scholarly journals Effects of thermal gradients on defect formation during the consolidation of partially impregnated prepregs

2017 ◽  
Vol 51 (28) ◽  
pp. 3987-4003 ◽  
Author(s):  
T Centea ◽  
G Peters ◽  
K Hendrie ◽  
SR Nutt
Keyword(s):  
Cross Sections ◽  
Process Design ◽  
Defect Formation ◽  
Formation Mechanisms ◽  
Thermal Gradients ◽  
X Ray ◽  
Gradient Magnitude ◽  
Lower Porosity ◽  
X Ray Computed ◽  
Nonisothermal Conditions

We describe the effects of thermal gradients on the consolidation of partially impregnated prepregs. Laminates were cured on a heated tool in isothermal and nonisothermal conditions. Key process parameters were varied, including thermal gradient magnitude, air evacuation direction, and vacuum quality. Laminate quality was assessed using microscopy of polished cross-sections and X-ray computed tomography, and interpreted relative to the evolution of resin and prepreg properties during cure. The results show that thermal gradients influenced the rate of impregnation of the prepreg and the rate of gas transport, and affected the amount and distribution of porosity when air was not fully evacuated. Temperature distributions that led to cold regions at the ply boundaries were advantageous, typically exhibiting lower porosity than isothermal baselines. Conversely, gradients resulting in hotter-than-average part perimeters effectively sealed air within the laminate, degrading quality. The results clarify fundamental defect formation mechanisms for partially impregnated prepregs and other processes reliant on air evacuation through an unsaturated preform and provide guidelines for part, tool, and process design.

scholarly journals Computed microtomography in the analysis of fiber migration in yarn

2013 ◽  
Vol 13 (1) ◽  
pp. 28-32 ◽  
Author(s):  
Marta Toda ◽  
Katarzyna Ewa Grabowska
Keyword(s):  
Cross Sections ◽  
Two Dimensional ◽  
X Ray ◽  
Testing Method ◽  
Computed Microtomography ◽  
X Ray Computed ◽  
Nondestructive Testing Method ◽  
2D And 3D ◽  
Migration Testing ◽  
Non Destructive

Abstract This study is a short analysis of the use of computer microphotography in fiber migration testing as a modern nondestructive testing method. Microtomography operates similarly to X-ray computed tomography systems used in medicine, but with much better resolution owing to the use of a smaller radiation spot. The internal structure is reconstructed as a series of two-dimensional cross-sections that are then used to create 2D and 3D morphological objects. This process is non-destructive and does not require special preparation of a testing material.

scholarly journals Topographic Arrangement of Crystallite Orientations in Rolled Copper

Texture ◽  
1972 ◽  
Vol 1 (2) ◽  
pp. 99-109 ◽  
Author(s):  
R. Gotthardt ◽  
G. Hoschek ◽  
O. Reimold ◽  
F. Haessner
Keyword(s):  
Electron Microscopy ◽  
Surface Layer ◽  
Single Crystals ◽  
Cross Sections ◽  
Rolling Plane ◽  
Correlated Data ◽  
Formation Mechanisms ◽  
Polycrystalline Copper ◽  
Polycrystalline Structure ◽  
X Ray

In single and polycrystalline copper rolled to a reduction of 95 %, the topographic arrangements of crystallite orientations were determined over large areas by means of electron microscopy. Correlated data on orientation, diffraction site, and transmission pictures in three cross-sections perpendicular to the normal, rolling and transverse directions were obtained and evaluated. These results were complemented by X-ray studies of the texture. The rolled polycrystalline structure consists of roughly disc-shaped regions of uniform orientation which are fairly strongly misoriented with respect to each other. The planes of the discs lie paral.lel to the rolling plane. Within these regions of uniform orientation lie elongated subgrains extended in the longitudinal and transverse directions. In a surface layer of a few microns thickness the dryly rolled single crystals have essentially a (100)[011] texture. This is independent of the orientation of the interior of the material. The observed structures are discussed with respect to possible formation mechanisms.

Characterization of Perovskite-Like Substrates for Thin Film Superconductors using Synchrotron X-Ray Topography

1991 ◽  
Vol 35 (A) ◽  
pp. 255-261
Author(s):  
G.-D. Yao ◽  
S.Y. Hon ◽  
M. Dudley ◽  
Julia M. Phillips
Keyword(s):  
Defect Formation ◽  
Chemical Properties ◽  
Substrate Material ◽  
Formation Mechanisms ◽  
X Ray ◽  
Physical And Chemical ◽  
Insight Into ◽  
Selection Of ◽  
Potential Substrate

AbstractThe characterization of defect configurations in various perovskite-like substrate materials for high Tc superconductor epitaxial films has been conducted using white beam synchrotron X-ray topography. The substrates were found to contain crystal lattice defects such as twins, dislocations and grain boundaries. It is shown that characterization of substrates can potentially afford insight into factors controlling the properties of the high Tc superconductor tilms supported on them. This can help in the selection of optimum substrate material. Defect formation mechanisms in individual materials as well as their respective influences on the films are discussed. Comparisons between the physical and chemical properties of several potential substrate materials are presented.

Structural and Electrical Characterization of the Initial Stage of Physical Vapor Transport Growth of 4H-SiC Crystals

2015 ◽  
Vol 821-823 ◽  
pp. 90-95
Author(s):  
Tatsuya Takahashi ◽  
Chikashi Ohshige ◽  
Noboru Ohtani ◽  
Masakazu Katsuno ◽  
Tatsuo Fujimoto ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Grown Crystal ◽  
Defect Formation ◽  
Vapor Transport ◽  
Physical Vapor Transport ◽  
Formation Mechanisms ◽  
X Ray Diffraction ◽  
X Ray ◽  
Initial Stage ◽  
Crystal Seed

Defect formation during the initial stage of physical vapor transport (PVT) growth of 4H-SiC crystals in the [000-1] and [11-20] directions was investigated by x-ray diffraction, defect-selective etching, and micro Raman scattering imaging. X-ray diffraction studies showed that the growths in the [000-1] and [11-20] directions exhibited markedly different behaviors with respect to the defect formation during the initial stage of growth. While a characteristic lattice plane bending was observed for the PVT growth along [000-1], a tilted domain structure was revealed near the grown crystal/seed interface for the growth in the [11-20] direction. Micro Raman scattering imaging revealed that nitrogen enrichment occurred near the grown crystal/seed interface and was associated with compressive stress parallel to the interface. Based on the results, the defect formation mechanisms during the initial stage of PVT growth of 4H-SiC are discussed.

scholarly journals A Study on Internal Defects of PREP Metallic Powders by Using X-ray Computed Tomography

Materials ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1177
Author(s):  
Yan Nie ◽  
Junjie Tang ◽  
Junfei Huang ◽  
Shu Yu ◽  
Yunping Li
Keyword(s):  
Computed Tomography ◽  
Defect Formation ◽  
Rotation Speed ◽  
Great Influence ◽  
Fine Powder ◽  
Coarse Particles ◽  
Internal Defects ◽  
Rotating Electrode ◽  
X Ray ◽  
X Ray Computed

In this study, the distribution, proportion and characteristics of internal defects in three kinds of powders of Ti-6Al-4V, 316-steel and Co-29Cr-6Mo alloys, produced by the plasma rotating electrode process (PREP) at various rotation speeds, are characterized by using both scanning electron microscopy (SEM) and synchrotron X-ray computed tomography (CT). The results show that in the powder of a given alloy, internal pores are formed more easily in coarse particles than in fine powder during PREP. The proportion of powder with pores can be reduced by appropriately increasing the rotation speed. In addition, the composition of an alloy has a great influence on the defect formation.

scholarly journals Filling, Feeding and Defect Formation of Thick-Walled AlSi7Mg0.3 Semi-Solid Castings

2016 ◽  
Vol 256 ◽  
pp. 222-227 ◽  
Author(s):  
Jorge Santos ◽  
Anders E.W. Jarfors ◽  
Arne K. Dahle
Keyword(s):  
High Pressure ◽  
Cross Sections ◽  
Surface Segregation ◽  
Defect Formation ◽  
Shear Bands ◽  
Casting Machine ◽  
Shrinkage Porosity ◽  
Cast Material ◽  
Lower Porosity ◽  
Semi Solid

Aluminium semi-solid castings have gained increased attention due to their superior mechanical properties, lower porosity compared to conventional high pressure die cast material. These characteristics suggests that semi-solid casting should be suitable to produce thick-walled structural components, yet most successful applications of semisolid casting have been for thin-walled components. There is a lack of understanding on filling and feeding related defect formation for semi-solid castings with thick-walled cross-sections. In the current study an AlSi7Mg0.3 aluminium alloy was used to produce semi-solid castings with a wall thickness of 10mm using a Vertical High Pressure Die Casting machine. The RheoMetalTM process was used for slurry preparation. The primary solid α-Al fraction in the slurry was varied together with die temperature. The evaluation of the filling related events was made through interrupted shots, stopping the plunger at different positions. Microscopy of full castings and interrupted test samples were performed identifying the presence of surface segregation layer, shear bands, gas entrapment, shrinkage porosity as well as burst feeding.

Results from burial experiments with simulated medieval glasses

2002 ◽  
Vol 757 ◽  
Author(s):  
Hannelore Roemich ◽  
Sandra Gerlach ◽  
Peter Mottner ◽  
Florias Mees ◽  
Patric Jacobs ◽  
...  
Keyword(s):  
Cross Sections ◽  
Laboratory Experiments ◽  
Glass Composition ◽  
Soil Conditions ◽  
Alkaline Soil ◽  
X Ray ◽  
Analytical Technique ◽  
X Ray Computed ◽  
Laminated Structures ◽  
Non Destructive

ABSTRACTDuring several hundred years of burial in the soil, glasses, especially those with medieval compositions, develop heavily corroded surfaces, showing phenomena such as local pitting, laminated layers and browning effects. For this study the damage phenomena have been characterised for three original glasses, using conventional methods (light microscopy and SEM of the surface and cross sections) and microfocus X-ray computed tomography (mCT), a new non-destructive analytical technique.The degradation of glass in the soil depends on a variety of parameters, concerned with the glass itself and with the burial environment. Since synergetic effects may complicate any mechanistic studies, laboratory experiments have been carried out under controlled conditions.Humid soil environments with a pH of 6.5 to 7.5 lead to the development of local microcracks on the surface, whereas more alkaline soil conditions (pH 8.0 to 9.0) favour the formation of laminated structures. The conclusions of the paper focus on the effect of glass composition (model glasses and archaeological glasses), soil conditions (variation of pH) and exposure time (23 months versus several centuries).

scholarly journals Scatter Corrections in X-Ray Computed Tomography: A Physics-Based Analysis

2019 ◽  
Vol 124 ◽  
Author(s):  
Zachary H. Levine ◽  
Timothy J. Blattner ◽  
Adele P. Peskin ◽  
Adam L. Pintar
Keyword(s):  
Computed Tomography ◽  
Elastic Scattering ◽  
Inelastic Scattering ◽  
Cross Sections ◽  
Forward Direction ◽  
Sampling Theorem ◽  
Computational Time ◽  
Fundamental Limits ◽  
X Ray ◽  
X Ray Computed

Fundamental limits for the calculation of scattering corrections within X-ray computed tomography (CT) are found within the independent atom approximation from an analysis of the cross sections, CT geometry, and the Nyquist sampling theorem, suggesting large reductions in computational time compared to existing methods. By modifying the scatter by less than 1 %, it is possible to treat some of the elastic scattering in the forward direction as inelastic to achieve a smoother elastic scattering distribution. We present an analysis showing that the number of samples required for the smoother distribution can be greatly reduced. We show that fixed forced detection can be used with many fewer points for inelastic scattering, but that for pure elastic scattering, a standard Monte Carlo calculation is preferred. We use smoothing for both elastic and inelastic scattering because the intrinsic angular resolution is much poorer than can be achieved for projective tomography. Representative numerical examples are given.

Sign in / Sign up

Export Citation Format

Share Document