scholarly journals Face Damage Growth of Sandwich Composites under Compressive Loading: Experiments, Analytical and Finite Element Modeling

Materials ◽  
2021 ◽  
Vol 14 (19) ◽  
pp. 5553
Author(s):  
Moustafa Kinawy ◽  
Felice Rubino ◽  
Giacomo Canale ◽  
Roberto Citarella ◽  
Richard Butler
Keyword(s):  
Analytical Model ◽  
Sandwich Structure ◽  
Impact Damage ◽  
Local Buckling ◽  
Image Correlation ◽  
Shear Mode ◽  
Mode I ◽  
Fe Model ◽  
Impact Compression ◽  
Direction Parallel

Sandwich panels with composite laminate skins having [(±45C)2,(0C,0G)4,(±45C)2] stacking sequence (subscript C for carbon fibers, G for glass) and containing barely visible impact damage (BVID) induced on the whole sandwich structure impacted at low energy, were tested in edge after-impact-compression with load direction parallel and transversal to the fibers direction (0-dir.). The morphology of impact damage on the sandwich structure was determined by using ultrasonic C-Scan and visual observation of laminate cross section. A Digital Image Correlation (DIC) system was used to measure the delamination evolution during the test. Two different failure behaviors were observed in two different impacted panels. Panel with fibers oriented transversally to the compressive load showed an opening (Mode-I) propagation of a delamination, while the panel with fibers parallel to the load showed shear (Mode-II) propagation. The static load such to determine local buckling of the composite face and failure was experimentally measured. An analytical model was implemented to predict the static strength of laminate with Mode-I opening. An FE model was instead built to predict the local buckling failure mode of the laminate with BVID, which is the first phenomenon to appear. The results of the analytical model and the numerical simulation correlate well with the test.

Fracture Toughness of Composite Joints With Carbon Nanotube Reinforcement

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
S. D. Faulkner ◽  
Y. W. Kwon
Keyword(s):  
Fracture Toughness ◽  
Carbon Nanotube ◽  
Image Correlation ◽  
Joint Interface ◽  
Shear Mode ◽  
Mode I ◽  
Mode Ii ◽  
Mode Ii Fracture ◽  
Mode Ii Fracture Toughness ◽  
Scarf Joint

Fracture toughness tests were conducted for carbon composite scarf joints with and without carbon nanotube (CNT) reinforcement in order to study the effect of CNT on enhancing the fracture toughness of the scarf joint interface. Both mode I (i.e., opening mode) and mode II (i.e., shear mode) fracture tests were undertaken with and without CNT applied locally at the joint interface. During the study, the image correlation technique was used to examine the fracture mechanisms altered by the introduction of CNT. The experimental study showed that CNT increased the fracture toughness of the composite interface significantly, especially for the mode II fracture, with altering the fracture mechanism. On the other hand, there was no significant change on mode I fracture caused by CNT reinforcement. The enhancement of mode II fracture toughness was considered to result from the mechanical interlocking between polymers and CNT at the scarf joint interface.

A novel model of Z-pin insertion in prepreg based on fracture mechanics

2021 ◽  
pp. 095440542110144
Author(s):  
Guobiao Ji ◽  
Liang Cheng ◽  
Shaohua Fei ◽  
Jiangxiong Li ◽  
Yinglin Ke
Keyword(s):  
Fracture Toughness ◽  
Fracture Mechanics ◽  
Analytical Model ◽  
Model Parameters ◽  
Force Model ◽  
Fe Model ◽  
Cohesive Elements ◽  
Fe Method ◽  
Insertion Force ◽  
Mechanics Model

Through-thickness reinforcement is a promising solution to the problem of delamination susceptibility in laminated composites. Modeling Z-pin–prepreg interaction is essential for accurate robotics-assisted Z-pin insertion. In this paper, a novel Z-pin insertion force model combining the classical cohesive finite element (FE) method with a dynamic analytical fracture mechanics model is proposed. The velocity-dependent cohesive elements, in which the fracture toughness is provided by the analytical model, are implemented in Z-pin insertion FE model to predict the crack initiation and propagation. Then Z-pin insertion experiments are performed on prepreg sample with metallic Z-pins at different velocities to identify the analytical model parameters and validate the simulation predictions offered by the model. Dynamics of Z-pin interaction with inhomogeneous prepreg is described and the effects of insertion velocity on prepreg contact force are studied. Results show that the force model agrees well with experiments and the fracture toughness rises with the increasing Z-pin insertion velocity.

scholarly journals Design and Control of a Magnetically Suspended Ceiling Actuator with Infinite Planar Stroke

2013 ◽  
Vol 416-417 ◽  
pp. 492-502 ◽  
Author(s):  
T.T. Overboom ◽  
J.P.C. Smeets ◽  
J.W. Jansen ◽  
E.A. Lomonova
Keyword(s):  
Permanent Magnet ◽  
Analytical Model ◽  
Normal Force ◽  
Tracking Error ◽  
Fe Model ◽  
Optimized Design ◽  
Three Phase ◽  
Linear Actuators ◽  
And Control ◽  
Infinite Planar

This paper presents the design and control of a magnetically suspended ceiling actuator which combines four iron-cored linear actuators and a checkerboard permanent magnet array for an infinite planar stroke. When the actuators are rotated with respect to the PM array, it is shown that the thrust and normal force produced by the three-phase linear actuators can be controlled by applying Park's transformation. The design of the iron-cored linear actuators is optimized for minimum losses when the translator inside the ceiling actuator and a payload are accelerated in the xy-plane. The optimization is performed using an analytical model is. Simulations of the optimized design with a 3D FE-model, show a maximum tracking error of 1 μm and rotations of 30 μrad when the translator is moved and controlled in 6 DOF.

Buckling Analysis of Sandwich Shell Structures Subjected to Hydrostatic Load

1994 ◽  
Vol 31 (02) ◽  
pp. 106-115
Author(s):  
C. Chryssostomidis ◽  
N.A. Papadakis
Keyword(s):  
Sandwich Structure ◽  
Critical Pressure ◽  
Thickness Distribution ◽  
Global Bifurcation ◽  
Local Buckling ◽  
Shell Structures ◽  
The Core ◽  
Bifurcation Buckling ◽  
Hydrostatic Load ◽  
Global Buckling

This paper examines the buckling phenomenon of sandwich cylindrical shell structures subjected to hydrostatic pressure. Global bifurcation buckling is considered, and the effect of discrete ring stiffeners on the critical pressure is analyzed. The local buckling problem is discussed, including the influence of the shape and the thickness of the core stiffeners on the critical load. Finally, the paper treats the sensitivity of local and global buckling on the thickness distribution between the inner and outer shells of the sandwich structure.

scholarly journals Experimental Investigations of Impact Damage Influence on Behavior of Thin-Walled Composite Beam Subjected to Pure Bending

Materials ◽  
2019 ◽  
Vol 12 (7) ◽  
pp. 1127 ◽  
Author(s):  
Tomasz Kubiak ◽  
Lukasz Borkowski ◽  
Nina Wiacek
Keyword(s):  
Impact Damage ◽  
Full Range ◽  
Image Correlation ◽  
Bending Test ◽  
Beam Deflection ◽  
Experimental Investigations ◽  
Pure Bending ◽  
Channel Section ◽  
Thin Walled ◽  
The Impact

The paper deals with buckling, postbuckling, and failure of pre-damaged channel section beam subjected to pure bending. The channel section beams made of eight-layered GFRP laminate with different symmetrical layups have been considered. The specimens with initially pre-damaged web or flange were investigated to access the influence of impact damage on work of thin-walled structure in the full range of load till failure. The bending tests of initially pre-damage beams have been performed on a universal tensile machine with especially designed grips. The digital image correlation system allowing to follow the beam deflection have been employed. The experimentally obtained results are presented in graphs presenting load-deflection or load vs. angle of rotation relations and in photos presenting impact damages areas before and after bending test. The results show that the impact pre-damages have no significant influence on the work of channel section beams.

scholarly journals Investigation by Digital Image Correlation of Mixed Mode I and II Fracture Behavior of Metallic IASCB Specimens with Additive Manufactured Crack-Like Notch

Metals ◽  
2020 ◽  
Vol 10 (3) ◽  
pp. 400 ◽  
Author(s):  
Ivo Campione ◽  
Tommaso Maria Brugo ◽  
Giangiacomo Minak ◽  
Jelena Janković Tomić ◽  
Nebojša Bogojević ◽  
...  
Keyword(s):  
Digital Image Correlation ◽  
Digital Image ◽  
Mixed Mode ◽  
Fracture Behavior ◽  
Selective Laser Sintering ◽  
Local Stress ◽  
Fatigue Loading ◽  
Image Correlation ◽  
Mode I ◽  
Displacement Fields

This work investigates the fracture behavior of maraging steel specimens manufactured by the selective laser sintering (SLS) technology, in which a crack-like notch (sharp notch) was directly produced during the additive manufacturing (AM) process. For the evaluation of the fracture toughness, the inclined asymmetrical semi-circular specimen subjected to three points loading (IASCB) was used, allowing to cover a wide variety of Mode I and II combinations. The effectiveness of manufacturing crack-like notches via the SLS technique in metals was evaluated by comparing the obtained experimental results with the ones obtained with pre-cracks induced by fatigue loading. The investigation was carried out by using the digital image correlation (DIC) technique, that allowed the evaluation of the full displacement fields around the crack tip. The displacement field was then used to compute the stress intensity factors (SIFs) for various combinations of Mode I and II, via a fitting technique which relies on the Williams’ model for the displacement. The SIFs obtained in this way were compared to the results obtained with the conventional critical load method. The results showed that the discrepancy between the two methods reduces by ranging from Mode I to Mode II loading condition. Finally, the experimental SIFs obtained by the two methods were described by the mixed mode local stress criterium.

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