based on finite element modeling. Both confirmed co-existence of stress concentration and crack initiation. Results show significant range for possible holes reaming - even with lowering stress level at critical area. These results were successfully used in overhaul practices and further turbine life time extension. It also allows to predict optimum hole layout and sizing at the design process for possible rotor disc notch effect reduction.