Repair of Composite Laminates-I: Test Results

A modified test fixture to measure the shear properties of composite laminates was designed and manufactured based upon Iosipescu shear test method. Tests on interlaminar shear propertis of T300/BMI composite laminates were conducted according to ASTM D 5379 test standard. Interlaminar shear stress/strain curves and shear failure modes were obtained. The test results showed that the modified shear test fixture and test method were effective in measuring the shear properties of composite laminates.

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Static and fatigue analysis of notched composite laminates

Journal of Composite Materials ◽

10.1177/0021998316635242 ◽

2016 ◽

Vol 50 (30) ◽

pp. 4307-4317 ◽

Cited By ~ 4

Author(s):

Christos Kassapoglou

Keyword(s):

Composite Laminates ◽

Fatigue Loading ◽

Test Results ◽

Characteristic Distance ◽

Hole Edge ◽

Additional Testing ◽

Number Of Cycles ◽

Static Failure ◽

Cycles To Failure ◽

Good Agreement

An approach to predict static and fatigue failure of composite laminates with holes is presented. Static failure is predicted when the stress averaged over a characteristic distance is equal to the un-notched failure strength. This averaging distance is determined analytically without the use of additional testing or need for extra material parameters. During fatigue loading, the size of the damage region next to the hole is calculated and the strains at the hole edge are determined. These are used along with the stresses just outside the damage region to determine whether failure starts at the hole edge or the edge of the damage region extends. A previously developed fatigue model based on the cycle-by-cycle probability of failure is used to calculate the number of cycles needed for the residual strain at hole edge or the residual strength at the edge of the damage region to fall below the corresponding applied values. The procedure is repeated until laminate failure. The method is also used to predict cycles to failure for impacted specimens. The predictions are in very good agreement with test results.

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Ultrasonic Detection of Fiber Orientation in Composite Laminates for Use of Vehicular Structures

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.297-300.2109 ◽

2005 ◽

Vol 297-300 ◽

pp. 2109-2114

Author(s):

Je Woong Park ◽

Kwang Hee Im ◽

David K. Hsu ◽

Seung Woo Na ◽

Young Nam Kim ◽

...

Keyword(s):

Fiber Orientation ◽

Composite Laminates ◽

Azimuthal Angle ◽

Normal Incidence ◽

Test Results ◽

Ultrasonic Signals ◽

Fiber Placement ◽

Reinforced Plastics ◽

Vector Decomposition ◽

Optical Test

The layup of a CFRP (carbon-fiber reinforced plastics) composite laminates affects the properties of the laminate, including stiffness, strength and thermal behavior. It is very important to detect ply error before the laminate is cured for both manual procedure and fiber placement procedure. An ultrasonic technique would be very beneficial, which could be used to test the part after and before curing laminates and requires less time than the optical test. Also cross-polarized scan is very sensitive to the layup errors and ply misorientations. Scanners were set out for different measurement modalities for acquiring ultrasonic signals as a function of in-plane azimuthal angle. Firstly, a manual scanner was built for making transmission measurements using a pair of normal-incidence shear wave transducers to find the effect of fiber misorientations of composite laminates. Also a method for nondestructively determining the ply layup in a composite laminate is presented. The method employs a normal-incidence longitudinal ultrasound to perform C-scan of ply interfaces of the laminate. And a ply-by-ply vector decomposition model has been utilized for evaluating layup errors in composite laminates fabricated from unidirectional plies. Test results between after and before curing laminates with model data were compared for a fiber orientation of the laminates.

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Low Velocity Impact of a Viscoelastic Beam

Journal of Engineering for Industry ◽

10.1115/1.3185821 ◽

1982 ◽

Vol 104 (2) ◽

pp. 210-215

Author(s):

R. E. Llorens ◽

E. J. McQuillen

Keyword(s):

Composite Laminates ◽

Low Velocity Impact ◽

Viscoelastic Beam ◽

Test Results ◽

Transverse Impact ◽

Low Velocity ◽

Euler Beam ◽

Numerical Predictions ◽

Linear Viscoelastic ◽

Good Agreement

A theoretical solution for the response of a viscoelastic beam to off-center low speed transverse impact is presented. The flexural model adopted for investigation consists of a uniform Bernoulli-Euler beam whose behavior has been generalized to include a linear viscoelastic constitutive relation for each element of the beam. Further, the beam and rigid impactor are assumed to remain in contact during the resulting motion and a consistent set of initial displacement and velocity distributions is adopted for the beam. The solution method utilizes two Laplace transforms, i.e., one with respect to space and the other with respect to time. Comparison of the numerical predictions of the theoretical model with central impact test results on graphite-epoxy composite laminates indicates a good agreement between theory and experiment.

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Study on Tensile Mechanical Behavior of Composite T-Joints

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.1142.146 ◽

2017 ◽

Vol 1142 ◽

pp. 146-151

Author(s):

Zhi Lin Liu ◽

Pu Rong Jia ◽

Tao Peng ◽

Zheng Lan Yao

Keyword(s):

Tensile Strength ◽

Composite Laminates ◽

Failure Process ◽

Load Condition ◽

Maximum Load ◽

Displacement Curve ◽

Test Results ◽

Reinforcement Effect ◽

T Joints ◽

Pin Reinforcement

Based on three kinds of composite T-joints with different connection way for tension test outside the plane, it was obtained contrastively that how the ordinary adhesive, Z-pin reinforcement and stitching reinforcement three different fitting influence tensile strength, damage failure process and failure mode of composite T-joints. The test results showed that compared with ordinary adhesive connection mode, tensile strength of the Z-pin reinforcement and stitching reinforcement T-joints increased by 13.6% and 11.4%, respectively; and the largest deformation increased by 19.2% and 15.1%, respectively. After reaching maximum load condition, the ordinary adhesive T-joints had brittle failures, but Z-pin reinforcement and stitching reinforcement T-joints all showed that the ductile damage behavior, corresponding to the load-displacement curve appeared saw-tooth wave platform. Obviously, the Z-pin reinforcement T-joints had the most significant reinforcement effect on tensile properties of composite laminates T-joints.

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Using Tolerance Bounds for Estimation of Characteristic Fatigue Curves for Composites with Confidence

Safety ◽

10.3390/safety8010001 ◽

2021 ◽

Vol 8 (1) ◽

pp. 1

Author(s):

Knut O. Ronold ◽

Andreas T. Echtermeyer

Keyword(s):

Composite Laminates ◽

Probability Distributions ◽

Fatigue Curve ◽

Statistical Procedure ◽

Test Results ◽

Stress Range ◽

Lower Tail ◽

Curve Estimation ◽

Dependent Variables ◽

Stress Cycles

Fatigue S–N curves provide the number of stress cycles that result in fatigue failure at stress range S and need to be measured for new engineering materials where data are not as readily available as they are for well-characterized and widely used metals. A simple statistical method for the estimation of characteristic fatigue curves defined in terms of lower-tail quantiles in probability distributions of dependent variables is presented. The method allows for the estimation of such quantiles with a specified confidence level, taking account of the statistical uncertainty caused by a limited number of experimental test results available for the estimation. The traditional general approach for estimating characteristic S–N curves by tolerance bounds is complicated and is not much used by engineers. The presented approach allows for calculating the curves with a simple spreadsheet. The only requirement is that the experimental log S data for the S–N curve are fairly uniformly distributed over a finite logS interval, where S denotes the stress range. Experimental fatigue test programs are often designed such that test data fulfil this assumption. Although developed with fatigue of composite laminates in mind, the presented statistical procedure and the presented associated charts are valid for fatigue curve estimation for any material.

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Numerical Simulation of Unidirectional Hoop Composite Laminates under Flexural Loads

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.334-335.217 ◽

2007 ◽

Vol 334-335 ◽

pp. 217-220

Author(s):

Li Li Tong ◽

Zhen Qing Wang ◽

Bao Hua Sun

Keyword(s):

Numerical Simulation ◽

Composite Laminates ◽

Calculated Result ◽

Composite Laminate ◽

Stiffness Degradation ◽

Test Results ◽

Degradation Model ◽

Compressive Stresses

Numerical simulation for unidirectional hoop composite laminates under flexural loads was finished. The change of tensile and compressive stresses, the position of local crush and delamination and stiffness degradation were analyzed with parametric program compiled by APDL language in ANSYS. The results showed that composite laminate could bear the load continually after local crush and delamination. Displacements of calculated result with stiffness degradation model matched test results well.

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Feasibility and Application on Ultrasonic-Polarized Shear Wave of Fiber Orientation Detection in Orthotropic Composite Laminates

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.324-325.911 ◽

2006 ◽

Vol 324-325 ◽

pp. 911-914

Author(s):

Je Woong Park ◽

Kwang Hee Im ◽

David K. Hsu ◽

Sun Kyu Kim ◽

In Young Yang

Keyword(s):

Shear Wave ◽

Fiber Orientation ◽

Composite Laminates ◽

Isosceles Triangle ◽

Test Results ◽

Model Data ◽

Orientation Error ◽

Orthotropic Composite ◽

Reinforced Plastics ◽

Fiber Reinforced Plastics

It is very important to detect fiber orientation error in orthotropic composite laminates because the layup of a CFRP (carbon-fiber reinforced plastics) composite laminates affects the properties of the laminate, including stiffness, strength and thermal behavior. In this study, an investigation of shear wave ultrasonic technique was carried out in order to detect stacking orientation error for the orthotropic composite laminates. During testing, the most significant problem is that the couplant conditions do not remain the same because of changing the viscosity of the couplant. Therefore, the design and use of a shear wave transducers would greatly aid in alleviating the couplant problem. A pyramid with an isosceles triangle with two 45o was made of aluminum to generate shear waves using two longitudinal transducers based on ultrasonicpolarized mechanism. Also, the signal splitter was connected to the pulser jack on the pulser/receiver and to the longitudinal transducers which were mounted with mineral oil. The shear transducer was mounted on the bottom as a receiver with burnt honey. It is found that the shear wave was generated at a maximum and a minimum based on the ultrasonic-polarized mechanism. Finally, test results with model data were compared for a fiber orientation of the laminates.

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