Ratcheting With No Thermal Bending and Membrane Stress

2016 ◽  
Author(s):  
R. Adibi-Asl ◽  
W. Reinhardt
Keyword(s):  
Thermal Stress ◽  
Thermal Loading ◽  
Mechanical Load ◽  
Failure Mechanisms ◽  
Extreme Case ◽  
Cyclic Stress ◽  
Maximum Temperature ◽  
Bending Stress ◽  
Thermal Bending ◽  
Stress States

The ASME B&PV Code provides design by analysis rules that address failure mechanisms under cyclic loading. One of these potential failure mechanisms is incremental plastic collapse, or ratcheting. Miller presented the technical basis for the present Code requirements in a technical paper in 1959. Miller’s equations for the ratchet boundary address a beam under a cyclic through-thickness thermal gradient acting together with a steady axial mechanical load. This ratchet boundary applies approximately to a pressurized cylinder with through-thickness thermal bending stress. Conditions arise sometimes in practice where cooling or heating is applied simultaneously to the inner and outer surface of pressure boundary. The extreme case of such a scenario arises when both surfaces experience the same thermal condition such that there is a cyclic thermal stress but both zero membrane thermal stress and zero thermal bending stress The question is, could ratcheting occur in this case? This paper derives the ratchet boundary for cases when the maximum temperature occurs mid-way through the thickness. The linearized stress due to thermal loading is zero. The solution is obtained using FE analysis and the Non-Cyclic Method (NCM) that has been proposed previously by the authors. The NCM is a generalization of the static shakedown theorem and allows the ratchet boundary to be calculated for both elastic and elastic-plastic cyclic stress states.

Ratchet Boundary for Superimposed Biaxial Membrane Stress States

2018 ◽  
Author(s):  
Wolf Reinhardt
Keyword(s):  
Thermal Expansion ◽  
Thermal Stress ◽  
Analytical Solution ◽  
Pressure Vessels ◽  
Stress Fields ◽  
Design Codes ◽  
Bending Stress ◽  
Membrane Stress ◽  
Asme Code ◽  
Stress States

Thermal membrane and bending stress fields exist where the thermal expansion of pressure vessel components is constrained. When such stress fields interact with pressure stresses in a shell, ratcheting can occur below the ratchet boundary indicated by the Bree diagram that is implemented in the design Codes. The interaction of primary and thermal membrane stress fields with arbitrary biaxiality is not implemented presently in the thermal stress ratchet rules of the ASME Code, and is examined in this paper. An analytical solution for the ratchet boundary is derived based on a non-cyclic method that uses a generalized static shakedown theorem. The solutions for specific applications in pressure vessels are discussed, and a comparison with the interaction diagrams for specific cases that can be found in the literature is performed.

On the Interaction of Thermal Membrane and Thermal Bending Stress in Shakedown Analysis

2008 ◽  
Author(s):  
Wolf Reinhardt
Keyword(s):  
Thermal Stress ◽  
Bending Stress ◽  
Membrane Stress ◽  
Secondary Stress ◽  
Elastic Plastic ◽  
Plastic Analysis ◽  
Thermal Bending ◽  
Asme Code ◽  
The Impact ◽  
Current Code

When the primary plus secondary stress range exceeds 3 Sm, the current ASME Code rules on simplified elastic-plastic analysis impose two separate requirements to evaluate the potential for ratcheting. The range of primary plus secondary stress excluding thermal bending must be less than 3 Sm, and the thermal stress must satisfy the Bree criterion for thermal stress ratchet. It has been shown previously that this method can be unconservative, i.e. predict shakedown when elastic-plastic analysis shows ratcheting. This paper clarifies the interaction between thermal membrane and bending stress in the presence of a primary membrane stress. An analytical model is used to derive the closed-form ratchet boundary for combined uniform loading of this type. The impact of having stress gradients along the wall that are typical for discontinuities is studied numerically. Simple modifications of the current Code methods are suggested that would achieve a clearer and better-justified set of rules.

Shakedown at Thermal Discontinuities Involving Thermal Membrane and Thermal Bending Stress

2012 ◽  
Author(s):  
Ali Asadkarami ◽  
Wolf Reinhardt
Keyword(s):  
Thermal Stress ◽  
Stress Gradient ◽  
Axial Direction ◽  
Bending Stress ◽  
Primary Stress ◽  
Perfectly Plastic ◽  
Thermal Bending ◽  
Asme Code ◽  
Elastic Perfectly Plastic ◽  
Shakedown Limit

The current ASME Code Section III NB-3200 rules on thermal stress ratchet require that the thermal stress must be less than the ratchet condition that Bree established for a cyclic pure thermal bending stress as a function of the level of primary membrane stress. It has been shown that this method can predict shakedown when elastic-perfectly plastic analysis shows ratcheting. However, there is also conservatism in the Code rules because the highest stresses that dominate the evaluation of a component are typically found at discontinuities, where there is a stress gradient at least in the axial direction. The stress limits, on the other hand, are based on stress distributions that are constant in the axial (and circumferential) direction. This paper investigates the effect of thermal discontinuities on the shakedown limit in the presence of a thermal through-wall gradient and a pressure-induced primary stress. The investigation is based on the simple model of a cylinder with an isolated thermal discontinuity. The effect of proximity to another discontinuity is explored, to obtain the minimum distance between two discontinuities that would allow them to be considered separately. Simple rules are developed and proposed to take potentially advantage of higher stress limits at an isolated discontinuity.

Optimum Design of Inductors Used for Wireless Power Transmission Micro-Module

2004 ◽  
Author(s):  
Chao-Liang Chang ◽  
Uei-Ming Jow ◽  
Chao-Ta Huang ◽  
Hsiang-Chi Liu ◽  
Jr-Yuan Jeng ◽  
...  
Keyword(s):  
Thermal Stress ◽  
Electrical Properties ◽  
Optimum Design ◽  
Thermal Loading ◽  
Power Transmission ◽  
Thermal Strain ◽  
Electrical Performance ◽  
Wireless Power ◽  
Wireless Power Transmission ◽  
Analysis Software

The micro-inductor is a key component in wireless power transmission micro modules. In this paper, an optimum design for the micro-inductor was studied and related MEMS fabrication techniques were also developed. Commercial electromagnetic property analysis software, ANSOFT, was used to screen the main design factors of the micro-inductor. It was found that the high inductance and high quality factors of the micro-inductor implied high power transmission efficiency for the micro-module’s wireless power transmission. The electrical performance of the micro-inductor was affected by the thermal stress and thermal strain induced in the operational environment of the wireless power transmission micro-module. In order to investigate the reliability of the micro-inductor, commercial stress analysis software, ANSYS, was used to calculate thermal stress and thermal strain. The deformed model of the micro-inductor was then imported into ANSOFT in order to calculate its electrical properties. Glass substrate Pyrex 7740 was used to reduce the substrate loss of the magnetic flux of the micro-inductor. The surface micromachining technique, a kind of MEMS processing, was chosen to fabricate the micro-inductor; the coil of the micro-inductor was electroplated with copper to reduce the series resistance. The minimum line width and line space of the coil were 20 μm and 20 μm respectively. Polyimide (PI) was used for supporting the structure of micro-inductors. The maximum shear stress was 74.09MPa and the maximum warpage was 2.197 μm at a thermal loading of 125°C. For the simulated data, the most suitable areas for 31-turn and 48-turn coils were at an area ratio of 1.27 and 2, respectively. The electrical properties of the inductors changed slightly under thermal loading.

FIRE PROTECTION DISTANCES BETWEEN CONSTRUCTIONS OF DIFFERENT PURPOSE. A FIRE IN A WAREHOUSE-TYPE PREMISE. SERIES OF CALCULATIONS

2020 ◽  
pp. 22-29
Author(s):  
Алексей Сергеевич Барановский ◽  
Петр Алексеевич Леончук ◽  
Станислав Анатольевич Зуев ◽  
Валерий Геннадьевич Шамонин
Keyword(s):  
Heat Exchange ◽  
Fire Protection ◽  
Extreme Case ◽  
Maximum Temperature ◽  
Isothermal Case

Проведена серия расчетов по оценке температуры в помещении при пожаре в режиме, регулируемом вентиляцией, поскольку при этом достигается максимальное значение температуры. Рассматривается предельный случай теплообмена со стенами помещения - изотермический. Проанализирован случай пожара в зданиях типа складских и стоянок автомобилей. There is performed the series of calculations to estimate the temperature in premise during a fire in ventilation-controlled mode, because the maximum temperature achieves in this case. There is considered the extreme case of heat exchange with the walls of the room - isothermal case. The case of fire in buildings such as warehouses and car parking is examined.

scholarly journals Hydration of the lower stratosphere by ice crystal geysers over land convective systems

2009 ◽  
Vol 9 (6) ◽  
pp. 2275-2287 ◽  
Author(s):  
S. Khaykin ◽  
J.-P. Pommereau ◽  
L. Korshunov ◽  
V. Yushkov ◽  
J. Nielsen ◽  
...  
Keyword(s):  
Water Vapour ◽  
Lower Stratosphere ◽  
Monsoon Season ◽  
Extreme Case ◽  
Fast Response ◽  
Maximum Temperature ◽  
Ice Crystal ◽  
Convective Systems ◽  
Mesoscale Convective ◽  
Summer Maximum

Abstract. The possible impact of deep convective overshooting over land has been explored by six simultaneous soundings of water vapour, particles and ozone in the lower stratosphere next to Mesoscale Convective Systems (MCSs) during the monsoon season over West Africa in Niamey, Niger in August 2006. The water vapour measurements were carried out using a fast response FLASH-B Lyman-alpha hygrometer. The high vertical resolution observations of the instrument show the presence of accumulation of enhanced water vapour layers between the tropopause at 370 K and the 420 K level. Most of these moist layers are shown connected with overshooting events occurring upwind as identified from satellite IR images over which the air mass probed by the sondes passed during the three previous days. In the case of a local overshoot identified by echo top turrets above the tropopause by the MIT C-band radar also in Niamey, tight coincidence was found between enhanced water vapour, ice crystal and ozone dip layers indicative of fast uplift of tropospheric air across the tropopause. The water vapour mixing ratio in the enriched layers exceeds frequently by 1–3 ppmv the average 6 ppmv saturation ratio at the tropopause and by up to 7 ppmv in the extreme case of local storm in coincidence with the presence of ice crystals. The presence of such layers strongly suggests hydration of the lower stratosphere by geyser-like injection of ice particles over overshooting turrets. The pile-like increase of water vapour up to 19 km seen by the high-resolution hygrometer during the season of maximum temperature of the tropopause, suggests that the above hydration mechanism may contribute to the summer maximum moisture in the lower stratosphere. If this interpretation is correct, hydration by ice geysers across the tropopause might be an important contributor to the stratospheric water vapour budget.

High Temperature Fatigue Assessment of a SiCf/SiC Ceramic Matrix Composite Using Advanced Monitoring Techniques

2019 ◽  
Author(s):  
Christopher D. Newton ◽  
Steven P. Jordan ◽  
Martin R. Bache ◽  
Louise Gale
Keyword(s):  
Silicon Carbide ◽  
Crack Opening ◽  
Ceramic Matrix Composite ◽  
Fatigue Loading ◽  
Cyclic Stress ◽  
Image Correlation ◽  
Material System ◽  
Damage Initiation ◽  
Macro Scale ◽  
Stress States

Abstract Laboratory based experiments to assess the “damage tolerance” of any new material system are a pre-requisite to engineering design, especially for aerospace components. In the case of CMCs, macro-scale specimens are preferred containing representative fibre-matrix architectures that support the definition of mechanical properties under service representative stress states. The combination of complex internal structure and inevitable processing artefacts within CMCs provides numerous sites for damage initiation. Damage then progresses in an inhomogeneous manner prior to ultimate failure at some critical location. Traditional techniques employed for strain measurement (extensometry/strain gauges) prove to be ineffective tools when testing these advanced composites. More complex characterization is essential in order to assess the localised response of the material. Advanced techniques, specifically digital image correlation and acoustic emission, have been applied to the evaluation of an CVI/MI silicon carbide reinforced/silicon carbide CMC tested at the elevated temperature of 800°C under fatigue loading. The spatial and temporal indications of damage were correlated to the observable forms of damage initiation and progression. Ancillary use of an in-situ SEM loading stage provided insight into the crack opening and closing mechanisms active within this material when under cyclic stress.

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