scholarly journals An experimental approach that assesses in-situ micro-scale damage mechanisms and fracture toughness in thermoplastic laminates under out-of-plane loading

2019 ◽  
Vol 207 ◽  
pp. 546-559 ◽  
Author(s):  
H. Wafai ◽  
A. Yudhanto ◽  
G. Lubineau ◽  
R. Yaldiz ◽  
N. Verghese
Keyword(s):  
Fracture Toughness ◽  
Experimental Approach ◽  
Damage Mechanisms ◽  
Micro Scale ◽  
Out Of Plane

In Situ Investigation of the Kinematics of Ply Interfaces During Composite Manufacturing

2020 ◽  
Vol 143 (2) ◽  
Author(s):  
Sandeep Chava ◽  
Sirish Namilae
Keyword(s):  
Carbon Fiber ◽  
Experimental Approach ◽  
Image Correlation ◽  
Radius Of Curvature ◽  
Micro Computed Tomography ◽  
In Situ Investigation ◽  
Out Of Plane ◽  
Set Up ◽  
Induced Defects

Abstract The kinematics of composite ply interfaces critically affects both the manufacturing processes and deformation mechanisms and is often responsible for the formation of defects such as wrinkles and delamination. In the present work, processing-induced defects in a carbon fiber prepreg composite are evaluated by devising a novel in situ experimental approach. Carbon fiber prepreg laminates are cured in a specially designed autoclave with viewports with plies laid up on a mold with cylindrical tooling set up to maximize the ply-movement. Four-ply layup orientations of [90/90]s, [90/0]s, [90/45]s, and [90/−45]s and three-mold configurations with cylindrical tools of diameter 9.5 mm (3/8 in.), 12.7 mm (1/2 in.), and 15.9 mm (5/8 in.) are used for the parametric study. Strains, ply-movement, and formation of defects are observed in situ using digital image correlation (DIC) during the autoclave cure cycle, through the viewports. The processing-induced defects in the composite are further characterized by X-ray micro-computed tomography (micro-CT). We observed that the mold with the larger radius of curvature (15.9 mm cylinder) leads to higher strains in both in-plane directions and higher displacement in out of plane directions. The maximum average out-of-plane ply movement, as well as the largest wrinkle, are observed for [90/−45]s layup on the mold with the highest radius of curvature.

In situ fatigue of Al-Li-X alloys

1989 ◽  
Vol 47 ◽  
pp. 624-625
Author(s):  
Kenneth S. Vecchio
Keyword(s):  
Fracture Toughness ◽  
Fatigue Crack ◽  
Crack Growth ◽  
Plane Crack ◽  
Alloy Development ◽  
Band Formation ◽  
Fatigue Crack Growth Resistance ◽  
Out Of Plane ◽  
Commercial Applications

The introduction of Al-Li based alloys into commercial applications has not occurred without some major difficulties in alloy development. Poor ductility and low fracture toughness in these alloys has hindered their use in structures where they must serve as integral load-carrying members. On the other hand, superior fatigue and stiffness properties of these alloys has provided great incentive to pursue further development. The reason for the low ductility and poor fracture toughness has been attributed to several possible mechanisms including: i) shear band formation due to planar slip., and ii) strain localization resulting from large grain boundary precipitates. The rather good fatigue crack propagation characteristics have been attributed to significant macroscopic out-of-plane crack growth. However, little work has aimed at understanding the micromechanisms of this out-of-plane crack growth during cyclic loading. In addition, the role of the numerous precipitates that can exist in these complex Al-Li-X alloys to the fatigue crack growth resistance has not been examined closely.In this research we have examined the microscopic evolution of fatigue deformation in two Al-Li-X alloys using in-situ fatigue experiments conducted within an intermediate voltage transmission electron microscope.

scholarly journals Effect of Mechanical Pretreatments on Damage Mechanisms and Fracture Toughness in CFRP/Epoxy Joints

Materials ◽  
2021 ◽  
Vol 14 (6) ◽  
pp. 1512
Author(s):  
Chiara Morano ◽  
Ran Tao ◽  
Marco Alfano ◽  
Gilles Lubineau
Keyword(s):  
Fracture Toughness ◽  
Carbon Fiber ◽  
Carbon Fibers ◽  
Polymer Matrix ◽  
Mechanical Tests ◽  
Adhesive Joints ◽  
Fiber Reinforced Polymers ◽  
Composite Joints ◽  
Damage Mechanisms ◽  
Grit Blasting

Adhesive bonding of carbon-fiber-reinforced polymers (CFRPs) is a key enabling technology for the assembly of lightweight structures. Surface pretreatment is necessary to remove contaminants related to material manufacturing and ensure bond reliability. The present experimental study focuses on the effect of mechanical abrasion on the damage mechanisms and fracture toughness of CFRP/epoxy joints. The analyzed CFRP plates were provided with a thin layer of surface epoxy matrix and featured enhanced sensitivity to surface preparation. Various degrees of morphological modification and fairly controllable carbon fiber exposure were obtained using sanding with emery paper and grit-blasting with glass particles. In the sanding process, different grit sizes of SiC paper were used, while the grit blasting treatment was carried by varying the sample-to-gun distance and the number of passes. Detailed surveys of surface topography and wettability were carried out using various methods, including scanning electron microscopy (SEM), contact profilometry, and wettability measurements. Mechanical tests were performed using double cantilever beam (DCB) adhesive joints. Two surface conditions were selected for the experiments: sanded interfaces mostly made of a polymer matrix and grit-blasted interfaces featuring a significant degree of exposed carbon fibers. Despite the different topographies, the selected surfaces displayed similar wettability. Besides, the adhesive joints with sanded interfaces had a smooth fracture response (steady-state crack growth). In contrast, the exposed fibers at grit-blasted interfaces enabled large-scale bridging and a significant R-curve behavior. While it is often predicated that quality composite joints require surfaces with a high percentage of the polymer matrix, our mechanical tests show that the exposure of carbon fibers can facilitate a remarkable toughening effect. These results open up for additional interesting prospects for future works concerning toughening of composite joints in automotive and aerospace applications.

Optimization on Influencing Factors of Fracture Toughness of Corundum-Mullite Toughened by In Situ Synthesized Mullite Whiskers by Response Surface Methodology

2012 ◽  
Vol 581-582 ◽  
pp. 819-822 ◽  
Author(s):  
Bin Meng ◽  
Jin Hui Peng
Keyword(s):  
Fracture Toughness ◽  
Response Surface Methodology ◽  
Response Surface ◽  
Response Surface Method ◽  
Sintering Temperature ◽  
Surface Method ◽  
Mullite Whiskers ◽  
Optimized Conditions ◽  
Addition Amount

The corundum-mullite was toughened by in-situ synthesized mullite whiskers and the process parameters influencing the fracture toughness of corundum-mullite, such as sintering temperature, addition amount of AlF3 and V2O5, were optimized by means of response surface method. Corundum-mullite with fracture toughness of 9.44 MPa.m-1/2 could be obtained under the optimized conditions, i.e. sintering temperature of 1400°C, 4.8 wt.% of AlF3 and 5.8 wt.% of V2O5. The results showed that it was feasible to prepare corundum-mullite toughened by in-situ synthesized mullite whiskers by the optimized parameters. In addition, an accurate model based on response surface method was proposed to predict the experimental results.

scholarly journals Thin film bi-epitaxy and transition characteristics of TiO2/TiN buffered VO2 on Si(100) substrates

MRS Advances ◽  
2016 ◽  
Vol 1 (37) ◽  
pp. 2635-2640 ◽  
Author(s):  
Adele Moatti ◽  
Reza Bayati ◽  
Srinivasa Rao Singamaneni ◽  
Jagdish Narayan
Keyword(s):  
Thin Film ◽  
Thin Films ◽  
Magnetic Properties ◽  
Frequency Factor ◽  
Misfit Strain ◽  
Buffer Layers ◽  
Intrinsic Defects ◽  
Domain Matching Epitaxy ◽  
Out Of Plane

ABSTRACTBi-epitaxial VO2 thin films with [011] out-of-plane orientation were integrated with Si(100) substrates through TiO2/TiN buffer layers. At the first step, TiN is grown epitaxially on Si(100), where a cube-on-cube epitaxy is achieved. Then, TiN was oxidized in-situ ending up having epitaxial r-TiO2. Finally, VO2 was deposited on top of TiO2. The alignment across the interfaces was stablished as VO2(011)║TiO2(110)║TiN(100)║Si(100) and VO2(110) /VO2(010)║TiO2(011)║TiN(112)║Si(112). The inter-planar spacing of VO2(010) and TiO2(011) equal to 2.26 and 2.50 Å, respectively. This results in a 9.78% tensile misfit strain in VO2(010) lattice which relaxes through 9/10 alteration domains with a frequency factor of 0.5, according to the domain matching epitaxy paradigm. Also, the inter-planar spacing of VO2(011) and TiO2(011) equals to 3.19 and 2.50 Å, respectively. This results in a 27.6% compressive misfit strain in VO2(011) lattice which relaxes through 3/4 alteration domains with a frequency factor of 0.57. We studied semiconductor to metal transition characteristics of VO2/TiO2/TiN/Si heterostructures and established a correlation between intrinsic defects and magnetic properties.

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