Numerical simulation of fracture mode transition in ductile plates

Fracture mode of ductile solids can vary depending on the history of stress state the material experienced. For example, ductile plates under remote in-plane loading are often found to rupture in mode I or mixed mode I/III. The distinct crack patterns are observed in many different metals and alloys, but until now the underlying physical principles, though highly debated, remain unresolved. Here we show that the existing theories are not capable of capturing the mixed mode I/III due to a missing ingredient in the constitutive equations. We introduce an azimuthal dependent fracture envelope and illustrate that two competing fracture mechanisms, governed by the pressure and the Lode angle of the stress tensor, respectively, exist ahead of the crack tip. Using the continuum damage plasticity model, we demonstrate that the distinctive features of the two crack propagation modes in ductile plates can be reproduced using three dimensional finite element simulations. The magnitude of the tunneling effect and the apparent crack growth resistance are calculated and agree with experimental observations. The finite element mesh size dependences of the fracture mode and the apparent crack growth resistance are also investigated.United States. Office of Naval Research. Multidisciplinary University Research Initiative (Massachusetts Institute of Technology

Prediction of plane strain fracture of AHSS sheets with post-initiation softening

In this investigation, the three-parameter Modified Mohr–Coulomb (MMC) fracture model and the determination of the material parameters are briefly described. The formulation of the post-initiation behavior is proposed by defining both the explicit softening law and the incremental damage evolution law. As opposed to the existing attempts to simulate slant fracture with material weakening before crack formation, softening is assumed to occur only in the post-initiation range. The justification of this assumption can be provided by the interrupted fracture tests, for example, Spencer et al. (2002). Element deletion with a gradual loss of strength is used to simulate crack propagation after fracture initiation. The main emphasis of the paper is the numerical prediction of slant fracture which is almost always observed in thin sheets. For that purpose, VUMAT subroutines of ABAQUS are coded with post-initiation behavior for both shell elements and plane strain elements. Fracture of flat-grooved tensile specimens cut from advanced high strength steel (AHSS) sheets are simulated by 2D plane strain element and shell element models.Advanced High Strength Steels Industry Consortiu

Numerical failure analysis of a stretch-bending test on dual-phase steel sheets using a phenomenological fracture model

Advanced High Strength Steels (AHSS) are increasingly used in automotive industry due to their superior strength and substantial weight advantage. However, their compromised ductility gives rise to numerous manufacturing issues. One of them is the so-called ‘shear fracture’ often observed on tight radii during stamping processes. Since traditional approaches, such as the Forming Limit Diagram (FLD), are unable to predict this type of fractures, great efforts have been made to develop failure criteria that could predict shear fractures. In this paper, a recently developed Modified Mohr–Coulomb (MMC) ductile fracture criterion (Bai and Wierzbicki, 2010) is adopted to analyze the failure behavior of a Dual Phase (DP) steel sheet during stretch-bending operations. The plasticity and ductile fracture of the present sheet are fully characterized by a Hill’48 orthotropic model and a MMC fracture model, respectively. Finite element models with three different element types (3D, shell and plane strain) were built for a Stretch Forming Simulator (SFS) test (Shih and Shi, 2008), numerical simulations with four different R/t values (die radius normalized by sheet thickness) were performed. It has been shown that the 3D and shell element simulations can predict failure location/mode, the upper die load–displacement responses as well as wall stress and wrap angle at the onset of fracture for all R/t values with good accuracy. Furthermore, a series of parametric studies were conducted on the 3D element model, and the effect of tension level (clamping distance), tooling friction, mesh size and fracture locus on failure modes and load–displacement responses were investigated.Advanced High-Strength Steel ConsortiumUnited States Steel Corporatio

Bridge Structures Cracks – What Made that Phenomena so Common?

AbstractThe common phenomena – cracks appearance on newly built reinforced concrete bridge structures - is being detected in Poland for several years now. That phenomena is regarded as threatening in case of bridge structures, despite the fact that reinforced concrete theory considers cracks as a standard concrete performance. Cracks are very likely to appear on concrete surface. Cracks are usually detected during concrete surface treatment before protective coating laying. Cracks appear on monolith structures, mainly at the slab spans and foreheads as well as, at support columns in a minor range. Concrete surface cracks openings reach up to 2mm size. The experience gained throughout consulting works on cracked structures are discussed in that paper. The influence of concrete surface mechanical cleaning prior the protective coatings laying on the crack “visual” intensification was also discussed herein. Crack openings measurement rules, as well as the most common mistakes made during the crack measurements and their real value assessment were described in the paper. The maximal crack opening allowances fluctuations in Polish and European concrete Codes were also discussed here. It was proved that the spotted crack opening increase is caused by the codes changes and by bold reinforcing cover. The bold cover is regarded as the corrosion protection of reinforcing bars. The cover bold and crack opening allowance dependency was discussed in the paper. The effect of Euro codes and the Minister of Transport and Maritime Economy Ordnance from May 30th 2000 titled “Technical requirements for highway engineering structures and their locations” simultaneous obligation on reinforced concrete structures cracks assessment was deliberated.At the conclusion the necessary modifications in crack assessment practice were claimed. The cracks should be assessed on the basis of homogenous code system. Their openings are dependent straight forward from the reinforcement cover thickness. One should avoid crack measurement at the sections, at which the crack edges are mechanically shattered. The crack opening assessment should be dependent on cover thickness. The rod anti shrinkage activity reaches the cover depth approximately to the depth equal to the rod diameter only. That fact should be taken under consideration during crack assessment

Fair resource allocation schemes and network dimensioning problems, Journal of Telecommunications and Information Technology, 2003, nr 3

Resource allocation problems are concerned with the allocation of limited resources among competing activities so as to achieve the best overall performances of the system but providing fair treatment of all the competitors. Telecommunication networks are facing the increasing demand for Internet services. Therefore, a problem of network dimensioning with elastic traffic arises which requires to allocate bandwidth to maximize service flows with fair treatment of all the services. In such applications, the so-called max-min fairness (MMF) solution concept is widely used to formulate the resource allocation scheme. This guarantees the fairness but may lead to significant losses in the overall throughput of the network. In this paper we show how multiple criteria optimization concepts can be used to generate various fair resource allocation schemes. The solution concepts are tested on the network dimensioning problem and their abilities to model various preferences are demonstrated

Ternary fuel mixture of diesel, rapeseed oil and tyre pyrolytic oil suitable for modern CRDI engines

The focus on seeking alternative fuels for combustion engines has been on the environmental and political scene for many years. Simultaneously there is a more and more serious problem of non-degradable waste utilization. In the present work an attempt has been made to asses both of those aspects by proposing a tailor-made, 3-component mixture consisting of mineral diesel, crude rapeseed oil and waste tyre pyrolytic oil. It was proven that the addition of pyrolytic oil can improve some basic drawbacks of rapeseed oil / diesel mixtures like high density and viscosity or low cold filter plugging point. On the basis of maximum bio-component share and optimum physicochemical properties a best fuel sample (40% mineral diesel oil, 55% rapeseed oil and 5% pyrolytic oil fraction) had been selected for engine tests, performed on a light-duty multi-cylinder Compression Ignition (CI) engine with electronic, Common Rail (CR) injection system. The steady state tests were performed for two rotational speeds and two injection strategies (single and sequential fuel injection), for each of which a full load sweep was performed. The engine research included in-cylinder pressure analysis along with efficiency estimation and exhaust gas emission measurements. The research confirmed the assumption that the selected fuel mixture is suitable for modern CI engines. The specific fuel consumption was similar or lower for the tested fuel compared to standard diesel, except the cases were sequential injection was incorporated. Emissions remained on similar levels as for both fuels except Total HydroCarbons (THC) at sequential injection operation points, which correlated with lower fuel conversion efficiency

WNT5A gene and protein expression in endometrial cancer

Introduction. WNT5A (Wnt family member 5A) belongs to the WNT family of secreted signaling glycoproteins that play essential role in developmental, physiological and pathological processes. WNT5A was shown to take part in carcinogenesis process playing both oncogenic and suppressor functions in various types of human malignancies. This study aimed to assess the expression of the WNT5A gene at the mRNA and protein levels in the specimens derived from endometrial cancer (EC) or unchanged control endometrium. The associations between the WNT5A expression levels and clinicopathological characteristics and survival of EC patients were evaluated. Materials and methods. Total RNA was isolated in order to assess the relative amounts of WNT5A mRNA by quantitative polymerase chain reaction (QPCR) in samples of unchanged endometrial control (n = 8) and tumor samples of EC patients (n = 28). Immunohistochemistry (IHC) was used to determine the presence of WNT5A protein in the sections of formalin-fixed, paraffin-embedded tissue specimens derived from unchanged endome­trial controls (n = 6) and EC tumors (n = 19). Significance of differences in WNT5A expression levels between the studied groups of EC patients and correlations between the WNT5A and demographic data, pathological features, hematological parameters and overall survival of the patients were evaluated by statistical analysis. Results. The level of WNT5A mRNA was decreased in EC in comparison to unchanged endometrium. WNT5A expression was associated with primary tumor invasion status exhibiting reduced level of transcripts in EC that involved organs beyond the uterus when compared to the uterus-confined cancers. WNT5A immunoreactivity was visualized in the cytoplasm and nuclei of EC cells as well as in the luminal and glandular epithelial cells of unchanged endometrium. WNT5A mRNA expression levels correlated negatively with cytoplasmic, and positively with nuclear immunoreactivity of the WNT5A protein in the EC cells. In addition, the relationships between blood leucocyte count (in particular granulocytes and lymphocytes) of patients with EC and their WNT5A mRNA and protein expression levels were established. A positive correlation between the nuclear immunoexpression of WNT5A protein in the cancer cells in cell nuclei and mean platelet volume in blood was also found. Conclusions. The results of the first study of WNT5A expression at the transcript and protein levels indicate that it could be considered as a potential marker of molecular changes that take place during EC development

Fulminant heart failure due to giant cell myocarditis affecting the left ventricle

A 56-year-old woman, previously healthy, was hospitalized after an episode of ventricular tachycardia in the course of infection. In view of the fulminant course of heart failure the patient was connected to an extracorporeal membrane oxygenation (ECMO) system. After 3 weeks of treatment with ECMO the patient received a heart transplant. A histopathological examination of the tissues of the explanted heart revealed giant cell myocarditis. The patient was treated with immunosuppression based on induction therapy followed by a standard regimen with steroids. Currently, the patient remains in good general condition with an left ventricular ejection fraction of 60%