Abstract: This paper concerns fracture dynamic problems for elastic cracked solids with allowance
for crack faces contact interaction. The contact problem for a penny-shaped crack with an initial
opening under normally incident tension-compression wave is solved by the method of boundary
integral equations. The solution is compared with those obtained without allowance for crack faces
contact interaction for various values of the initial opening.
Abstract: A series of fracture toughness tests have been conducted on a type of coarse grain
marble. The tests were carried out either in pure mode I or in pure mode II conditions by using the
cracked chevron notched Brazilian disc (CCNBD) specimen. A total number of 44 CCNBD
specimens were tested, half in pure mode I and the rest in pure mode II, to obtain reliable values for
mode I and mode II fracture toughness (KIc and KIIc) of the tested marble. The average value of KIc
for this marble was approximately about 1.12 MPa m showing a good agreement with those reported
for similar coarse grain marbles. The mode II fracture toughness was found to be 2.25 MPa m in
average which is approximately twice the mode I fracture toughness. However, the conventional
fracture criteria suggest that the mode I fracture toughness should be higher than the mode II
fracture toughness, (KIc>KIIc). According to these criteria, the ratio of KIIc / KIc is a figure typically
between 0.63 and 0.96. It is shown in this paper that enhanced mode II fracture toughness of
CCNBD specimen could be due to the effects of highly negative T-stress when the specimen is
subjected to mode II. It is also shown that an improved prediction for the ratio KIIc / KIc can be
achieved when the effect of T-stress is taken into account.
Abstract: The mechanical properties of composite laminates play a key role in the success of
composite reinforcement method, but various investigations suggest that the stiffness of epoxybased
composites is sensitive to the variation of moisture ratio and temperature of the working
environment. The aim in this research is to characterize the effect of hygrothermal aged composite
patch on the strength of repaired cracks, under mixed mode I/II conditions. For this purpose a
reinforced sheet, i.e. a crack fastener hole specimen is examined by using a finite element
simulation. The crack tip parameters and fracture characteristics of repaired cracks are determined
as a function of the total amount of moisture inside the composite patch. The results of this study
show that the performance of composite reinforcement technique depends on the amount of water
absorption within the bonded patches.
Abstract: The ISO 6267 standard defines a damping measuring method in terms of the half-time of
the vibration of clamped alpine skis that is mainly related to the first vibration mode only. By means
of the experimental test done in laboratory, it is shown that this method is not able to completely
characterize the damping of the skis that depends on the vibration mode considered. For example in
the case a ski sample, damping ratio varies from 0.45%±0.05% of the first mode to 2.1%±0.1% of
the fourth one.
The experimental test done on ski tracks by means of piezo-accelerometers placed on the skis
running at speed of 12.5 m/s showed that the skis vibrate according to a combination of at least the
first 4 vibration modes and that the snow better excites frequencies greater than the first one.
As the excitation frequencies on the skis during the descent are much higher than the first natural
frequency of the ski, it appears not correct to hypothesize that only the damping coefficient relative
to the first natural frequency is representative of the ski vibrations.
To improve the UNI ISO 6267 standard, a new method based on the Fourier Transform filtering
to separate the time history into the vibration components is proposed for the characterization of the
ski damping that is variable with its natural modes.
Abstract: In this study the natural frequencies and mode shapes of the kth order of nonhomogeneous
(deterministic and stochastic) rods are found. The solution is based on the functional
perturbation method (FPM). The natural frequency and mode shape of the kth order is found
analytically to any desired degree of accuracy. In the deterministic it is shown that the FPM
accuracy range for the frequency ω and the mode shape is less then 1%. The stochastic case
demonstrates the power of this method. The material and geometrical properties will be considered
as statistically homogeneous random field with exponential two-point correlation. It is shown that
the accuracy depends on the stochastic information used, the correlation distance (roughly the
“grain size”), and whether we are interested in the properties of ω or ω2.
Abstract: This paper focuses on the investigation of the autoparametric coupling effects and modal
interactions in a suspension rope system with a time varying length. Equations of motion of a
multi-degree-of-freedom discrete, non-stationary and non-linear model are presented and are used
to analyze the dynamic response of an elevator suspension rope system under resonance conditions.
The equations of motion involve quadratic and cubic non-linear terms which are responsible for the
modal interaction between the lateral and longitudinal oscillations of the rope and the car motions.
The model takes into account the periodic excitations caused by motion of the host structure. The
results confirm that adverse responses may arise and internal autoparametric resonance phenomena
Abstract: This paper presents the application of modal analysis and parameter identification
using data of random vibration test to a cylinder structure. It is deduced that the impulse
response function can be substituted by the cross-correlation function computed directly
from the response-only data based on the white noise excitation or broadband input. So the
modal parameter identification can be done by the least squares complex exponential
(LSCE) method. And the modal parameters are obtained from the random vibration test data
by the complex exponential method. Compared with the results of traditional modal test, the
results of random vibration test are proved to be correct, and also the feasibility of this idea
is proved well.
Abstract: This paper deals with the mathematical model of dynamic behaviour of a beam resting
on viscoelastic random foundation for which the modulus of subgrade reaction is assumed to be a
homogeneous random function of the space variable. An approximate analytical solution for the
fourth-order differential equation with random parameters is obtained in the case of a
correlation function. This higher order regularity of correlation function implies the regularity of
associated stochastic function  in the sense of the mean-square analysis . The numerical results
for the average displacement have been obtained by using Bourret’s approximation method. A
special method of finding inverse Laplace transform based on the wavelet theory is adopted and
used in the numerical examples.
Abstract: This work was motivated by the recent NATO funded research on preventing disasters
from collapse and improving the safety of aircraft structures. It considers the problem for vibrationbased
damage detection in aircraft panels modelled as isotropic plates. The explored method does
not use any assumptions of model or linearity, it is simply based on pure signal analysis of the
vibration response of plates. FE modelling is used to model the plate’s dynamic response in its
intact and in its damaged state. The signals obtained are analysed using multivariate analysis applied
in the measured frequency domain. This reduces the data dimensionality and is expected to have a
clustering effect. At this stage the measured data is transformed into features – new variables- which
have smaller dimension than the initial ones and make the categories more distinguishable. Then a
very simple pattern recognition (PR) method is applied to discriminate between the two categories
of data -data coming from the undamaged plate and data coming from the damaged plate. This is the
second stage when the obtained features are used for the actual recognition between the defined
categories. The paper suggests the use of the Karhunen-Loeve transform in order to extract features
from the measured frequency response functions of the plate. When the data dimensionality is
brought down to two the response of the plate can be visualised. The clustering effect on the
features coming from undamaged plate and those from the damaged is obvious.