bluuebunny/crossref_metadata_2025 huggingface dataset:
An Upper Bound Solution for a Two-Layer Cylinder Subject to Compression and Twist
Authors: Tzou Gow Yi , Alexandrov Sergei
Published: March 2009

The choice of a kinematically admissible velocity field has a great effect on the predictive
capacity of upper bound solutions. It is always advantageous, in addition to the formal requirements
of the upper bound theorem, to select a class of velocity fields satisfying some additional conditions
that follow from the exact formulation of the problem. In the case of maximum friction law, such an
additional condition is that the real velocity field is singular in the vicinity of the friction surface. In
the present paper this additional condition is incorporated in the class of kinematically admissible
velocity fields chosen for a theoretical analysis of two - layer cylinders subject to compression and
twist. An effect of the angular velocity of the die on process parameters is emphasized and discussed.
Effect of Temperature on the Low Cycle Fatigue of Cast Inconel 792-5A
Authors: Petrenec Martin , Obrtlík Karel , Polák Jaroslav , Man Jiří
Published: March 2009

Cyclic strain control tests have been performed on cylindrical specimens of cast
polycrystalline Inconel 792-5A superalloy at 23, 500, 700 and 800 °C in laboratory atmosphere to
study the effect of temperature on the fatigue behavior. Cyclic hardening-softening curves and fatigue
life curves were measured. Scanning electron microscopy was used to investigate the surface relief.
Low amplitude straining was characterized by saturation of the stress amplitude. In room temperature
high amplitude straining cyclic hardening was followed by marked saturation. Pronounced
continuous hardening until failure was observed at 500 °C. Initial cyclic hardening was followed by
softening at 800 °C. A systematic shift of the Manson-Coffin and of the Basquin curves to lower
fatigue lives was found when temperature was increased. Fatigue cracks were observed to initiate
from surface slip markings at all temperatures.
Soft Surface Layer of Age-Hardened Al-Zn Alloys and Its Effect on the Fatigue Strength
Authors: Kanadani Teruto , Nakagawa Keiyu , Hosokawa Norio
Published: March 2009

The surface layer of binary Al-Zn alloy specimen, ever after a long time aging, remains
softer than the interior when the specimens are age-hardened at around room temperature after
quenching from high temperature. In this study, effects of the soft surface layer on the fatigue
strength of Al-Zn alloys were studied under repeated tensile loading. Vickers microharhness test
revealed that there existed less hardened region in the vicinity of grain boundary and specimens
surface, and that the region extends 50 to 100μm from the surface inward. From the plot of the
stress amplitude against the number of cycles to failure, it is concluded that the presence of less
hardened surface layer increases fatigue resistance of age-hardened Al-Zn alloys containing 8 to 16
mass%Zn under the repeated tensile loading.
Fracture Assessment of Flaws in Weldments using FITNET FFS Procedure: An Overview
Authors: Koçak Mustafa , Webster Stephen , Hadley Isabel
Published: March 2009

Recently a European community funded thematic network project (participation of 17
countries) FITNET (www.eurofitnet.org) has completed a new and unified engineering assessment
procedure (FITNET FFS Procedure) of flaws in metallic structures and welds. This newly
developed procedure (under CEN Workshop Agreement WA22) provides assessment rules for
flaws or damage due to fracture, fatigue, creep and corrosion to demonstrate the structural integrity
of the component. This paper gives an overview of the FITNET Fitness-for-Service (FFS)
Procedure and specifically presents the features and basic equations of the Fracture Module. It also
presents two brief examples for the validation of the procedure using laser welded specimens.
Application of ANN Back-Propagation for Fracture Design Parameters of Medium Carbon Steel in Extra-Low Cycle Axial Fatigue Loading
Authors: Duan Hong Yan , Li You Tang , Tan Shuai
Published: March 2009

The fracture problems of medium carbon steel under extra-low cycle axial fatigue
loading were studied using artificial neural network in this paper. The training data were used in the
formation of training set of artificial neural network. The artificial neural network model exhibited
excellent comparison with the experimental results. It was concluded that predicted fracture design
parameters by the trained neural network model seem more reasonable compared to approximate
methods. Training artificial neural network model was introduced at first. And then the Training
data for the development of the neural network model was obtained from the experiments. The
input parameters, notch depth and tip radius of the notch, and the output, the cycle times of fracture
were used during the network training. The neural network architecture is designed. The artificial
neural network model was developed using back propagation architecture with three layers jump
connections, where every layer was connected or linked to every previous layer. The number of
hidden neurons was determined according to special formula. The performance of system is
summarized at last. The result show that the training model has good performance, and the
experimental data and predicted data from artificial neural network are in good coherence.
Effects of Alloying Elements on Fracture Properties of Niobium Stabilized Austenitic Steels at Elevated Temperature
Authors: Yoon Ji Hyun , Yoon Eui Pak , Lee Bong Sang
Published: March 2009

The present work is a further investigation into the effects of the carbon (C), nitrogen (N)
and niobium (Nb) contents on then fracture properties of the Type 347 stainless steels at 316oC. 9
heats of systematically designed alloys were examined. Through SEM-EDS, TEM and XRD analyses,
two kinds of precipitates, Nb(C,N), CrNbN were identified in the Type 347 steels with a high ratio of
wt% N to wt% C, on the other hand only Nb(C,N)s were found in the Type 347 steels with a low ratio
of wt% N to wt% C. The tearing moduli were decreased in the range of 52~60% as the carbon content
increased from 0.03wt% to 0.05wt%. The tearing moduli were lowered by 52~59% in the alloys with
a high nitrogen. It was deduced from the microstructure analysis results that the coarse Nb-rich
precipitates control the fracture resistance of the Type 347 as they act as the potential sites for the
nucleation of micro-voids.
Evaluation of Fracture Toughness Distribution in Ceramic-Metal Functionally Graded Materials
Authors: Tohgo Keiichiro , Araki Hiroyasu , Shimamura Yoshinobu
Published: March 2009

This paper deals with evaluation of fracture toughness in functionally graded materials
(FGMs) consisting of partially stabilized zirconia (PSZ) and austenitic stainless steel SUS 304. FGMs
and non-graded composites (non-FGMs) with fine and coarse microstructures are fabricated by
powder metallurgy using PSZ and two kinds of SUS 304 powders. The fracture toughness is
determined by conventional tests for several non-FGMs with each material composition and by a
method utilizing stable crack growth for FGMs. Based on the experimental results, fracture
mechanism, influences of microstructure on fracture toughness, and difference in fracture toughness
between the FGMs and non-FGMs has been discussed.
Effect of Local Wall Thinning on Maximum Load Carrying Capacities of Elbows under Bending
Authors: Kim Jong Hyun , Ahn Joong Hyuk , Hong Seok Pyo , Kim Yun Jae , Park Chi Yong
Published: March 2009

This paper provides closed-form plastic limit load solutions for elbows with local wall
thinning under in-plane bending, via three-dimensional (3-D), small strain FE limit analyses using
elastic-perfectly plastic materials. Wide ranges of elbow and thinning geometries are considered.
Extending Creep and Superplasticity to Materials with Submicrometer Grain Sizes
Authors: Kawasaki Megumi , Xu Cheng , Horita Z. , Langdon Terence G.
Published: March 2009

The mechanisms of creep and superplasticity occurring in conventional large-grained
materials are now understood reasonably well. However, very recent advances in the processing of
theoretically-dense metals with submicrometer grain sizes have provided the opportunity to extend
the understanding of flow behavior to include materials where the grains are exceptionally small.
Using processing through the application of severe plastic deformation, as in procedures such as
equal-channel angular pressing, it is now feasible to fabricate relatively large samples having
ultrafine grain sizes in the submicrometer or nanometer range. This paper examines these recent
advances and gives examples of the flow behavior in ultrafine-grained aluminum alloys.
Superplastic Characteristics and Diffusion Bonding of Ti-6Al-4V Alloy
Authors: Lee Ho Sung , Yoon Jong Hoon , Yi Yeong Moo , Shin Dong Hyuk
Published: March 2009

It is known that Ti-6Al-4V alloy is one of the excellent candidates for aerospace
structure due to their high specific strength.However, its higher cost and low formability relative to
other materials tend to limit the wide usage of the material.The purpose of this study is to characterize
the superplasticity of this alloy so to obtain materials and process parameters for superplastic forming
and diffusion bonding for industrial application. High temperature tensile tests was carried out at the
strain rate range of 10-4 to 10-2 s-1 and temperature range of 1123°C to 1223°C. According to the results of
the experiment, the optimum diffusion bonding condition was obtained at 1148°C, applying pressure
of 4MPa for 1 hour in argon gas environment, which condition is more practical than expensive
vacuum condition. It is shown that at the optimum condition for diffusion bonding with parent metal,
the oxide film becomes unstable and the oxygen is diffused into the bulk. At this condition, the
mechanical and microstructural integrity at the bonding interface was observed in a sandwich
structure and a heavy block of titanium part from massive diffusion bonding process.
Effect of Microstructural Inhomogeneity on Creep Response of Mg-Sn Alloys
Authors: Huang Yuan Ding , Hort Norbert , Leil Tarek Abu , Kainer Karl Ulrich , Liu Yi Lin
Published: March 2009

The development of new creep resistant magnesium alloys has become a major issue in
recent years. The alloys investigated in the present work are based on the binary system Mg-Sn. Sn
as major alloying element was chosen due to its high solid solubility over a wide temperature range
and due to the possible formation of Mg2Sn intermetallic precipitates with a high melting
temperature of about 770°C. These characteristics suggest that a fairly large volume fraction of
thermally stable Mg2Sn particles can be formed during solidification. This makes it possible that the
Mg-Sn alloys can be developed as creep resistant magnesium alloys. In fact, previous investigations
indicate that the Mg-Sn alloys have a comparable or even better creep property than AE42 alloy.
The present work investigates the microstructure of Mg-Sn alloys with and without creep
deformation using SEM and TEM technique. The effects of microstructural inhomogeneity on the
creep response are presented. Based on the microstructural analysis, the mechanism responsible for
improving the creep resistance will be discussed. It is shown that the grain boundary sliding is a
dominant creep mechanism for the Mg-Sn binary alloy.
Recrystallization and Grain Growth Behavior of Alloy 718 Casting during Hot Working
Authors: Yoon Jong Won , Kim Nam Yong , Kim Jeoung Han , Yeom Jong Taek , Park Nho Kwang
Published: March 2009

Recrystallization and grain growth behavior of alloy 718 casting were investigated to
obtain homogeneous microstructure during hot forging. For this purpose, compression tests were
carried out for cylindrical specimens at the temperature range of 1000 to 1150°C and the strain rate of
10-1 and 10sec-1. The dynamic recrystallization behavior caused by the hot compression was
investigated in terms of the recrystallized area fraction and average grain size. Reheating was
followed to the hot compressed samples at the temperature range of 1050 to 1150°C for 100, 600 and
1800sec, and the static recrystallization behavior caused by the reheating was also investigated. As
hot deformation temperature increased from 1000 to 1150°C, both the area fraction and average grain
size of dynamically recrystallized grains increased. When higher strain rate of 10 sec-1 was used, the
area fraction of dynamically recrystallized grains increased substantially, but the average grain size
was not affected. When reheating the hot compressed samples at 1050°C for 100, 600 and 1800sec,
respectively, microstructural change including grain growth was not noticed. On the other hand, when
reheating the samples at higher temperatures, 1100°C and 1150°C, both the area fraction and the
average grain size of the statically recrystallized grains increased considerably as the holding time
increased from 100 to 1800sec.
Influence of Solute Content and Secondary Phases on the Nano-Creep Behavior of Mg-Al-Ca Alloys
Authors: Han Li Hong , Northwood Derek O. , Hu Henry
Published: March 2009

Mg-Al-Ca alloys with 1wt.% and 2 wt.% Ca additions (AC51 and AC52) were cast by
the Permanent Mold technique. The microstructures of the as-cast Mg-Al-Ca alloys were observed
by SEM with EDS analysis. The secondary phases were mainly precipitated along the grain
boundaries and exhibited a continuous network microstructure for the AC52 alloy and a divorced
microstructure for the AC51 alloy. EDS microanalysis showed that the solute (Ca) content in the
grains of the AC52 alloy is higher than that in the AC51. A three-sided pyramidal (Berkovich)
diamond indenter was used to characterize the local nano-creep behavior at room temperature
within the α-Mg in grains. The nano-creep results showed that the AC52 alloy has better creep
resistance than the AC51 alloy at all loads at room temperature. The creep exponent n, obtained
from the indentation creep data, changes from 6.3 to 3.0 for AC51 alloy and from 6.6 to 3.2 for
AC52 alloy at a critical stress (132 MPa for the AC51 and 145 MPa for the AC52). The transition in
creep behavior at higher stresses is associated with a change in the deformation mechanisms.
Influence of Temperature on the Fretting Wear of Advanced Nuclear Fuel Cladding Tube against Supporting Grid
Authors: Park Young Chang , Jeong Sung Hoon , Kim Yong Hwan , Lee Seung Jae , Lee Young Ze
Published: March 2009

The experimental investigation was performed to find the associated changes in
characteristics of fretting wear with various water temperatures. Fretting can be defined as the
oscillatory motion with very small amplitudes, which usually occur between two contacting surfaces.
The fretting wear, which occurs between cladding tubes of nuclear fuel rod and grids, causes in
damages the cladding tubes by flow induced vibration in a nuclear reactor. In this paper, the fretting
wear tests were carried out using the zirconium alloy tubes and the grids with increasing the water
temperature. The tube materials in water of 20, 50 and 80 were tested with the applied load of
20N and the relative amplitude of 200. The worn surfaces were observed by SEM, EDX and 2D
surface profiler. As the water temperature increased, the wear volume was decreased. However, oxide
layer was increased on the worn surface. The abrasive wear mechanism was observed at water
temperature of 20 and adhesive wear mechanism occurred at water temperature of 50 and 80.
As the water temperature increased, surface micro-hardness was decreased. Also, wear depth and
wear width were decreased due to increasing stick phenomenon. Stick regime occurred due to the
formation of oxide layer on the worn surface with increasing water temperatures.
An Approach to Prediction of Evolution of Material Properties in the Vicinity of Frictional Interfaces in Metal Forming
Authors: Lyamina Elena , Alexandrov Sergei , Grabco Daria , Shikimaka Olga
Published: March 2009

The quality of surface of the product of metal forming processes depends on physical
processes in the vicinity of frictional interfaces between the material and tool. It is well known that
material properties in a narrow layer in the vicinity of such interfaces are usually quite different
from the properties in the bulk. It is therefore necessary to develop a special approach to account for
this feature of the distribution of material properties. A possible approach is proposed in the present
paper. It is based on the concept of strain rate intensity factor.
Strength Reliability of Micro Polycrystalline Silicon Structure
Authors: Hamada Shigeru , Hashizume Kenji
Published: March 2009

In order to evaluate strength reliability of micron size polycrystalline silicon (poly-Si)
structure, bending tests of cantilever beam and Weibull analysis are performed. Recently, the
importance of microelectromechanical systems (MEMS) in society is increasing, and the number of
production is also increasing. The MEMS devices, which contain mechanical movement, have to
maintain their reliability in face of external shock, thermal stress and residual stress from
manufacturing processes. In greeting the mass production era of the MEMS, in case the material
strength design of MEMS is performed, required strength data is not average value but the variation,
especially minimum value of the material. Micron size poly-Si structure is widely employed in the
MEMS such as microsensor, switching device and so on. Then, in order to evaluate strength
reliability of micron size poly-Si structure, tests and analysis are performed. The specimen is made by
chemical vapor deposition (CVD) process and thickness is 3.5, 6.4 and 8.3 micrometer and the
specimen has notch. The test specimen used for the test changed characteristics of (1) film thickness
(2) stress concentration, and investigation about the influence each effects of the variation in a
bending strength are discussed.
Modeling of the Damage Accumulation and Fracture: Structural-Statistical Aspects
Authors: Lepov V.V. , Ivanova Anastassia , Achikasova Valentina , Lepova Kiounna
Published: March 2009

In this paper, an attempt is made to describe the structural-statistical aspects of the
damage accumulation and fracture of structural steel by means of experimental and numerical
micromacromodeling. The new approach of multiscale modeling of structure element fracture based
on evolution of microstructure levels is proposed. The lifetime is considered as an ultimate state in a
local volume of material, or a critical value of the local damage approaching.
Long Wave-Length Buckling of Periodic Open-Cell Foams Subjected to Uniaxial Compression
Authors: Okumura Dai , Okada Atsushi , Ohno Nobutada
Published: March 2009

In this study, the elastic buckling strength of cubic open-cell foams subjected to uniaxial
compression is investigated using the homogenization framework developed by the present authors
(Ohno et al., JMPS 2002; Okumura et al., JMPS 2004). First of all, based on the framework, the
microscopic bifurcation and macroscopic instability of cubic open-cell foams are numerically
analyzed by performing finite element analysis. It is thus shown that long wavelength buckling is the
primary mode and occurs just after the onset of macroscopic instability. Then, a solution for
predicting the stress of long wavelength buckling is analytically derived from the onset condition of
macroscopic instability. The validity of this analytical solution is demonstrated by the finite element
results.
Fatigue Crack Growth Experiments of Resonating Micro-Samples
Authors: Cambruzzi Andrea , Dual Jürg
Published: March 2009

The reliability and optimal design of Micro Electro Mechanical Systems (MEMS) can be
achieved only with the determination of material properties at the micro-scale. The major
challenges in performing fatigue tests at the micro-scale are related to the accurate measurement of
tiny deformations, to the control of very low forces and to the preparation, handling and positioning
of μm-sized samples. In order to investigate the fatigue behaviour of MEMS components a new
experimental setup based on the Phase Lock Loop (PLL) technique and a continuum mechanical
model were developed for the characterization of micro-sized test samples. The main advantage of
PLL is the achievable resolution in the crack length measurement, which increases with the
decreasing of specimen size. Therefore, micro-beams with notches and without notches were
prepared by electroplating Nickel in a SU8 photoresist mold (UV-LIGA). Investigations on the
initiation and near-threshold crack growth behavior were performed to improve the understanding
of the micro-mechanisms involved in fatigue phenomena.
Simulation of Texture Evolution during Hot Rolling Deformation in FCC Materials
Authors: Choi Shi Hoon , Song Y.S. , Kim B.J. , Kim Hyoung Wook , Kang Suk Bong
Published: March 2009

The evolution of hot rolling texture in FCC materials has been simulated numerically
using a visco-plastic self-consistent (VPSC) polycrystal model. A finite element (FE) analysis with
ABAQUS/StandardTM was conducted to evaluate the deformation gradients during hot rolling
deformation. In order to capture crystallographic rotation during hot rolling deformation, an
octahedral slip system was considered in a microscopic hardening model. The FE analysis with the
VPSC polycrystal simulations successfully predicted the inhomogeneous texture development
through the thickness direction in the hot-rolled Al-5wt%Mg alloy sheets.
Elasto-Plastic Analysis of 3-D Inner Cracks Using the Finite Element Alternating Method
Authors: Park Sang Yun , Park Jai Hak
Published: March 2009

The finite element alternating method (FEAM) was extended to obtain fracture mechanics
parameters and elasto-plastic stress fields for 3-D inner cracks. For solving a problem of a 3-D finite
body with cracks, the FEAM alternates independently the finite element method (FEM) solution for
the uncracked body and the solution for the crack in an infinite body. As the required solution for a
crack in an infinite body, the symmetric Galerkin boundary element method formulated by Li and
Mear was used. For elasto-plastic numerical analysis, the initial stress method proposed by
Zienkiewicz and co-workers and the iteration procedure proposed by Nikishkov and Atluri were used
after modification. The extended FEAM was examined through comparing with the results of
commercial FEM program for several example 3-D crack problems.
Numerical Simulation on Thermal Strain Characteristics of Casting Mold for Automobile Tire
Authors: Kim Yong Bum , Yang Ho Dong , Oh Yool Kwon
Published: March 2009

In the present study, aluminum alloy casting mold which consist of eight pieces is
introduced as a new technique of tire manufacturing. For the numerical analysis, finite element
method (FEM) was used to investigate the thermal strain of casting mold using aluminum alloy
during the cooling process. In the concrete, the temperature distributions on the inside of each casting
mold, the displacement and stress occurred by temperature variations are investigated to predict the
accurate measurement variations of casting mold during the cooling process. In the end, numerical
simulation results such as temperature distributions, displacement and stress are presented to help to
make the effective and the best mold products. Moreover, the introduced technique of numerical
simulation applying a FEM is very useful and important things in the mechanical behavior of
materials, especially needs the accuracy improvement such as aluminum alloy casting mold products.
Stress Analysis of the Heavy Duty Diesel Engine with Compacted Graphite Iron
Authors: Lee Young Shin , Lee Jae Ok , Choi Young Jin , Lee Se Hoon , Lee Hyun Seung , Jun Joon Tak , Kim Jae Hoon
Published: March 2009

The combat car used the heavy duty diesel engine must have a large output for
maintaining excellent mobility. The compacted graphite iron (CGI) is a material currently under
study for the heavy duty diesel engine demanded for high torque, durability, stiffness, fatigue. In
this study, three dimensional finite element model of a heavy-duty diesel engine was developed to
conduct the stress analysis by using property of CGI. The use of CGI property on the FE model was
expected to result in improved distribution of distortions and stresses. The loading conditions of
engine are assembly load and operational gas load.
Phase-Field Simulation during Spherulite Formation of Polymer
Authors: Takaki Tomohiro , Asanishi M. , Yamanaka A. , Tomita Yoshihiro
Published: March 2009

The establishment of the coupled numerical model which enable to simulate the spherulite
formation and its mechanical behavior continuously is our final goal. In this paper, we have developed
Phase-field model for spherulte growth of polymer by generalizing the model proposed by Granasy et.
al.. The numerical simulations for single spherulite and multi-sperulites have been performed with
isotropic interface energy.
Notch Effect on the Corrosion Fatigue Behavior of an Austenitic Stainless Steel
Authors: Lin Chih Kuang , Kuo Po Fu
Published: March 2009

The objective of this study is to characterize the influence of notch effect on the
high-cycle corrosion fatigue properties of AISI 347 stainless steel in various environments, namely,
air, water, NaCl, NaCl plus inhibitor, and H2SO4 solutions. For smooth-surface and semi-circular
notch specimens, the rank of fatigue strength in all of the given environments generally took the
following order: air ≈ salt water plus inhibitor > deionized water > salt water > sulfuric acid
solution. For V-notch specimens, the S-N curves were separated into two groups, i.e. one with air
and 3.5% NaCl plus inhibitor and the other with deionized water, 3.5% NaCl and H2SO4. This
was attributed to a greater effect of localized acidification occurring at the root of V-notch as
compared to the smooth surface and semi-circular notch.
Damage Localization in Systems with Unknown Inputs
Authors: Bernal Dionisio
Published: March 2009

The Dynamic Damage Locating Vector (DDLV) technique localizes damage by
interrogating changes in transfer matrices G. It is shown that although G cannot be computed in a
stochastic setting a surrogate matrix whose null space is related to that of G can be extracted and
this matrix suffices. The paper reviews the theoretical support for the DDLV approach, discusses
the constraints used to obtain the surrogate for G, and illustrates the technique using a 12-DOF
shear beam monitored with 6 sensors.
Guided Waves in Steel Rails – Experimental Works and Wavelet Signal Processing
Authors: Rucka Magdalena , Wilde Krzysztof
Published: March 2009

This paper presents experimental study on dispersive waves propagation in steel rails.
The propagation of longitudinal and transverse waves was generated by an impulse hammer and
measured in three points. Wavelet transform (WT) and short time Fourier transform (STFT) were
applied to analyze the time signals. Analysis of signal by STFT does not provide a proper timefrequency
representation due to a fixed size window. The wavelet transform can effectively identify
the time-frequency components in waves. The wavelet signal processing of the experimental wave
propagation signals is intended to be used for rail flaw detection.
Experimental Application of a Damage Localisation Technique Based on Smoothed Proper Orthogonal Modes
Authors: Galvanetto U. , Monopoli L. , Surace Cecilia , Tassotti Alessandra
Published: March 2009

The paper presents an experimental application of the Proper Orthogonal Decomposition
(POD) to damage detection in steel beams. A damaged beam has been excited with a sinusoidal
force, the acceleration response at points regularly spaced along the structure has been recorded and
the relevant Proper Orthogonal Modes calculated. In this way it is possible to locate damage by
comparing the measured dominant Proper Orthogonal Mode with a smoothed version of it which
does not exhibit apparent peaks in correspondence with the damage.
One of the principal advantages of the proposed damage detection technique is that it does not
require vibration measurements to be performed on the undamaged structure. Moreover the
‘optimality’ of the proper orthogonal modes only requires the use of a few (one-two) of them which
can be computed in real time during lab experiments or while the structure is functioning in the
field.
Identification of Structural Property Degradations by Computational Model Updating
Authors: Link Michael , Stöhr Stefan , Weiland Matthias
Published: March 2009

Computational model updating techniques are used to adjust selected parameters of finite
element models in order to make the models compatible with experimental data. This is done by
minimizing the differences of analytical and experimental data, for example, natural frequencies
and mode shapes by numerical optimization procedures. For a long time updating techniques have
also been investigated with regard to their ability to localize and quantify structural damage. The
success of such an approach is mainly governed by the quality of the damage model and its ability
to describe the structural property changes due to damage in a physical meaningful way. Our
experience has shown that due to unavoidable modelling simplifications and measurement errors
the changes of the corresponding damage parameters do not always indicate structural
modifications introduced by damage alone but indicate also the existence of other modelling
uncertainties which may be distributed all over the structure. This means that there are two types of
parameters which have to be distinguished: the damage parameters and the other parameters
accounting for general modelling and test data uncertainties. Although these general parameters
may be physically meaningless they are necessary to achieve a good fit of the test data and it might
happen that they cannot be distinguished from the damage parameters. For complex industrial
structures it is seldom possible to generate unique structural models covering all possible damage
scenarios so that one has to expect, that the parameters introduced for describing the damage will
not be fully consistent with the physical reality. This is the reason why in the scientific community
there is still some doubt if model based techniques can be used at all for practical purposes of
damage detection and quantification under in-situ environment conditions.
In the present paper we summarize the methodology of computational model updating and report
about our experience with damage identification exemplified by practical examples. A new
technique and an application of localising and quantifying the damage from updating the parameters
of the damaged and the undamaged models simultaneously using the differences of the test data
from the damaged and the undamaged structure is also presented. In this application we used the
deflections (influence lines) of a beam structure measured under a slowly moving load.
Experimental Seismic Damage Quantification in a 3-Storey Laboratory Structure
Authors: de Lautour Oliver R. , Omenzetter Piotr
Published: March 2009

Time series based Structural Health Monitoring (SHM) methods are being increasingly
explored. In this study, Autoregressive (AR) models were used to fit the acceleration time histories
of a 3-storey laboratory structure under excitation by earthquake records in several damaged and
undamaged states. The coefficients of the AR models were used as inputs into an Artificial Neural
Network (ANN) and the ANN was trained to relate the AR coefficients to the damage at each
storey. The results showed that proposed method was able to detect, locate and quantify the damage
in the structure with a very high accuracy.
Fatigue and Fracture Evaluation of a 70 Year Old Steel Bridge
Authors: Wang Chun Sheng , Qian Hui , Zhan Ang , Xu Yue , Hu Da Lin
Published: March 2009

Nen’jiang No.1 Bridge has been used for 70 year, so fatigue, fracture and corrosion
dominate the remaining life of this bridge. Obviously the designer did not take into consideration the
fatigue problem at that time. In order to keep this bridge in service economically as long as possible,
bridge owner decides to take measures to preserve its service safety. Thus the remaining fatigue life
and fracture failure risk need to be evaluated. The analytical results according to the fracture mechanic
based concept show that the diagonal edge members U0L1 and U9L8 have the shortest remaining
fatigue life, and some members have a potential risk of brittle failure. The fracture failure risk
evaluation results show that the toughness of main truss member steel is lower than the code
requirement, and members such as U0L1 and U9L8 have brittle fracture failure risk in cold winter. So
this bridge should be temporarily closed traffic in winter.
Design and Numerical Simulation of an Optic Fibre Sensor for Damage Assessment of Structures
Authors: Delprete Cristiana , Rosso Carlo
Published: March 2009

The paper presents the design of a new optic fibre sensor that simultaneously measures normal deformation, cross-sectional deformation and temperature with the minimum number of sensible elements. It is based on two assembled in phase quadrature traditional Fabry-Perot sensors. Lightness and the extreme compactness make the proposed sensor suitable to equipe composite materials with low specific weight and various percentage in fibre volume, that it can be used for aeronautical and/or automotive applications without modifying mechanical characteristics. The example host material is Ti-6Al-4V/SiC composite characterized with the volume fraction of carbon fibres of 35%; it permits to insert the sensor at low temperature by means of Cold-Gas Spray technology. Sensor construction is quite easy and does not require great economical effort in comparison with other types of optic fibre sensors reported in literature. The sensor has the capability of independently measuring the thermal and mechanical (bending and traction) loads. It has a great sensibility indeed it allows evaluating μm displacements and bending angle of the order of one hundredth of degree, operating in a temperature range between −190°C and 750°C. The paper concludes with the description of the mathematical model of the proposed sensor and with the correspondent numerical characterization in order to estimate sensor capabilities. Numerical simulation points out the potentials of the new proposed sensor.
Broadband Source-Based Interrogation Scheme of Fiber Bragg Grating Sensors for Structural Health Monitoring
Authors: Tosi Daniele , Olivero Massimo , Perrone Guido
Published: March 2009

In the present work we report on the development of a low cost interrogation system of
fiber Bragg grating sensors for structural health monitoring. The developed scheme uses two
gratings and a directional coupler as sensing point, and it includes self-compensation of temperature
effects. The reading equipment consists of a standard photodiode for telecom applications with
custom signal-conditioning electronics. The characterization of multiplexed sensors, carried out in
real framework conditions, shows that the system can work in a temperature range of -20÷+40°C,
making strain measurements up to at least 320με with an accuracy of ~3% and an acquisition rate of
12 samples/min. Further, a budget evaluation is drawn to asses the feasibility of our interrogation
system as a low cost solution to increase the extent of structural health monitoring in funds-limited
applications.
Modelling Damage Progression by a Statistical Energy-Balance Algorithm
Authors: Bosia Federico , Pugno Nicola Maria , Lacidogna Giuseppe , Carpinteri Alberto
Published: March 2009

In this contribution some characteristics and predictive capabilities are discussed of a
recently introduced model for damage progression and energy release, in view of modelling
Acoustic Emission. The specimen is discretized in a network of connected springs, similar to a
Fibre Bundle Model approach, with the spring intrinsic strengths statistically distributed according
to a Weibull distribution. Rigorous energy balance considerations allow the determination of the
dissipated energy due to crack surface formation and kinetic energy propagation. Based on results of
simulations, the macroscopic behaviour emerging from different choices at “mesoscopic” level is
discussed, in particular the relevance of model parameters such as the distribution of spring cross
sections, Weibull modulus values, and discretization parameters in determining results like stressstrain
curves and energy scaling versus time or specimen size.
Finite Element Analysis of an Improved Center Crack Specimen
Authors: Ayatollahi Majid R. , Aliha M.R.M. , Rahmanian S.
Published: March 2009

A new crack specimen called the diagonally loaded square plate (DLSP) containing an
angled central crack is analyzed using the finite element method. The stress intensity factors and the
T-stress are calculated for the new specimen in the full range from pure mode I to pure mode II.
Unlike the conventional center cracked specimen under uniaxial loading, the improved specimen is
able to provide pure mode II. It is shown that the effect of non-singular stress component T in the
DLSP specimen is not ignorable relative to the singular stress terms, particularly for mode II
dominated loading conditions.
Output-Only Technique for Parameter Identification of Nonlinear Systems Working under Operational Loads
Authors: Iwaniec Joanna
Published: March 2009

Vast majority of industrial mechanical systems do not behave in linear way around any
operating point and work under non-measurable operational loads. Identification of such systems
can’t be carried out by means of the classical nonlinear system identification methods. The paper
concerns the method combining restoring force, boundary perturbation and direct parameter
estimation techniques that, on the contrary to classical methods, requires neither input measurement
nor linear behaviour of the considered system around an operating point. There are also presented
results of method application to parameter identification of machine shaft flexible support.
Dynamics of Structures with Piezoelectric Sensors and Actuators for Structural Health Monitoring
Authors: Mateescu Dan , Han Yong , Misra Arun
Published: March 2009

The dynamic analysis of structures with piezoelectric sensors and actuators is used in this
paper to establish a method for crack detection in aerospace structures. Piezoelectric strips used as
sensors and actuators are bonded on both sides of a thin structure which executes flexural
oscillations. The differential voltage outputs of the piezoelectric sensors are used to detect the
presence of cracks in the structure. The structural analysis uses a finite element formulation for the
piezoelectric strips coupled with the structure and a nonlinear model for the cracks. This paper
presents first the results of the dynamic analysis in the frequency domain of healthy and cracked
plates undergoing forced flexural vibrations generated by a pair of piezoelectric actuators submitted
to an oscillatory voltage excitation. The peaks in the differential voltage output obtained in the case
of a cracked plate at several frequencies during the frequency sweep were found to be indicative
measures for the presence of a crack in the structure. The results of the dynamic analysis in the time
domain have also shown that this method has a good sensitivity in detecting cracks in the structures.
Displacement Measurement of an Existing Long Span Steel Box-Girder Using Terrestrial Laser Scanning
Authors: Lee H.M. , Kwon Y.H. , Park Hyo Seon , Lee I.
Published: March 2009

To make use of a new technology in the field of structural health monitoring, various
displacement measuring techniques such as a global positioning system (GPS) and vision-based
techniques have been studied and proposed. It was previously introduced a new displacement
measuring technique using terrestrial laser scanning (TLS) that remotely samples the surface of an
object using laser pulses and generates the three-dimensional (3D) coordinates of numerous points on
the surface. In this paper, for an assessment of the capabilities of the measuring technique about
existing structures, the field tests for vertical displacement measurement of an existing long span steel
box-girder are experimentally carried out. The performance of the technique is evaluated by
comparing the displacements obtained from TLS system and displacements directly measured from
linear variable displacement transducer (LVDT).
Damage Assessment of Adhesively Bonded FRP Beams Using Modal Parameters
Authors: Ali A.M. , Abdel Wahab M.M. , Crocombe A.D. , Ashcroft Ian A.
Published: March 2009

This paper describes a dynamic test carried out on intact and damaged FRP composite
beams with fixed-fixed boundary condition. Hammer excitation is used to excite the beam at fixed
locations. The modal parameters are extracted from the time response using a time domain analysis,
i.e. the stochastic subspace identification technique. In order to introduce damage, two sections of
the beam are bonded together using an epoxy adhesive, and then a static test is carried out. For the
static test, a 3-point bending -configuration is used, i.e. the beam is fixed at both ends and a static
load is gradually applied in the middle of the beam using a screw jack. Different static load steps,
and in turn different damage stages, are considered. After each load step, dynamic measurements
are carried out. The results obtained from both tests are presented and analysed.
Experimental and Numerical Coupling Proof of Conical Frictional Joints
Authors: Szwedowicz Dariusz , Bedolla Jorge
Published: March 2009

Conical rings are used to joint a shaft with other mechanical parts through frictional
forces induced by clamping of the inner ring into the outer one. In design, their coupling strength
and the allowable torque are determined with the well known analytical formulas. However, the
assumption of rigid and smooth contacts considered in the analytical solution generates technical
uncertainties for reliability of conical joints especially for their small dimensions. The coupling
strength of the conical rings is investigated at a set-up and by using Finite Element (FE) Method. A
FE model of the analytically analysed conical joint is created with friction contact conditions on all
interfaces of the joint. For a very fine mesh with the smooth interfaces, the FE contact forces differ
remarkably from the analytical solution. This confirms that the elasticity of parts has to be taken
into account in the design process. To assess an influence of real contact profiles on the coupling
performance, contours of contact surfaces are measured at a Mitutoyo coordinate measuring
machine. Based on the measured height variation in the normal to the contact plane, the surface
profiles are extrapolated by approximation functions. Then, the FE mesh is modified locally on the
contact with respect to the extrapolated profile functions and coupling strength of the conical joint
is computed with friction sliding. According to the obtained results, the implementation of the real
profile of the contact is needed in the design process to avoid failures under real operation
conditions of conical joints. According to the obtained FE static results, the contour irregularities
induces local separations in the contact, which can be monitored by measuring electrical resistance
between the outer and inner conical rings.
Damage Mechanisms Interpreted by Acoustic Emission Signal Analysis
Authors: Carpinteri Alberto , Lacidogna Giuseppe , Manuello Amedeo
Published: March 2009

Acoustic emissions (AE) are ultrasonic waves generated by the rapid release of energy from discontinuities or cracks spreading in materials subject to a stress and strain field. By identifying the complete shape of the signals and taking into account a larger quantity of data, it becomes possible to ascertain the three-dimensional location of damage sources from AE sensor records. In this connection, the authors have fine-tuned an original procedure that uses seismic analysis techniques, such as the moment-tensor solution. The experimental program consisted of tests conducted in situ on masonry walls of historical buildings.
A Novel Ultrasonic Technique to Detect Damage Evolution in Quasi-Brittle Materials
Authors: Antonaci Paola , Bocca Pietro G. , Masera Davide , Pugno Nicola Maria , Scalerandi Marco , Sellone Fabrizio
Published: March 2009

The results of an experimental research on plain concrete are presented. The non-linear
behavior of both virgin and damaged samples is investigated by means of ultrasonic tests: recent
theoretical models, indeed, have pointed out that mono-frequency ultrasonic excitations bring to
light such phenomena as harmonic generation and sidebands production, which are essentially due
to the material classical or hysteretic non-linearity. The estimation of the harmonic components
parameters (amplitudes and phases) is achieved through a signal processing technique based on
MUltiple SIgnal Classification (MUSIC) system, which reveals to be optimal for the specific signal
model here considered. The experiments described in this paper show that the material non-linear
features increase with increasing level of internal micro-cracking, thus suggesting the possibility to
use the ultrasonic signal analysis in the frequency domain as a valuable tool for damage assessment.
Damage Assessment through Impact Force History Recording
Authors: Constantin Nicolae , Găvan Mircea , Sandu Marin , Sorohan Ştefan , Anghel Viorel
Published: March 2009

Low velocity impact is a frequent and inevitable in-service event, with higher occurrence
in transportation structures. The damages following such an event are more diverse, extended and
with more severe consequences in the case of composite materials and structures. The research
work presented here concerns fibre reinforced polymeric composites in the forms of plates and
pipes. It is continuing an effort meant to allow customers exploiting such structures to have a short
cut in monitoring the integrity of this kind of structures. To this end, it is proposed a careful
following of the impact force history recording, which can offer valuable and more direct
information about the damage level produced under this insidious loading.
Active Vibration Control of a Cracked Composite Beam by MSM Actuators
Authors: Majewska Katarzyna , Zak Arkadiusz , Ostachowicz Wiesław M.
Published: March 2009

In this paper the authors present a new one-dimensional phenomenological model of the
magnetic shape memory effect (MSME) observed in magnetic shape memory alloys (MSMAs). The
model takes into account elementary processes associated with the magnetisation of MSMAs. Its
correctness has been checked against selected models known from the literature. The model
developed by the authors has been verified in the case of a rod element made out of a MSMA by the
use of the finite element method (FEM). A study on the influence of activation of MSMA beam
actuators in the case of forced vibration of a composite beam has been performed. The authors have
also carried out investigation connected with the influence of a transverse and open crack on the
effectiveness of vibration reduction in the case of a composite beam by the use of MSM actuators.
Cyclic Plastic Response and Fatigue Life of Materials
Authors: Polák Jaroslav
Published: March 2009

Recently the decisive role of plastic strain amplitude for the initiation and the growth rate
of short cracks has been demonstrated. The plastic strain amplitude can be related to the rate of
short crack growth and also to the fatigue life. Since the cyclic stress-strain response of a material
determines the plastic strain amplitude it influences basically its fatigue life. The experiments in
stress and plastic strain controlled loading and short crack growth are presented and used to
demonstrate the importance of the cyclic plastic response for the evaluation of the fatigue life.