28,634 research outputs found
A phase-field model for fractures in incompressible solids
Within this work, we develop a phase-field description for simulating
fractures in incompressible materials. Standard formulations are subject to
volume-locking when the solid is (nearly) incompressible. We propose an
approach that builds on a mixed form of the displacement equation with two
unknowns: a displacement field and a hydro-static pressure variable.
Corresponding function spaces have to be chosen properly. On the discrete
level, stable Taylor-Hood elements are employed for the displacement-pressure
system. Two additional variables describe the phase-field solution and the
crack irreversibility constraint. Therefore, the final system contains four
variables: displacements, pressure, phase-field, and a Lagrange multiplier. The
resulting discrete system is nonlinear and solved monolithically with a
Newton-type method. Our proposed model is demonstrated by means of several
numerical studies based on two numerical tests. First, different finite element
choices are compared in order to investigate the influence of higher-order
elements in the proposed settings. Further, numerical results including spatial
mesh refinement studies and variations in Poisson's ratio approaching the
incompressible limit, are presented
A nonlinear vehicle-structure interaction methodology with wheel-rail detachment and reattachment
. A vehicle-structure interaction methodology with a nonlinear contact formulation
based on contact and target elements has been developed. To solve the dynamic equations of
motion, an incremental formulation has been used due to the nonlinear nature of the contact
mechanics, while a procedure based on the Lagrange multiplier method imposes the contact
constraint equations when contact occurs. The system of nonlinear equations is solved by an
efficient block factorization solver that reorders the system matrix and isolates the nonlinear
terms that belong to the contact elements or to other nonlinear elements that may be incorporated
in the model. Such procedure avoids multiple unnecessary factorizations of the linear
terms during each Newton iteration, making the formulation efficient and computationally
attractive. A numerical example has been carried out to validate the accuracy and efficiency
of the present methodology. The obtained results have shown a good agreement with the results
obtained with the commercial finite element software ANSY
A direct method for analyzing the nonlinear vehicleâstructure interaction
This article presents an accurate, efficient and stable algorithm to analyze the nonlinear vertical
vehicle-structure interaction. The governing equilibrium equations of the vehicle and structure are
complemented with additional constraint equations that relate the displacements of the vehicle with the
corresponding displacements of the structure. These equations form a single system, with displacements
and contact forces as unknowns, that is solved using an optimized block factorization algorithm. Due to
the nonlinear nature of contact, an incremental formulation based on the Newton method is adopted. The
vehicles, track and structure are modeled using finite elements to take into account all the significant
deformations. The numerical example presented clearly demonstrates the accuracy and computational
efficiency of the proposed method
Predicted vs Measured Initial Camber in Precast Prestressed Concrete Girders
Prestressing of concrete is the introduction of permanent internal stresses in a structure or system in order to improve its performance. Concrete is strong in compression but weak in tension. The tensile strength of concrete is approximately 10% of the concreteâs compressive strength. Prestressing strands helps counteract this by introducing compressive stress in the area that will experience tensile stress because of the service load. In precast prestressed concrete girders, strands are placed in the bottom flange of the girder. These strands are tensioned to approximately 75% of their ultimate tensile capacity. After placing the concrete and after the required compressive strength has been achieved, the strands are cut and the tension forces transfer from the strands to the concrete. This creates a large compressive stress in the bottom flange. The eccentricity of the pretensioned strands in the prestressed concrete girders creates a bending moment that causes the girder to deflect upward, and this is called camber. This camber is reduced by the downward deflection of the girder due to the girder self-weight.
Camber in prestressed concrete girders is effected by several factors, such as the girderâs cross sectional properties, concrete material properties, strand stress, ambient temperature, and relative humidity. Some methods of predicting camber use the initial camber that occurs immediately after cutting the strands to predict the camber at the time of girder erection. There are many sources of errors in predicting camber in a concrete girder including the differences in the actual and the design value of concrete properties and of strand stress.
In this study, the difference between the measured and the predicted initial camber will be investigated on six AASHTO Type VI girders. The initial camber was predicted using the simple elastic analysis. The measured initial camber was then compared with the design camber. The difference between using the gross section properties and the transformed section properties to predict camber was quantified. Actual concrete properties including compressive strength, elastic modulus and unit weight were used to assess the current design method. Camber obtained from the actual, measured concrete properties will be called the predicted camber in this study. The effect of using the actual and the design elastic shortening losses on the estimation of the initial camber was also quantified
Multi-field modelling and simulation of large deformation ductile fracture
In the present contribution we focus on a phase-ïŹeld approach to ductile fracture applied to large deformation contact problems. Phase-ïŹeld approaches to fracture allow for an eïŹcient numerical investigation of complex three-dimensional fracture problems, as they arise in contact and impact situations. To account for large deformations the underlying formulation is based on a multiplicative decomposition of the deformation gradient into an elastic and plastic part. Moreover, we make use of a fourth-order crack regularization combined with gradient plasticity. Eventually, a demonstrative example shows the capability of the proposed framework
Study of the effectiveness of outrigger system for high-rise composite buildings for cyclonic region
The demands of taller structures are becoming imperative almost everywhere in the world in addition to the challenges of material and labor cost, project time line etc. This paper conducted a study keeping in view the challenging nature of high-rise construction with no generic rules for deflection minimizations and frequency control. The effects of cyclonic wind and provision of outriggers on 28-storey, 42-storey and 57-storey are examined in this paper and certain conclusions are made which would pave way for researchers to conduct further study in this particular area of civil engineering. The results show that plan dimensions have vital impacts on structural heights. Increase of height while keeping the plan dimensions same, leads to the reduction in the lateral rigidity. To achieve required stiffness increase of bracings sizes as well as introduction of additional lateral resisting system such as belt truss and outriggers is required
Evaluating the Impact of Critical Factors in Agile Continuous Delivery Process: A System Dynamics Approach
Continuous Delivery is aimed at the frequent delivery of good quality software in a speedy, reliable and efficient fashion â with strong emphasis on automation and team collaboration. However, even with this new paradigm, repeatability of project outcome is still not guaranteed: project performance varies due to the various interacting and inter-related factors in the Continuous Delivery 'system'. This paper presents results from the investigation of various factors, in particular agile practices, on the quality of the developed software in the Continuous Delivery process. Results show that customer involvement and the cognitive ability of the QA have the most significant individual effects on the quality of software in continuous delivery
From fracture to fragmentation: discrete element modeling -- Complexity of crackling noise and fragmentation phenomena revealed by discrete element simulations
Discrete element modelling (DEM) is one of the most efficient computational
approaches to the fracture processes of heterogeneous materials on mesoscopic
scales. From the dynamics of single crack propagation through the statistics of
crack ensembles to the rapid fragmentation of materials DEM had a substantial
contribution to our understanding over the past decades. Recently, the
combination of DEM with other simulation techniques like Finite Element
Modelling further extended the field of applicability. In this paper we briefly
review the motivations and basic idea behind the DEM approach to cohesive
particulate matter and then we give an overview of on-going developments and
applications of the method focusing on two fields where recent success has been
achieved. We discuss current challenges of this rapidly evolving field and
outline possible future perspectives and debates
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