PREDICTION OF NUMBER OF CYCLES FROM FATIGUE TEST CONDITIONS AND TRANSVERSE CRACK DENSITY OF CFRP CROSS-PLY LAMINATES

2021 ◽  
Author(s):  
YOUZOU KITAGAWA ◽  
KOTARO HIRAIWA ◽  
MASAHIRO ARAI ◽  
AKINORI YOSHIMURA ◽  
KEITZ GOTO
Keyword(s):  
Fatigue Test ◽  
Transverse Crack ◽  
Crack Density ◽  
Stiffness Degradation ◽  
Remaining Life ◽  
Transverse Cracks ◽  
Cfrp Laminates ◽  
Matrix Cracks ◽  
Test Conditions ◽  
Number Of Cycles

In the present paper, we proposed a methodology that can predict the number of applied load cycles in tension-tension fatigue test of CFRP laminates from microscopic damages and test conditions. It is difficult to predict the fracture of CFRP laminates and to estimate the remaining life of CFRP laminates for ensuring the long-term reliability of the CFRP components because the fracture process of CFRP laminates is quite complex. The damage process of CFRP consists of various microscopic damage such as matrix cracks, fiber/matrix interfacial debondings, delamination and so on. In order to quantitatively estimate the remaining life of CFRPs, we focused on the degree of the microscopic damages and relate that to the remaining life of them. The tension-tension fatigue tests of CFRP cross-ply laminates were carried out, and we suspended the tests at arbitrary cycles. When the tests were suspended, we counted the number of transverse cracks occurred on the specimens by a replica method, and measured the stiffness degradation of the specimens. We formulated an equation that can predict the stiffness degradation using fatigue test conditions. The predicted stiffness degradation to the number of cycles using the formula agreed well with the experimental results. The result demonstrated that the formula can predict the number of subjected cycles from fatigue test conditions and transverse crack density.

NUMERICAL PREDICTION OF STIFFNESS DEGRADATION OF THIN-PLY CFRP LAMINATES UNDER FATIGUE LOADING

2021 ◽  
Author(s):  
RYOMA AOKI ◽  
RYO HIGUCHI ◽  
TOMOHIRO YOKOZEKI
Keyword(s):  
Composite Laminates ◽  
Damage Mechanics ◽  
Crack Density ◽  
Continuum Damage Mechanics ◽  
Fatigue Loading ◽  
Stiffness Degradation ◽  
Cfrp Laminates ◽  
Mechanics Model ◽  
Element Simulation ◽  
Proposed Model

This study aims to conduct a fatigue simulation for predicting the stiffness degradation of thin-ply composite laminates with several ply thicknesses. For the simulation, a fatigue evolution model of intra-laminar damage in thin-ply composite laminates considering the effect of ply thickness was proposed. The intra-laminar damage evolution was modeled using the continuum damage mechanics model and the static and fatigue evolution law were formulated by relating the transverse crack density to the damage variable. The finite element simulation using the proposed model was conducted to predict the stiffness degradation of the laminates as a function of the number of loading cycles. The simulation results show that the experimental data can be reproduced by using the proposed fatigue model.

scholarly journals Modeling Stiffness Degradation of Fiber-Reinforced Polymers Based on Crack Densities Observed in Off-Axis Plies

2021 ◽  
Vol 6 (1) ◽  
pp. 10
Author(s):  
Matthias Drvoderic ◽  
Martin Pletz ◽  
Clara Schuecker
Keyword(s):  
Shear Stress ◽  
Crack Detection ◽  
Crack Density ◽  
Damage Parameter ◽  
Fatigue Tests ◽  
Fiber Reinforced Polymers ◽  
Stiffness Degradation ◽  
Plane Shear ◽  
Matrix Cracks ◽  
Using Data

A model that predicts the stiffness degradation in multidirectional reinforced laminates due to off-axis matrix cracks is proposed and evaluated using data from fatigue experiments. Off-axis cracks are detected in images from the fatigue tests with automated crack detection to compute the crack density of the off-axis cracks which is used as the damage parameter for the degradation model. The purpose of this study is to test the effect of off-axis cracks on laminate stiffness for different laminate configurations. The hypothesis is that off-axis cracks have the same effect on the stiffness of a ply regardless of the acting stress components as long as the transverse stress is positive. This hypothesis proves to be wrong. The model is able to predict the stiffness degradation well for laminates with a ply orientation similar to the one used for calibration but deviates for plies with different in-plane shear stress. This behavior can be explained by the theory that off-axis cracks develop by two different micro damage modes depending on the level of in-plane shear stress. It is found that besides influencing the initiation and growth of off-axis cracks, the stiffness degradation is also mode dependent.

DAMAGE EVOLUTION IN CROSS-PLY LAMINATES UNDER VARIABLE AMPLITUDE CYCLIC LOADINGS

2021 ◽  
Author(s):  
PAOLO CARRARO ◽  
SIMONETTO MIRKO ◽  
LUCIO MARAGONI ◽  
MARINO QUARESIMIN
Keyword(s):  
Crack Initiation ◽  
Damage Accumulation ◽  
Prediction Models ◽  
Crack Density ◽  
Fatigue Tests ◽  
Point Of View ◽  
Multiple Cracks ◽  
Transverse Cracks ◽  
Variable Amplitude ◽  
Number Of Cycles

Predicting the initiation and propagation of multiple off-axis cracks in multidirectional laminates under cyclic loadings is essential in a stiffness-driven design approach. Even under a constant amplitude cyclic load, the multiple crack initiation represents always an inherently variable amplitude (VA) problem. Indeed, the initiation of cracks causes a stress re-distribution so that each point in a laminate is subjected to a stress state that changes continuously during the fatigue life. At present, no models or experimental evidences on the crack initiation phenomenon under VA loadings are available in the literature. Crack density prediction models usually rely on a simple linear damage accumulation rule, even if its validity has not been proved yet. In this work, two types of fatigue tests were carried out on glass/epoxy cross-ply laminates under VA two-block loadings: 1) Initially, the number of cycles in the first block was chosen low enough to prevent the initiation of transverse cracks in the first block; then the load was changed and the crack initiation phenomenon was characterized in the second block. 2) Then, two block loadings were applied on other specimens, with a high enough number of cycles in the first block to promote the initiation of multiple cracks; the crack density evolution was thus characterized in both blocks. A model recently developed by the authors was applied to the experimental data, revealing the suitability of the linear damage accumulation rule under block loadings, at least from a phenomenological point of view.

Fatigue Behavior of a Nanocomposite under a Fighter Aircraft Spectrum Load Sequence

2013 ◽  
Vol 24 ◽  
pp. 58-66 ◽  
Author(s):  
C.M. Manjunatha ◽  
Ramesh Bojja ◽  
N. Jagannathan
Keyword(s):  
Fatigue Life ◽  
Fatigue Test ◽  
Epoxy Matrix ◽  
Fatigue Behavior ◽  
Crack Density ◽  
Load Spectrum ◽  
Fighter Aircraft ◽  
Matrix Cracks ◽  
The Matrix ◽  
Load Sequence

Two different E-glass fiber reinforced plastic (GFRP) composite laminates having quasi isotropic [(+45/-45/0/90)2]S layup sequence were fabricated viz., GFRP with neat epoxy matrix (GFRP-neat) and GFRP with modified epoxy matrix (GFRP-nano) containing 9 wt. % of CTBN rubber micro-particles and 10 wt.% of silica nanoparticles. Standard fatigue test specimens were machined from the laminates and end-tabbed. Spectrum fatigue tests under a standard fighter aircraft load spectrum, mini-FALSTAFF, were conducted on both the composites at various reference stress levels and the experimental fatigue life expressed as number of blocks to fail, were determined. The stiffness of the specimen was determined from the load-displacement data acquired at regular intervals during the fatigue test. The matrix cracks development in the test specimens with fatigue cycling was determined through optical photographic images. The fatigue life of GFRP-nanocomposite under mini-FALSTAFF load sequence was observed to be enhanced by about four times when compared to that of GFRP-neat composite due to presence of micro-and nanoparticles in the matrix. The stiffness degradation rate and matrix crack density was considerably lower in GFRP-nanocomposite when compared to that of GFRP-neat composite. The underlying mechanisms for improved fatigue performance of GFRP-nanocomposite are discussed.

scholarly journals A Study of Matrix Crack Tip Delaminations and their Influence on Composite Laminate Stiffness

1999 ◽  
Vol 8 (4) ◽  
pp. 096369359900800 ◽  
Author(s):  
Maria Kashtalyan ◽  
Costas Soutis
Keyword(s):  
Transverse Crack ◽  
Crack Density ◽  
Crack Tip ◽  
Implicit Functions ◽  
Transverse Cracks ◽  
Transverse Cracking ◽  
Stiffness Properties ◽  
Equivalent Constraint Model ◽  
Constraint Model ◽  
Stiffness Loss

Reduction of the stiffness properties of cross-ply [0m/90n]s laminates due to delaminations, growing at the 0/90 interface from the tips of transverse cracks in the 90° plies and splits in the 0° plies, is analysed by means of a theoretical approach based on the Equivalent Constraint Model (ECM). Reduced stiffness properties of the damaged lamina are derived as explicit functions of the crack density and relative delamination area associated with that lamina and implicit functions of the two damage parameters associated with the neighbouring laminae. Transverse crack tip delaminations are found to cause significant reduction in the laminate shear modulus and Poisson's ratio. Contribution of each damage mode (transverse cracking, transverse crack tip delaminations, splitting and split tip delaminations) into stiffness loss is established.

scholarly journals Numerical prediction of the ballistic performance of hygrothermally aged CFRP laminates using a multi-scale modelling approach

2021 ◽  
Vol 250 ◽  
pp. 03008
Author(s):  
D. Thomson ◽  
D. E. Sommer ◽  
O. Falcó ◽  
G. Quino ◽  
H. Cui ◽  
...  
Keyword(s):  
Crack Density ◽  
Material Model ◽  
Transverse Cracks ◽  
Ballistic Performance ◽  
Cfrp Laminates ◽  
Micro Scale ◽  
Multi Scale ◽  
Hygrothermal Ageing ◽  
Scale Modelling ◽  
Meso Scale

A multi-scale modelling strategy is proposed to investigate the potential effects of hygrothermal ageing on the ballistic performance of CFRP laminates. At the micro-scale, damage evolution due to cyclic hygrothermal loads is simulated on a representative microstructure using an adapted fatigue damage law. Then, the results of the micro-mechanical analysis are used to measure the predicted transverse crack density and calibrate a meso-scale material model with the effects of micro-scale damage. Finally, a meso-scale impact model is generated with seeded transverse cracks at the predicted crack density and the calibrated material properties from the homogenisation step, which allows for the performance of the laminate to be compared at different stages of hygrothermal ageing damage.

scholarly journals Evaluation of Transverse Crack Initiation in Cross-Ply CFRP Laminates under Fatigue Loading

2011 ◽  
Vol 77 (779) ◽  
pp. 1123-1134 ◽  
Author(s):  
Keigo TAKAMURA ◽  
Atsushi HOSOI ◽  
Narumichi SATO ◽  
Hiroyuki KAWADA
Keyword(s):  
Crack Initiation ◽  
Transverse Crack ◽  
Fatigue Loading ◽  
Cfrp Laminates

Analytical Buckling Loads of Columns Weakened Simultaneously with Transverse Cracks and Partial Delamination

2019 ◽  
Vol 19 (03) ◽  
pp. 1950027 ◽  
Author(s):  
Igor Planinc ◽  
Simon Schnabl
Keyword(s):  
Mathematical Model ◽  
Analytical Solution ◽  
Boundary Conditions ◽  
Parametric Study ◽  
Transverse Crack ◽  
Transverse Cracks ◽  
Buckling Loads ◽  
Crack Location ◽  
Benchmark Solution ◽  
First Time

This paper focuses on development of a new mathematical model and its analytical solution for buckling analysis of elastic columns weakened simultaneously with transverse open cracks and partial longitudinal delamination. Consequently, the analytical solution for buckling loads is derived for the first time. The critical buckling loads are calculated using the proposed analytical model. A parametric study is performed to investigate the effects of transverse crack location and magnitude, length and degree of partial longitudinal delamination, and different boundary conditions on critical buckling loads of weakened columns. It is shown that the critical buckling loads of weakened columns can be greatly affected by all the analyzed parameters. Finally, the presented results can be used as a benchmark solution.

Evaluation of Microscopic Deformation in CFRP Laminates with Delamination by Micro-Grid Methods

1998 ◽  
Vol 32 (1) ◽  
pp. 83-100 ◽  
Author(s):  
Nobuo Takeda ◽  
Shinji Ogihara ◽  
Satoshi Suzuki ◽  
Akira Kobayashi
Keyword(s):  
Crack Opening ◽  
Displacement Fields ◽  
Transverse Cracks ◽  
Opening Displacement ◽  
Cfrp Laminates ◽  
Edge Surface ◽  
Micro Grid ◽  
Microscopic Deformation ◽  
Micro Grids ◽  
Specimen Edge

Micro-grid methods were applied to measure displacements in 90° ply in CFRP cross-ply laminates with only transverse cracks or with both transverse cracks and delaminations. The COD (crack opening displacement) of the transverse cracks were also measured. Micro-grids were printed on the specimen edge surfaces by using the photo-lithography technique. The displacement fields of the specimen edge surface obtained from the experiment were compared with McCartney's [1] and Lee et al.'s [2] analyses which predicted the displacement field of a cross-ply laminate with only transverse cracks. Furthermore these analyses were modified to consider the existence of delamination.

Sign in / Sign up

Export Citation Format

Share Document