Fracture Mechanics

This work examines the effect of weld strength mismatch on J and CTOD fracture parameters
using single edge notch tension (SE(T)) specimens. A central objective of the study is
to enlarge on previous J and CTOD estimation procedures based upon plastic eta factors (g)
described in Part I for centerline-cracked welds. The present analyses provide a large set of
g-factors for a wide range of crack sizes (a/W-ratio) and material properties, including different
levels of weld strength mismatch, which are applicable in improved estimation
equations for J and CTOD for weld centerline notched SE(T) specimens.

The fractal geometry is introduced in the dynamic fracture to describe the ruggedness
during the crack propagation characterizing the morphology of generated surfaces. It is shown that
the fractal dimension has a strong influence about the limit speed of fast crack propagation. It is also
shown that the inatingibility of speed of waves Rayleigh by cracks in some materials can be
correlated to the ruggedness of fracture surfaces by means of exponent Hurst, H, that measures the
ruggedness dimension. The experimental results of Fineberg et al [FINEBERG 1991; FINEBERG
1992] they were adjusted by the model. The unstability coefficient was calculated for Fineberg et al
measurements in agreement with the definition proposed by SANDER [1984]. One concluded that
exist an intrinsic unstability to the phenomenon that produces the ruggedness of surfaces, limiting
this way the maximum of crack propagation speed for a smaller value than the speed of waves
Rayleigh in the material.

The static fracture toughness of a series of eutectic Al-Si casting alloy with different microstructural features has been evaluated. The dominant influence of eutectic silicon in controlling the fracture toughness is thus clarified. The relationship between the fracture toughness and the microstructure was established. Fracture toughness was found to be strongly associated with the size and morphology of silicon particles. The other feature which greatly influences the fracture toughness is the ratio (/DE)Si, i.e. the silicon particle spacing divided by the equivalent particle diameter, rather than the silicon particle spacing, Si. Fracture toughness also correlates well with the void growth parameter, VGP (=y (/DE)Si), proposed by the authors. The results of the present work can be used to develop an understanding of the variation of fracture toughness with the microstructural features of eutectic Al-Si alloys.

Uncertainties associated with modelling of deteriorating bridges strongly affect management decisions, such as inspection, maintenance and repair actions. These uncertainties can be reduced by the effective use of health monitoring systems, through which information regarding in situ performance can be incorporated in the management of bridges.The objectives of this paper are twofold; first, an improved chloride induced deterioration model for concrete bridges is proposed that can quantify degradation in performance soon after chlorides are deposited on the bridge, rather than when initiation of corrosion at the reinforcement level takes place. As a result, the implications of introducing proactive health monitoring can be assessed using probabilistic durability criteria. Thus, the second objective of the paper is to present a methodology for performance updating of deteriorating concrete bridges fitted with a proactive health monitoring system.This methodology is illustrated via a simple example of a typical bridge element, such as a beam or a part of a slab. The results highlight the benefits from introducing ‘smart’ technology in managing bridges subject to deterioration, and quantify the reduction in uncertainties and their subsequent effect on predictions of future bridge performance.

Linearno-elastična mehanika loma (LEML) se može korisno primeniti sve dok je veličina plastične zone na vrhu prsline mala u poređenju sa dužinom prsline. Ovo je obično slučaj kod materijala kod kojih se lom pojavljuje pri naponima koji su znatno ispod napona tečenja i u uslovima ravnog stanja deformacija. U takvim okolnostima lom se može definisati pomoću K-faktora i odgovarajuće žilavosti loma K Ic. Kada prevlada ravno stanje napona veličina plastične zone je veća, ali i dalje znatno manja od dužine prsline. Lom se i u tim uslovima pojavljuje pri naponima manjim od napona tečenja pa se primenom modifikovane LEML, kao na primer preko R-krivih, mogu dobiti zadovoljavajuće procene preostale nosivosti. Postupci LEML se najviše koriste u avionskoj i raketnoj industriji, gde je kriterijum smanjenja težine od primarnog interesa, zbog čega se moraju koristiti materijali visoke čvrstoće, koji su istovremeno i krti. Ukoliko je veličina plastične zone velika u odnosu na dužinu prsline tada LEML više ne važi, već se moraju primeniti metode elasto-plastične mehanike loma (EPML). Shematski prikaz oblasti primene metoda LEML i EPML sa stanovišta relativne veličine plastične zone za prolaznu prslinu u ploči je dat na sl. 1. Slika 1. Oblasti primene metoda LEML i EPML za definisanje pojave loma. 2. USLOVI ZA PRIMENU EPML Problem veličine plastične zone ima dva aspekta. Na prvom mestu je to problem kratkih prslina kod materijala male žilavosti loma. Za njih je napon loma F 0 7 3 c = KIc/ F 0 D 6 F 0 7 0 a i F 0 7 3 c teži beskonačnosti kada se dužina prsline 2a približava nuli (sl. 2). Kako je ovo nemoguće, očigledno je da napon loma ne može biti definisan pomoću LEML. Preostala čvrstoća pri dužini prsline (2a/W) 1 je definisana tačkom B, što je niže od napona u tački A određenog primenom LEML, a viša od graničnog napona

Two aluminum metal matrix composites (MMC) reinforced with 13 vol.% of SiC or B4C particles were made by stir casting followed by hot extrusion. Effects of sliding velocity on the wear, friction and tribochemistry of the worn surfaces of both composites sliding against a commercial phenolic brake pad have been investigated under dry condition. The wear tests were carried out using a pin-on-disc type apparatus at two linear sliding speeds: 1.62 and 4.17 m s-1 under a constant contact pressure of 0.75 MPa for a sliding distance of 5832 m. The coefficient of friction was recorded and wear rate of the MMC pins calculated from mass loss measurement. Scanning electron microscope (SEM) equipped with energy dispersive X-ray spectroscopy (EDX) was used to investigated the worn surface. It is observed that higher sliding velocity leads to lower wear rate and lower friction coefficient for both MMCs. Formation of a compact transfer layer has been identified in the matrix region of the worn surface of the MMCs. The transfer layer mostly consists of constituents of the phenolic pad material which acted as counterbody. The amount of the constituents of the counterbody in the transfer layer is seen to increase as sliding velocity increases. It is suggested that the transfer layer on MMC acts as a protective cover and helps reduce both wear rate and friction coefficient.

SYNOPSIS Over the last decade Spoornet's Integrated Train Condition Monitoring System (ITCMS) has grown into a formidable engineering tool. The system consists of a wide range of measuring stations that continuously measure the condition of rolling stock down to component level. It raises alarms when critical events are detected and has the ability to order that a train be stopped when such conditions occur. With the available database of thousands of recordings of train condition, new possibilities arise. One area that is currently being explored is that of condition trending. In this approach data can be analysed over time to detect deterioration and to predict eventual failure of components or subsystems. Trends can then also be used to plan maintenance interventions in advance. This paper presents an overview of how train condition data is currently used and examines possibilities of enhancing the function of the ITCMS in terms of prediction of the rate of deterioration. It also considers the use of the ITCMS to evaluate new measuring systems.

Fatigue plays a significant role in the crack growth of the fuselage skin structures. In addition, the fuselage may suffer also from the corrosion damage, and the wear defects. The proper maintenance and scheduled test intervals can avoid the sudden skin failure. Therefore, the inspection interval has to be shortened. Nevertheless, the young machines may be also suffering from the unexpected skin rupture. The cracks are emanating from the rivets and the holes under cyclic loading. The stress concentration around the notch has an effective role under the effect of cyclic loading. The cracks propagate toward the high stressed area such as the notches or other crack locations. The propagation into a critical crack size is rather fast and causes a sudden aircraft fuselage cracking. Hence, the number of cycles to failure will be decreased dramatically. During the last decades, the fracture toughness, design, and the new alloying element have been enhanced. The previous fuselage failures show that the inspections against the cracking are recommended even after a few thousand of cycles. To prevent the crack extending, the crack arresting is recommended to use around the fuselage.

Ceramics are extensively used in protective structures which are often subjected to projectile impacts. During an impact process of a ceramic target by a projectile, fragmentation occurs in both the target and the projectile. It is challenging to simulate such events and predict residual mass and velocity of the projectile. In this work, we attempt to use smoothed particle hydrodynamics (SPH) in LS-DYNA to reproduce fragmentation of the target and the projectile and predict residual mass and velocity of the projectile during a projectile impact of a ceramic target. SPH models for an alumina ceramic tile impacted by a blunt tungsten heavy alloy projectile are established. SPH simulation results of residual mass and velocity of the projectile as well as ejecta and bulge movements of the ceramic tile are obtained and compared with experimental data and simulation results of other numerical approaches. It is found that SPH simulation can properly reproduce the impact fragmentation of the target and the projectile, and shows advantages over existing numerical approaches in the prediction accuracy of residual mass and velocity. Moreover, effects of some numerical aspects of SPH, including particle spacing, contact treatment and parameters in artificial viscosity and smoothing length, on simulation results are identified. A simple approach using identical smoothing length and balanced artificial viscosity is proposed to reduce particle spacing sensitivity. The observed parametric effects and the proposed approach will provide guidance to set appropriate parameters values for SPH simulation of impact fragmentation.

In this work, the mode I fracture toughness behavior of dissimilar metal-composite adhesive joints is experimentally investigated utilizing the double cantilever beam (DCB) test. The under-study joint is envisioned to be applied in the hybrid laminar flow control system of future aircraft and it consists of a thin titanium sheet and a thin carbon fiber reinforced plastic (CFRP) laminate. Four different industrial technologies for the joining of the titanium and CFRP adherents are evaluated; co-bonding with and without adhesive and secondary bonding using either a thermoset or a thermoplastic composite. First, the vacuum-assisted resin transfer molding (VARTM) technique is employed for the manufacturing of the titanium-CFRP joint. After manufacturing, the joint is stiffened from both titanium and composite sides with two aluminum backing beams to ensure the non-yielding of the titanium during the subsequent DCB tests. Towards the fracture toughness determination from the experimental data, an analytical model recently developed by the authors, that considers the bending-extension coupling of each sub-laminate of the joint as well as the manufacturing-induced residual thermal stresses effect, is applied. The load-displacement behaviors, failure patterns, and fracture toughness performances for each of the four manufacturing options (MO) investigated are presented and compared.

For the first time, nested sub-modeling approach and Finite Element Analysis have been used to analyze the structural mechanical of 3D Printed part, whereas the details of 3D printing patterns included in sub-model. The results present a general tool which can improve the quality of 3D printed parts, which have multidisciplinary application in various fields. It is found that the Maximum Principle stress is highly concentrated at 3D printed layers. For a specific 3D printing pattern, the stress intensity factor has been calculated to have the value of 4. Results have been discussed from theoretical, simulation and experimental observation point of view.

This book outlines the basics of fractography
and fracture mechanics from the premise that
these are essential to lithic research. That is,
understanding the formation, meaning and
analytical potential of fracture markings — known to lithicists as attributes is fundamental to a complete comprehension of
lithic chaîne opératoire.

The ability of Minkowski Functionals to characterize local structure in different biological tissue types has been demonstrated in a variety of medical image processing tasks. We introduce anisotropic Minkowski Functionals (AMFs) as a novel variant that captures the inherent anisotropy of the underlying gray-level structures. To quantify the anisotropy characterized by our approach, we further introduce a method to compute a quantitative measure motivated by a technique utilized in MR diffusion tensor imaging, namely fractional anisotropy. We showcase the applicability of our method in the research context of characterizing the local structure properties of trabecular bone micro-architecture in the proximal femur as visualized on multi-detector CT. To this end, AMFs were computed locally for each pixel of ROIs extracted from the head, neck and trochanter regions. Fractional anisotropy was then used to quantify the local anisotropy of the trabecular structures found in these ROIs and to compare its distribution in different anatomical regions. Our results suggest a significantly greater concentration of anisotropic trabecular structures in the head and neck regions when compared to the trochanter region (p < 10-4). We also evaluated the ability of such AMFs to predict bone strength in the femoral head of proximal femur specimens obtained from 50 donors. Our results suggest that such AMFs, when used in conjunction with multi-regression models, can outperform more conventional features such as BMD in predicting failure load. We conclude that such anisotropic Minkowski Functionals can capture valuable information regarding directional attributes of local structure, which may be useful in a wide scope of biomedical imaging applications.

This paper presents a methodology for automating the processingof highway pavement video images using an integration of artificial neural network models with conventional image-processing techniques. The methodology developed is able to classify pavement surface cracking by the type, severity, and extent of cracks detected in video images. The approach is divided into five major steps: (1) image segmentation, which involves reduction of a raw gray-scale pavement image into a binary image, (2) feature extraction, (3) decomposition of the image into tiles and identification of tiles with cracking, (4) integration of the results from step (3) and classification of the type of cracking in each image, and (5) computation of the severities and extents of cracking detected in each image. In this methodology, artificial neural network models are used in automatic thresholding of the images in stage (1) and in the classification stages (3) and (4). The results obtained in each stage of the process are presented and discussed in this paper. The research results demonstrate the feasibility of this new approach for the detection, classification, and quantification of highway pavement surface cracking.

Three types of material whose fracture toughness tests were previously performed by using circumferentially notched bars, namely (1) a dual-phase steel with three different morphologies; (2) an Al-Zn-Mg-Cu wrought alloy; and (3) Al-Si-cast alloys with three different Si contents, were investigated in terms of accuracy and reliability of the testing method. Also, the advantages of using circumferentially notched bars
for fracture toughness determination of metallic materials were discussed. With the help of stress concentration
factors, which are associated with the bluntness of the notch, correction factors for the fracture toughness calculations are derived. The corrected fracture toughness values are found to be close to the uncorrected ones, implying that the testing procedure is reliable.

(Esp)
Aproximación a los artefactos líticos desde una perspectiva que poco tiene que ver con las tipologías, los sistemas de clasificación analíticos o su funcionalidad, con las cronologías e incluso con la arqueología experimental. En este trabajo penetraremos en el mundo de la talla a través de una disciplina que nos habla de números y fórmulas, de velocidades de propagación y de distribución de tensiones en sólidos, de movimientos y desplazamientos de partículas y de geometrías complejas: la ruptura frágil de sólidos elásticos.

(Ing)
Approach to lithic artifacts from a perspective that has nothing to do with lithic tipology, analytical classification, chronlogies or even experimental archeology. In this paper we will penetrate in the field of knapping through a discipline that talks about numbers and formulas, rate propagation speed and solid stress distribution, movements and displacements of particles and complex geometries: the brittle fracture of elastic solids.