Delamination resistance of composite laminated structures reinforced with angled, threaded, and anchored Z-pins

2018 ◽  
Vol 53 (11) ◽  
pp. 1507-1519 ◽  
Author(s):  
Ananth Virakthi ◽  
Soonwook Kwon ◽  
Sung W Lee ◽  
Mark E Robeson
Keyword(s):  
Fracture Toughness ◽  
Double Cantilever Beam ◽  
Nonlinear Finite Element ◽  
Mode I ◽  
Finite Element Models ◽  
Mechanical Interlocking ◽  
Delamination Resistance ◽  
Novel Approaches ◽  
Laminated Structures ◽  
Cohesive Zones

The delamination resistance of Z-pinned laminates is directly dependent on the strength of the pin–laminate bonding at the interface. In this paper, we investigate novel approaches to the Z-pinning technology in order to increase delamination strength via enhancing mechanical interlocking of the pins. Toward this end, we study the effect of pin insertion at an angle to the vertical in contrast to the conventional vertical pin insertion. Subsequently, a novel variety of pin, namely the threaded pin, is studied as a candidate for reinforcement which increases mechanical interlocking between the pin and the laminate as well as the epoxy-pin contact area, thus delaying delamination. In addition, the effect of anchoring reveals the length of smooth metal pins on to the surface of the laminate before curing on delamination strength is investigated. Experiments performed show increase in tensile pullout strengths when angled, threaded, or anchored pins are used. These experimental results for tensile pullout strengths validate nonlinear finite element models incorporating cohesive zones at the pin–laminate interface. In addition, fracture toughness and delamination resistance under mode-I loading are investigated by performing experiments on double cantilever beam specimens. Results demonstrate the superior delamination resistance properties for angled, threaded, and anchored pin inserts.

Double Cantilever Beam Measurement and Finite Element Analysis of Cryogenic Mode I Interlaminar Fracture Toughness of Glass-Cloth/Epoxy Laminates

2000 ◽  
Vol 123 (2) ◽  
pp. 191-197 ◽  
Author(s):  
Y. Shindo ◽  
K. Horiguchi ◽  
R. Wang ◽  
H. Kudo
Keyword(s):  
Fracture Toughness ◽  
Finite Element Analysis ◽  
Finite Element ◽  
Cantilever Beam ◽  
Double Cantilever Beam ◽  
Mode I ◽  
Interlaminar Fracture Toughness ◽  
Element Analysis ◽  
Interlaminar Fracture ◽  
Delamination Crack

An experimental and analytical investigation in cryogenic Mode I interlaminar fracture behavior and toughness of SL-E woven glass-epoxy laminates was conducted. Double cantilever beam (DCB) tests were performed at room temperature (R.T.), liquid nitrogen temperature (77 K), and liquid helium temperature (4 K) to evaluate the effect of temperature and geometrical variations on the interlaminar fracture toughness. The fracture surfaces were examined by scanning electron microscopy to verify the fracture mechanisms. A finite element model was used to perform the delamination crack analysis. Critical load levels and the geometric and material properties of the test specimens were input data for the analysis which evaluated the Mode I energy release rate at the onset of delamination crack propagation. The results of the finite element analysis are utilized to supplement the experimental data.

Influence of Temperature on Interlaminar Fracture Toughness of a Carbon Fiber-Epoxy Composite Material

2016 ◽  
Vol 1135 ◽  
pp. 35-51 ◽  
Author(s):  
Rita de Cássia Mendonça Sales ◽  
Bianca Lis Rossi Dias Endo ◽  
Maurício Vicente Donadon
Keyword(s):  
Fracture Toughness ◽  
Mixed Mode ◽  
Mechanical Resistance ◽  
Mode I ◽  
Mode Ii ◽  
Interlaminar Fracture Toughness ◽  
Interlaminar Fracture ◽  
Delamination Resistance ◽  
Different Temperatures ◽  
Influence Of Temperature On

Composite materials have been increasingly used in the aerospace industry for the manufacturing of structures, because of the associated properties of low weight and high mechanical resistance. On the other hand, they have low delamination resistance. This paper presents the results of an experimental study performed to obtain the values of interlaminar fracture toughness (G) of a laminate under three different temperatures, using 0º carbon-epoxy prepreg fabric plies and manufactured via Hand lay up cured in autoclave (HLUP). Double Cantilever Beam (DCB) tests were performed to evaluate mode I toughness, Four Point Bend End Notched Flexure (4ENF) for mode II and Mixed Mode Bending (MMB) for mixed mode I / mode II at -54°C, 25°C and 80°C. The data were collected and analyzed using a routine developed in Matlab®. Finally, the relation between GI and GII through the failure envelope and the temperature influence on the interlaminar fracture toughness was assessed.

scholarly journals Large Displacement J-Integral Double Cantilever Beam (DCB) Test Method for Mode I Fracture Toughness

2020 ◽  
Author(s):  
Joshua Gunderson
Keyword(s):  
Fracture Toughness ◽  
Double Cantilever Beam ◽  
Test Method ◽  
Large Displacement ◽  
Mode I ◽  
Mode I Fracture ◽  
Mode I Fracture Toughness ◽  
Linear Elastic ◽  
True Value ◽  
Nonlinear Elastic

The J-integral is used to develop an alternative double cantilever beam (DCB) test method for the Mode I fracture toughness suitable for both small and large displacements. The current focus is the experimental determination of the Mode I interlaminar fracture toughness of composite materials, but the method is generally applicable to other similar tests and material systems, such as to the Mode I fracture toughness of adhesives. A series of five identical specimens are tested to compare the linear-elastic fracture mechanics method recommended by ASTM, which makes use of linear beam theory with root rotation, large displacement, and end block corrections, with the new nonlinear-elastic and elastic-plastic fracture mechanics method, which does not require these corrections. Experimental results show excellent agreement between the two methods over a series of five tests of primarily linear-elastic DCB specimens subjected to moderate to large displacements as defined in the ASTM standard. Furthermore, an agreement is found between the results of the derivations for the two methods being compared, whereby the large displacement equation for JIc presented in this work is identical to the equation given by J. G. Williams (1987) and which he found to be the true value of GIc. It is the true value of GIc that the large displacement and root rotation correction factors were intended to approximate, and the test method presented here allows for direct measurement of its parameters and evaluation. This method has the added benefit that specimens can be primarily linear-elastic or nonlinear-elastic at the crack tip and may extend to those that are elastic-plastic at the crack tip.

A Study on the Fracture Characteristics of Plasma-Treated Graphite/Epoxy Laminated Composites

2006 ◽  
Vol 321-323 ◽  
pp. 869-872 ◽  
Author(s):  
M.H. Kim ◽  
Kyong Yop Rhee ◽  
Young Nam Paik ◽  
S.H. Ryu
Keyword(s):  
Contact Angle ◽  
Double Cantilever Beam ◽  
Treatment Time ◽  
Laminated Composites ◽  
Mode I ◽  
Fracture Characteristics ◽  
Delamination Fracture ◽  
Delamination Resistance ◽  
Fracture Tests ◽  
Mode I Delamination

For a present study, the surfaces of graphite/epoxy prepregs were modified using plasma treatment to improve the delamination resistance behavior of graphite/epoxy laminated composites. The optimal treatment time was determined by measuring the change of contact angle with treatment time. Unidirectional DCB (double cantilever beam) specimens were used in the mode I delamination fracture tests. The delamination resistance curve of regular (untreated) specimen was compared with that of plasma-treated specimen in order to determine the effect of prepreg treatment on the resistance behavior. It was found that contact angle was changed from ~64° to ~47° depending on the treatment time. The contact angle was a minimum for a 30 min treatment time. It was also found that delamination resistance behavior of graphite/epoxy composites was improved about 20%.

Mode I Interlaminar Fracture Toughness of Through-Thickness Reinforced Laminated Structures

2011 ◽  
Vol 423 ◽  
pp. 154-165 ◽  
Author(s):  
M. Tarfaoui ◽  
L. Hamitouche
Keyword(s):  
Fracture Toughness ◽  
Laminated Composite ◽  
Element Model ◽  
Critical Energy ◽  
Mode I ◽  
Interlaminar Fracture Toughness ◽  
Critical Energy Release Rate ◽  
Interlaminar Fracture ◽  
Laminated Composite Materials ◽  
Laminated Structures

The main objective of the study is to understand the mechanisms of the preform reinforcement (2D, stitched and 2.5D) in laminated composite materials. The study is focusing on the mode I interlaminar fracture toughness for glass/vinylester based composites. Starting from DCB tests we quantify the critical energy release rate for the various cases of reinforcement, conclusive that 2.5D reinforcement can increase resistance x7 in comparison with the standard composite. Moreover, the existence of z-fibres made the fracture more complex and caused several characteristic phenomena, so that the required fracture energy for crack propagation was strongly increased. It is shown that a finite element model is successful in reproducing qualitatively the cracking initiation and propagation through the un-reinforced and 3D reinforced sample provided that the action of the through-thickness reinforcement is modelled by discrete nodal forces so as to replicate the physical phenomena.

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