Limit Stress Intensity Factor Research Articles

Combined effect on properties and durability performance of nanomodified basalt fiber blended with bottom ash-based cement concrete: ANOVA evaluation

A control of a cement composite structure formation from modern positions should be carried out taking into account the synergistic effect of its components. The goal of the article is to study the combined effect of nanomodified basalt fiber (NBF) and bottom ash (BA) as structural elements of concrete using a two-factor analysis of variance ANOVA. The tasks for achieving this goal are the development of nanomodified basalt fiber bottom ash-cement concretes, as well as the study of their fresh, physical and mechanical properties (slump, slump flow, average density, compressive and flexural strength, elastic modulus and crack resistance) and durability performances (water, frost, and abrasion resistance). Nanomodified basalt-fiber-reinforced concretes (from 0 to 7 wt % NBF) have been developed, in which the economical Portland cement CEM I 32.5 N is replaced by up to 45 wt % mechanically activated bottom ash (400 m2/kg). Achieving uniform flowability of the compositions (slump 20–22 cm and slump flow 45–52 cm) was carried out by varying the dosage of an economical superplasticizer with a high water-reducing ability (35%). The joint effect of the BA and NBF provides control over the structure formation of cement materials, which ensures the redistribution of internal stresses from shrinkage deformations throughout the entire volume of the composite; during loading, the process of crack formation is retarded, stress concentration near structural defects is reduced, and stresses are redistributed in the microstructure of the cement composite between its components.High values of mechanical properties (compressive strength up to 59.2 MPa, flexural strength up to 17.8 MPa, elastic modulus up to 52.6 GPa, limit stress intensity factor 0.507 MPa m0.5) are explained by the complex effect of bottom ash and nanomodified basalt fibers. For the composition with 30 wt % BA and 5 wt % NBF, W18 water resistance grade, F400 frost resistance grade, and the abrasion resistance of 0.59 g/cm2 were achieved, which characterizes the high durability of the developed materials.

2802 定常温度揺らぎ下各種円筒内表面き裂の応力拡大係数範囲上限値比較(S10-1 熱応力(1),S10 熱応力,応力特異性と強度評価)

2802 定常温度揺らぎ下各種円筒内表面き裂の応力拡大係数範囲上限値比較(S10-1 熱応力(1),S10 熱応力,応力特異性と強度評価)

Simplified Evaluation Method of a Steady State Stress Intensity Factor Range Upper Limit for a Circumferential Crack in a Cylinder

We propose a simplified method to evaluate the upper limit stress intensity factor (SIF) range of an inner-surface circumferential crack in a thin-to thick-walled cylinder under steady state thermal striping in this paper. The key idea of the method is to combine our analytical temperature solution for the problem and our semi-analytical numerical SIF evaluation method for the crack, so that we can derive an approximate value of the desired upper limit steady state SIF range. Numerical results showed that our method is valid for cylinders in a range of γm/W=10 to 1.

104 定常温度揺らぎ下各種円筒内表面き裂の応力拡大係数範囲上限値(OS2-1 計算固体力学の最新応用(1),オーガナイズドセッション:2 計算固体力学の最新応用)

104 定常温度揺らぎ下各種円筒内表面き裂の応力拡大係数範囲上限値(OS2-1 計算固体力学の最新応用(1),オーガナイズドセッション:2 計算固体力学の最新応用)

Simplified method to evaluate upper limit stress intensity factor range of an inner-surface circumferential crack under steady state thermal striping

Simplified method to evaluate the upper limit stress intensity factor (SIF) range of an inner-surface circumferential crack in a thin- to thick-walled cylinder under steady state thermal striping was considered in this paper. The edges of the cylinder were rotation-restrained and the outer surface was adiabatically insulated. The inner surface of the cylinder was heated by a fluid with constant heat transfer coefficient whose temperature fluctuated sinusoidally at constant amplitude Δ T. By combining our analytical temperature solution for the problem and our semi-analytical-numerical SIF evaluation method for the crack, we showed that the desired maximum steady state SIF range can be evaluated with an engineering accuracy after Δ T, the mean radius to wall thickness ratio r m/ W of the cylinder, the thermal expansion coefficient and Poisson's ratio are specified. By applying our method, no transient SIF analysis nor sensitivity analysis of the striping frequency on the SIF range is necessary. Numerical results showed that our method is valid for cylinders in a range of r m/ W = 10–1.

Enhancement of delayed failure resistance by partial unloading method

The effects of two types of pre-stressing, i.e. partial unloading (0 →K max → K) and perfect unloading (0 → K max → 0 → K) on the delayed failure strength were investigated using pre-cracked specimens of JIS SNCM8 steel quenched and tempered, where K max is the maximum stress intensity factor at pre-stressing, and K is the stress intensity factor under which delayed failure test is carried out. Both pre-stress methods can markedly increase the delayed failure strength or the lower limit stress intensity factor K ISCC . The partial unloading method is superior to the perfect unloading method in each tempering condition (200 or 400°C) and in each environment (distilled water or 3% NaCl water). The reason why K ISCC is increased by each pre-stressing can be explained by the decrease of surface stress at crack tip, which will suppress the corrosion reaction and prevent the invasion of hydrogen atoms into the material.