Abstract: A finite element analysis was conducted to determine
the effect of moisture diffusion and hygroscopic swelling in rice. A
parallel simple stochastic modeling was performed to predict the
number of grains cracked as a result of moisture absorption and
hygroscopic swelling. Rice grains were soaked in thermally (25 oC)
controlled water and then tested for compressive stress. The
destructive compressive stress tests revealed through compressive
stress calculation that the peak force required to cause cracking in
grains soaked in water reduced with time as soaking duration was
extended. Results of the experiment showed that several grains had
their value of the predicted compressive stress below the von Mises
stress and were interpreted as grains which become cracked and/or
broke during soaking. The technique developed in this experiment
will facilitate the approximation of the number of grains which will
crack during soaking.
Abstract: Hot tear cracking and residual stress are two different consequences of thermal stress both of which can be considered as casting problem. The purpose of the present study is simulation of the effect of casting shape characteristic on hot tearing and residual stress. This study shows that the temperature range for simulation of hot tearing and residual stress are different. In this study, in order to study the development of thermal stress and to predict the hot tearing and residual stress of shaped casting, MAGMASOFT simulation program was used. The strategy of this research was the prediction of hot tear location using pinpointing hot spot and thermal stress concentration zones. The results shows that existing of stress concentration zone increases the hot tearing probability and consequently reduces the amount of remaining residual stress in casting parts.
Abstract: In recent years, a new numerical method has been
developed, the extended finite element method (X-FEM). The
objective of this work is to exploit the (X-FEM) for the treatment of
the fracture mechanics problems on 3D geometries, where we
showed the ability of this method to simulate the fatigue crack
growth into two cases: edge and central crack. In the results we
compared the six first natural frequencies of mode shapes uncracking
with the cracking initiation in the structure, and showed the stress
intensity factor (SIF) evolution function as crack size propagation
into structure, the analytical validation of (SIF) is presented. For to
evidence the aspects of this method, all result is compared between
FEA and X-FEM.
Abstract: In pressure vessels contain hydrogen, the role of
hydrogen will be important because of hydrogen cracking problem. It
is difficult to predict what is happened in metallurgical field spite of a
lot of studies have been searched. The main role in controlling the
mass diffusion as driving force is related to stress. In this study, finite
element analysis is implemented to estimate material-s behavior
associated with hydrogen embrittlement. For this purpose, one model
of a pressure vessel is introduced that it has definite boundary and
initial conditions. In fact, finite element is employed to solve the
sequentially coupled mass diffusion with stress near a crack front in a
pressure vessel. Modeling simulation intergrarnular fracture of AISI
4135 steel due to hydrogen is investigated. So, distribution of
hydrogen and stress are obtained and they indicate that their
maximum amounts occur near the crack front. This phenomenon is
happened exactly the region between elastic and plastic field.
Therefore, hydrogen is highly mobile and can diffuse through crystal
lattice so that this zone is potential to trap high volume of hydrogen.
Consequently, crack growth and fast fracture will be happened.
Abstract: Road industry has challenged the prospect of ecoconstruction. Pavements may fit within the framework of sustainable development. Hence, research implements assessments of conventional pavements impacts on environment in use of life cycle approach. To meet global, and often national, targets on pollution control, newly introduced pavement designs are under study. This is the case of Cyprus demonstration, which occurred within EcoLanes project work. This alternative pavement differs on concrete layer reinforced with tire recycling product. Processing of post-consumer tires produces steel fibers improving strength capacity against cracking. Thus maintenance works are relevantly limited in comparison to flexible pavement. This enables to be more ecofriendly, referenced to current study outputs. More specific, proposed concrete pavement life cycle processes emits 15 % less air pollutants and consumes 28 % less embodied energy than those of the asphalt pavement. In addition there is also a reduction on costs by 0.06 %.
Abstract: Multi-site damage (MSD) has been a challenge to
aircraft, civil and power plant structures. In real life components are subjected to cracking at many vulnerable locations such as the bolt
holes. However, we do not consider for the presence of multiple cracks. Unlike components with a single crack, these components are
difficult to predict. When two cracks approach one another, their
stress fields influence each other and produce enhancing or shielding effect depending on the position of the cracks. In the present study,
numerical studies on fracture analysis have been conducted by using
the developed code based on the modified virtual crack closure integral (MVCCI) technique and finite element analysis (FEA) software ABAQUS for computing SIF of plates with multiple cracks.
Various parametric studies have been carried out and the results have
been compared with literature where ever available and also with the solution, obtained by using ABAQUS. By conducting extensive
numerical studies expressions for SIF have been obtained for collinear cracks and non-aligned cracks.
Abstract: Fatigue cracking continues to be the main challenges in
improving the performance of bituminous mixture pavements. The
purpose of this paper is to look at some aspects of the effects of fine
aggregate properties on the fatigue behaviour of hot mixture asphalt.
Two types of sand (quarry and mining sand) with two conventional
bitumen (PEN 50/60 & PEN 80/100) and four polymers modified
bitumen PMB (PM1_82, PM1_76, PM2_82 and PM2_76) were used.
Physical, chemical and mechanical tests were performed on the sands
to determine their effect when incorporated with a bituminous
mixture. According to the beam fatigue results, quarry sand that has
more angularity, rougher, higher shear strength and a higher
percentage of Aluminium oxide presented higher resistance to
fatigue. Also a PMB mixture gives better fatigue results than
conventional mixtures, this is due to the PMB having better viscosity
property than that of the conventional bitumen.
Abstract: In this study, a longitudinal joint connection was
proposed for the short-span slab-type modular bridges with rapid
construction. The slab-type modular bridge consists of a number of
precast slab modules and has the joint connection between the
modules in the longitudinal direction of the bridge. A finite element
based parameter analysis was conducted to design the shape and the
dimensions of the longitudinal joint connection. Numbers of shear
keys within the joint, height and depth of the shear key, tooth angle,
and the spacing were considered as the design parameters. Using the
local cracking load at the corner of the shear key and the
cross-sectional area of the joint, an efficiency factor was proposed to
evaluate the effectiveness of the longitudinal joint connection. The
dimensions of shear key were determined by comparing the cracking
loads and the efficiency factors obtained from the finite element
analysis.
Abstract: Environment-assisted cracking (EAC) is one of the most serious causes of structural failure over a broad range of industrial applications including offshore structures. In EAC condition there is not a definite relation such as Paris equation in Linear Elastic Fracture Mechanics (LEFM). According to studying and searching a lot what the researchers said either a material has contact with hydrogen or any other corrosive environment, phenomenon of electrical and chemical reactions of material with its environment will be happened. In the literature, there are many different works to consider fatigue crack growing and solve it but they are experimental works. Thus, in this paper, authors have an aim to evaluate mathematically the pervious works in LEFM. Obviously, if an environment is more sour and corrosive, the changes of stress intensity factor is more and the calculation of stress intensity factor is difficult. A mathematical relation to deal with the stress intensity factor during the diffusion of sour environment especially hydrogen in a marine pipeline is presented. By using this relation having and some experimental relation an analytical formulation will be presented which enables the fatigue crack growth and critical crack length under cyclic loading to be predicted. In addition, we can calculate KSCC and stress intensity factor in the pipeline caused by EAC.
Abstract: Fracture process in mechanically loaded steel fiber
reinforced high-strength (SFRHSC) concrete is characterized by
fibers bridging the crack providing resistance to its opening.
Structural SFRHSC fracture model was created; material fracture
process was modeled, based on single fiber pull-out laws, which were
determined experimentally (for straight fibers, fibers with end hooks
(Dramix), and corrugated fibers (Tabix)) as well as obtained
numerically ( using FEM simulations). For this purpose experimental
program was realized and pull-out force versus pull-out fiber length
was obtained (for fibers embedded into concrete at different depth
and under different angle). Model predictions were validated by
15x15x60cm prisms 4 point bending tests. Fracture surfaces analysis
was realized for broken prisms with the goal to improve elaborated
model assumptions. Optimal SFRHSC structures were recognized.