Abstract: On the basis of the dynamic equations of the Jeffcott rotor-stator model with imbalance,
the reliability of the rotor-stator systems with rubbing is examined. A statistical fourth moment
method is developed to determine the first four moments of system response and state function. The
distribution function of the system state function is approximately determined by the standard
normal distribution functions using the Edgeworth series technique. The reliability is obtained and
the effect on reliability of shaft stiffness and damping, stator stiffness and damping, radial clearance
and stator radial stiffness is studied. Numerical results are also presented and discussed.
Abstract: The failure analysis of uncertain multi-degree-of-freedom (MDOF) nonlinear vibration
systems with uncorrelated failure modes subjected to random excitation is examined. An earlier
version of the statistical fourth-moment method is extended to vector-valued and matrix-valued
functions and is developed to determine the first four moments of the system response and state
function. Random variables and system derivatives are conveniently arranged into 2D matrices by
means of Kronecker products. The distribution function of the system state function is
approximately determined by the standard normal distribution functions using Edgeworth series
technique and its failure probability is obtained. The method is based on matrix calculus. Kronecker
algebra is used in the mathematical development.
Abstract: Hydrogen-induced corrosion is a common damage in petrochemical industry. It can rise
crack and bubbling on the surface of metal materials when the hydrogen corrosion is in the stage of
severity. In the present, it is hard to evaluate the material conditions nondestructively under
hydrogen attack. In this paper, the possibility of the relationship between ultrasonic propagation
properties and the content of hydrogen corrosion was investigated. We have found that the surface
wave velocity is a parameter, which can be directly correlated with the hydrogen content. The
sensitivity has been found to be acceptable.
Abstract: A typical mechanical character of rock is that the tensile strength is far less than the
compressive strength. Meanwhile, the test data of tensile strength is very dispersive. Because the
direct tensile tests always result in failure due to the difficulty in clamping the rock sample, the
splitting test is used to determine the tensile strength of rock. There are four kinds of loading modes
in the splitting test in actual laboratory test: angle pad splitting, round pad splitting, aclinic loading
platen splitting, arc loading platen splitting. In this paper, the direct tensile test, the splitting test and
the influence of different loading modes on rock tensile strength were studied. In order to study the
stress distribution, the progressive splitting failure process was numerically modeled under the four
kinds of loading cases by the Realistic Failure Process Analysis code (RFPA2D). Results show that
the stress states under angle pad splitting, round pad splitting are similar to the stress states under
diametrical compressive state. Regarding that the round pad splitting test is easy to implement, and
its numerical results are also stable relatively, the round pad loading mode was suggested to be
Abstract: Since the number of fatigue crack propagation data is related to cost and time and the crack
propagation data are generally finite, adopting median rank or average rank as the probability value of
a test datum will result in significant error. On the basis of analyzing disadvantages of traditional
methods to identify distribution functions, which begin with overall fitting effect, this paper proposed
a method by applying numerical simulation and fuzzy linear regression. It can be used to determine
the distribution function of crack propagation data. Through fuzzy linear regression, the result that
crack propagation size under certain load cycles are in logarithmic normal distribution can be
acquired. In the same way, the number of load cycles is also in logarithmic normal distribution when
the crack propagates to a certain size.
Abstract: The reliability estimation of pipeline is performed in accordance with the probabilistic
methods such as the FORM (first order reliability method) and the SORM (second order reliability
method). A limit state function has been formulated with help of the FAD (failure assessment
diagram). Various types of distribution of random variables are assumed to investigate its effect on
the failure probability. It is noted that the failure probability increases with the increase of the dent
depth, the operating pressure and the outside radius, and the decrease of the wall thickness.
Furthermore it is found that the failure probability for the random variables having the Weibull
distribution is larger than those of the normal and the lognormal distributions.
Abstract: In this paper, by employing a three dimensional geomechanics model test whose scale is
1:250, the dam cracking process was observed, and integrity stability was analyzed and evaluated
under overloading test. The experimental results show that: the stress and strain of the dam can
basically meet the requirements of dam safety under normal water load, and the dam failure mode of
the left abutment is different from that in the right side because of different types of dam figure and
geological conditions. Firstly, the local slip fracture is formed on the foundation, then extends along
the bottom of dam, and leads to instability and final failure. In overloading process, crack initiate from
dam heel under twice normal water pressure, and form a small cracking zone, then yielding
continuously and crack band appearing in downstream surface under 4.5th normal water pressure, and
overall failure under 8.5th normal water pressure. The integrity stability is shown strong enough with
experimental dam shape (XLD03 Figure) and the configuration of its foundation.
Abstract: With the increasing needs of the more convenient transportation, wheelchairs are often
used by people with mobility disabilities and the elderly people. However, as wheelchairs are
primarily designed for the mobility assistive devices, not for the vehicle seats, wheelchair users are
exposed to risk factors for neck and upper body injury caused by automobile accidents.
In this paper, in accordance with the ANSI/RESNA WC-19, a fixed vehicle mounted wheelchair
occupant restraint system (FWORS), wheelchair integrated restraint system (WIRS), and wheelchair
integrated x-bend restraint system (WIXRS) are evaluated using computer simulations for the case
when a wheelchair is subjected to the frontal impact (20 g, 48 km/h).
Abstract: In recent years, several electronics manufacturers have been working toward introducing
lead-free solder and halogen-free print circuit boards (PCBs) into their products. The key drivers for
the change in materials have been the impending environmental legislations, particularly in Europe
and Japan as well as the market appeal of ‘green’ products. The reliability of the new materials is an
important determinant of the pace of adoption. Fairly extensive mechanical fatigue reliability data is
also available for micro-joining soldered joint such as Ball Grid Array (BGA) with tin-lead solder.
However, similar data is not available for BGAs assembled with lead-free solder. Mechanical
reliability is a critical indicator for phone and BGA survival during repeated keypress, and to some
extent during drop. In this paper, the mechanical bend fatigue of BGAs with tin-lead and lead-free
solders on halogen-free substrates are examined respectively. A tin-silver-copper alloy was used as
lead-free solder due to its increasing acceptance, and the results were compared to those from samples
assembled with Sn63Pb37 solder. The reliability was examined at both low cycle and high cycle
fatigue. Results show that the mechanical bend fatigue reliability of BGA assemblies with lead-free
solder is higher than that of BGA assembly with tin-lead solder. Cross section and failure analysis
indicated two distinct failure modes - solder joint and PCB failure. A 3-D parametric finite element
model was developed to correlate the local PCB strains and solder joint plastic strains with the fatigue
life of the assembly. The intermetallic compoumd (IMC) of micro-joining joint interface was
analysised in the future in order to study on the effect of IMC on the reliability.