Kinetic Theory of Creep and Long-Term Strength of Metals

This chapter deals with the simulation of the creep process and the effect of long-term strength of metals, notably, in both uniaxial and complex stress states. A description of a creep experiment and the simplest creep models are presented, that is, the theory of steady creep, the theory of ageing, the theory of flow and the theory of hardening. In creep process simulation, a kinetic theory based on the introduction of structural parameters characterising the state of the metal at a given time is widely used. Among such parameters, metal damage in the creep process, work of stresses on creep deformations (energy version) and concentration of an aggressive medium in the metal were studied. The coupled problem of creep and long tensile strength is also considered taking into account the mutual influence of damage accumulation and one-dimensional diffusion of the aggressive medium. The times to fracture are determined both in the presence of an aggressive medium and in the absence of one. A significant contribution of Soviet (Russian), European, American and Japanese scientists to the development of continuum damage mechanics is highlighted

Calculation of mechanical stresses in adjoint system of electronic component and compound and strength assessment

The paper represents mathematical model and formulas developed for project calculations which are applied to sealed electronic units and provide assessing strength of passive electronic components having revolution shape (capacitors, resistors, diodes, pins, etc.). The stress calculation has been produced for materials of resistor and compound in the temperature interval (from –60 to +70°C) along the radius of resistor and compound

Calculation of mechanical stresses in adjoint system of electronic component and compound and strength assessment

The paper represents mathematical model and formulas developed for project calculations which are applied to sealed electronic units and provide assessing strength of passive electronic components having revolution shape (capacitors, resistors, diodes, pins, etc.). The stress calculation has been produced for materials of resistor and compound in the temperature interval (from –60 to +70°C) along the radius of resistor and compound

Calculation of mechanical stresses in adjoint system of electronic component and compound and strength assessment

The paper represents mathematical model and formulas developed for project calculations which are applied to sealed electronic units and provide assessing strength of passive electronic components having revolution shape (capacitors, resistors, diodes, pins, etc.). The stress calculation has been produced for materials of resistor and compound in the temperature interval (from –60 to +70°C) along the radius of resistor and compound

Determination of limit levels of damage in materials after operating time under thermomechanical loading

Представлено результати аналізу можливих варіантів практичного використання концепції розсіяних дефектів у розрахунках конструкцій за допустимою пошкоджуваністю матеріалу. Опрацьовано, отримані методом LМ-твердості, й узагальнено експериментальні дані з граничної пошкоджуваності деяких широко використовуваних у машинобудуванні сплавів на зруйнованих після напрацювання в умовах повзучості й малоциклової втоми зразках. Установлено лінійну кореляцію рівнів граничної пошкоджуваності з робочими напруженнями при напрацюванні. Запропоновано варіант методики визначення параметрів кореляційного рівняння за результатами базових дослідів.The results of the analysis of possible variants of using the concept of scattered defects for structural calculations with allowable material damage are presented. The experimental data on the limit damage to some alloys, which are widely used in mechanical engineering, are obtained by the LM-hardness test method on the specimens fractured after accrued operating time under creep and low-cycle fatigue conditions. These data are processed and generalized. A linear correlation between levels of limit damage and working stress under operating time is established. A variant of the method for determining the parameters for equation of correlation from the basic test results is proposed

History-sensitive accumulation rules for life-time prediction under variable loading

This is the post-print version of the article. The official published version can be obtained from the link below - Copyright @ 2011 SpringerA general form of temporal strength conditions under variable creep loading is employed to formulate several new phenomenological accumulation rules based on the constant-loading durability diagram. Unlike the well-known Robinson rule of linear accumulation of partial life-times, the new rules allow to describe the life-time sensibility to the load sequence, observed in experiments. Comparison of the new rules with experimental data shows that they fit the data much more accurately than the Robinson rule

The impact of increasing urban surface albedo on outdoor summer thermal comfort within a university campus

The impact of increasing urban surface albedo on outdoor thermal comfort was studied in two phases: Firstly, the thermal conditions of three locations with different ground surface materials were compared. The study used CFD modelling followed by a measurement campaign to validate the control simulation. It was observed that the physiological equivalent temperature (PET as the outdoor thermal comfort index) in the campus park (covered with grass) was 11.0 °C lower than the parking lot (paved with concrete) at 16:00 CET. As the next step, the albedo of the roofs and walls were increased from 0.2 (control) to 0.3, 0.4, 0.5 and 0.6. It was found that increasing the albedo made the open space of the courtyard uncomfortable due to the higher reflectivity of high-albedo materials. An increase of every 0.1 albedo of the surfaces led to 1.2 °C higher mean radiant temperature, and consequently, 0.8 °C higher PET. The study also showed that the increase of albedo radiated more sun to the ground surface. This increased average ground surface sensible heat flux (6.7 W/m2) and surface temperature (0.4 °C) during the day. This finding shows that the position and orientation of high albedo materials can significantly affect pedestrians' thermal comfort in urban open spaces