Experimental damage tolerance evaluation of thick fabric carbon/epoxy laminates under low-velocity and high-velocity impact and compression-after-impact

Impact experiments of thick fabric carbon/epoxy laminate specimens, with small thickness ratio, are conducted at distinct energy levels and thicknesses to characterise the damage process. These specimens and loading conditions are representative of a new generation of critical structural components in aviation, such as wing spars, landing gear beams and fittings, that are increasingly being made entirely from composites. The tests address the need to better understand the damage process for specimens with a small thickness ratio since existing experimental impact data for large thickness ratio (thin laminates) may not be directly applicable. Two energy levels, two different fabric layups and two impact methods (drop-weight and gas-cannon) were used. Data from high-speed cameras were processed in a novel way, providing the force during impact. C-scans and micrographs were used to characterise damage. The results show that specimens with a thickness ratio of 5 (20 mm thick) experience more bending compared to specimens with a ratio 2.5 (40 mm thick). For gas-cannon impacts, this results in a higher delaminated area. The drop-weight impacts show almost no differences in damage size for the thickness range analysed. The influence of layup on the global impact response is negligible, but locally it can result in significant variations in dent depth. The dent depth scales linearly with the impact energy and the delaminated area linearly with the impact velocity. There is no clear correlation between the compression-after-impact failure mechanisms and the residual strength. Impact damage, at the current energy levels, showed a minimal reduction of residual strength.

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Effect of Thermal Ageing on the Impact Damage Resistance and Tolerance of Carbon-Fibre-Reinforced Epoxy Laminates

Polymers ◽

10.3390/polym11010160 ◽

2019 ◽

Vol 11 (1) ◽

pp. 160 ◽

Cited By ~ 12

Author(s):

Irene García-Moreno ◽

Miguel Caminero ◽

Gloria Rodríguez ◽

Juan López-Cela

Keyword(s):

Carbon Fibre ◽

Residual Strength ◽

Composite Structures ◽

Impact Resistance ◽

Thermal Ageing ◽

Low Velocity Impact ◽

Impact Tests ◽

Compression After Impact ◽

Structural Applications ◽

The Impact

Composite structures are particularly vulnerable to impact, which drastically reduces their residual strength, in particular, at high temperatures. The glass-transition temperature (Tg) of a polymer is a critical factor that can modify the mechanical properties of the material, affecting its density, hardness and rigidity. In this work, the influence of thermal ageing on the low-velocity impact resistance and tolerance of composites is investigated by means of compression after impact (CAI) tests. Carbon-fibre-reinforced polymer (CFRP) laminates with a Tg of 195 °C were manufactured and subjected to thermal ageing treatments at 190 and 210 °C for 10 and 20 days. Drop-weight impact tests were carried out to determine the impact response of the different composite laminates. Compression after impact tests were performed in a non-standard CAI device in order to obtain the compression residual strength. Ultrasonic C-scanning of impacted samples were examined to assess the failure mechanisms of the different configurations as a function of temperature. It was observed that damage tolerance decreases as temperature increases. Nevertheless, a post-curing process was found at temperatures below the Tg that enhances the adhesion between matrix and fibres and improves the impact resistance. Finally, the results obtained demonstrate that temperature can cause significant changes to the impact behaviour of composites and must be taken to account when designing for structural applications.

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Comparative Study on Fatigue Life of CFRP Composites with Damages

Fatigue of Aircraft Structures ◽

10.2478/fas-2019-0004 ◽

2019 ◽

Vol 2019 (11) ◽

pp. 28-38

Author(s):

Marta Baran ◽

Piotr Synaszko ◽

Janusz Lisiecki ◽

Sylwester Kłysz

Keyword(s):

Residual Strength ◽

Stress Ratio ◽

Fatigue Tests ◽

Equivalent Diameter ◽

Compression After Impact ◽

Strength Tests ◽

Cfrp Composite ◽

Sinusoidal Shape ◽

Weight Impact ◽

The Impact

AbstractIn this work, the compressive residual strength tests results, Compression After Impact (CAI), are presented. The specimens were made of carbon-epoxy prepreg E722-02 UHS 130-14. Two variants of specimens were tested: samples undamaged and samples with damage that was centrally introduced by a drop-weight impact, as per the ASTM D7136/7136M standard. An impactor with potential energy equal to 15J and the type of support required by the standard were used. The size of impacted damages, defined as an area of damage on a plane perpendicular to the impact direction, and the equivalent diameter were specified using the flash thermography method.The tests were performed using the fixtures manufactured according to the ASTM D7137/7137M standard. The specimens were compressed to determine the residual strength. This value was afterwards used to specify the force levels for the fatigue tests. The fatigue tests were carried out under force control – with a sinusoidal shape, stress ratio R equal to 0.1 and frequency f 1Hz. Maximum force in a loading cycle Pmax was being increased after each thousand of cycles N until its value was close to the residual strength determined in the previously mentioned tests. In this work, the following relationships were presented: force-displacement P-δ for both static and fatigue tests and displacement-loading cycles δ-N for fatigue tests.A method of conducting the fatigue tests of CFRP composite was proposed, in which both the CAI specimens and CAI fixture were used. This allowed researchers to accelerate making initial comparisons between the two groups of specimens with damages – grouped relative to the way of conditioning.

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Impact Damage Tolerance and Fatigue Durability of GLARE Laminates

Journal of Engineering Materials and Technology ◽

10.1115/1.2969253 ◽

2008 ◽

Vol 130 (4) ◽

Cited By ~ 9

Author(s):

Hyoungseock Seo ◽

H. T. Hahn ◽

Jenn-Ming Yang

Keyword(s):

Residual Strength ◽

Impact Test ◽

Damage Tolerance ◽

Impact Damage ◽

Fatigue Behavior ◽

Energy Levels ◽

Damage Initiation ◽

Fatigue Durability ◽

Weight Impact ◽

The Impact

The fatigue behavior and residual strength of postimpacted GLARE 4-3/2, GLARE 5-2/1, and monolithic aluminum 2024-T3 alloy were investigated experimentally. Drop-weight impact was applied at a variety of energy levels to inflict a barely visible impact damage, a clearly visible impact damage, and a penetration damage. After the impact test, constant-amplitude tension-tension fatigue was done to delineate the modes of damage initiation and growth and the effect of damage on fatigue life and residual strength. The results showed that GLARE laminates exhibit superior postimpact fatigue durability when compared with the monolithic 2024-T3 aluminum alloy.

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APPARATUS AND METHOD FOR CALCULATING PENETRATION FORCE BY DROP WEIGHT IMPACT TECHNIQUE

Journal of Engineering and Sustainable Development ◽

10.31272/jeasd.conf.2.2.2 ◽

2021 ◽

Vol 25 (Special) ◽

pp. 2-9-2-14

Author(s):

Mohammed H. Khalaf ◽

◽

Suhad D. Salman ◽

Keyword(s):

Energy Levels ◽

Real Life ◽

Guide Tube ◽

Damage Resistance ◽

Drop Weight ◽

Penetration Force ◽

Izod Impact ◽

Weight Impact ◽

The Impact ◽

High Range

Because of the limitations that are experienced when trying to perform Charpy and Izod impact tests, the drop weight impact test is preferred over the more conventional impact methods to determine whether the material is brittle or ductile. The drop weight impact technique indicates the conditions under which real-life components would be subject to impact loading. In this study, a drop-weight impact instrument has been designed and manufactured using a dropping weight which impacts the specimens, falls through a perpendicular guide tube with a high range of impact energy levels. Force - deformation and acceleration –time graphs, could be determined by using various sensor systems were installed to calculate the impactor's velocity and the magnitude of the impact force. Consequently, the energy absorption of different materials can be measured and the damage resistance could be indicated.

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Experimental and numerical study of the response to various impact energy levels for composite sandwich plates with different face thicknesses

Journal of Sandwich Structures & Materials ◽

10.1177/1099636219837133 ◽

2019 ◽

Vol 21 (5) ◽

pp. 1654-1682

Author(s):

Moeen S Rajput ◽

Magnus Burman ◽

Fredrik Forsberg ◽

Stefan Hallström

Keyword(s):

Impact Energy ◽

Impact Damage ◽

Energy Levels ◽

Impact Response ◽

Low Velocity Impact ◽

Absorbed Energy ◽

Low Velocity ◽

Composite Sandwich ◽

The Impact ◽

Dent Depth

Composite sandwich structures find wide application in the aerospace sector thanks to their lightweight characteristics. However, composite structures are highly susceptible to low-velocity impact damage and therefore thorough characterization of the impact response and damage process for the used material configurations is necessary. The present study investigates the effect of face-sheet thickness on the impact response and damage mechanisms, experimentally and numerically. A uni-directional, non-crimp fabric is used as reinforcement in the face-sheets, and a closed cell Rohacell 200 Hero polymer foam is used as core material. Low-velocity impact tests are performed in a novel instrumented drop-weight rig that is able to capture the true impact response. A range of impact energies are initially utilized in order to identify when low level damage (LLD), barely visible impact damage (BVID) and visible impact damage (VID) occur. A thorough fractography investigation is performed to characterize the impact damage using both destructive and non-destructive testing. The damage from the impacts in terms of dent depth, peak contact force, deflection and absorbed energy is measured. The results show bilinear responses in dent depth vs. impact energy and absorbed energy vs. impact energy. It is found than the BVID energy works well as an indication for the onset of excessive damage. Fractography reveals that there is a failure mode shift between the LLD and the VID energy levels, and that delaminations predominantly grow along the fiber direction and rotate in a spiral pattern through the thickness, following the laminate ply orientations. Finally, a progressive damage finite element model is developed to simulate both the impact response and the delamination extent, incorporating both intra-laminar and inter-laminar damage modes. The simulation shows good agreement with the experiments.

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Development of a mathematical model to analyze residual strength of composites after low-velocity impact

The Journal of Strain Analysis for Engineering Design ◽

10.1177/0309324718802546 ◽

2018 ◽

Vol 53 (8) ◽

pp. 738-745 ◽

Cited By ~ 2

Author(s):

Camila Medeiros Dantas de Azevedo ◽

Rayane Dantas da Cunha ◽

Raimundo Carlos Silverio Freire Junior ◽

Wanderley Ferreira de Amorim Junior

Keyword(s):

Residual Strength ◽

Composite Laminates ◽

Repair Process ◽

Low Velocity Impact ◽

Low Velocity ◽

Velocity Impact ◽

Three Point Bending ◽

Compression After Impact ◽

Strength And Stiffness ◽

The Impact

This study aimed to develop a model to analyze the residual strength of composites after low-velocity impact, using three-point bending and compression after impact tests. Two types of composite laminates with an orthophthalic polymer matrix were used: one reinforced with bidirectional E-glass fabric and the other reinforced with bidirectional Kevlar-49 fabric. To that end, an equation was developed to assess loss of strength and stiffness after impact at different distances from the impact point, and this equation was not found in any previously searched article. The results demonstrate that the laminate based in glass fiber is more appropriate for the repair process.

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Does kraft hardwood and softwood pulp viscosity correlate to paper properties?

TAPPI Journal ◽

10.32964/tj15.10.643 ◽

2016 ◽

Vol 15 (10) ◽

pp. 643-651 ◽

Cited By ~ 1

Author(s):

ROBERT J. OGLESBY ◽

HUMPHREY J. MOYNIHAN ◽

RICARDO B. SANTOS ◽

ASHOK GHOSH ◽

PETER W. HART

Keyword(s):

Physical Properties ◽

Strength Loss ◽

Strength Properties ◽

Clear Correlation ◽

Paper Properties ◽

Physical Strength ◽

Pulp Viscosity ◽

Softwood Pulp ◽

The Impact ◽

Adjustment of Whey:Casein Ratio from 20:80 to 60:40 in Milk Formulation Affects Food Intake and Brainstem and Hypothalamic Neuronal Activation and Gene Expression in Laboratory Mice

Foods ◽

10.3390/foods10030658 ◽

2021 ◽

Vol 10 (3) ◽

pp. 658

Author(s):

Erin L. Wood ◽

David G. Christian ◽

Mohammed Arafat ◽

Laura K. McColl ◽

Colin G. Prosser ◽

...

Keyword(s):

Food Intake ◽

Area Postrema ◽

Energy Levels ◽

Early Gene ◽

Hypothalamic Nucleus ◽

Laboratory Mice ◽

Neuronal Activation ◽

Short Term ◽

Animal Milk ◽

The Impact

Adjustment of protein content in milk formulations modifies protein and energy levels, ensures amino acid intake and affects satiety. The shift from the natural whey:casein ratio of ~20:80 in animal milk is oftentimes done to reflect the 60:40 ratio of human milk. Studies show that 20:80 versus 60:40 whey:casein milks differently affect glucose metabolism and hormone release; these data parallel animal model findings. It is unknown whether the adjustment from the 20:80 to 60:40 ratio affects appetite and brain processes related to food intake. In this set of studies, we focused on the impact of the 20:80 vs. 60:40 whey:casein content in milk on food intake and feeding-related brain processes in the adult organism. By utilising laboratory mice, we found that the 20:80 whey:casein milk formulation was consumed less avidly and was less preferred than the 60:40 formulation in short-term choice and no-choice feeding paradigms. The relative PCR analyses in the hypothalamus and brain stem revealed that the 20:80 whey:casein milk intake upregulated genes involved in early termination of feeding and in an interplay between reward and satiety, such as melanocortin 3 receptor (MC3R), oxytocin (OXT), proopiomelanocortin (POMC) and glucagon-like peptide-1 receptor (GLP1R). The 20:80 versus 60:40 whey:casein formulation intake differently affected brain neuronal activation (assessed through c-Fos, an immediate-early gene product) in the nucleus of the solitary tract, area postrema, ventromedial hypothalamic nucleus and supraoptic nucleus. We conclude that the shift from the 20:80 to 60:40 whey:casein ratio in milk affects short-term feeding and relevant brain processes.

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Acoustic emission based investigation on the effect of temperature and hybridization on drop weight impact and post-impact residual strength of hemp and basalt fibres reinforced polymer composite laminates

Composites Part B Engineering ◽

10.1016/j.compositesb.2019.106962 ◽

2019 ◽

Vol 173 ◽

pp. 106962 ◽

Cited By ~ 7

Author(s):

C. Suresh Kumar ◽

Mohamad Fotouhi ◽

Milad Saeedifar ◽

V. Arumugam

Keyword(s):

Acoustic Emission ◽

Polymer Composite ◽

Residual Strength ◽

Composite Laminates ◽

Effect Of Temperature ◽

Reinforced Polymer ◽

Drop Weight ◽

Post Impact ◽

Weight Impact

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Rupture by impact-induced fatigue of a copper foil strip embedded in a multifunctional composite material

Journal of Composite Materials ◽

10.1177/0021998321994327 ◽

2021 ◽

pp. 002199832199432

Author(s):

Yacine Ouroua ◽

Said Abdi ◽

Imene Bachirbey

Keyword(s):

Composite Material ◽

Mechanical Characteristics ◽

Glass Fibers ◽

Energy Levels ◽

Fatigue Tests ◽

Repeated Impact ◽

Aeronautical Industry ◽

Repeated Impacts ◽

Cracking Mode ◽

The Impact

Multifunctional composite materials are highly sought-after by the aerospace and aeronautical industry but their performance depends on their ability to sustain various forms of damages, in particular damages due to repeated impacts. In this work we studied the mechanical behavior of a layered glass-epoxy composite with copper inserts subjected to fatigue under repeated impacts with different energy levels. Damage evolution as a function of impact energy was carefully monitored in order to determine the effect of the copper inserts on mechanical characteristics of the multifunctional composite, such as endurance and life. Results of repeated impact tests show that electric current interruption in the copper inserts occurs prior to the total perforation of the composite material, and after about 75% of the total number of impacts to failure. This is the case for the three energy levels considered in this study, [Formula: see text] = 2, 3 and 4 Joules. The epoxy resin was dissolved chemically in order to preserve the mechanical structure of the damaged copper inserts and the composite fibers for further inspection and analysis. Scanning electron microscopy (SEM) of the fractured copper inserts revealed interesting information on the nature of the damage, including information on plastic deformation, strain hardening, cracking mode, temperature increase during the impacts, and most importantly the glass fibers and their roles during the impact-fatigue tests.

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