Correlation among selected fracture-mechanical parameters of concrete obtained from experiments and inverse analyses

2016 ◽  
Vol 17 (6) ◽  
pp. 1094-1103 ◽  
Author(s):  
Thomas Zimmermann ◽  
David Lehký ◽  
Alfred Strauss
Keyword(s):  
Mechanical Parameters ◽  
Fracture Mechanical Parameters

Effect of Welded Mechanical Heterogeneity on Fracture Parameters at the Crack Tip

2014 ◽  
Vol 687-691 ◽  
pp. 378-381
Author(s):  
He Xue ◽  
Xiao Qing Tao ◽  
Wei Bing Wang ◽  
Zhen Wen Wang ◽  
Ying Ru Wang ◽  
...  
Keyword(s):  
Welded Joint ◽  
Crack Tip ◽  
Mechanical Parameters ◽  
Continuous Change ◽  
Analysis Software ◽  
Element Analysis ◽  
Mechanical Heterogeneity ◽  
New Approach ◽  
Fracture Parameters ◽  
Fracture Mechanical Parameters

The welded joint is the critical area in the structure integrity investigation. To understand the influence of the mechanical heterogeneous on the fracture parameters in welded joint, the represented way of the welded mechanical heterogeneity and its effect on the mechanical parameters at the crack tip are analyzed by using an elastic-plastic finite element analysis software in this paper. The investigated results indicate that continuous change of material mechanical properties could express the effect of the actual welded mechanical heterogeneity on the fracture mechanical parameters change in the welded joint more accurately, which provide a new approach on the fracture problem investigation in welded joints.

Fracture-Mechanical Parameters for Modeling of Quasi-Brittle Materials and Structures

2015 ◽  
Vol 1106 ◽  
pp. 106-109
Author(s):  
Radomír Pukl ◽  
Tereza Sajdlová ◽  
Drahomír Novák ◽  
David Lehký
Keyword(s):  
Inverse Analysis ◽  
High Performance ◽  
High Performance Concrete ◽  
Numerical Models ◽  
Brittle Materials ◽  
Cementitious Materials ◽  
Mechanical Parameters ◽  
Ultra High Performance Concrete ◽  
Open Questions ◽  
Fracture Mechanical Parameters

The scatter of experimental results using specimens made of quasi-brittle materials, such as concrete, fibre-reinforced concrete, ultra high performance concrete etc., can be due to their heterogeneity rather high. An assessment of fracture-mechanical parameters is then difficult and problematic. To remain at deterministic level is therefore unrealistic and without virtual statistical approach, simulation and probabilistic result assessment the consequent practical design of quasi-brittle material-based structures can be risky. A key parameter of nonlinear fracture mechanics modeling is fracture energy of concrete. Numerical simulation of concrete failure and fracture phenomena in concrete as well as other cementitious materials became a field of an intensive research in the recent years. With respect to accuracy and efficiency of corresponding numerical models some few still open questions have to be focused. How the heterogeneity of cementitious materials can be taken into consideration in the most realistic way using commercially available finite element programs? A sophisticated option to get the parameters of the computational model indirectly is based on combination of fracture test with inverse analysis. This paper describes a methodology to get such parameters using experimental data from three-point bending tests used in inverse analysis based on combination of artificial neural networks and stochastic analysis.

Influence of Aeration of Concrete on Acoustic Emission and Fracture Mechanical Parameters Obtained from Three-Point Bending Tests

2015 ◽  
Vol 1124 ◽  
pp. 237-242
Author(s):  
Libor Topolář ◽  
Hana Šimonová ◽  
Petr Misák ◽  
Petr Daněk ◽  
Zbyněk Keršner ◽  
...  
Keyword(s):  
Acoustic Emission ◽  
Mechanical Parameters ◽  
Bending Tests ◽  
Three Point Bending ◽  
Concrete Mixtures ◽  
Acoustic Emission Sensors ◽  
Fracture Tests ◽  
Stress Behaviour ◽  
Bending Fracture ◽  
Fracture Mechanical Parameters

This paper examines the analysis of acoustic emission signals captured during three-point bending fracture tests of concrete specimens with similar water-cement ratio, but one set of specimens was prepared from aerated concrete. The acoustic emission method is an experimental tool well suited for monitoring fracture processes in material. The typical parameters of acoustic emission signals were identified from the acoustic emission records for two different concrete mixtures to further describe the under-the-stress behaviour and failure development. An understanding of microstructure–performance relationships is the key to true understanding of material behaviour. The crack growth was continuously monitored using four acoustic emission sensors mounted on the specimen. The acoustic emission results are accompanied by selected fracture mechanical parameters determined via evaluation of load versus displacement diagrams recorded during three-point bending fracture tests.

Stochastic fracture-mechanical parameters for the performance-based design of concrete structures

2014 ◽  
Vol 15 (3) ◽  
pp. 380-394 ◽  
Author(s):  
Alfred Strauss ◽  
Thomas Zimmermann ◽  
David Lehký ◽  
Drahomír Novák ◽  
Zbyněk Keršner
Keyword(s):  
Concrete Structures ◽  
Performance Based Design ◽  
Mechanical Parameters ◽  
Fracture Mechanical Parameters

Analysis of Efficiency of Drilling of Large-Diameter Wells With a Profiled Wing Bit / Badania Efektywności Wiercenia Studni Wielkośrednicowych Świdrem Skrawającym z Profilowanymi Skrzydłami

2012 ◽  
Vol 57 (2) ◽  
pp. 363-373
Author(s):  
Jan Macuda
Keyword(s):  
Average Rate ◽  
Large Diameter ◽  
Open Pit ◽  
Mechanical Parameters ◽  
Drilling Rate ◽  
Geological Conditions ◽  
Rock Drillability ◽  
Drilling Technology ◽  
Weight On Bit ◽  
Rotary Speed

Abstract In Poland all lignite mines are dewatered with the use of large-diameter wells. Drilling of such wells is inefficient owing to the presence of loose Quaternary and Tertiary material and considerable dewatering of rock mass within the open pit area. Difficult geological conditions significantly elongate the time in which large-diameter dewatering wells are drilled, and various drilling complications and break-downs related to the caving may occur. Obtaining higher drilling rates in large-diameter wells can be achieved only when new cutter bits designs are worked out and rock drillability tests performed for optimum mechanical parameters of drilling technology. Those tests were performed for a bit ø 1.16 m in separated macroscopically homogeneous layers of similar drillability. Depending on the designed thickness of the drilled layer, there were determined measurement sections from 0.2 to 1.0 m long, and each of the sections was drilled at constant rotary speed and weight on bit values. Prior to drillability tests, accounting for the technical characteristic of the rig and strength of the string and the cutter bit, there were established limitations for mechanical parameters of drilling technology: P ∈ (Pmin; Pmax) n ∈ (nmin; nmax) where: Pmin; Pmax - lowest and highest values of weight on bit, nmin; nmax - lowest and highest values of rotary speed of bit, For finding the dependence of the rate of penetration on weight on bit and rotary speed of bit various regression models have been analyzed. The most satisfactory results were obtained for the exponential model illustrating the influence of weight on bit and rotary speed of bit on drilling rate. The regression coefficients and statistical parameters prove the good fit of the model to measurement data, presented in tables 4-6. The average drilling rate for a cutter bit with profiled wings has been described with the form: Vśr= Z ·Pa· nb where: Vśr- average drilling rate, Z - drillability coefficient, P - weight on bit, n - rotary speed of bit, a - coefficient of influence of weight on bit on drilling rate, b - coefficient of influence of rotary speed of bit on drilling rate. Industrial tests were performed for assessing the efficiency of drilling of large-diameter wells with a cutter bit having profiled wings ø 1.16 m according to elaborated model of average rate of drilling. The obtained values of average rate of drilling during industrial tests ranged from 8.33×10-4 to 1.94×10-3 m/s and were higher than the ones obtained so far, i.e. from 181.21 to 262.11%.

Effects of extrusion on mechanical damage and mechanical parameters of litchi

2014 ◽  
Vol 39 (6) ◽  
pp. 688-692
Author(s):  
Yan CHEN ◽  
He-ping XIANG ◽  
Jian-hao TAN ◽  
Xiang-jun ZOU ◽  
Guo-gang HUANG ◽  
...  
Keyword(s):  
Mechanical Damage ◽  
Mechanical Parameters
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