Key Engineering Materials
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Vols. 324-325
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Vols. 321-323
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Key Engineering Materials Vols. 324-325
Paper Title Page
Abstract: This work presents the investigation results of laser remelting and alloying
especially the laser parameters and its influence on the structure and properties of the surface
of the 32CrMoV12-28 hot work steel, using the high power diode laser (HPDL). As a result
structure changes in form of fragmentation were determined. The reason of this work was to
determine the optimal laser treatment parameters, particularly the laser power to achieve good
layer hardness for protection of this hot work tool steel from losing their work stability and to
make the tool surface more resistant to action in hard conditions. For alloying the tantalum
carbide, tungsten carbide and vanadium carbide powders were used. For investigations
hardness measurements of the different remelting areas were performed. The remelted layers
which were formed in the surface of investigated hot work steel were examined
metallographically and analyzed using light and electron microscope. Three phases of
carbides, TaC, VC and WC, were observed.
1233
Abstract: The effect of strain rate on the dynamic compressive of carbon/epoxy composite materials
was investigated via the split Hopkinson pressure bar (SHPB) technique. The specimens were tested
in the thickness, as well as in the in-plane direction at different high strain rates. The macro- and
micro-fracture morphology of the damaged laminated specimens was obtained utilizing the scanning
electron microscope (SEM). The experimental results showed that the compressive properties could
be significantly affected by the strain rates. The compressive strength and the ultimate strain in the
in-plane direction were obviously lower than that in the thickness direction. As the strain rate
increased, the laminate had not enough time to respond, the splitting failure of 0° ply of laminates
loaded in-plane along 0° was firstly found, then interfacial crack and delamination were induced, the
specimens were crushed to fragments at the highest strain rate. No obvious damage of laminates
loaded through the thickness could be observed at strain rate below 2000 s-1. The main way of the
dynamic compressive failures through the thickness was shear failure due to the brittle fracture of
the fiber at 2260 s-1.
1237
Abstract: A series of strain fatigue tests were carried out on small bugle-like slice-specimens of
Zr-4 alloy at 20 and 400. According to Elastic and Plastic Finite Element Analysis
and assumption of local damage equivalence, a strain formula was given to transform transverse
strain of the specimen to uniaxial strain. Based on the test results of the alloy and the strain transform
formula, M-C (Manson-Coffin) models to be used for estimating uniaxial fatigue life of Zr-4
alloy were obtained. The results show that, the alloy mainly behaves as cyclic softening at 20 and
as cyclic hardening at 400, and the elevated temperature can lead serious additional fatigue damage
of the alloy and the effect of the elevated temperature impairs gradually with increasing of amplitude
strain. A conclusion is helpful that prediction life by using M-C model based on traditional
strain transform equation is quite conservative when uniaxial strain amplitude is less than 0.5%.
1241
Abstract: The boundary element analysis is attempted to investigate the relaxation behavior of the
bolt load in a single bolted joint fastening thermosetting polymers. More than 10 % relaxation is
obtained after 4,000 minutes. The loss of bolt stress is more important because the stress in the
polymer is much smaller. Such relaxation of the bolt stress can cause loosening for fasteners and loss
of fastener effectiveness for bolts that rely on clamping force or preload to achieve needed joining
forces. The experimental evaluation is required to clarify the effect of the loss of bolt load on function
of the assembly.
1245
Abstract: Polymeric materials such as epoxy are widely used as coating layers for the containment
building of the nuclear power plant. These layers may be damaged through a hygrothermal process
and residual stresses can reach significant levels near the free edges, possibly leading to interface
debonding or delamination. Interfacial stress singularities induced in a laminate model consisting of
the epoxy coating layer and the concrete substrate is investigated using the time-domain boundary
element method. The epoxy layer is assumed to be a linear viscoelastic material and moisture effects
are assumed to be analogous to thermal effects. The overall stress intensity factor for the case of a
small interfacial edge crack of length a has been computed.
1249
Abstract: The magnetic coercivity of ferritic 12Cr steel was experimentally studied in order to
characterize its microstructures and mechanical properties during isothermal aging. As the aging time
increased, the M23C6 carbide coarsened and additional precipitation of Fe2W phase was induced. The
width of martensite lath increased to about 0.4μm after 4000 hrs of aging. The coercivity decreased as
the number of precipitate decreased and the width of martensite lath increased. The hardness was
proportional to the magnetic coercivity. These empirical linear relations suggested that the change in
the microstructures and strength of ferritic 12Cr steel during thermal aging could be evaluated by
monitoring the magnetic coercivity.
1253
Abstract: Natural human tooth consists of multiple layered quasi-brittle biomaterials, which make
dental restorations experience a complex stress state under masticatory contact loading. As such,
many restorations are prone to failure and a constant effort is made to improve the mechanical
characteristics of the restorative materials. Clinical observations have shown that improved
strengths and fracture toughness in ceramic materials do not necessarily lead to an anticipated
higher functional longevity of the restoration. While substantial experimental investigations have
been carried out to identify the contact induced fracture in such multi-layer material systems,
numerical modelling of this event was largely unexplored. This paper presents a new numerical
method to account for micro-damage driven fracture in various multi-layered biomaterial structures.
In this study, a Rankine constitutive model is adopted and the crack initiation and propagation are
automatically implemented in an explicit finite element (FE) framework. The effects of indenter
radius, surface curvature and thickness of layered biomaterials on the cracking patterns are
investigated. The results show good agreement with the experimental studies in literature.
1257
Abstract: In this paper, an isotropic elastic damage analysis is presented by using a meshless
boundary element method (BEM) without internal cells. First, nonlinear boundary-domain integral
equations are derived by using the fundamental solutions for undamaged, homogeneous, isotropic and
linear elastic solids and the concept of normalized displacements, which results in boundary-domain
integral equations without an involvement of the displacement gradients in the domain-integral. Then,
the arising domain-integral due to the damage effects is converted into a boundary integral by
approximating the normalized displacements in the domain-integral by a series of prescribed radial
basis functions (RBF) and using the radial integration method (RIM). The damage variable used in the
paper is the ratio of the damaged area to the total area of the material, and an exponential evolution
equation for the damage variable is adopted. A numerical example is given to demonstrate the
efficiency of the present meshless BEM.
1261
Abstract: A fatigue analysis program to calculate fatigue lives of mechanical components and
structures from FE(Finite Element) results is developed. The useful characteristic of this program is
operated under Web environment. So, any designer who design fatigue strength of components and
structures can use without other program installation. For the assessment of multi-axial fatigue
damage, signed equivalent stress method and critical plane approach have been employed. Each
method is compared and the results of Signed von Mises stress method has similar to the results of
Smith-Waston-Topper's parameter using critical plane approach. The results were compared with
those from commercial program FE-Fatigue6.0 and it was observed that fatigue life and cumulative
damage distribution calculated applying same fatigue resistance curve. The results of calculated
fatigue life using Web based program agree well with those from FE-Fatigue6.0.
1265
Abstract: In this study, the fatigue life evaluation of automatic transfer devices under stress
concentrations due to the notch effect is performed. To investigate residual life of a notched
component, load histories were obtained through strain measurement. A fatigue test was performed
on a specimen imitating a real component and results were compared with each notch root radius of
the concentration area. Three-dimensional finite element analysis was also performed to evaluate the
local stress fields. Miner’s rule was used to predict the fatigue life calculation. As a result, the
predicted life of a notched component was in good agreement with a real component and introduced a
special method for measuring load using real machine components.
1269