Theoretical and experimental investigations on failure mechanisms occuring during long-term cycling of electrostatic actuators

2014 ◽  
Author(s):  
R. Behlert ◽  
T. Kunzig ◽  
G. Schrag ◽  
G. Wachutka
Keyword(s):  
Failure Mechanisms ◽  
Experimental Investigations ◽  
Electrostatic Actuators

scholarly journals Influence of material degradation on weld seam quality in hot gas butt welding of polyamides

2021 ◽  
Author(s):  
Max Bialaschik ◽  
Volker Schöppner ◽  
Mirko Albrecht ◽  
Michael Gehde
Keyword(s):  
Weld Seam ◽  
Experimental Investigations ◽  
Heating Process ◽  
Butt Welding ◽  
Hot Gas ◽  
Process Gas ◽  
Glass Fiber Reinforced ◽  
Extrusion Welding ◽  
Different Gases

AbstractThe joining of plastics is required because component geometries are severely restricted in conventional manufacturing processes such as injection molding or extrusion. In addition to established processes such as hot plate welding, infrared welding, or vibration welding, hot gas butt welding is becoming more and more important industrially due to its advantages. The main benefits are the contactless heating process, the suitability for glass fiber reinforced, and high-temperature plastics as well as complex component geometries. However, various degradation phenomena can occur during the heating process used for economic reasons, due to the presence of oxygen in the air and to the high gas temperatures. In addition, the current patent situation suggests that welding with an oxidizing gas is not permissible depending on the material. On the other hand, however, there is experience from extrusion welding, with which long-term resistant weld seams can be produced using air. Investigations have shown that the same weld seam properties can be achieved with polypropylene using either air or nitrogen as the process gas. Experimental investigations have now been carried out on the suitability of different gases with regard to the weld seam quality when welding polyamides, which are generally regarded as more prone to oxidation. The results show that weld strengths are higher when nitrogen is used as process gas. However, equal weld strengths can be achieved with air and nitrogen when the material contains heat stabilizers.

Species interactions in mixed-community crystalline biofilms on urinary catheters

2007 ◽  
Vol 56 (11) ◽  
pp. 1549-1557 ◽  
Author(s):  
Sarah M. Macleod ◽  
David J. Stickler
Keyword(s):  
Urinary Tract ◽  
Species Interactions ◽  
The Other ◽  
Experimental Investigations ◽  
Crystal Formation ◽  
Urinary Catheters ◽  
E Coli ◽  
Pure Cultures ◽  
Providencia Stuartii

Previous experimental investigations of the crystalline biofilms that colonize and block urinary catheters have focussed on their formation by pure cultures of Proteus mirabilis. In the urine of patients undergoing long-term catheterization, P. mirabilis is commonly found in mixed communities with other urinary tract pathogens. Little is known about the effect that the other species have on the rate at which P. mirabilis encrusts catheters. In the present study, a set of data on the nature of the bacterial communities on 106 catheter biofilms has been analysed and it was found that while species such as Providencia stuartii and Klebsiella pneumoniae were commonly associated with P. mirabilis, when Escherichia coli, Morganella morganii or Enterobacter cloacae were present, P. mirabilis was rarely or never found. The hypothesis that the absence of P. mirabilis from some biofilm communities could be due to its active exclusion by other species has also been examined. Experiments in laboratory models showed that co-infection of P. mirabilis with M. morganii, K. pneumoniae or E. coli had no effect on the ability of P. mirabilis to encrust and block catheters. Co-infection with Ent. cloacae or Pseudomonas aeruginosa, however, significantly increased the time that catheters took to block (P <0.05). The growth of Ent. cloacae, M. morganii, K. pneumoniae or E. coli in the model for 72 h prior to superinfection with P. mirabilis significantly delayed catheter blockage. In the case of Ent. cloacae, for example, the mean time to blockage was extended from 28.7 h to 60.7 h (P ≤0.01). In all cases, however, P. mirabilis was able to generate alkaline urine, colonize the biofilms, induce crystal formation and block the catheters. The results suggest that although there is a degree of antagonism between P. mirabilis and some of the other urinary tract organisms, the effects are temporary and whatever the pre-existing urinary microbiota, infection with P. mirabilis is thus likely to lead to catheter encrustation and blockage.

Progressive stress response of the anaerobic granular sludge to nickel nanoparticles: experimental investigations and mathematic modelling

2019 ◽  
Vol 6 (5) ◽  
pp. 1536-1548 ◽  
Author(s):  
Chuan-Shu He ◽  
Liang Huang ◽  
Rong-Rong Ding ◽  
Hou-Yun Yang ◽  
Yi-Xuan Wang ◽  
...  
Keyword(s):  
Stress Response ◽  
Nickel Nanoparticles ◽  
Granular Sludge ◽  
Experimental Investigations ◽  
Anaerobic Granular Sludge

Long-term exposure to Ni-NPs induced progressive and unrecoverable inhibition of the activity of the AGS.

scholarly journals Bond-Slip Models for FPR-Concrete Interfaces Subjected to Moisture Conditions

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Justin Shrestha ◽  
Dawei Zhang ◽  
Tamon Ueda
Keyword(s):  
Fiber Reinforced Polymers ◽  
Experimental Investigations ◽  
Reinforced Polymers ◽  
Bond Slip ◽  
Exposure Effect ◽  
Pull Out ◽  
Proposed Model ◽  
Maximum Period ◽  
Moisture Conditions

Environmental related durability issues have been of great concerns in the structures strengthened with the fiber reinforced polymers (FRPs). In marine environment, moisture is one of the dominant factors that adversely affect the material properties and the bond interfaces. Several short-term and long-term laboratory experimental investigations have been conducted to study such behaviors but, still, there are insufficient constitutive bond models which could incorporate moisture exposure conditions. This paper proposed a very simple approach in determining the nonlinear bond-slip models for the FRP-concrete interface considering the effect of moisture conditions. The proposed models are based on the strain results of the experimental investigation conducted by the authors using 6 different commercial FRP systems exposed to the moisture conditions for the maximum period of 18 months. The exposure effect in the moisture conditions seems to have great dependency on the FRP system. Based on the contrasting differences in the results under moisture conditions, separate bond-slip models have been proposed for the wet-layup FRP and prefabricated FRP systems. As for the verification of the proposed model under moisture conditions, predicted pull-out load was compared with the experimental pull-out load. The results showed good agreement for all the FRP systems under investigation.

The Thermal-Mechanical Behavior of Selected Si3N4 and SiC Ceramics

1996 ◽  
Author(s):  
Norman L. Hecht ◽  
Hongsang Rho ◽  
Nora R. Osborne ◽  
Dale E. McCullum ◽  
Steven M. Goodrich
Keyword(s):  
Mechanical Behavior ◽  
Room Temperature ◽  
Failure Mechanisms ◽  
Property Values ◽  
Heat Engine ◽  
Cyclic Fatigue ◽  
Sic Ceramics ◽  
Environment Temperature ◽  
Fatigue And Fracture

This paper presents the results of a long term program initiated in December of 1984 to investigate the effects of environment (temperature, atmosphere, and stress) on the mechanical behavior of eight Si3N4 and three SiC ceramics being considered for heat engine applications. Microstructure, chemistry, and physical properties were determined. The mechanical behavior of these materials was investigated from room temperature to 1400°C by employing tests for flexural and tensile strength, dynamic, static and cyclic fatigue, and fracture toughness. The results obtained from these evaluations showed that the thermal mechanical behavior was quite varied, depending on the composition and processing methods employed. Batch to batch differences were also found to cause variances in the property values measured. Insights gained from this work about the failure mechanisms and potential service life are also discussed.

scholarly journals Long-Term Durability of Carbon-Reinforced Concrete: An Overview and Experimental Investigations

2019 ◽  
Vol 9 (8) ◽  
pp. 1651 ◽  
Author(s):  
Arne Spelter ◽  
Sarah Bergmann ◽  
Jan Bielak ◽  
Josef Hegger
Keyword(s):  
Reinforced Concrete ◽  
Environmental Factors ◽  
Tensile Tests ◽  
Reduction Factor ◽  
Experimental Investigations ◽  
Time To Failure ◽  
Technical Textiles ◽  
Residual Capacity ◽  
Ultimate Failure

Despite intensive research on material properties of non-metallic technical textiles for internal reinforcement in concrete, the long-term durability is not yet fully understood. In this work, results of preloaded long-term durability tensile tests on carbon-reinforced concrete specimens under environmental factors of stress, temperature, moisture and alkalinity are presented. Based on investigations of non-metallic glass fiber reinforcements with polymer matrices, where strength losses occur over time, it was planned to derive a time to failure curve and to determine a reduction factor for the tensile strength of the carbon textile reinforcement. However, no loss of strength was discovered in residual capacity tests due to the high material resistance and therefore no reduction factor due to the environmental factors could be derived. After more than 5000 h of testing, the residual capacity tests showed an increase in the ultimate failure stress in comparison with the short-term tests. In addition to the long term-durability tests, the influence of the preloading was investigated. The preload was applied to the long-term tests and led to a straighter alignment and loading of the filaments and thus to an increase in the ultimate capacity.

Analysis of Failure Mechanisms During the Long-Term Retention Operation in 3-D NAND Flash Memories

2020 ◽  
Vol 67 (12) ◽  
pp. 5472-5478
Author(s):  
Shinkeun Kim ◽  
Kyunghwan Lee ◽  
Changbeom Woo ◽  
Yuchul Hwang ◽  
Hyungcheol Shin
Keyword(s):  
Failure Mechanisms ◽  
Nand Flash ◽  
Flash Memories ◽  
Term Retention ◽  
Long Term Retention

Prediction of Retarded Fatigue Life due to a Single Overload Spike Using an Exponential Model

2013 ◽  
Vol 446-447 ◽  
pp. 240-244
Author(s):  
Nian Li Lu ◽  
Wei Gang Zhan ◽  
Yan Mei Wang
Keyword(s):  
Fatigue Life ◽  
Life Prediction ◽  
Failure Mechanisms ◽  
Exponential Model ◽  
Construction Machinery ◽  
Proposed Model ◽  
Actual Service ◽  
Single Spike ◽  
Single Overload

Fatigue is the most common failure mechanisms in structures of construction machinery with inherent defects under variable amplitude loading, which have to endure for a long term cycle loadings in the actual service. In the present investigation an exponential model is proposed for fatigue life prediction with retardation caused by a single spike under constant amplitude loading. Comparisons between the predicted life and the experimental data are provided to demonstrate the utility and robustness of the proposed model.

Numerical Simulation of Vortex Induced Vibration Using the K-ε Model

2006 ◽  
Author(s):  
Juan B. V. Wanderley ◽  
Gisele H. B. Souza ◽  
Carlos Levi
Keyword(s):  
Numerical Simulation ◽  
Stokes Equations ◽  
Body Motion ◽  
Navier Stokes ◽  
Experimental Investigations ◽  
Real Problem ◽  
Navier Stokes Equations ◽  
Vortex Induced Vibration ◽  
Selection Of

Numerical simulations of Vortex Induced Vibration have been failing to duplicate accurately experimental data mostly due to the complexity of the physics involved in the real problem. Therefore, a careful and comprehensive investigation on CFD algorithms is still required to indicate the most suitable numerical scheme to handle such a complicate problem. Grid generation, boundary condition implementation, and coupling between the fluid flow governing equations and body motion equation are known to have strong influence on the qualities of the numerical results. This work presents results obtained from a long-term investigation featuring different CFD methods. The investigations enabled the selection of a very effective algorithm that showed an outstanding agreement between experiment and numerical simulation of the VIV phenomenon. Good agreement is obtained in the entire range of reduced velocity covered by the experimental investigations. The successful algorithm discussed here applies the Beam and Warming implicit scheme to solve the two-dimensional slightly compressible Navier–Stokes equations with the K-ε turbulence model to simulate the turbulent flow at the wake of the cylinder.

The effect of resin properties on the strength of filamentary structures

1989 ◽  
Vol 24 (2) ◽  
pp. 107-113 ◽  
Author(s):  
T J Lu ◽  
X Ji ◽  
X R Gu
Keyword(s):  
Failure Mechanisms ◽  
Critical Factor ◽  
Pressure Vessels ◽  
Resin Matrix ◽  
Experimental Investigations ◽  
Filamentary Structure ◽  
Burst Strength ◽  
Advanced Composite Materials ◽  
Matrix Properties ◽  
Area Of Concern

The adoption of advanced composite materials has significantly improved the performance of solid motor cases, but the failure mechanisms of this kind of filamentary structure are still far from understood, especially with respect to the influence of resin properties. Experimental investigations are reported in the present paper and the results show that the effect of resin matrix properties on burst strength of fibre-wound pressure vessels can be as large as 20—35 per cent. Hence, how to optimize resin matrix properties is a key area of concern in the rocket motor industry. Using improved netting analysis, delamination observed in the head area of the pressure vessels is concluded to be the critical factor leading to burst-strength degradation. Various pressure vessels failure mechanisms are also discussed.

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