Multi-scale numerical simulation analysis for influence of combined leaching and frost deteriorations on mechanical properties of concrete

2016 ◽  
Vol 12 (4) ◽  
pp. 648-671 ◽  
Author(s):  
Jiang Hu
Keyword(s):  
Mechanical Properties ◽  
Numerical Simulation ◽  
Frost Damage ◽  
Hydraulic Pressure ◽  
Structural Level ◽  
Content Type ◽  
Calcium Leaching ◽  
Multi Scale ◽  
Random Aggregate

Purpose The multi-scale numerical simulation method, able to represent the complexity of the random structures and capture phase degradation, is an effective way to investigate the long-term behavior of concrete in service and bridges the gap between research on the material and on the structural level. However, the combined chemical-physical deterioration mechanisms of concrete remain a challenging task. The purpose of this paper is to investigate the degradation mechanism of concrete at the waterline in cold regions induced by combined calcium leaching and frost damage. Design/methodology/approach With the help of the NIST’s three-dimensional (3D) hydration model and the random aggregate model, realistic 3D representative volume elements (RVEs) of concrete at the micro-, the meso-, and the macro-scales can be reconstructed. The boundary problem method is introduced to compute the homogenized mechanical properties for both sound and damaged RVEs. According to the damage characteristics, the staggering method including a random dissolution model and a thermo-mechanical coupling model is developed to simulate the synergy deterioration effects of interacted calcium leaching and frost attacks. The coupled damage procedure for the frost damage process is based on the hydraulic pressure theory and the ice lens growth theory considering the relationship between the frozen temperature and the radius of the capillary pore. Finally, regarding calcium leaching as the leading role in actual engineering, the numerical methodology for combined leaching and frost damage on concrete property is proposed using a successive multi-scale method. Findings On the basis of available experimental data, this methodology is employed to explore the deterioration process. The results agree with the experimental ones to some extent, chemical leaching leads to the nucleation of some micro-cracks (i.e. damage), and consequently, to the decrease of the frost resistance. Originality/value It is demonstrated that the multi-scale numerical methodology can capture potential aging and deterioration evolution processes, and can give an insight into the macroscopic property degradation of concrete under long-term aggressive conditions.

Investigation and multi-scale optimization design of woven composite cut-out structures

2020 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Duc Hai Nguyen ◽  
Hu Wang ◽  
Fan Ye ◽  
Wei Hu
Keyword(s):  
Mechanical Properties ◽  
Composite Structures ◽  
Optimization Design ◽  
Material Behavior ◽  
Efficient Global Optimization ◽  
Support Vector ◽  
Woven Composite ◽  
Content Type ◽  
Multi Scale ◽  
Ply Orientation

Purpose The purpose of this paper is to investigate the mechanical properties’ behaviors of woven composite cut-out structures with specific parameters. Because of the complexity of micro-scale and meso-scale structure, it is difficult to accurately predict the mechanical material behavior of woven composites. Numerical simulations are increasingly necessary for the design and optimization of test procedures for composite structures made by the woven composite. The results of the proposed method are well satisfied with the results obtained from the experiment and other studies. Moreover, parametric studies on different plates based on the stacking sequences are investigated. Design/methodology/approach A multi-scale modeling approach is suggested. Back-propagation neural networks (BPNN), radial basis function (RBF) and least square support vector regression are integrated with efficient global optimization (EGO) to reduce the weight of assigned structure. Optimization results are verified by finite element analysis. Findings Compared with other similar studies, the advantage of the suggested strategy uses homogenized properties behaviors with more complex analysis of woven composite structures. According to investigation results, it can be found that 450/−450 ply-orientation is the best buckling load value for all the cut-out shape requirements. According to the optimal results, the BPNN-EGO is the best candidate for the EGO to optimize the woven composite structures. Originality/value A multi-scale approach is used to investigate the mechanical properties of a complex woven composite material architecture. Buckling of different cut-out shapes with the same area is surveyed. According to investigation, 45°/−45° ply-orientation is the best for all cut-out shapes. Different surrogate models are integrated in EGO for optimization. The BPNN surrogate model is the best choice for EGO to optimization difficult problems of woven composite materials.

Ageing processes in laser sintered and injection moulded PA12 following hygienic reprocessing

2015 ◽  
Vol 21 (3) ◽  
pp. 279-286 ◽  
Author(s):  
Miriam Johanna Haerst ◽  
Romano Wolf ◽  
Markus Schönberger ◽  
Erich Wintermantel ◽  
Kurt Engelsing ◽  
...  
Keyword(s):  
Mechanical Properties ◽  
Cyclic Stress ◽  
Patient Specific ◽  
Systematic Research ◽  
Clinical Use ◽  
Processing Methods ◽  
Content Type ◽  
Polyamide 12 ◽  
Important Message

Purpose – The purpose of this paper is to describe the ageing behaviour of polyamide 12 (PA12) after clinical use. The research is focused on the comparison of the processing methods injection moulding and laser sintering. Design/methodology/approach – Test specimens are subjected to a cyclic stress of defined bending, cleaning, disinfection and sterilization. The focus of interest in this research is the degradation and reduction of mechanical properties. Findings – Mechanical and optical changes of the materials after clinical use and hygienic reprocessing are evaluated and discussed. Research limitations/implications – This article is focused on PA12 and, therefore, enables a very specific statement for the clinical use of PA12. The processing methods could have different impacts depending on the polymer. Originality/value – With the increasing application of polymers in medical devices, the mechanical properties must be ensured even after long-term clinical use. A systematic research with a realistic and still-defined cyclic stress is shown in this paper. Especially the testing of laser sintered polymers compared to injection moulded material has an important message for future patient-specific products.

Thermal and mechanical properties of sintered Ag layers for power module assembly

2015 ◽  
Vol 32 (1) ◽  
pp. 37-42 ◽  
Author(s):  
Marcin Myśliwiec ◽  
Ryszard Kisiel
Keyword(s):  
Mechanical Properties ◽  
Thermal Resistance ◽  
Point Of View ◽  
Future Research ◽  
Temperature Sensitive ◽  
Thermal And Mechanical Properties ◽  
Power Module ◽  
Content Type ◽  
Sintered Ag

Purpose – The purpose of our paper is to investigate thermal and mechanical properties of Ag sintered layers used for assembly of SiC diode to Direct Bonding Copper (DBC) interposer. How SiC devices are assembled to ceramic package defines efficiency of heat transfer and mechanical support. Design/methodology/approach – Ag microparticles, sized 2-4 μm and flake shaped, were used as joining material. The parameters of sintering process were as follows: temperature 400°C, pressure 10 MPa and time 40 min. It was found that after sintering and long-term aging in air at 350°C the adhesion is in the range of 10 MPa, which is enough from a practical point of view. The thermal properties of the SiC die assembled into a ceramic package were also investigated. In the first step, the calibration of the temperature-sensitive parameter VF (IF = 2 mA) was done and the relation between VF and temperature was found. In the next step, the thermal resistance between junction and case was determined knowing junction and case temperature. Findings – For SiC diode with Au bottom metallization joined to the DBC interposer by Ni/Au metallization by Ag microparticle layer, Rth j-c is in the range of 2-3.5°C/W, and for SiC diode with Ag bottom metallization joined to DBC interposer with Ag metallization by Ag microparticle layer, Rth j-c is in the range of 4.5-5.5°C/W. Research limitations/implications – In the future, research on thermal resistance of SiC diodes assembled onto the DBC interposer with Au and Ag metallization in the temperature range up to 350°C needs to be carried out. To do this, it necessary to find a solution for the attaches that leads to ceramic package able to work at such high temperature. Originality/value – Obtained results are comparable with results mentioned by other studies for eutectic Au/Sn or SAC solder joints; however, the solution proposed by us can properly work at significantly higher temperatures.

scholarly journals Multi-scale computational modeling for concrete damage by mixed pore pressures – case of coupled alkali–silica reaction and cyclic freeze/thaw

2018 ◽  
Vol 35 (6) ◽  
pp. 2367-2385 ◽  
Author(s):  
Fuyuan Gong ◽  
Yuya Takahashi ◽  
Koichi Maekawa
Keyword(s):  
Coupling Effect ◽  
Mechanical Damage ◽  
Frost Damage ◽  
Alkali Silica Reaction ◽  
Content Type ◽  
Freeze Thaw ◽  
Multi Scale ◽  
Pore Pressures ◽  
Macro Scale ◽  
Air Entrained Concrete

Purpose This paper aims to propose a multi-scale simulation approach for the concrete macro-mechanical damage caused by mixed micro-pore pressures, such as the coupled alkali–silica reaction (ASR) and freeze-thaw cycles (FTC). Design/methodology/approach The micro-physical events are computationally modeled by considering the coupling effect between ASR gel and condensed water in the mixed pressure and motion. The pressures and transport of pore substances are also linked with the concrete matrix deformation at macro-scale through a poro-mechanical approach, and affect each other, reciprocally. Once the crack happens in the nonlinear analysis, both the micro-events (water and gel motion) and the macro mechanics will be mutually interacted. Finally, different sequences of combined ASR and FTC are simulated. Findings The multi-chemo mechanistic computation can reproduce complex events in pore structures, and further the macro-damages. The results show that ASR can reduce the FTC expansion for non-air-entrained concrete, but may increase the frost damage for air-entrained concrete. The simulation is examined to bring about the observed phenomena. Originality/value This paper numerically clarifies the strong linkage between macro-mechanical deformation and micro-chemo-physical events for concrete composites under coupled ASR and FTC.

Effects of calcium leaching on the physical and mechanical properties of aerial lime-cement mortars

2019 ◽  
Vol 17 (3) ◽  
pp. 649-666
Author(s):  
Soufyane Bellifa ◽  
Nadir Boumechra
Keyword(s):  
Mechanical Properties ◽  
Compressive Strength ◽  
Calcium Hydroxide ◽  
Nitrate Solution ◽  
Physical And Mechanical Properties ◽  
Rate Of Change ◽  
Content Type ◽  
Calcium Leaching ◽  
Ammonium Nitrate Solution ◽  
Cement Mortars

Purpose This paper aims to assess the effects of chemically accelerated leaching on the physical and mechanical properties of aerial lime–cement mortars (LCMs). Design/methodology/approach Two aerial LCMs, differencing mainly in their calcium hydroxide content, were degraded by the use of an ammonium nitrate solution as a leaching agent. The leaching effects were studied by evaluating the rate of change in physical (sorptivity and mass loss) and mechanical (flexural and compressive strength) characteristics of aerial LCMs. To quantify the evolution and kinetics of degradation, the leached depth was then characterized at different levels of degradation by means of a phenolphthalein solution. Findings The experimental results showed that the dissolution of binder decreases the mass, alkalinity and strength of aerial LCMs but increases their sorptivity. A linear relationship was derived by plotting the values of leached depth against the square root of immersion time in an aggressive solution. It was found that the leached depth followed diffusion-controlled kinetics. Originality/value It was found that the global loss of compressive strength of aerial LCMs because of complete dissolution of calcium hydroxide can reach up to 80 per cent.

Dynamic co-movement and interdependency among real estate index in China: a multi-scale multiple correlation analysis

2021 ◽  
Vol ahead-of-print (ahead-of-print) ◽  
Author(s):  
Rabeh Khalfaoui ◽  
Aviral Kumar Tiwari ◽  
Faisal Alqahtani ◽  
Shawkat Hammoudeh ◽  
Suleman Sarwar
Keyword(s):  
Empirical Relationship ◽  
Portfolio Diversification ◽  
Multiple Correlation ◽  
Security Investment ◽  
Content Type ◽  
Time Frequency ◽  
Chinese Investment ◽  
Multi Scale ◽  
Multiple Correlation Analysis

Purpose This study aims to investigate the dynamic co-movement and interconnection among 69 security investment indices in China using the multi-time scale framework. Design/methodology/approach The authors first use the multiple coherence analysis method to exhibit the degree of relationships among the variables under study. In addition, the wavelet multiple correlation and wavelet multiple cross-correlation analyses are used to examine the time-frequency synchronization interdependence structure among the variables. Findings From the empirical findings, one may infer less opportunity for portfolio diversification at higher time scales. Obviously, at these scales, the authors find that the 69 Chinese investment indices generate a simple security investment class, as indicated by higher interconnection between the indices. Research limitations/implications Further research can increase the sample size to re-investigate the empirical relationship for security investment indices. Practical implications In the nutshell, the results demonstrate the potential for Chinese investors to invest in security investment indices to earn from portfolio diversification at lower time frequencies. The Chinese investment market indices under study yield further opportunities of portfolio diversification toward the short-term investors than the long-term investors. Originality/value To the best of the authors’ knowledge, this is the first paper to examine the dynamic co-movement and interconnection for security investment indices in China.

Mechanical properties of SMD interconnections on flexible and rigid substrates

2016 ◽  
Vol 28 (1) ◽  
pp. 27-32 ◽  
Author(s):  
Damian Nowak ◽  
Andrzej Dziedzic ◽  
Zbigniew Żaluk ◽  
Henryk Roguszczak ◽  
Mariusz Węglarski
Keyword(s):  
Mechanical Properties ◽  
Shear Strength ◽  
Thick Film ◽  
Thermal Ageing ◽  
Flexible Substrates ◽  
Conductive Adhesives ◽  
Content Type ◽  
Electrically Conductive Adhesive ◽  
Thermally Conductive

Purpose – The paper aims to investigate on the mechanical properties of surface-mount device (SMD) interconnections made on flexible and rigid substrates. Design/methodology/approach – The durability of joints to shear strength was measured with tensile machine. Investigations were carried out for 0402- and 0603-sized ceramic passives and integrated circuits in SOIC-8, TSSOP-8, XSON3 and XSON6 packages. Three types of flexible substrates (Kapton, Mylar and Pyralux) and two types of rigid substrates (LTCC and alumina) were used. SMD components were mounted with SAC solder or electrically conductive adhesive. Contact pads were made of Ag-based polymer paste on flexible substrates and PdAg-based cermet paste on ceramics. The shear strength was measured for as-made and long-term thermally aged test structures. The average durability and standard deviation were compared for different combination of materials. Moreover, mechanical properties of interconnections made of polymer thick-film pastes or electrically/thermally conductive adhesives between ceramic chips and flexible/ceramic substrates were investigated. Findings – The mechanical properties of joints strongly depend on configuration of applied materials. Some of them exhibit high durability to shear strength, while other should not be recommended due to very weak connections. Additionally, long-term thermal ageing showed that exploitation of such connections at elevated temperature in some cases might increase their strength. However, for some materials, it leads to accelerated degradation of joints. Originality/value – This paper provides practical information about SMD interconnections made with standard materials (lead-free solder, electrically/thermally conductive adhesives) and proposed non-standard procedures, e.g. assembling of ceramic chips with low temperature cermet or polymer thick-film conductive pastes.

Dual-isotope single-photon emission computerized tomography scanning in patients with glioblastoma multiforme: association with patient survival and histopathological characteristics of tumor after high-dose radiotherapy

1998 ◽  
Vol 89 (1) ◽  
pp. 60-68 ◽  
Author(s):  
Richard B. Schwartz ◽  
B. Leonard Holman ◽  
Joseph F. Polak ◽  
Basem M. Garada ◽  
Marc S. Schwartz ◽  
...  
Keyword(s):  
Survival Rate ◽  
Glioblastoma Multiforme ◽  
Single Photon ◽  
Photon Emission ◽  
High Dose ◽  
Term Survival ◽  
Content Type ◽  
Dual Isotope ◽  
Fine Print

Object. The study was conducted to determine the association between dual-isotope single-photon emission computerized tomography (SPECT) scanning and histopathological findings of tumor recurrence and survival in patients treated with high-dose radiotherapy for glioblastoma multiforme. Methods. Studies in which SPECT with 201Tl and 99mTc-hexamethypropyleneamine oxime (HMPAO) were used were performed 1 day before reoperation in 47 patients with glioblastoma multiforme who had previously been treated by surgery and high-dose radiotherapy. Maximum uptake of 201Tl in the lesion was expressed as a ratio to that in the contralateral scalp, and uptake of 99mTc-HMPAO was expressed as a ratio to that in the cerebellar cortex. Patients were stratified into groups based on the maximum radioisotope uptake values in their tumor beds. The significance of differences in patient gender, histological characteristics of tissue at reoperation, and SPECT uptake group with respect to 1-year survival was elucidated by using the chi-square statistic. Comparisons of patient ages and time to tumor recurrence as functions of 1-year survival were made using the t-test. Survival data at 1 year were presented according to the Kaplan—Meier method, and the significance of potential differences was evaluated using the log-rank method. The effects of different variables (tumor type, time to recurrence, and SPECT grouping) on long-term survival were evaluated using Cox proportional models that controlled for age and gender. All patients in Group I (201Tl ratio < 2 and 99mTc-HMPAO ratio < 0.5) showed radiation changes in their biopsy specimens: they had an 83.3% 1-year survival rate. Group II patients (201T1 ratio < 2 and 99mTc-HMPAO ratio of ≥ 0.5 or 201Tl ratio between 2 and 3.5 regardless of 99mTc-HMPAO ratio) had predominantly infiltrating tumor (66.6%); they had a 29.2% 1-year survival rate. Almost all of the patients in Group III (201Tl ratio > 3.5 and 99mTc-HMPAO ratio ≥ 0.5) had solid tumor (88.2%) and they had a 6.7% 1-year survival rate. Histological data were associated with 1-year survival (p < 0.01); however, SPECT grouping was more closely associated with 1-year survival (p < 0.001) and was the only variable significantly associated with long-term survival (p < 0.005). Conclusions. Dual-isotope SPECT data correlate with histopathological findings made at reoperation and with survival in patients with malignant gliomas after surgical and high-dose radiation therapy.

Long-term management of patients with multiple brain metastases after shaped beam radiosurgery

2004 ◽  
pp. 406-412
Author(s):  
Paul Okunieff ◽  
Michael C. Schell ◽  
Russell Ruo ◽  
E. Ronald Hale ◽  
Walter G. O'Dell ◽  
...  
Keyword(s):  
Brain Metastases ◽  
Tumor Control ◽  
Content Type ◽  
Negative Results ◽  
Multiple Metastases ◽  
Extracranial Disease ◽  
Successful Control ◽  
The Brain

✓ The role of radiosurgery in the treatment of patients with advanced-stage metastatic disease is currently under debate. Previous randomized studies have not consistently supported the use of radiosurgery to treat patients with numbers of brain metastases. In negative-results studies, however, intracranial tumor control was high but extracranial disease progressed; thus, patient survival was not greatly affected, although neurocognitive function was generally maintained until death. Because the future promises improved systemic (extracranial) therapy, the successful control of brain disease is that much more crucial. Thus, for selected patients with multiple metastases to the brain who remain in good neurological condition, aggressive lesion-targeting radiosurgery should be very useful. Although a major limitation to success of this therapy is the lack of control of extracranial disease in most patients, it is clear that well-designed, aggressive treatment substantially decreases the progression of brain metastases and also improves neurocognitive survival. The authors present the management and a methodology for rational treatment of a patient with breast cancer who has harbored 24 brain metastases during a 3-year period.

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