Modelling Ultra High Pressure Compaction of Powder

The use of high pressure high temperature (HPHT) equipment varies; in mineral physics research the equipment is used for investigation of the earth’s interior and in industry it is used for commercially produced synthetic diamonds and other polycrystalline products. The common denominator for almost all high pressure systems is to use capsules where a powder material encloses the core material. Numerical analysis of the manufacturing processes with working conditions which reaches ultra high pressure (above 10 GPa) requires a constitutive model which can handle the specific behaviours of the powder from a low density to solid state. Calcium carbonate (CaCO3) is a mineral that can be used in high pressure processes and is very common in the earth core. A constitutive model for calcium carbonate applied to high pressure compaction is presented. The plastic response of powder is non-linear and described in a rate-independent cap plasticity model. The cap model has been developed to capture the behaviour of minerals in high pressure applications. The yield function consists of a failure envelope fitted to a strain-hardening cap. Experimental tests with a Bridgman anvil set-up using calcium carbonate powder discs are performed. Numerical analysis using the finite element method is done to virtually reproduce the experiments. Results from the analysis are compared to measured experimental results. The numerical analyses agree reasonably well with the experimental results

PFEM-based modeling of industrial granular flows

The potential of numerical methods for the solution and optimization of industrial granular flows problems is widely accepted by the industries of this field, the challenge being to promote effectively their industrial practice. In this paper, we attempt to make an exploratory step in this regard by using a numerical model based on continuous mechanics and on the so-called Particle Finite Element Method (PFEM). This goal is achieved by focusing two specific industrial applications in mining industry and pellet manufacturing: silo discharge and calculation of power draw in tumbling mills. Both examples are representative of variations on the granular material mechanical response—varying from a stagnant configuration to a flow condition. The silo discharge is validated using the experimental data, collected on a full-scale flat bottomed cylindrical silo. The simulation is conducted with the aim of characterizing and understanding the correlation between flow patterns and pressures for concentric discharges. In the second example, the potential of PFEM as a numerical tool to track the positions of the particles inside the drum is analyzed. Pressures and wall pressures distribution are also studied. The power draw is also computed and validated against experiments in which the power is plotted in terms of the rotational speed of the drum

Pharmacological targeting of MTHFD2 suppresses acute myeloid leukemia by inducing thymidine depletion and replication stress

The folate metabolism enzyme MTHFD2 (methylenetetrahydrofolate dehydrogenase/cyclohydrolase) is consistently overexpressed in cancer but its roles are not fully characterized, and current candidate inhibitors have limited potency for clinical development. In the present study, we demonstrate a role for MTHFD2 in DNA replication and genomic stability in cancer cells, and perform a drug screen to identify potent and selective nanomolar MTHFD2 inhibitors; protein cocrystal structures demonstrated binding to the active site of MTHFD2 and target engagement. MTHFD2 inhibitors reduced replication fork speed and induced replication stress followed by S-phase arrest and apoptosis of acute myeloid leukemia cells in vitro and in vivo, with a therapeutic window spanning four orders of magnitude compared with nontumorigenic cells. Mechanistically, MTHFD2 inhibitors prevented thymidine production leading to misincorporation of uracil into DNA and replication stress. Overall, these results demonstrate a functional link between MTHFD2-dependent cancer metabolism and replication stress that can be exploited therapeutically with this new class of inhibitors

Informe del Taller Regional de Estadísticas Ambientales: "Hacia el desarrollo de un conjunto básico de estadísticas ambientales", Santiago de Chile, 26 al 28 de noviembre de 2003"

The prediction of transient granular material flow is of fundamental industrial importance. The potential of using numerical methods in system design for increasing the operating efficiency of industrial processes involving granular material flow is huge. In the present study, a numerical tool for modelling dense transient granular material flow is presented and validated against experiments. The granular materials are modelled as continuous materials using two different constitutive models. The choice of constitutive models is made with the aim to predict the mechanical behaviour of a granular material during the transition from stationary to flowing and back to stationary state. The particle finite element method (PFEM) is employed as a numerical tool to simulate the transient granular material flow. Use of the PFEM enables a robust treatment of large deformations and free surfaces. The fundamental problem of collapsing rectangular columns of granular material is studied experimentally employing a novel approach for in-plane velocity measurements by digital image correlation. The proposed numerical model is used to simulate the experimentally studied column collapses. The model prediction of the in-plane velocity field during the collapse agrees well with experiments.Validerad;2021;Nivå 2;2021-01-22 (alebob);Finansiär: KIC RawMaterials (17152)</p

Effects of aspect ratio and specimen size on uniaxial failure stress of iron green bodies at high strain rates

Powder metallurgy is used for the production of a number of mechanical parts and is an essential production method. These are great advantages such as product cost effectiveness and product uniqueness. In general, however parts created by powder metallurgy have low strength because of low density. In order to increase strength as well as density, new techniques such as high-velocity-compaction (HVC) was developed and further investigation has been conducted on improvement of techniques and optimum condition using computer simulation. In this study, the effects of aspect ratio and specimen size of iron green bodies on failure strength of uniaxial compression and failure behavior were examined using a split Hopkinson pressure Bar. The diameters of specimens were 12.5 mm and 25 mm the aspect ratios (thickness/diameter) were 0.8 and 1.2

Evaluation of dynamic compressive properties of PLA polymer blends using split Hopkinson pressure bar

Poly(lactic acid) (PLA) has been used as a biomaterial for bone fixation devices in oral and orthopedic surgery because of good biocompatibility and bioabsorbability. Because Poly(ε-Caprolactone) (PCL) is a ductile, bioabsorbable and biodegradable polymer, many types of PLA/PCL polymer blends have been developed to improve its material strength and impact resistance. The stress-strain curves of PLA and PLA/PCL polymer blends were measured using a split Hopkinson pressure bar (Kolsky bar) method and a universal testing machine. The effect of PCL content on Young's modulus and yield stress was examined. The values of constants in Cowper-Symonds equation with respect to yield stress were determined for PLA and PLA/PCL polymer blend specimens. PLA/PCL specimens were observed using a scanning electron microscope

Effects of aspect ratio and specimen size on uniaxial failure stress of iron green bodies at high strain rates

Powder metallurgy is used for the production of a number of mechanical parts and is an essential production method. These are great advantages such as product cost effectiveness and product uniqueness. In general, however parts created by powder metallurgy have low strength because of low density. In order to increase strength as well as density, new techniques such as high-velocity-compaction (HVC) was developed and further investigation has been conducted on improvement of techniques and optimum condition using computer simulation. In this study, the effects of aspect ratio and specimen size of iron green bodies on failure strength of uniaxial compression and failure behavior were examined using a split Hopkinson pressure Bar. The diameters of specimens were 12.5 mm and 25 mm the aspect ratios (thickness/diameter) were 0.8 and 1.2

The role of load testing in the assessment and repair of bridges

One-day seminar held Oxford (GB), 8 Apr 1997Available from British Library Document Supply Centre-DSC:99/11362 / BLDSC - British Library Document Supply CentreSIGLEGBUnited Kingdo

Biomechanics Determination of dynamic material properties for poly(L-lactic acid)/ poly(∊-caprolactone) blends: Experiments and simulation using split Hopkinson pressure bars

Coefficients of Cowper-Symonds constitutive equation for PLLA/PCL = 80/20 were determined using the results of compressive tests at high and low strain rates. The simulation of split Hopkinson pressure bar using the coefficients was carried out under the same condition as the experiments. The diameter and thickness of specimens were measured by a high-speed video camera. The stress and strain histories of specimens, the thickness and the diameter in the simulations at high strain rate were compared with those in the experiments