Key Engineering Materials
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Key Engineering Materials Vols. 324-325
Paper Title Page
Mechanical Performances and Failure Modes of Direct Diffusion Bonding Joints of 316L Stainless Steel
Abstract: Direct diffusion bonding of 316L stainless steel was performed at 850-1100°C for 1-3 h
under a pressure of 10MPa in this study. The effect of bonding temperature and holding time on
mechanical performances of the joints was investigated. Tensile tests were conducted to evaluate
strength and elongation of the joints at room temperature and elevated temperature of 550°C. The
microstructure and fracture surfaces of the joints were examined by optical microscope (OM) and
scanning electronic microscope (SEM). The results indicated that the elongation of the joints
increased with the increase of bonding temperature and holding time. However, overlong holding
time had a side effect on the strength of the joint. Moreover, the change of the mechanical properties
was closely related to the variation of the microstructure of the joints. The X-ray diffraction (XRD)
analysis revealed that FeCr and Fe0.64Ni0.36 were formed at the DB6 joint during bonding process. It is
suggested that FeCr should be detrimental to the improvement of high temperature strength of the
joint.
979
Abstract: In this paper, the effect of imperfect inner interface on the stress fields in the coated
inclusion composite is investigated, the spring-layer of vanishing thickness model is introduced to
simulate the imperfect interface, assuming that across the interface between the inclusion and the
coating the interfacial traction is continuous while displacement discontinuities are permitted
through interfacial traction-displacement jump relations. Numerical examples corresponding to the
composites containing single coated spherical and fibrous inclusion, respectively, under shear
loading at infinity, are calculated, which indicate that the imperfect inner interfaces have
significant effect on stress fields of the composites.
983
Abstract: Rail dark spot defect, also termed as squat failure or shelling, is a rolling contact fatigue
failure which occurs frequently on the high speed traffic railway rails. The main goal of this study is to
develop a computational model for simulation of the squat phenomena on rails in rail-wheel contact.
The proposed computational model consists of two parts: (i) Contact Fatigue Crack Initiation (CFCI)
and (ii) Contact Fatigue Crack Propagation (CFCP). The results of proposed unified model enable a
computational prediction of a probable number of loading cycles that a wheel-rail system can sustain
before development of the initial crack in the rail, as well as the number of loading cycles required for
a crack to propagate from initial to critical length, when the final fatigue failure (squat) can be
expected to occur.
987
Abstract: The rate effect on concrete tensile strength can be modeled by the description of crack
extension in a fictitious fracture plane [1,2].The plane represents the initial, internal damage and the
geometry of the final fracture plane. In the paper, the same approach is applied to model the failure
envelope for the biaxial loading condition of static lateral compression and axial impact tensile
load. The predicted failure envelope is compared with data from experimental work.
991
Abstract: Even though the application of fiber reinforced polymer (FRP) as a concrete
reinforcement becomes more common with various advantages, one of the inherent shortcomings
may include its brittleness and on-site fabrication and handling. Therefore, the shape of FRP
products has been limited only to a straight bar or sheet type. This study suggests a new technique
to use glass fiber reinforced polymer (GFRP) bars for the shear reinforcement in concrete beams,
and investigates its applicability. The developed GFRP stirrup was used in the concrete instead of
ordinary steel stirrups. The experimental program herein evaluates the effectiveness of the GFRP
stirrups with respect to different shear reinforcing ratios under three different shear span-to-depth
testing schemes. At the same shear reinforcing ratio, the ultimate loads of the beams were similar
regardless the shear reinforcing materials. Once a major crack occurs in concrete, however, the
failure modes seemed to be relatively brittle with GFRP stirrups. From the measured strains on the
surface of concrete, the shear stresses sustained by the stirrups were calculated and the efficiency of
the GFRP stirrups was shown to be 91% to 106% depending on the shear span-to-depth ratio.
995
Abstract: Free vibration characteristics of an elastic simple beam with a fatigue notch crack
damage located any where of the beam is investigated. The notch crack is modeled by an elastic
torsion spring whose stiffness is taken to be finite and is determined from fracture mechanic theory.
On the assumption that the crack is always open when the beam vibrates transversely, the motion
equation and the boundary conditions of a simple-supported beam with a crack located anywhere of
the beam is deduced. The first-order to the sixth-order frequencies varying with the crack depth and
the crack location are calculated.
999
Abstract: Understanding dynamic behavior of a rotor system with a transverse crack is of great
significance for operation reliability of rotating machinery. The transfer matrix method is widely
used for rotor dynamic analysis, but it encounters difficulties modeling a crack. This study proposes
a finite-width crack model that simulates the local stiffness reduction effect of a gaping crack in
transfer matrix method. This model is obtained by comparing finite element analysis results of a
shaft with a zero-width crack and its counterpart transfer matrix calculation results with a trial
equivalent finite-width slot. Different shaft geometry and loading modes are considered to improve
the generality of the model. An application example is given that uses the proposed model to
calculate critical speeds of a multi-disk rotor system with a transverse crack at different positions.
1003
Abstract: The objective was to quantify the variation of stress intensity factor to weld root flaw sizes
in steel frame connections. Finite-element analyses were used to study fracture toughness in welded
beam-column connections. Investigations of fracture behavior mainly focused on the standard
pre-Northridge connection geometry. Finite element analysis was performed using the ANSYS
computer program. Stress intensity factor was calculated through a J-integral approach. Results show
that stress intensity factor is not uniform and is largest in the middle of beam flange. Stress intensity
factor increases nearly linear with the increase of flaw size. Backing bars have little effect on weld
fractures.
1007
Abstract: The spacer grid assembly, which is an interconnected array of slotted grid straps and
welded at the intersections to form an egg crate structure, is one of the main structural components
of the nuclear fuel assemblies of a Pressurized light Water Reactor (PWR). The spacer grid
assembly is structurally required to have enough crush strength under lateral loads due to lateral
seismic accelerations, lateral Loss Of Coolant Accident (LOCA) blowdown forces, and shipping
and handling loads so that the fuel rods are maintained within a coolable geometry, and that the
control rods are able to be inserted. The ability of the spacer grid assembly to resist the lateral loads
is usually characterized in terms of its dynamic and static crush strengths, which are acquired from
the relevant tests. In this study, dynamic buckling tests and finite element analyses on spacer grid
assembly specimens are carried out. As a result of the comparisons, the analysis results are in good
agreement with the test results to within an 8 % difference range. Therefore, we could predict the
crush strength of a spacer grid assembly in advance before performing the dynamic buckling test.
1011