scholarly journals A Review Of Mechanisms And Fracture Mechanics Of Moisture Ingress In Composite Systems

2021 ◽  
Author(s):  
Janani S. Gopu
Keyword(s):  
Fracture Mechanics ◽  
Composite Structures ◽  
Composite System ◽  
Aerospace Industry ◽  
Weight Ratio ◽  
High Strength ◽  
Honeycomb Structure ◽  
Sandwich Composite ◽  
Composite Systems ◽  
Water Accumulation

Composite materials help realize high strength to weight ratio requirements of the Aerospace Industry. Composite structures and sandwich composite structures are susceptible to moisture ingress. Moisture ingress causes degradation of thermo-mechanical properties of the composite panels. Water accumulation in sandwich composite structures causes rapid degradation of face to core bondline, damage of cells frozen water and even blow off skins owing to sudden pressure build up in the cells of the honeycomb structure. Mechanisms of moisture ingress can be broadly classified into direct and indirect mechanisms. Direct ingress occurs through pre-existing pathways formed by defects in the composite system. Indirect mechanisms are diffusion, Capillary actions, Wicking actions, and Osmosis. The first form of damage in FRP materials is microcracking. The rate of microcracking increases with moisture ingress. Microcracking fracture toughness is a material property for the susceptibility of a composite system to the formation of microcracks. This work implores the mechanisms and the fracture mechanics dominating the formation of microcracks.

scholarly journals A Review Of Mechanisms And Fracture Mechanics Of Moisture Ingress In Composite Systems

2021 ◽  
Author(s):  
Janani S. Gopu
Keyword(s):  
Fracture Mechanics ◽  
Composite Structures ◽  
Composite System ◽  
Aerospace Industry ◽  
Weight Ratio ◽  
High Strength ◽  
Honeycomb Structure ◽  
Sandwich Composite ◽  
Composite Systems ◽  
Water Accumulation

Composite materials help realize high strength to weight ratio requirements of the Aerospace Industry. Composite structures and sandwich composite structures are susceptible to moisture ingress. Moisture ingress causes degradation of thermo-mechanical properties of the composite panels. Water accumulation in sandwich composite structures causes rapid degradation of face to core bondline, damage of cells frozen water and even blow off skins owing to sudden pressure build up in the cells of the honeycomb structure. Mechanisms of moisture ingress can be broadly classified into direct and indirect mechanisms. Direct ingress occurs through pre-existing pathways formed by defects in the composite system. Indirect mechanisms are diffusion, Capillary actions, Wicking actions, and Osmosis. The first form of damage in FRP materials is microcracking. The rate of microcracking increases with moisture ingress. Microcracking fracture toughness is a material property for the susceptibility of a composite system to the formation of microcracks. This work implores the mechanisms and the fracture mechanics dominating the formation of microcracks.

ONR REVIEW: ARCHITECTED COMPOSITES FOR DAMAGE TOLERANCE IN EXTREME CONDITIONS

2021 ◽  
Author(s):  
PAVANA PRABHAKAR ◽  
VINAY DAMODARAN, ◽  
ABARINATHAN PUSHPARAJ SUBRAMANIYAN
Keyword(s):  
Energy Dissipation ◽  
Composite Structures ◽  
Computational Models ◽  
Peak Load ◽  
Moisture Diffusion ◽  
Honeycomb Structure ◽  
Sandwich Composite ◽  
Extreme Conditions ◽  
Improved Performance ◽  
Damage Tolerant

The long-term goal of this ONR funded project is to facilitate the design of architected composites that play a key role in damage tolerant and resilient structures. The main emphasis is on developing new composite structures with improved performance and durability as compared to conventional structural composites. To that end, we will present our work in detail on the following within the realm of sandwich composites along with a novel Machine Learning framework for stress prediction in composites: 1) Novel recoverable sandwich composite structures: Traditional sandwich cores such as foam core or honeycomb structures are good options for enabling lightweight and stiff structures. Although, these cores are known to dissipate energy under extreme conditions such as impact loading, they experience permanent damage. Here, our goal is to design core structures that undergo substantial deformation without accumulating damage and recover their original geometric configuration after the loading is removed. In contrast to a traditional foam or honeycomb structure, we have developed a multi-layer architected core design that facilitates significant deformation beyond the initial peak load, yielding a larger energy dissipation during impact and other extreme loading scenarios. We utilize the concept of pseudo-bistability of truncated cone unit cells to achieve elastic buckling for energy dissipation and shape recovery of core structures. 2) Tailoring of sandwich composite facings: Our objective is to establish the influence of fiber architecture on moisture diffusion pathways in FRPC facings for enabling damage tolerant facing designs. To that end, we have evaluated the moisture kinetics in FRPCs by developing micromechanics based computational models within FEM. We have explained the effect of tortuous diffusion pathways that manifest within FRPCs due to internal fiber architectures. Finally, we established the relationship between tortuosity and diffusivity that can be used for studying moisture diffusion in other FRPCs.

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.

scholarly journals THE EFFECT OF DIFFERENT FORMS OF OXYGEN ON PROPERTIES OF BETA TITANIUM ALLOYS

2018 ◽  
Vol 58 (3) ◽  
pp. 179 ◽  
Author(s):  
Jaroslav Málek ◽  
František Hnilica ◽  
Sonia Bartáková ◽  
Patrik Míka ◽  
Jaroslav Veselý
Keyword(s):  
Mechanical Properties ◽  
Solid Solution ◽  
Titanium Alloys ◽  
Titanium Powder ◽  
Aerospace Industry ◽  
Weight Ratio ◽  
High Strength ◽  
Beta Titanium ◽  
Oxide Particles ◽  
Beta Titanium Alloys

The beta-titanium alloys are widely used in many applications (medicine, aerospace industry etc.) due to their superior properties, such as corrosion resistance, biocompatibility and high strength to weight ratio. One of the ways how to increase the strength of those alloys is the addition of oxygen. The oxygen can be present in various forms in the alloy – in a solid solution or in the form of oxides. In this work, the effect of two forms of oxygen (i.e., solid solution and dispersion particles) was studied. Two alloys, one arc melted with different oxygen additions and one prepared via powder metallurgy where the titanium powder was oxidized, were prepared. The microstructure and mechanical properties were studied. A significant increase in strength with increasing the oxygen content in the solid solution has been observed. However, the powder oxidation has almost no effect on a tensile strength probably due to quite large interparticle distances between titanium oxide particles.

Tensile Properties of Angle Cured Laminated Composites Structures under Gravity Effects

2013 ◽  
Vol 465-466 ◽  
pp. 101-105
Author(s):  
Mohd Yuhazri bin Yaakob ◽  
T.T.T. Jennise ◽  
H. Sihombing ◽  
Md Radzai bin Said ◽  
U. Nirmal ◽  
...  
Keyword(s):  
Tensile Properties ◽  
Composite Structures ◽  
Weight Ratio ◽  
Laminated Composite ◽  
High Strength ◽  
Maximum Force ◽  
Composites Materials ◽  
Laminated Composite Structures ◽  
Gravity Effects ◽  
Optimum Productivity

As the usage of composites materials are significant in the industries of automobiles, shipping and constructions due to their non-corrosive and high strength to weight ratio. Anyway, the production of composites needed to be increased to meet the demand. At this stage, problem faced by Small and Medium Industries / Entrepreneurs (SMI/E) is the confined and limited space available that restricts the optimum productivity. They commonly cure the composites horizontally that requires ample space and unable to afford for high-end equipment such as mechanical oven and autoclave in the production as a result of high capital cost.This research is carried out to study the feasibility of the gravity effects on curing position of the laminated composite structures to enhance the curing space needed. The aim of the research was to investigate the tensile properties of the thermosetting laminated composite by curing the laminate at different angle using vacuum bagging technique. From the testing, SN 5 which denominated to be 60 ̊ found to have the best tensile properties in term of maximum force exerted and Youngs modulus.

scholarly journals Design and Analysis of Composite Leaf Spring

2013 ◽  
pp. 209-212
Author(s):  
Y. N. V. Santhosh Kumar ◽  
M. Vimal Teja
Keyword(s):  
Composite Materials ◽  
Automobile Industry ◽  
Composite Structures ◽  
Weight Ratio ◽  
High Strength ◽  
Design Parameters ◽  
Leaf Spring ◽  
Metallic Structures ◽  
Conventional Steel ◽  
Fiberglass Composite

In these paper, composite structures for conventional metallic structures has many advantages because of higher specific stiffness and strength of composite materials is discussed. The automobile industry has shown increased interest in the replacement of steel spring with fiberglass composite leaf spring due to high strength to weight ratio. This work deals with the replacement of conventional steel leaf spring with a Mono Composite leaf spring using E-Glass/Epoxy. The design parameters were selected and analyzed with the objective of minimizing weight of the composite leaf spring as compar

scholarly journals Mechanical behavior of sandwich structure composites for helicopters

2020 ◽  
Vol 12 (4) ◽  
pp. 155-162
Author(s):  
George PELIN ◽  
Cristina-Elisabeta PELIN ◽  
Adriana STEFAN ◽  
Alexandra PETRE ◽  
Alina DRAGOMIRESCU
Keyword(s):  
Mechanical Behavior ◽  
Composite Structure ◽  
Weight Ratio ◽  
High Strength ◽  
Mechanical Tests ◽  
Impact Behavior ◽  
Sandwich Composite ◽  
Maximum Efficiency ◽  
Commercial Aircraft ◽  
Sandwich Composite Structure

The visible part of the floors of a commercial aircraft has long been a standard issue for virtually every commercial aircraft, mainly due to the weight of the materials from which they were made. Floor parts must provide mechanical strength and dimensional stability, while keeping the weight of the aircraft as low as possible for maximum efficiency. The design of the 787 Dreamliner and the Airbus A380 aircraft brought new opportunities in the use of the sandwich composite structure, mainly due to their light weight and high strength-to-weight ratio. Thus, this paper investigates the mechanical behavior of sandwich composite panels composed of two sides of carbon fiber laminate and Nomex honeycomb core obtained in the autoclave and developed under the RoRCraft CompAct grant. The technical approaches of this work are mainly focused on the compression behavior and especially on the compression after impact behavior of the hybrid sandwich composite structure, for defining and obtaining an optimal structure for the floors. These mechanical tests are decisive for such materials and have been performed in accordance with international ASTM standards.

Stream of Variation Modeling and Analysis for Compliant Composite Part Assembly—Part I: Single-Station Processes

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Tingyu Zhang ◽  
Jianjun Shi
Keyword(s):  
New York ◽  
Composite Structures ◽  
Weight Ratio ◽  
High Strength ◽  
Laminated Plates ◽  
Composite Part ◽  
Modeling And Analysis ◽  
Single Station ◽  
Assembly Deviation ◽  
The Impact

Composite structures are widely used due to their superior properties, such as low density, high strength, and high stiffness-to-weight ratio (Mallick, 1993, Fiber-Reinforced Composites: Materials, Manufacturing, and Design, Marcel Dekker, New York). However, the lack of methodologies for variation modeling and analysis of composite part assembly has imposed a significant constraint on developing dimensional control for composite assembly processes. This paper develops a modeling method to predict assembly deviation for compliant composite parts in a single-station assembly process. The approach is discussed in two steps: considering the part manufacturing error (PME) only and considering both the PME and the fixture position error (FPE). Finite element method (FEM) and homogenous coordinate transformation are used to reveal the impact of the PME and the FPE. The validity of the method is verified with two case studies on assembly deviation prediction of two composite laminated plates considering the PME only and both the PME and the FPE, respectively. The proposed method provides the basis for assembly deviation prediction in the multistation composite assembly.

Stiffness Analysis of Delaminated Composite Beams Using Roller Clamps

2021 ◽  
Author(s):  
P. G. Vivek ◽  
Ankuran Saha ◽  
Apurba Das ◽  
Kazuaki Inaba ◽  
Amit Karmakar
Keyword(s):  
Free Vibration ◽  
Composite Beam ◽  
Composite Structures ◽  
Structural Parameters ◽  
Weight Ratio ◽  
Laminated Composite ◽  
High Strength ◽  
Simulation Software ◽  
Complex Activity ◽  
Aerospace Applications

Abstract Composites are favored over other traditional materials in many aerospace applications because of their high stiffness and strength-to-weight ratio. Taylor made material properties can be achieved by scheming the structural parameters making the material light, high strength and durable. Present work deals with a novel approach to enhance the strength of a layered delaminated composite beam using roller clamps to improve stiffness by providing uniform transverse force. Composite beam stiffness significantly degrades due to adverse environmental condition, impact loading and delamination effect. Composite structures are prone to delamination during its life span. Therefore in depth knowledge is needed to find the effect of roller clamps on the dynamic behavior of beam with varying delamination sizes. Present approach will be useful to enhance the stiffness of composite structure with delamination. The free vibration of a clamped cantilever beam is investigated, and the results are compared to those of an unclamped and undelaminated beam. The findings are supported by experimentally obtained responses (modal analysis). Furthermore, the complex activity of the laminated structure is numerically computed and the obtained data is compared to those available in open literature to ensure correctness. The laminated composite beam’s static and free vibration responses are calculated using finite element simulation software (ANSYS).

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