scholarly journals Fiber Bridging Induced Toughening Effects on the Delamination Behavior of Composite Stiffened Panels under Bending Loading: A Numerical/Experimental Study

Materials ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2407 ◽  
Author(s):  
Angela Russo ◽  
Mauro Zarrelli ◽  
Andrea Sellitto ◽  
Aniello Riccio
Keyword(s):  
Experimental Data ◽  
Fracture Toughness ◽  
Composite Structures ◽  
Numerical Procedure ◽  
Research Activity ◽  
Stiffened Panels ◽  
Mode I Fracture Toughness ◽  
Fiber Bridging ◽  
Out Of Plane ◽  
Bending Loading

In this paper, a research activity, focused on the investigation of new reinforcements able to improve the toughness of composite materials systems, is introduced. The overall aim is to delay the delamination propagation and, consequently, to increase the carrying load capability of composite structures by exploiting the fiber bridging effects. Indeed, the influence of fiber bridging related Mode I fracture toughness (GIc) values on the onset and propagation of delaminations in stiffened composite panels, under three-point bending loading conditions, have been experimentally and numerically studied. The investigated stiffened panels have been manufactured by using epoxy resin/carbon fibers material systems, characterized by different GIc values, which can be associated with the material fiber bridging sensitivity. Experimental data, in terms of load and delaminated area as a function of the out-of-plane displacements, have been obtained for each tested sample. Non-Destructive Inspection (NDI) has been performed to identify the debonding extension and position. To completely understand the evolution of the delamination and its dependence on the material characteristics, experiments have been numerically simulated using a newly developed robust numerical procedure for the delamination growth simulation, able to take into account the influence of the fracture toughness changes, associated with the materials’ fiber bridging sensitivity. The combined use of numerical results and experimental data has allowed introducing interesting considerations of the capability of the fiber bridging to substantially slow down the evolution of the debonding between skin and reinforcements in composite stiffened panels.

PROGRESSIVE DAMAGE FAILURE ANALYSIS OF POST-BUCKLED COMPOSITE SINGLE-STRINGER PANEL WITH TEFLON INSERTS

2021 ◽  
Author(s):  
VIJAY K. GOYAL ◽  
AUSTIN PENNINGTON ◽  
JASON ACTION
Keyword(s):  
Experimental Data ◽  
Composite Structures ◽  
Laminated Composites ◽  
Compressive Loading ◽  
Weight Ratio ◽  
High Strength ◽  
Material Model ◽  
Stiffened Panels ◽  
Damage Initiation ◽  
Critical Aspects

The high strength-to-weight and stiffness-to-weight ratio materials, such as laminated composites, are advantageous for modern aircraft. Laminated composites with initial flaws are susceptible to delamination under buckling loads. PDA tools help enhance the industry’s understanding of the mechanisms for damage initiation and growth in composite structures while assisting in the design, analysis, and sustainment methods of these composite structures. The global-local modeling approach for the single-stringer post-buckled panel was evaluated through this effort, using Teflon inserts to simulate the defect of damage during manufacturing. This understanding is essential for designing the post-buckled structure, reducing weight while predicting damage initiation location, and addressing a potential design review for future aircraft repairs. In this work, the initial damage was captured with Teflon inserts as the starting configuration; and any reference to the damage initiation refers to any damage beyond the “initial unbonded region.” The effort aims to develop, evaluate, and enhance methods to predict damage initiation and progression and the failure of post-buckled hat-stiffened panels using multiple Abaqus FEA Virtual Crack Closure Technique (VCCT) definitions. Validation of the PDA using the VCCT material model was performed on a large single-stringer panel subjected to compressive loading. The compressive loading of the panel caused the skin to buckle before any damage began to occur locally. In addition, comparisons are made for critical aspects of the damage morphology, such as a growth pattern that included delamination from the skin-stiffener interface to the skin and ply interfaces. When compared against the experimental data produced through the NASA Advanced Composites Project (ACP), the present model captured damage migration from one surface to another, and model validations were ~5% of the experimental data.

Effect of fixation stitches on out-of-plane response of textile non-crimp fabric composites

2018 ◽  
Vol 48 (7) ◽  
pp. 1151-1166 ◽  
Author(s):  
Somen K Bhudolia ◽  
Kenneth KC Kam ◽  
Pavel Perrotey ◽  
Sunil C Joshi
Keyword(s):  
Fracture Toughness ◽  
Composite Laminates ◽  
Peak Load ◽  
Experimental Studies ◽  
Critical Energy ◽  
Critical Energy Release Rate ◽  
Mode I Fracture Toughness ◽  
Out Of Plane ◽  
Static Indentation ◽  
Sem Investigation

Non-crimp fabrics are fabric tapes stitched to an adjacent orthogonal fabric with no associated crimp. In the current research, the effect of fixation polyester stitches in improving through-the-thickness properties of non-crimp fabric composite laminates is investigated. Detailed experimental studies on interlaminar fracture toughness and static indentation properties of stitched and unstitched thin ply carbon fibre epoxy composites have been conducted. About 23% higher peak load and 37% higher energy absorption were noticed during static indentation tests for the stitched ply composites. A detailed SEM investigation has shown that the stitch-stitch interaction ‘within a bi-angle ply’ and ‘between the bi-angle ply’ plays a significant role in reducing the delamination extent. The critical energy release rate during Mode I fracture toughness of stitched composites was found to be 26.5% higher and SEM investigation depicted that the stitches promote the intra-laminar delamination and enhance the toughness of the composite.

scholarly journals Mechanical Behavior of Steel Pipe Bends: An Overview

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Spyros A. Karamanos
Keyword(s):  
Experimental Data ◽  
Finite Element ◽  
Mechanical Behavior ◽  
Cross Section ◽  
Steel Pipe ◽  
Buried Pipelines ◽  
Cross Sectional ◽  
Out Of Plane ◽  
Bending Capacity ◽  
Bending Loading

An overview of the mechanical behavior of steel pipe (elbows) is offered, based on previously reported analytical solutions, numerical results, and experimental data. The behavior of pipe bends is characterized by significant deformations and stresses, quite higher than the ones developed in straight pipes with the same cross section. Under bending loading (in-plane and out-of-plane), the main feature of the response is cross-sectional ovalization, which influences bending capacity and is affected by the level of internal pressure. Bends subjected to cyclic in-plane bending exhibit fatigue damage, leading to base metal cracking at the elbow flank. Using advanced finite-element tools, the response of pipe elbows in buried pipelines subjected to ground-induced actions is also addressed, with emphasis on soil–pipeline interaction. Finally, the efficiency of special-purpose finite elements for modeling pipes and elbows is briefly discussed.

Improved fracture toughness of carbon fiber fabric/epoxy composite laminates using polyether sulfone fibers

2018 ◽  
Vol 31 (8) ◽  
pp. 996-1005
Author(s):  
Wenjian Zheng ◽  
Zhengjun Yao ◽  
Haiyan Lin ◽  
Jintang Zhou ◽  
Haishuo Cai ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Carbon Fiber ◽  
Composite Laminates ◽  
Composite Structures ◽  
Secondary Phase ◽  
Average Value ◽  
Mode I Fracture Toughness ◽  
Polyether Sulfone ◽  
The Matrix ◽  
Carbon Fiber Epoxy

This study demonstrated that the addition of dissolvable polyether sulfone fibers to the interlaminar area of carbon fiber/epoxy composites can effectively increase the toughness with very high accuracy. Resin film infusion (RFI) is used to fabricate composite structures. RFI was applied to obtain polyether sulfone as an interleaf of chopped fibers between fabric piles of carbon fibers. The thermoplastic polyether sulfone fiber dissolved in the epoxy when it was cured at a high temperature. A phase-separated morphology with a polyether sulfone-rich secondary phase was formed during the curing process. Experimental results indicated that G Ic, which is the average value of Mode-I fracture toughness, was increased fivefold with the addition of 10 wt% polyether sulfone fiber (with respect to the gross content of the matrix). No detrimental effects were observed in other characteristics such as thermal stability, Young’s modulus, and tensile strength. In addition, the thermal and mechanical characteristics of neat epoxy–polyether sulfone blends were analyzed for comparison.

scholarly journals Cross-Influence between Intra-Laminar Damages and Fibre Bridging at the Skin–Stringer Interface in Stiffened Composite Panels under Compression

Materials ◽  
2019 ◽  
Vol 12 (11) ◽  
pp. 1856 ◽  
Author(s):  
Angela Russo ◽  
Andrea Sellitto ◽  
Salvatore Saputo ◽  
Valerio Acanfora ◽  
Aniello Riccio
Keyword(s):  
Fracture Toughness ◽  
Numerical Procedure ◽  
Stiffened Panel ◽  
Mode I ◽  
Composite Panels ◽  
Material System ◽  
Mode I Fracture Toughness ◽  
Fibre Bridging ◽  
Stiffened Composite Panels ◽  
Material Systems

In this paper, the skin–stringer separation phenomenon that occurs in stiffened composite panels under compression is numerically studied. Since the mode I fracture toughness and, consequently, the skin–stringer separation can be influenced by the fibre bridging phenomenon at the skin–stringer interface, in this study, comparisons among three different material systems with different fibre bridging sensitivities have been carried out. Indeed, a reference material system has been compared, in terms of toughness performance, against two materials with different degrees of sensitivity to fibre bridging. A robust numerical procedure for the delamination assessment has been used to mimic the skin–stringer separation. When analysing the global compressive behaviour of the stiffened panel, intra-laminar damages have been considered in conjunction with skin–stringer debonding to evaluate the effect of the fibre and matrix breakage on the separation between the skin and the stringer for the three analysed material systems. The latter are characterised by different toughness characteristics and fibre bridging sensitivities, resulting in a different material toughness.

scholarly journals Numerical Investigation on Guided Waves Dispersion and Scattering Phenomena in Stiffened Panels

Materials ◽  
2021 ◽  
Vol 15 (1) ◽  
pp. 74
Author(s):  
Alessandro De Luca ◽  
Donato Perfetto ◽  
Giuseppe Lamanna ◽  
Antonio Aversano ◽  
Francesco Caputo
Keyword(s):  
Composite Structures ◽  
Guided Waves ◽  
Mode Conversion ◽  
Analytical Data ◽  
Experimental Tests ◽  
Detection Sensitivity ◽  
Research Activity ◽  
Fe Method ◽  
Stiffened Panels ◽  
Reflected Waves

The aim of this work is to propose a numerical methodology based on the finite element (FE) method to investigate the dispersive behavior of guided waves transmitted, converted, and reflected by reinforced aluminum and composite structures, highlighting their differences. The dispersion curves of such modes can help designers in improving the damage detection sensitivity of Lamb wave based structural health monitoring (SHM) systems. A preliminary phase has been carried out to assess the reliability of the modelling technique. The accuracy of the results has been demonstrated for aluminum and composite flat panels by comparing them against experimental tests and semi-analytical data, respectively. Since the good agreement, the FE method has been used to analyze the phenomena of dispersion, scattering, and mode conversion in aluminum and composite panels characterized by a structural discontinuity, as a stiffener. The research activity allowed emphasizing modes conversion at the stiffener, offering new observations with respect to state of the art. Converted modes propagate with a slightly slower speed than the incident ones. Reflected waves, instead, have been found to travel with the same velocity of the incident ones. Moreover, waves reflected in the composite stiffened plate appeared different from those that occurred in the aluminum one for the aspects herein discussed.

Comparative analysis and verification of engineering methods of shallow cracks effect for fracture toughness prediction for reactor pressure vessels

2020 ◽  
pp. 140-165
Author(s):  
V. I. Kostylev ◽  
B. Z. Margolin
Keyword(s):  
Experimental Data ◽  
Fracture Toughness ◽  
Comparative Analysis ◽  
Nuclear Reactor ◽  
Probabilistic Approach ◽  
Pressure Vessels ◽  
Local Methods ◽  
European Method ◽  
Shallow Crack ◽  
Reactor Pressure

The main features of shallow cracks fracture are considered, and a brief analysis of methods allowing to predict the temperature dependence of the fracture toughness KJC (T) for specimens with shallow cracks is given. These methods include DA-method, (JQ)-method, (J-T)-method, “local methods” with its multiparameter probabilistic approach, GP method uses power approach, and also two engineering methods – RMSC (Russian Method for Shallow Crack) and EMSC (European Method for Shallow Crack). On the basis of 13 sets of experimental data for national and foreign steels, a detailed verification and comparative analysis of these two engineering methods were carried out on the materials of the VVER and PWR nuclear reactor vessels considering the effect of shallow cracks.

scholarly journals Effect of Testing Method Type and Specimen Size on Mode I Fracture Toughness of Kimachi Sandstone

2019 ◽  
Vol 135 (5) ◽  
pp. 33-41 ◽  
Author(s):  
Minami KATAOKA ◽  
Yuzo OBARA ◽  
Leona VAVRO ◽  
Kamil SOUCEK ◽  
Sang-Ho CHO ◽  
...  
Keyword(s):  
Fracture Toughness ◽  
Specimen Size ◽  
Mode I ◽  
Mode I Fracture ◽  
Mode I Fracture Toughness ◽  
Testing Method
Sign in / Sign up

Export Citation Format

Share Document