Application of a multisurface discrete crack model for clear wood taking into account the inherent microstructural characteristics of wood cells

Holzforschung ◽  
2016 ◽  
Vol 70 (9) ◽  
pp. 845-853 ◽  
Author(s):  
Markus Lukacevic ◽  
Josef Füssl
Keyword(s):  
Building Materials ◽  
Load Capacity ◽  
Failure Mechanisms ◽  
Failure Criteria ◽  
Failure Behavior ◽  
Crack Model ◽  
Clear Wood ◽  
Discrete Crack ◽  
Splitting Test ◽  
Definition Of

Abstract A more accurate prediction of the mechanical behavior of wood is needed to increase its ability to compete with other building materials. Especially, when it comes to estimate failure loads, the lack of appropriate prediction tools becomes obvious. The present work contributes to this goal in two different ways: First, a damage concept for wood is revisited, which allows for transferring information about failure processes through different scales of observation. In this concept, the failure behavior of clear wood is linked to the different characteristic of earlywood and latewood layers in softwoods. This reduces the number of empirically determined strength parameters, while the definition of multisurface failure criteria is still possible. Secondly, it will be demonstrated that the combination of these models with discrete crack modeling based on the extended finite element method provides a numerical simulation tool capable to describe failure mechanisms more realistically than existing approaches. The results obtained by numerical calculations and experiments by means of a micro wedge splitting test show very good agreement, especially, if the load capacity and failure mechanisms are in focus. The presented approach shows a much better performance compared to linear elastic or elastoplastic simulations.

Fracture Events Localization by Numerical Simulations of Cementitious Composites

2015 ◽  
Vol 665 ◽  
pp. 253-256
Author(s):  
Jakub Sobek ◽  
Michal Štafa ◽  
Václav Veselý
Keyword(s):  
Numerical Simulations ◽  
Building Materials ◽  
Numerical Study ◽  
Aggregate Size ◽  
Cohesive Crack ◽  
Type Model ◽  
Failure Behavior ◽  
Crack Model ◽  
Simulation Tools ◽  
Splitting Test

This paper presents a numerical study of failure behavior of cementitious composite materials differing in their composition (aggregate size). A set of four different materials was tested in atypical splitting test geometry. During these tests, apart from the typical outputs such as the load–displacement curves, signals from failure events causing acoustic emission (AE) were recorded. However, reliability of the procedures of the failure events localization might seem questionable in some cases – therefore, the test evaluation procedures were accompanied by analyses using 3D numerical simulation tools based on nonlinear fracture-mechanics approach and propagation of fracture events in the specimens are performed using two computational codes. One is a commercial non-linear FEM code with implementation of cohesive crack model (in the smeared cracks formulation). The second one is an own developed discrete lattice-type model. The comparison of AE records from the tests with the results of the performed numerical simulations can answer questions on the distribution and magnitude (and possibly the energy dissipation amount) of the recorded failure events and generally help in the interpretation and exploitation of AE in the research of failure of non-electric building materials.

Failure Prediction for Textile Composites Via Micromechanics

Materials ◽  
2003 ◽  
Author(s):  
Brian Cox ◽  
Qingda Yang
Keyword(s):  
Single Point ◽  
Failure Mechanisms ◽  
Material Constant ◽  
Local Stress ◽  
Failure Criteria ◽  
Textile Composites ◽  
Local Damage ◽  
Stress Components ◽  
Definition Of ◽  
2D And 3D

The question of failure criteria for textile composites is taken up, with reference to the micormechanics of known failure mechanisms in broad classes of 2D and 3D textile composites. Of primary importance is the definition of the measure of local stress or strain that should be compared against a putative material constant to predict local damage. In most prior work, some combination of strain or stress components evaluated at a single point has been used. Due to the complexity and inevitahle irregularity of textile composites, this approach is not favoured. Instead, micromechanical considreations recommend using strains averaged over gauge volumes whose dimensions are greater than or equal to approximately half the width dimensions of a single tow. Engineering tests that can be used for calibration are suggested but remain to be proven repeatable and consistent.

scholarly journals Viscoelastic phase-field fracture using the framework of representative crack elements

2021 ◽  
Author(s):  
Bo Yin ◽  
Johannes Storm ◽  
Michael Kaliske
Keyword(s):  
Phase Field ◽  
Consistency Condition ◽  
Field Method ◽  
Anisotropic Elasticity ◽  
Phase Field Method ◽  
Internal Variables ◽  
Crack Model ◽  
Material Degradation ◽  
Discrete Crack ◽  
Deformation State

AbstractThe promising phase-field method has been intensively studied for crack approximation in brittle materials. The realistic representation of material degradation at a fully evolved crack is still one of the main challenges. Several energy split formulations have been postulated to describe the crack evolution physically. A recent approach based on the concept of representative crack elements (RCE) in Storm et al. (The concept of representative crack elements (RCE) for phase-field fracture: anisotropic elasticity and thermo-elasticity. Int J Numer Methods Eng 121:779–805, 2020) introduces a variational framework to derive the kinematically consistent material degradation. The realistic material degradation is further tested using the self-consistency condition, which is particularly compared to a discrete crack model. This work extends the brittle RCE phase-field modeling towards rate-dependent fracture evolution in a viscoelastic continuum. The novelty of this paper is taking internal variables due to viscoelasticity into account to determine the crack deformation state. Meanwhile, a transient extension from Storm et al. (The concept of representative crack elements (RCE) for phase-field fracture: anisotropic elasticity and thermo-elasticity. Int J Numer Methods Eng 121:779–805, 2020) is also considered. The model is derived thermodynamic-consistently and implemented into the FE framework. Several representative numerical examples are investigated, and consequently, the according findings and potential perspectives are discussed to close this paper.

scholarly journals Modeling and analysis of mission thread of weapon system of systems based on O-PPN

2021 ◽  
Vol 39 (1) ◽  
pp. 197-207
Author(s):  
Yuqi Chen ◽  
Tingxue Xu ◽  
Xiaotong Zhao ◽  
Cheng Lu
Keyword(s):  
Petri Net ◽  
Success Probability ◽  
Failure Criteria ◽  
Performance Degradation ◽  
Operation Performance ◽  
Modeling And Analysis ◽  
Reliability Parameters ◽  
Mission Success ◽  
Definition Of ◽  
Equipment System

Aiming at the problem that the current WSoS mission modeling and analysis methods are difficult to describe the property of multi-state of each equipment system, combining with Petri net and Markov process, an O-PPN based mission thread modeling and analysis method is proposed in this paper. Based on the definition of WSoS, the mission of WSoS is formally described. To improve the traditional Petri net, an operation performance Petri net (O-PPN) is constructed, in order to meet the modeling needs of the general mission thread of the WSoS; and aiming at the problems of the performance degradation of the equipment system and the possible "ahead of time" state, the performance degradation model of the equipment system based on Markov is constructed. The corresponding state probability set is obtained by inputting the reliability parameters of each equipment system. And according to the requirements of each operation in the mission thread for the performance level of each equipment system and combined with the mission success and failure criteria of the combat task and operation, the mission success probability of the whole WSoS is calculated. Finally, the feasibility of the proposed method is verified by the simulation of the case.

scholarly journals PECULIARITIES OF MATERIAL RESOURCE MANAGEMENT OF ENTERPRISES OF BUILDING MATERIALS

2021 ◽  
Author(s):  
Iryna Hobyr ◽  
Lidiia Hobyr
Keyword(s):  
Inventory Management ◽  
Building Materials ◽  
Construction Materials ◽  
Design And Technology ◽  
Resource Saving ◽  
New Production ◽  
Utilization Factor ◽  
Resources Management ◽  
Material Resources ◽  
Definition Of

In a market economy, it becomes important to improve the organization of enterprise management and, above all, the production process, efficient use of financial, material resources and inventories. Effective management of material resources increases profits and provides the necessary investment. To maintain high profitability and liquidity, the management of current activities of enterprises, in particular inventory management plays a significant role. The categorical apparatus of material resources management at the enterprise is considered, the definition of “material resources” is generalized, the definition of "material resources management" is offered, and also the system of material resources management at the enterprise is considered. In the management of material resources at the enterprise there are 2 approaches – logistics and reengineering. The main tasks of the mechanism of management of material resources of the enterprise of building materials are defined. These are: increasing the efficiency of material resources and choosing cheap sources of funding; introduction of new production, resource-saving technologies; minimization of costs for procurement, production and marketing activities; increasing the interest of employees of all services in the effective performance of their duties; product quality management. The analysis of efficiency of use of material resources at the enterprises of building materials which has shown, that manufacture of production is rather material-intensive is carried out. This is evidenced by the share of material costs in the cost of work, and the value of the utilization factor of materials indicates the economical use of material resources in production. Reserves for improving the efficiency of material resources at construction materials enterprises have been identified. The ways of the most rational use of material resources of construction materials enterprises are offered, in particular it is improvement of a design and technology of manufacturing of products, introduction of more progressive norms of expenses of resources, use of substitute materials, and reduction of losses at stages of transportation, storage and industrial use.

scholarly journals LSSVM-Based Rock Failure Criterion and Its Application in Numerical Simulation

2015 ◽  
Vol 2015 ◽  
pp. 1-13 ◽  
Author(s):  
Changxing Zhu ◽  
Hongbo Zhao ◽  
Zhongliang Ru
Keyword(s):  
Rock Mass ◽  
Failure Criterion ◽  
Nonlinear Problems ◽  
Failure Criteria ◽  
Rock Failure ◽  
Support Vector ◽  
Failure Behavior ◽  
Circular Tunnel ◽  
Vector Machines

A rock failure criterion is very important for the prediction of the failure of rocks or rock masses in rock mechanics and engineering. Least squares support vector machines (LSSVM) are a powerful tool for addressing complex nonlinear problems. This paper describes a LSSVM-based rock failure criterion for analyzing the deformation of a circular tunnel under differentin situstresses without assuming a function form. First, LSSVM was used to represent the nonlinear relationship between the mechanical properties of rock and the failure behavior of the rock in order to construct a rock failure criterion based on experimental data. Then, this was used in a hypothetical numerical analysis of a circular tunnel to analyze the mechanical behavior of the rock mass surrounding the tunnel. The Mohr-Coulomb and Hoek-Brown failure criteria were also used to analyze the same case, and the results were compared; these clearly indicate that LSSVM can be used to establish a rock failure criterion and to predict the failure of a rock mass during excavation of a circular tunnel.

Wedge-Splitting Test – Determination of Minimal Starting Notch Length for Various Cement Based Composites Part I: Cohesive Crack Modelling

2010 ◽  
Vol 452-453 ◽  
pp. 77-80 ◽  
Author(s):  
Václav Veselý ◽  
Ladislav Řoutil ◽  
Stanislav Seitl
Keyword(s):  
Fracture Mechanics ◽  
Cohesive Crack ◽  
Crack Model ◽  
Singular Stress ◽  
Initiation Point ◽  
Linear Elastic ◽  
Wedge Splitting Test ◽  
Splitting Test ◽  
Notch Length ◽  
Wedge Splitting

The geometric proportions of cube-shaped specimens subjected to wedge-splitting tests are numerically studied in the paper. The minimal notch length for specimens made of cement based composites varying in characteristic length of the material (a measure of material brittle-ness/heterogeneity) is verified using finite element method code with an implemented cohesive crack model (ATENA). The problem of assigning the crack initiation point (the notch tip vs. the groove corner in the load-imposing area of the specimen) is solved numerically also using both the theory of linear elastic fracture mechanics and the theory of the fracture mechanics of generalized singular stress concentrators in the second part of the two-part paper. Results ob-tained by the different approaches are compared. The minimal notch length is recommended.

Identification of Forming Limits for Unidirectional Carbon Textiles in Reality and Mesoscopic Simulation

2013 ◽  
Vol 554-557 ◽  
pp. 423-432 ◽  
Author(s):  
Patrick Böhler ◽  
Frank Härtel ◽  
Peter Middendorf
Keyword(s):  
Raw Materials ◽  
Weight Ratio ◽  
Experimental Tests ◽  
Simulation Method ◽  
Failure Criteria ◽  
Forming Process ◽  
Mesoscopic Simulation ◽  
Sewing Thread ◽  
Young’S Moduli ◽  
Definition Of

In several fields of engineering the use of carbon fibre reinforced material (CFRP) is increasing. Minimized weight due to CFRPs could lead to lower consumption of raw materials especially in the automotive area. The goal within the research project TC² is the decrease of costs and production time for composite materials. To achieve better performance to weight ratio and to get acceptable production conditions the draping of dry unidirectional textiles and a following RTM process is investigated. Due to the high degree of complexity of automotive structures the forming process is challenging. Gapping in the textile could appear at corners as well as wrinkling or flexion of the fibres. To be able to define the amount and direction of layers or patches it is necessary to know the limits of forming for unidirectional material and to be able to predict the behaviour of the textile during the forming process. For the definition of the process limits several draping strategies are performed on different corner blend geometries. The goal of that work is to define the critical gradient of the flange to get first failures such as wrinkling or gapping. It is also important to understand the influence of different draping strategies. Parallel to the experimental tests a mesoscopic simulation method using an approach with roving and sewing thread is developed and presented. It is able to predict the material behaviour in critical areas (gapping, wrinkling). Different Young’s moduli and failure criteria can be implemented for the two main directions as well as for the bending of the textile. A validation with the experimental results is performed with the aim to enable the prediction of the textile behaviour using simulation methods.

scholarly journals Technical Note: Implementation of a geodatabase of published and unpublished data on the catastrophic Vaiont landslide

2010 ◽  
Vol 10 (4) ◽  
pp. 865-873 ◽  
Author(s):  
L. Superchi ◽  
M. Floris ◽  
M. Ghirotti ◽  
R. Genevois ◽  
M. Jaboyedoff ◽  
...  
Keyword(s):  
Failure Mechanisms ◽  
Technical Note ◽  
Bibliographic Database ◽  
Southern Slope ◽  
Dam Reservoir ◽  
Methods And Techniques ◽  
Slope Collapse ◽  
Electronic Bibliographic Database ◽  
Definition Of ◽  
The Town

Abstract. On 9 October 1963 a catastrophic landslide suddenly occurred on the southern slope of the Vaiont dam reservoir. A mass of approximately 270 million m3 collapsed into the reservoir generating a wave that overtopped the dam and hit the town of Longarone and other villages nearby. Several investigations and interpretations of the slope collapse have been carried out during the last 45 years, however, a comprehensive explanation of both the triggering and the dynamics of the phenomenon has yet to be provided. In order to re-evaluate the currently existing information on the slide, an electronic bibliographic database and an ESRI-geodatabase have been developed. The chronology of the collected documentation showed that most of the studies for re-evaluating the failure mechanisms were conducted in the last decade, as a consequence of knowledge, methods and techniques recently acquired. The current contents of the geodatabase will improve definition of the structural setting that influenced the slide and led to the the propagation of the displaced rock mass. The objectives, structure and contents of the e-bibliography and Geodatabase are indicated, together with a brief description on the possible use of the alphanumeric and spatial contents of the databases.

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