PREDICTION OF PEEK RESIN PROPERTIES FOR PROCESSING MODELING USING MOLECULAR DYNAMICS

2021 ◽  
Author(s):  
KHATEREH KASHMARI ◽  
PRATHAMESH DESHPANDE ◽  
SAGAR PATIL ◽  
SAGAR SHAH ◽  
MARIANNA MAIARU ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Residual Stresses ◽  
Crystallization Kinetics ◽  
Material Properties ◽  
Elevated Temperatures ◽  
Processing Parameters ◽  
Thermomechanical Properties ◽  
Volumetric Shrinkage ◽  
Processing Temperature ◽  
Wide Range

Polymer Matrix Composites (PMCs) have been the subject of many recent studies due to their outstanding characteristics. For the processing of PMCs, a wide range of elevated temperatures is typically applied to the material, leading to the development of internal residual stresses during the final cool-down step. These residual stresses may lead to net shape deformations or internal damage. Also, volumetric shrinkage, and thus additional residual stresses, could be created during crystallization of the semi-crystalline thermoplastic matrix. Furthermore, the thermomechanical properties of semi-crystalline polymers are susceptible to the crystallinity content, which is tightly controlled by the processing parameters (processing temperature, temperature holding time) and material properties (melting and crystallization temperatures). Hence, it is vital to have a precise understanding of crystallization kinetics and its impact on the final component's performance to accurately predict induced residual stresses during the processing of these materials. To enable multi-scale process modeling of thermoplastic composites, molecular-level material properties must be determined for a wide range of crystallinity levels. In this study, the thermomechanical properties and volumetric shrinkage of the thermoplastic Poly Ether Ether Ketone (PEEK) resin are predicted as a function of crystallinity content and temperature using molecular dynamics (MD) modeling. Using crystallization-kinetics models, the thermo-mechanical properties are directly related to processing time and temperature. This research can ultimately predict the residual stress evolution in PEEK composites as a function of processing parameters.

Ab Initio Molecular Dynamics Reveals New Active Sites in Atomically Dispersed Pt1/TiO2 Catalysts

2020 ◽  
Author(s):  
Nicholas Humphrey ◽  
Selin Bac ◽  
Shaama Mallikarjun Sharada
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Active Sites ◽  
Density Functional ◽  
Elevated Temperatures ◽  
Water Gas Shift ◽  
Ab Initio Molecular Dynamics ◽  
Catalytic Surface ◽  
Wide Range ◽  
Water Gas

<div> <div> <div> <p>We present a multi-scale modeling study of atomically dispersed Pt on the (110) surface of rutile TiO2. Using density functional theory (DFT) and ab initio molecular dynamics (AIMD), we probe the dynamic evolution of the catalytic surface at elevated temperatures. We identify metal atom diffusion as well as support atom mobility as important dynamical phenomena that enable the formation of new active sites. Among the eight new dynamically formed sites that are distinct from prior experimental and DFT reports, two sites exhibit anionic, near-linear O−Pt−O configurations. Such configurations are neither intuitive nor easily located using static methods such as DFT. Therefore, DFT alone is not sufficient to obtain a complete, dynamic description of the catalytic surface. Furthermore, the near-linear O−Pt−O sites exhibit CO binding characteristics that are markedly distinct from their parent sites, with possibly higher activity towards CO oxidation and water-gas shift reactions. Based on the wide range of adsorbate affinities exhibited by the DFT and AIMD-generated sites in this study, our aim going forward is to probe site-sensitivity of water-gas shift kinetics with these catalysts. </p> </div> </div> </div>

Laminated Ceramic Structures within Alumina / YTZP System Obtained by Low Pressure Joining

2007 ◽  
Vol 333 ◽  
pp. 219-222 ◽  
Author(s):  
Jonas Gurauskis ◽  
Antonio Javier Sanchez-Herencia ◽  
Carmen Baudín
Keyword(s):  
Finite Element Method ◽  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Material Properties ◽  
Layered Materials ◽  
Processing Parameters ◽  
Spectroscopic Technique ◽  
Reinforcement Mechanism ◽  
Laminated Structures

The production of multilayer ceramics by laminating stacked green ceramic tapes is one of the most attractive methods to fabricate layered materials. In this work, a new lamination technique was employed to obtain laminated ceramic structures in the aluminazirconia system with residual stress compression at the outer layers. This reinforcement mechanism would lead to ceramics with changed material properties and R-curve behaviour. The optimization of processing parameters for fabrication of defect free monolithic and laminated structures is described. The residual stresses developed in the laminated structures are discussed in terms of the results obtained from piezo-spectroscopic technique measurements and finite element method calculations.

Optimization of SLM productivity by aligning 17-4PH material properties on part requirements

2014 ◽  
Vol 20 (6) ◽  
pp. 444-448 ◽  
Author(s):  
A. B. Spierings ◽  
M. Schoepf ◽  
R. Kiesel ◽  
K. Wegener
Keyword(s):  
Mechanical Properties ◽  
Material Properties ◽  
Processing Parameters ◽  
Powder Layer ◽  
Clear Correlation ◽  
Porosity Level ◽  
Content Type ◽  
Wide Range ◽  
Material Porosity ◽  
Process Productivity

Purpose – The purpose of this study is the development of a global SLM-manufacturing optimization strategy taking into account material porosity and SLM process productivity. Selective laser melting (SLM) is a master forming process generating not only a near net shape geometry, but also the material with its properties. Research focuses primarily on optimal processing parameters for maximised material properties. However, the process allows also designing the material structure by internal porosity, affecting global material properties and the process productivity. Design/methodology/approach – The study investigates the influence of the main SLM process parameters on material porosity and consequently on the static mechanical properties of hardened SS17-4PH material. Furthermore, a model for the SLM scanning productivity is developed based on the SLM processing parameters. Findings – The results show a clear correlation between porosity level and mechanical properties. Thereby, the mechanical strength and material modulus can be varied in a wide range. The degree of internal material porosity can be correlated to the energy input defined by a set of SLM processing parameters, such as Laser power, powder layer thickness and scan speed, allowing pre-definition of a specific degree of porosity. Originality/value – Aligning of the SLM processing parameters to the technical material requirements of the parts to be produced, e.g. maximal stresses in service, required E-modulus or lightweight aspects, enlarges the general design space significantly. In combination with the presented model for the scanning productivity, it is further possible to optimize the SLM build rate.

Ab Initio Molecular Dynamics Reveals New Active Sites in Atomically Dispersed Pt1/TiO2 Catalysts

2020 ◽  
Author(s):  
Nicholas Humphrey ◽  
Selin Bac ◽  
Shaama Mallikarjun Sharada
Keyword(s):  
Molecular Dynamics ◽  
Ab Initio ◽  
Active Sites ◽  
Density Functional ◽  
Elevated Temperatures ◽  
Water Gas Shift ◽  
Ab Initio Molecular Dynamics ◽  
Catalytic Surface ◽  
Wide Range ◽  
Water Gas

<div> <div> <div> <p>We present a multi-scale modeling study of atomically dispersed Pt on the (110) surface of rutile TiO2. Using density functional theory (DFT) and ab initio molecular dynamics (AIMD), we probe the dynamic evolution of the catalytic surface at elevated temperatures. We identify metal atom diffusion as well as support atom mobility as important dynamical phenomena that enable the formation of new active sites. Among the eight new dynamically formed sites that are distinct from prior experimental and DFT reports, two sites exhibit anionic, near-linear O−Pt−O configurations. Such configurations are neither intuitive nor easily located using static methods such as DFT. Therefore, DFT alone is not sufficient to obtain a complete, dynamic description of the catalytic surface. Furthermore, the near-linear O−Pt−O sites exhibit CO binding characteristics that are markedly distinct from their parent sites, with possibly higher activity towards CO oxidation and water-gas shift reactions. Based on the wide range of adsorbate affinities exhibited by the DFT and AIMD-generated sites in this study, our aim going forward is to probe site-sensitivity of water-gas shift kinetics with these catalysts. </p> </div> </div> </div>

On the Stress Development in SA508 Autogenous Weld

2014 ◽  
Vol 783-786 ◽  
pp. 2123-2128 ◽  
Author(s):  
Hamidreza Abdolvand ◽  
Mike Keavey ◽  
H. Dai ◽  
Alison Mark ◽  
N. O’Meara ◽  
...  
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Phase Transformations ◽  
High Speed ◽  
Elevated Temperatures ◽  
Kinematic Hardening ◽  
Stress Development ◽  
Wide Range ◽  
Martensitic Phase Transformations ◽  
Welding Processes

Considering the significant role that residual stresses play in determining the lifetime-service of materials, it is mandatory to have a good understanding of and a means of predicting those that develop during welding processes. For this purpose, a User MATerial subroutine (UMAT) is developed to study the effects of various parameters that influence solid state phase transformations and residual stress evolution during welding of SA508 ferritic steel. The temperature dependent elastic and kinematic hardening parameters for each of the individual phases that can potentially develop during cooling from elevated temperatures are measured and are used for calculating stress development during low (75 mm/min) and high (300 mm/min) speed gas-tungsten arc welding (GTAW) on SA508 grade 3. These two speeds are selected to cover a wide range of cooling rates in the heat affected zone so that different phase proportions would be present. The results of the numerical simulations for residual stresses are compared against those measured by neutron diffraction. It is shown here that a low speed weld results in bainite formation whereas a high speed weld results in bainitic as well as subsequent martensitic phase transformations where each welding rate results in different residual stress development.

scholarly journals Preliminary Analysis of an Aged RPV Subjected to Station Blackout

Energies ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4394
Author(s):  
Rosa Lo Frano ◽  
Salvatore Angelo Cancemi ◽  
Piotr Darnowski ◽  
Riccardo Ciolini ◽  
Sandro Paci
Keyword(s):  
Finite Element ◽  
Material Properties ◽  
Nuclear Power ◽  
Power Plants ◽  
Elevated Temperatures ◽  
Thermomechanical Properties ◽  
Nuclear Industry ◽  
Fe Model ◽  
Term Operation ◽  
Station Blackout

Today, 46% of operating Nuclear Power Plants (NPP) have a lifetime between 31 and 40 years, while 19% have been in operation for more than 40 years. Long Term Operation (LTO) is an urgent requirement for all of the nuclear industry. The aim of this study is to assess the performance of a reactor pressure vessel (RPV) subjected to a station blackout (SBO) event. Alterations suffered by the material properties and creep at elevated temperatures are considered. In this study, coupling between MELCOR and Finite Element Method (FEM) codes is carried out. In the Finite Element (FE) model, the combined effects of ageing and creep are implemented through degraded material properties and a viscoplastic model. The reliability of the model is validated by comparing the FOREVER/C1 experimental results. The results show that the RPV lower head bends downwards with a maximum radial expansion of about 260 mm and RPV thermomechanical properties are reduced by more than 50% at high temperatures. The effects of ageing, creep and long heat-up strongly affect the resistance of the RPV system until the point of compromising it in the absence of/delayed emergency intervention. Aged RPV at end-of-life may collapse earlier, and in less time, with the same accidental conditions.

Mechanical Properties and Dislocation Structure of Single Crystal Cdte Deformed in Compression at 300°C

1976 ◽  
Vol 34 ◽  
pp. 592-593
Author(s):  
Ernest L. Hall ◽  
J. B. Vander Sande
Keyword(s):  
Mechanical Properties ◽  
Single Crystal ◽  
Dislocation Structure ◽  
Room Temperature ◽  
Elevated Temperatures ◽  
Strain Curve ◽  
Optical Devices ◽  
Semiconductor Compound ◽  
Wide Range ◽  
Sample Orientation

The present paper describes research on the mechanical properties and related dislocation structure of CdTe, a II-VI semiconductor compound with a wide range of uses in electrical and optical devices. At room temperature CdTe exhibits little plasticity and at the same time relatively low strength and hardness. The mechanical behavior of CdTe was examined at elevated temperatures with the goal of understanding plastic flow in this material and eventually improving the room temperature properties. Several samples of single crystal CdTe of identical size and crystallographic orientation were deformed in compression at 300°C to various levels of total strain. A resolved shear stress vs. compressive glide strain curve (Figure la) was derived from the results of the tests and the knowledge of the sample orientation.

Theoretical study of the prestressing strand's stress by computer modeling methods

2020 ◽  
Vol 76 (11) ◽  
pp. 1139-1148
Author(s):  
A. G. Korchunov ◽  
E. M. Medvedeva ◽  
E. M. Golubchik
Keyword(s):  
Residual Stresses ◽  
High Strength ◽  
Pearlitic Steel ◽  
Internal Stresses ◽  
Steel Microstructure ◽  
Compressive Stresses ◽  
Wide Range ◽  
Prestressing Strands ◽  
Increasing Temperature ◽  
Wire Strand

The modern construction industry widely uses reinforced concrete structures, where high-strength prestressing strands are used. Key parameters determining strength and relaxation resistance are a steel microstructure and internal stresses. The aim of the work was a computer research of a stage-by-stage formation of internal stresses during production of prestressing strands of structure 1х7(1+6), 12.5 mm diameter, 1770 MPa strength grade, made of pearlitic steel, as well as study of various modes of mechanical and thermal treatment (MTT) influence on their distribution. To study the effect of every strand manufacturing operation on internal stresses of its wires, the authors developed three models: stranding and reducing a 7-wire strand; straightening of a laid strand, stranding and MTT of a 7-wire strand. It was shown that absolute values of residual stresses and their distribution in a wire used for strands of a specified structure significantly influence performance properties of strands. The use of MTT makes it possible to control in a wide range a redistribution of residual stresses in steel resulting from drawing and strand laying processes. It was established that during drawing of up to 80% degree, compressive stresses of 1100-1200 MPa degree are generated in the central layers of wire. The residual stresses on the wire surface accounted for 450-500 MPa and were tension in nature. The tension within a range of 70 kN to 82 kN combined with a temperature range of 360-380°С contributes to a two-fold decrease in residual stresses both in the central and surface layers of wire. When increasing temperature up to 400°С and maintaining the tension, it is possible to achieve maximum balance of residual stresses. Stranding stresses, whose high values entail failure of lay length and geometry of the studied strand may be fully eliminated only at tension of 82 kN and temperature of 400°С. Otherwise, stranding stresses result in opening of strands.

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