Guidelines and Limitations of the Compact Compression Specimen

2019 ◽  
Author(s):  
David J. Plechaty ◽  
Kevin T. Carpenter ◽  
John P. Parmigiani
Keyword(s):  
Carbon Fiber ◽  
Test Specimen ◽  
Loading Rate ◽  
Material Models ◽  
Damage Initiation ◽  
Matrix Compression ◽  
Initiation And Propagation ◽  
Back Edge ◽  
Notch Length ◽  
Compression Damage

Abstract Damage initiation and propagation material models for carbon fiber composites can be categorized according to the loading applied to constituent components. An example of such categorization is fiber tension, fiber compression, matrix tension, and matrix compression material models. Of these, matrix compression has been by far the least studied based on amount of published literature. Recent work at Oregon State University (OSU) has begun to address this lack of study. OSU researchers have published several papers culminating in the specification of an effective test specimen for isolating matrix compression damage initiation and propagation in carbon fiber laminates. While providing compelling results indicating the effectiveness and usefulness of this test specimen, little or no information has been provided regarding its manufacture, usable notch lengths, and optimum loading rate during testing. Experience at OSU has shown that this information is critical and not trivial to obtain. The purpose of this paper is to provide specific guidelines and “lessons learned” needed for other researchers to efficiently and effectively use this specimen in a comprehensive study. Test specimens are manufactured in the OSU Composites Materials Manufacturing Laboratory using typical commercial pre-peg carbon fiber following the specified layup and curing procedures. Once the material was cured the carbon fiber plate was then water-jet cut into the desired geometry and notch length. Usable notch length and optimum loading rate was determined by testing a series of specimens. All testing was conducted at an OSU lab using a universal testing machine with Digital Image Correlation (DIC) data collected. Specimens were preloaded and matrix compression initiation and propagation data collected until tensile failure occurred on the back edge of the specimen. Testing showed that shorter notch lengths result in inconsistent data and longer in effective initiation but limited propagation due to reduced ligament length. Testing suggested that a speed less than 5 mm/min gave the best results as faster displacement rates caused less crack propagation to occur, while increasing the likelihood of the specimen to fail in tension along its back edge. Through the use of these guidelines, researchers are able to manufacture and use an effective test specimen for the investigation of matrix compression damage initiation and propagation.

Experimental Specimen for Classification of Matrix Compression Damage in Carbon Fiber Reinforced Polymers

2018 ◽  
Author(s):  
Taylor J. Rawlings ◽  
Kevin T. Carpenter ◽  
John P. Parmigiani
Keyword(s):  
Carbon Fiber ◽  
Crack Propagation ◽  
Visible Region ◽  
Material Model ◽  
Image Correlation ◽  
Fiber Reinforced Polymers ◽  
Fiber Reinforced ◽  
Matrix Compression ◽  
Carbon Fiber Reinforced ◽  
Compression Damage

Composite materials are becoming increasingly common in the aerospace industry. In order for simulation and modeling to accurately predict failure of composites, a material model based on observed damage mechanisms is required. Composites are commonly classified into four damage categories based on the composite constituents and their loading condition: fiber tension, fiber compression, matrix tension, and matrix compression. Previous work identified a compact compression (CC) specimen as a suitable option for isolating matrix compression damage. However upon continued testing, stable crack propagation in the specimen was limited to a relatively low material failure ratio (σCompressive/σTension). This paper presents specimen geometry that can isolate matrix compression damage in materials with a failure ratio greater than two, the limit of the compact compression specimens. Initial specimen selection used the compact compression specimens from previous research and added additional specimens based on commonly used compressions specimens for different materials. The added specimens included center notched compression (CNC), edge notch compression (ENC), and four-point bending (4PB). All specimens were evaluated experimentally with the success criteria of controlled propagation of a matrix compression crack. In addition to propagating a controlled matrix compression crack, specimens were required to have a visible region around the stress concentrator to allow for digital image correlation (DIC) image capture during the experiments. The specimens were manufactured from a carbon fiber reinforced polymer (CFRP) with a failure ratio greater than six. CC and 4PB specimens were unable to produce a compression crack before any other failure methods were present. CNC specimens produced an unstable compression crack that progressed from the notch to the edge of the specimen too rapidly to acquire meaningful crack propagation data. ENC specimens showed some ability to stably propagate a crack, however some tests resulted in an unstable crack propagation similar to the CNC specimens. In order to increase the test repeatability, a tapered thickness was added to the specimen around the notch tip. The resulting tapered ENC (TENC) produced repeatable controlled matrix compression crack propagation. Ultimately, the specimen fails when the crack has propagated through the entire width of the specimen. TENC specimens show promise for isolating matrix compression damage in materials with high failure ratios. Continued testing of CFRP with TENC specimens could be used to refine the material model for finite element analysis.

Development of Novel Compact Compression Specimen for Matrix Compression Damage Initiation and Propagation Behavior in Fiber Reinforced Composites

2018 ◽  
Author(s):  
Tim A. McKinley ◽  
Kevin T. Carpenter ◽  
John P. Parmigiani
Keyword(s):  
High Performance ◽  
Tensile Failure ◽  
Fiber Reinforced Polymers ◽  
Fiber Reinforced ◽  
Damage Initiation ◽  
Propagation Behavior ◽  
Matrix Compression ◽  
The Matrix ◽  
Compression Damage

Robust design and analysis of carbon fiber reinforced polymers (CFRP) mandates a thorough understanding of the onset and propagation of damaging mechanisms. Damage can manifest from fiber tension, fiber compression, matrix tension, and matrix compression. Of these damage forms, matrix compression has seen the least attention. Previous work has developed experimental specimens that enabled characterization of the onset and propagation of matrix compression damage. However, if high performance composite materials are used complications can arise when the matrix compression strength (σMC) exceeds the matrix tension strength (σMT). When the σMC/σMT ratio is greater than 2, compact compression (CC) specimens can exhibit matrix tension damage before the onset of matrix compression damage. The onset of matrix tension damage prevents proper characterization of matrix compression damage mechanisms. This paper presents the development of a novel stepped compact compression specimen. The reduced thickness of the stepped region allows significant matrix-compression damage to occur prior to tensile failure. Specimens comprised of 90° plies were fabricated using either a machined taper or a layering process. Both methods were successful however variability in machining generated substantial inconsistency and layering was found to be superior.

Impact of Specimen Configuration and Characteristics on Illinois Flexibility Index

2018 ◽  
Vol 2672 (28) ◽  
pp. 383-393 ◽  
Author(s):  
Jose Rivera-Perez ◽  
Hasan Ozer ◽  
Imad L. Al-Qadi
Keyword(s):  
Correction Factor ◽  
Loading Rate ◽  
Void Content ◽  
Displacement Curve ◽  
Specimen Thickness ◽  
Index Test ◽  
Notch Length ◽  
Air Void ◽  
Flexibility Index ◽  
Air Void Content

The Illinois Department of Transportation adopted the Illinois Flexibility Index Test (I-FIT) to evaluate the cracking vulnerability of asphalt concrete (AC) mixtures that was often shown to increase with the addition of recycled materials such as reclaimed asphalt pavement and recycled asphalt shingles. The test consists of a semi-circular AC sample that has a notch, loaded along the symmetric axis. Fracture energy (FE), post-peak slope, and the flexibility index (FI) are computed from the load displacement curve. These results can be influenced by specimen geometry and test parameters such as loading rate, AC voids content, and so forth. Therefore, this study investigated the effect of notch length, specimen thickness, loading rate, and AC air void content on the I-FIT results. It was found that an increase in the specimen thickness or loading rate resulted in a steeper post-peak slope without affecting the FE. As a result, the FI decreased. An increase in the notch length or AC air void content resulted in a flatter post-peak slope, thus, increasing the FI. From the results, it was concluded that existing correction factors to address the variations caused by specimen thickness and air void content are appropriate. A correction factor to address notch length variations is proposed. A unique correction factor for loading rate could not be developed because of the varying rate dependency of each AC mixture.

scholarly journals Implications of free-edge effect at thin plain-woven carbon fiber reinforced plastic laminates with out-of-plane waviness under cyclic loading

2021 ◽  
pp. 002199832110417
Author(s):  
Lukas Heinzlmeier ◽  
Stefan Sieberer ◽  
Christoph Kralovec ◽  
Martin Schagerl
Keyword(s):  
Carbon Fiber ◽  
Edge Effect ◽  
Fatigue Testing ◽  
Free Edge ◽  
Numerical Calculations ◽  
Carbon Fiber Reinforced Plastic ◽  
Damage Initiation ◽  
Fiber Reinforced Plastic ◽  
Reinforced Plastic ◽  
Out Of Plane

The onset of damage caused by the free-edge effect in plain-woven carbon fiber reinforced plastic (CFRP) specimens with an out-of-plane waviness under tension-tension fatigue loading is investigated. Numerical calculations show that interlaminar and intralaminar stresses close to the out-of-plane waviness are higher than the equivalent stresses at the surrounding edge regions. Using submodels, the influence of the chosen out-of-plane waviness can be better assessed. The free-edge effect of the considered specimens, which originates from stress gradients between plies of different orientation, is altered by the change in the stress field caused by the out-of-plane waviness. Large interlaminar stresses between plies of the same orientation are obtained, which contrasts with existing literature. In experimental fatigue testing it is found that cracks at the free edge appeared at the predicted locations, and after reaching crack saturation, in regions close to the out-of-plane waviness, interlaminar and intralaminar stresses lead to additional cracks along the whole free edges. The experimental tests are supported by a three dimensional image correlation system (3D-DIC), a thermal-imager and a digital photographic camera, which allows detailed examination of selected areas. Visual observation during fatigue testing and post-mortem inspection show good agreement between experimental data and numerical calculations in relation to the location of the damage initiation. As a result, out-of-plane waviness at free edges must be considered as an additional significant fatigue damage initiation location in laminate analysis.

Numerical and digital image correlation analysis of tensile behavior of thin-ply hybrid laminates with discontinuous carbon sandwiched by continuous glass and carbon

2021 ◽  
pp. 002199832110565
Author(s):  
Amos Ichenihi ◽  
Wei Li ◽  
Li Zhe
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Element Model ◽  
Image Correlation ◽  
Continuous Glass ◽  
Damage Initiation ◽  
3D Digital Image Correlation ◽  
Initiation And Propagation ◽  
Hybrid Laminates ◽  
Strain Increase

Thin-ply hybrid laminates of glass and carbon fibers have been widely adopted in engineering pseudo-ductility. In this study, a Finite Element model is proposed using Abaqus to predict pseudo-ductility in thin-ply laminates consisting of three materials. These materials comprise continuous carbon (CC) and continuous glass sandwiching partial discontinuous carbon (DC). The model adopts the Hashin criterion for damage initiation in the fibers and the mixed-mode Benzeggagh-Kenane criterion on cohesive surfaces for delamination initiation and propagation. Numerically predicted stress–strain results are verified with experimental results under tensile loading. Results show pseudo-ductility increases with the increase in DC layers, and pseudo-yield strength and strain increase with the increase in CC layers. 3D-Digital Image Correlation results indicate delamination growth on pseudo-ductile laminates, and the calculated Poisson’s ratios show pseudo-ductility occurs below 0.27. Moreover, Poisson’s ratio decreases with an increase in pseudo-ductility.

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