New Parameter For Characterization Research Articles

New Parameter for Characterization of Dispersed Systems

A new parameter was proposed, with the help of which a specific disperse system was characterized. In addition, a regularity was found showing the relationship between the structural characteristics of structural units (particle size distribution, standard deviation, intensity and average diameter). Various highly dispersed systems have been investigated, including polystyrene latex, Sucrose and latex.

A new parameter for characterization of tablet friability based on a systematical study of five excipients

In this paper, a new parameter highly relevant to tablet friability is proposed based on a systematical study of the tablet quality attributes and texture performances of five different direct compression excipients, including microcrystalline cellulose, starch, lactose, mannitol, and dicalcium phosphate anhydrous. The new parameter, named Strain/Stress Max, could indicate the tablet’s ability against external force to maintain integrity. It was directly obtained from the diametrical breaking test which is extensively used to assess tablet mechanical strength, and thus no extra work is required. The values varied significantly among the tablets formed by materials with different mechanical properties under the same compression pressure. A design space was developed to achieve <1% tablet friability at various combinations of Strain/Stress Max and tensile strength. Additionally, data from binary mixture tablets validated the availability of the constructed design space. And the upper limit of Strain/Stress Max value was advisable for 1.5 MPa−1 for pharmaceutical tablets. In conclusion, the new parameter and design space are available for fast identification of the tablets with acceptable friability to facilitate the development of tablet formulation using as few active pharmaceutic ingredients as possible.

Loading history effect on creep-fatigue crack growth in pipe bend

This study is concerned with assessing the structural integrity of power plant pipes that operate under creep and fatigue conditions. In the process of manufacturing pipe bends, it is difficult to avoid thickening on the inner radius of the pipe bend and thinning on the outer radius of the pipe bend. The cross-section of the bend also becomes non-circular due to the bending process, which tends to cause ovality in pipe bends. The acceptability of pipe bends is based on the induced level of shape imperfections considered. The influence of internal pressure, operation time and shape imperfections of a pipe bend on stress-strain redistributions and creep-fatigue crack growth rates was investigated using FE-analysis and experiments at elevated temperature. Full-size stress-strain state analysis of pipe bends was performed for different stages of lifetime while considering various loading conditions. As a result, it was determined that the combined effect of ovality and thinning cross-sections is significant and is a function of creep time. The tensile and creep tests were performed for determination of the main mechanical properties of the material of the pipe bends after loading history. The smooth and compact specimens were cut out from four tension and compression critical zones of the same pipe bend with given ovality and thinning cross-sections, as well as operating time. The creep-fatigue crack growth rate tests were performed on a specially designed program test-cycle. A comparison demonstrates that the tensile properties of 12Cr1MoV steel were degraded by long-term high-temperature service, whereas a comparison of the creep-fatigue crack growth rate characteristics indicates that they are a function of the critical zone positions in the considered pipe bend. A new parameter for characterization of the crack growth resistance for power plant materials and structures under elevated temperature was used in the form of a creep stress intensity factor.

Nonlinear stress intensity factors in fracture mechanics and their applications

A new parameters for characterization of the crack growth resistance for a power law hardening materials and structures under normal and elevated temperature are introduced in the form of plastic and creep stress intensity factors. A numerical method is proposed for estimating the governing parameter of the elastic-plastic and creep crack tip fields in the form of an In-integral along the through-the-thickness straight and curved crack fronts. Equations are also proposed for calculating the In-factor at both the deepest point along the crack front and the crack tip on the surface. Static and fatigue crack growth and in-plane and out-of-plane constraint effects are studied through experiments and computations for the material different properties. It is further demonstrated that for moderately large-scale yielding conditions or plastic deformations, the fracture process can be controlled by the single parameter KP based on the elastic-plastic numerical solutions and, therefore, is reflected in the influence of the cracked body geometry and loading conditions. Keeping in mind the purpose of practical application of the introduced nonlinear stress intensity factors, an engineering approach to the prediction of residual lifetime of cracked steam turbine rotors components which operate at maintenance under cyclic loading conditions is proposed. Using the nonlinear stress intensity factors approximate estimations of carrying capacity are presented for the different stress-strain state of steam turbine disks at the operation. As result it is stated that a one-parameter approach based on the plastic and creep stress intensity factors are more convenient for practical use in assessing the fracture resistance under monotonic and cyclic loading of materials and structural elements with respect to the two parameters fracture theories.

A creep stress intensity factor approach to creep–fatigue crack growth

A new parameter for characterization of the crack growth resistance for power plant materials and structures under elevated temperature is introduced in the form of creep stress intensity factor. On this base a crack growth rate approach is developed for the case of creep and fatigue interaction. A numerical method is proposed for estimating the governing parameter of the creep crack tip field in the form of an In-integral along the through-the-thickness straight and curved crack fronts. The application of the introduced parameters through experimental study of the creep–fatigue crack growth rate confirms effectiveness of the proposed approach.

Effect of Pipe Bend Shape Imperfections on Creep-fatigue Crack Growth

This study is concerned with assessing the structural integrity of power plant pipes which operate under creep and fatigue conditions. In the manufacturing process of pipe bends it is difficult to avoid thickening on the inner radius of the pipe bend and thinning on the outer radius of the pipe bend. The cross section of the bend also becomes non circular due to bending process; this tends to cause ovality in pipe bends. The acceptability of pipe bends is based on the induced level of shape imperfections considered. The influence of internal pressure, operation time and shape imperfections of pipe bend on stress-strain redistributions and creep-fatigue crack growth rate was investigated using FE-analysis and experiments at elevated temperature. Full-size stress-strain state analysis of pipe bend was performed for different stage of lifetime under considering loading conditions. As a result it was found that the effect of ovality and thinning cross sections interaction is significant and is a function of creep time. The tensile tests were performed for determination the main mechanical properties of pipe bend's material after loading history. The smooth and compact specimens were cut out from four tension and compression critical zones of the same pipe bend with given ovality and thinning cross sections as well as operating time. The creep-fatigue crack growth rate tests were performed on special designed program test-cycle. Comparison between new and old materials shows tensile properties of 12Cr1MoV steel have degraded by long-term high-temperature service; while comparison between the creep-fatigue crack growth rate characteristics indicates that they are a function of the critical zone positions in the considered pipe bend. A new parameter for characterization of the crack growth resistance for power plant materials and structures under elevated temperature is used in the form of creep stress intensity factor.

Urethral pressure reflectometry during intra‐abdominal pressure increase—an improved technique to characterize the urethral closure function in continent and stress urinary incontinent women

to assess the urethral closure function by urethral pressure reflectometry (UPR) during intra-abdominal pressure-increase in SUI and continent women. Twenty-five urodynamically proven SUI women and eight continent volunteer women were assessed by ICIQ-SF, pad-weighing test, incontinence diary, and UPR. UPR was conducted during resting and increased intra-abdominal pressure (P(Abd)) by straining. Related values of P(Abd) and urethral opening pressure (P(o)) were plotted into an abdomino-urethral pressuregram. Linear regression of the values was conducted, and the slope of the line ("APIR") and the intercept with the y-axis found. By the equation of the line, Po was calculated for various values of P(Abd), for example, 50 cm H2O (P(o-Abd 50)). The resting P(o) (P(o-rest)) and APIR, respectively, significantly differed in SUI and continent women but could not separate the two groups. The urethral closure equation (UCE) based on P(o-rest) and APIR provided a more detailed characterization of a woman's closure function based on the permanent closure forces (primarily generated by the urethral sphincteric unit) and the adjunctive closure forces (primarily generated by the support system). P(o-Abd 50) and UCE, respectively, which express the combined permanent and adjunctive closure forces and estimate the efficiency of the closure function, separated SUI and continent women and were highly significantly negatively correlated with ICIQ-SF, pad test, and the number of incontinence episodes. New parameters for characterization of the urethral closure function and possible dysfunctions and its efficiency were provided. P(o-Abd 50) and UCE may be used as diagnostic tests and severity measures.