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1

Precursory deformation responses in different directions to catastrophic failure of uniaxially compressed sandstones

Cheng L., Hao S., Lu C.

Archives of Mechanics

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2024

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Vol. 76, nr 1-2

39--60

EN

The precursory acceleration of deformation is widely validated as a method for predicting the failure time. Damage evolution inside rocks generally results in complex strain patterns in the vicinity of failure and various responses of deformation in different directions. However, it is still unclear what the differences and similarities are during the evolution of strain components. In this paper, we compare the evolving properties of strain components in different directions based on experiments of sandstones under uniaxial compression. It is shown that the temporal patterns of vertical strains are much more complex in spatial distributions than that of horizontal strains. The horizontal strain presents two kinds of time courses characterized by precursory accelerations in both the strain localized zone and its surrounding areas, and the evolution without accelerations in positions is far from the strain localized zone. However, the vertical strain components corresponding to loading direction present complex evolving patterns with five kinds of time courses. The final amplitudes of horizontal strains are much higher than vertical components. Horizontal strains follow the power law acceleration with the well-defined exponents, but the exponents for vertical components are more scattered. Thus, horizontal strains can be applied to predict the failure time.

2

Cyclic performance of reinforced legs in retrofitted transmission towers

Lu C., Ma X., Mills J. E.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 4

1608--1625

EN

In Australia, thousands of aging steel transmission towers need upgrading in order to meet the demands of additional communication devices being placed on them and the increased wind loads according to newly revised design standards. One effective retrofitting approach to increase their load capacity is to attach a reinforcing member to the original leg member through a bolted cruciform connector. This paper addresses the structural behaviour of retrofitted tower leg members under dynamic loading conditions that replicate the in-service conditions due to wind loading on real towers. A series of experimental tests and FEM modelling were conducted. The experimental results and numerical models show that the bolt pretension continuously decreases with the increasing loading cycles and magnitudes, which further reduces the bolt-slip load in cruciform connectors. The bolt-slip phenomenon changes the load-sharing rate between original members and reinforcing members in retrofitted legs. The dynamic loading procedure reduces the structural stiffness of retrofitted leg members due to the surface smoothing and bolt pretension loss. A further parametric study shows an obvious reduction in load-carrying capacity of retrofitted leg segments under long term dynamic loading periods. In addition, retrofitted segments with splice connectors in original members are more sensitive to loading cycle numbers.

3

Ultrasonic Phased Array Inspection for Gas Pressure Welds Joint of High Speed Railway

Lu C., Deng D., Li L.

Przegląd Elektrotechniczny

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2012

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R. 88, nr 1b

173-176

EN

Ultrasonic phased arrays offer many advantages for industrial inspection due to increased flexibility over methods involving single-element probes. This paper will compare and contrast two previously-developed methods for the inspection of gas pressure rail welds involving phased arrays: the swept sector scan and the total focusing method, with particular emphasis on the latter. The total focusing method requires the acquisition of the full data set of time-domain signals from every possible send-receive combination in an ultrasonic array and the computation of time delay laws that will allow focusing at the post-processing stage. While applying conventional single probe ultrasound tests methods to detect the gas pressure rail welds, it is needed to use various beam angles for different detecting regions, resulting in long time and low efficiency of testing process. In comparison, ultrasonic phased array technique has the advantage of flexibly adjusting scan angle so as to improve testing efficiency. By using the CTS-602 type phased array instrument and trails on the gas pressure welding rail joint sample with artificial defects, the reasonable inspection parameters and testing programs could be determined, Experiments results show that the ultrasonic phased array inspection provides excellent test quality and good test efficiency. Based on combination of S-scan and B-scan plotted into 2-D isometric part, the defects features could be reconstructed and measured into a soft package. Comparison between A-scan plotted data and S-scan image data of defect sizes and position are also presented.

PL

Przedstawiono fazowa matrycę ultradźwiękową do przemysłowego badania nieniszczącego. Porównano różne systemy do badania połączeń spawanych w systemach kolejowych. System wymaga zebrania całego zestawu danych z matrycy ultradźwiękowej a następnie przetwarzania numerycznego danych. W proponowanym systemie nie jest konieczne badanie spawu pod wieloma kątami co zwykle jest czasochłonne.

4

Positive grass diversity-productivity relationships and controlling factors along an elevation gradient in Central Asian alpine grasslands

Li K., Fangmeier A., Hu Y., Lu C., Liu X.

Polish Journal of Ecology

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2012

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Vol. 60, nr 1

123-131

EN

The productivity-diversity relationship in grasslands is of great interest with regard to species loss in natural ecosystems, where species extinction is not random but directed. We carried out a three-year investigation from 2005 to 2007 along an elevation gradient in alpine grasslands of Central Asia in an area of 70 x 20 km2 at Bayinbuluk, Tianshan Mountains. We selected 9 sites (10 x10 m2) and 117 plots (1 x 1 m2) from 2460 to 3260 m a.s.l. with 100 m intervals of altitude. Species richness, productivity, soil characteristics, air temperature and relative humidity (May.August) were recorded. The relationship between plant diversity and productivity was significant and positive. We used ordination techniques such as Canonical Correspondence Analysis (CCA) to examine the relationship between vegetation and the environmental factors. The results showed that plant species composition, species richness and productivity were significantly affected by air temperature, soil pH and relative humidity across the study area.