Hygroscopic Effects in Aramid Fiber/Epoxy Composite

1988 ◽  
Vol 110 (2) ◽  
pp. 153-157 ◽  
Author(s):  
H. T. Hahn ◽  
K. S. Kim
Keyword(s):  
Experimental Data ◽  
Radial Stress ◽  
Moisture Absorption ◽  
Epoxy Composite ◽  
Moisture Diffusion ◽  
Fiber Composites ◽  
Aramid Fiber ◽  
Moisture Concentration ◽  
Micromechanics Models

Hygroscopic effects in aramid fiber composites are assessed semi-empirically using a combination of micromechanics models and experimental data. It is pointed out that the in situ moisture concentration of the fiber should be known as it affects diffusional as well as expansional properties. The micromechanics models for moisture absorption indicate that the in situ moisture concentration is lower than the bulk value. The interfacial radial stress can be tensile in wet unidirectional composites, and ply cracks are shown to increase moisture diffusion in laminates.

Hygrothermal Damage in Graphite/Epoxy Laminates

1987 ◽  
Vol 109 (1) ◽  
pp. 3-11 ◽  
Author(s):  
H. T. Hahn
Keyword(s):  
Residual Stresses ◽  
Moisture Absorption ◽  
Moisture Diffusion ◽  
Moisture Diffusivity ◽  
Moisture Concentration ◽  
Bulk Diffusivity ◽  
Hygrothermal Environments ◽  
Swelling Strain

The use of micromechanics equations for moisture diffusivity shows that the in situ diffusivity is slightly lower than the bulk diffusivity for matrix resins, thereby indicating absence of any matrix damage in virgin composites. When exposed to hygrothermal environments, however, composites undergo degradation which manifests itself in anomalous moisture diffusion behavior and reduced structural performance. The hygrothermal degradation is the result of matrix plasticization, microvoid formation, and microcracking. The time dependence of plasticization as well as the tensile stress resulting from steep moisture gradient is responsible for the damage induced by thermal spiking of wet composites. Swelling of neat resins is frequently less than predicted by the volume additivity. A simple micromechanics analysis provides a good estimate of composite swelling strain from resin properties. The bilinearity and the hysteresis observed in relations between swelling and moisture content are attributed to the existence of a threshold moisture concentration below which swelling is negligible. Relaxation of residual stresses is a long-term process under nonhostile environments. However, it is accelerated considerably around and above the glass transition temperature. The fast stress relaxation can change the transverse ply stress from compressive to tensile after thermal spiking, thereby inducing ply cracking and accelerating the subsequent moisture absorption. How residual stresses can affect ply cracking and delamination is shown through a fracture mechanics analysis.

The Effect of Masked Isocyanates on the Mechanical Properties of My720/dds Epoxy Resin

1989 ◽  
Vol 171 ◽  
Author(s):  
N. Rungsimuntakul ◽  
S.V. Lonikar ◽  
R. E. Fornes ◽  
R.D. Gilbert
Keyword(s):  
Mechanical Properties ◽  
Epoxy Resin ◽  
Epoxy Resins ◽  
Moisture Absorption ◽  
Peak Stress ◽  
Fiber Composites ◽  
Elongation At Break ◽  
Initial Modulus ◽  
Better Than

ABSTRACTThe mechanical properties of epoxy resins and epoxy resin/graphite fiber composites are adversely affected by moisture absorption. Incorporation of masked isocyanates that unmask to release isocyanates in situ at the cure temperatures (150-177ºC) reduce the equilibrium absorption up to ∼70%. Dynamic mechanical analyses and stress-strain properties of epoxy resins containing masked isocyanates were examined to determine their effect on mechanical properties. The ultimate Tg of the epoxy is reduced by incorporation of masked isocyanate, but the actual Tg is comparable to the “as cured” Tg of the epoxy. The dynamic moduli up to the Tg are relatively unaffected. Ina number of cases, the initial modulus, elongation at break and peak stress are equal or better than the unmodified resins.

scholarly journals In situ formation of a carbon nanotube buckypaper for improving the interlaminar properties of carbon fiber composites

2021 ◽  
Vol 202 ◽  
pp. 109535
Author(s):  
Yadong Wu ◽  
Xiuyan Cheng ◽  
Shaoyun Chen ◽  
Bo Qu ◽  
Rui Wang ◽  
...  
Keyword(s):  
Carbon Nanotube ◽  
Carbon Fiber ◽  
Fiber Composites ◽  
Carbon Fiber Composites ◽  
In Situ Formation

scholarly journals Effects of processing, moisture, and storage length on the fermentation profile, particle size, and ruminal disappearance of reconstituted corn grain

2020 ◽  
Vol 98 (11) ◽  
Author(s):  
Ana L M Gomes ◽  
Antonio V I Bueno ◽  
Fernando A Jacovaci ◽  
Guilherme Donadel ◽  
Luiz F Ferraretto ◽  
...  
Keyword(s):  
Particle Size ◽  
Lactic Acid ◽  
Butyric Acid ◽  
Hammer Mill ◽  
Moisture Concentration ◽  
Fermentation Profile ◽  
And Storage ◽  
Ground Corn ◽  
Corn Grain

Abstract Our objective was to examine the effects of processing, moisture, and anaerobic storage length of reconstituted corn grain (RCG) on the fermentation profile, geometric mean particle size (GMPS), and ruminal dry matter disappearance (DMD). Dry corn kernels were ground (hammer mill, 5-mm screen) or rolled, then rehydrated to 30%, 35%, or 40% moisture, and stored for 0, 14, 30, 60, 90, 120, or 180 d in laboratory silos. Rolled corn had an increased GMPS compared with ground corn (2.24 and 1.13 mm, respectively, at ensiling). However, there was a trend for an interaction between processing and moisture concentration to affect particle size, with GMPS increasing with increased moisture concentration, especially in ground corn. Longer storage periods also slightly increased GMPS. Processing, moisture, and storage length interacted to affect the fermentation pattern (two- or three-way interactions). Overall, pH decreased, whereas lactic acid, acetic acid, ethanol, and NH3-N increased with storage length. RCG with 30% moisture had less lactic acid than corn with 35% and 40% moisture, indicating that fermentation might have been curtailed and also due to the clostridial fermentation that converts lactic acid to butyric acid. Ensiling reconstituted ground corn with 30% of moisture led to greater concentrations of ethanol and butyric acid, resulting in greater DM loss than grain rehydrated to 35% or 40% of moisture. Ammonia-N and in situ ruminal DMD were highest for reconstituted ground corn with 35% or 40% of moisture, mainly after 60 d of storage. Therefore, longer storage periods and greater moisture contents did not offset the negative effect of greater particle size on the in situ ruminal DMD of rolled RCG. Nonetheless, RCG should be ensiled with more than 30% moisture and stored for at least 2 mo to improve the ruminal DMD and reduce the formation of ethanol and butyric acid.

scholarly journals On the Fluctuation Induced Excess Conductivity in Stainless Steel Sheathed MgB2 Tapes

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Suchitra Rajput ◽  
Sujeet Chaudhary
Keyword(s):  
Magnetic Field ◽  
Experimental Data ◽  
Stainless Steel ◽  
Coherence Length ◽  
Three Dimensional ◽  
Excess Conductivity ◽  
Scaling Functions ◽  
Critical Fluctuations ◽  
Scaling Models

We report on the analyses of fluctuation induced excess conductivity in the - behavior in the in situ prepared MgB2 tapes. The scaling functions for critical fluctuations are employed to investigate the excess conductivity of these tapes around transition. Two scaling models for excess conductivity in the absence of magnetic field, namely, first, Aslamazov and Larkin model, second, Lawrence and Doniach model, have been employed for the study. Fitting the experimental - data with these models indicates the three-dimensional nature of conduction of the carriers as opposed to the 2D character exhibited by the HTSCs. The estimated amplitude of coherence length from the fitted model is ~21 Å.

Investigation of Emulsion Flow in Steam-Assisted Gravity Drainage

SPE Journal ◽  
2013 ◽  
Vol 18 (03) ◽  
pp. 440-447 ◽  
Author(s):  
C.C.. C. Ezeuko ◽  
J.. Wang ◽  
I.D.. D. Gates
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Oil Recovery ◽  
Vital Role ◽  
Gravity Drainage ◽  
Steam Assisted Gravity Drainage ◽  
Emulsion Flow ◽  
Very High ◽  
Effective Representation

Summary We present a numerical simulation approach that allows incorporation of emulsion modeling into steam-assisted gravity-drainage (SAGD) simulations with commercial reservoir simulators by means of a two-stage pseudochemical reaction. Numerical simulation results show excellent agreement with experimental data for low-pressure SAGD, accounting for approximately 24% deficiency in simulated oil recovery, compared with experimental data. Incorporating viscosity alteration, multiphase effect, and enthalpy of emulsification appears sufficient for effective representation of in-situ emulsion physics during SAGD in very-high-permeability systems. We observed that multiphase effects appear to dominate the viscosity effect of emulsion flow under SAGD conditions of heavy-oil (bitumen) recovery. Results also show that in-situ emulsification may play a vital role within the reservoir during SAGD, increasing bitumen mobility and thereby decreasing cumulative steam/oil ratio (cSOR). Results from this work extend understanding of SAGD by examining its performance in the presence of in-situ emulsification and associated flow of emulsion with bitumen in porous media.

Edge Delamination and Residual Properties of Drilled Carbon Fiber Composites with and without Short-Aramid-Fiber Interleaf

2016 ◽  
Vol 23 (5) ◽  
pp. 973-985 ◽  
Author(s):  
Zhi Sun ◽  
Xiaozhi Hu ◽  
Shanshan Shi ◽  
Xu Guo ◽  
Yupeng Zhang ◽  
...  
Keyword(s):  
Carbon Fiber ◽  
Fiber Composites ◽  
Aramid Fiber ◽  
Carbon Fiber Composites ◽  
Residual Properties ◽  
Edge Delamination
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