1,720,985 research outputs found
Experimental and Numerical Assessment of Sheet Molding Compound Composite Crushing Behavior
No full textThis study investigates the crashworthiness properties of carbon fiber sheet molding compound (CF-SMC) material, highlighting its potential for applications requiring effective energy absorption. While CF-SMC exhibits promising specific energy absorption values, further optimization of both the material and its geometrical design is necessary to enhance performance. Notably, CF-SMC's manufacturing advantages, including faster production and the capability to integrate recycled fibers, make it a cost-effective and sustainable option for industries prioritizing efficiency and environmental responsibility. The short-fiber material model implemented within the ESI-VPS software was calibrated by means of tensile and compressive test simulations, and it was validated through crash simulations. The results indicate a strong correlation between experimental data and numerical predictions, confirming the effectiveness of the modeling approach
Comparative Analysis on Modelling Approaches for the Simulation of Fatigue Disbonding with Cohesive Zone Models
Full text linkAdhesively bonded joints are essential in the aeronautical industry, offering benefits such as weight reduction and enhanced sustainability. However, certifying these joints is challenging due to unreliable methods for assessing their strength and the development of predictive models for fatigue-driven disbonding remains an ongoing effort. This manuscript presents the implementation and validation of a cohesive zone model for studying high-cycle fatigue disbonding under Mode I and Mixed-Mode loading. The model was integrated into the commercial finite element analysis software Abaqus using user-defined material subroutine (UMAT). Two modelling approaches were investigated: one replacing the adhesive with a cohesive layer, and the other incorporating a cohesive layer at the adhesive’s mid-plane while modelling its entire thickness, using both 2D and 3D techniques. Validation was conducted against experimental data from the literature that examined the influence of adhesive thickness on fatigue behaviour in DCB and CLS tests. The findings of this study confirm that the model accurately predicts fatigue disbonding across all cases examined. Additionally, the analysis reveals that modelling adhesive thickness plays a critical role in the simulation’s outcomes. Variations in adhesive thickness can significantly alter the crack growth behaviour, highlighting the importance of carefully considering this parameter in future assessments and applications
Hygrothermal Ageing Influence on BVI-Damaged Carbon/Epoxy Coupons under Compression Load
Full text linkComposite materials usage in several industrial fields is now widespread, and this leads
to the necessity of overcoming issues that are still currently open. In the aeronautic industry, this is
especially true for Barely Visible Impact Damage (BVID) and humidity uptake issues. BVID is the
most insidious kind of impact damage, being rather common and not easily detectable. These, along
with the ageing that a composite structure could face during its operative life, could be a cause of fatal
failures. In this paper, the influence of water absorption on impacted specimens compressive residual
strength was studied. Specimens were impacted using a modified Charpy pendulum. Two different
locations were chosen for comparison: Near-Edge (NE) and Central (CI). Accelerated hygrothermal
ageing was conducted on impacted and reference nonimpacted coupons, placing them in a waterfilled
jar at 70 °C. Compressive tests were performed in accordance with the Combined Loading
Compression (CLC) test method. A Dynamic Mechanical Analysis (DMA) was performed as well.
The results showed the influence of hygrothermal ageing, as expected. Nevertheless, the influence of
impact location on compressive residual strength is not clearly noticeable in aged specimens, leading
to the conclusion that hygrothermal ageing may have a greater effect on composite compressive
strength than the analysed BVI damage
Experimental and Numerical Assessment of Crashworthiness Properties of Composite Materials: A Review
Full text linkCrashworthiness is a critical property that enables aerospace structures to minimise injuries and equipment damage during impact scenarios. This review examines the current state of crashworthiness research, with a focus on regulatory frameworks, experimental testing, and numerical modelling techniques. Stringent safety standards set by the Federal Aviation Administration (FAA) and the European Union Aviation Safety Agency (EASA) guide the design and certification protocols for aeronautical structures. Experimental crash testing, which includes both full-scale and subscale impact tests, provides essential data for validating material behaviour and energy absorption capabilities under both quasi-static and dynamic loading conditions. Advanced numerical modelling tools offer significant insights into crash behaviour, enabling optimisation of structural designs whilst reducing reliance on costly physical testing. This review highlights the integration of regulations, empirical data, and computational tools in advancing crashworthiness research, with an emphasis on developing safer, more efficient, and sustainable aerospace designs. Future directions should prioritise the use of sustainable materials and optimise crashworthy designs through artificial intelligence (AI) and advanced numerical models to enhance structural performance and safety
Effect of Adhesive Thickness on Fatigue Disbonding Through a Cohesive Zone Modelling Approach
Full text linkAdhesively bonded joints are crucial to the aeronautical industry, contributing to
weight reduction and more sustainable flights. However, certifying these joints is still a
topic of debate due to the lack of reliable inspection methods to determine their strength.
Additionally, prediction models for crack growth under fatigue loading are still being
developed. This manuscript describes the implementation and validation of a cohesive
zone model to evaluate high cycle fatigue disbonding under mode I opening. This model
was integrated into the commercial finite element analysis software Abaqus using user-
defined subroutines, specifically a UMAT. The experimental data from the literature on the
effect of adhesive thickness during fatigue loading of a double cantilever beam were used
for model validation. Three modelling techniques were explored, including substitution of
the adhesive with the cohesive zone (2D and 3D) and the addition of a cohesive layer in the
mid-plane of the adhesive (2D only). The results have confirmed that the model is effective
in accurately predicting fatigue crack growth in all the simulated cases. Additionally, it
has been shown that the adhesive’s thickness has an impact on the simulation results,
particularly with thicker bondlines and low strain energy release rate
CFRP Crash Absorbers in Small UAV: Design and Optimization
No full textThe high number of hull losses is a main concern in the UAV field, mostly due to the high cost of on-board equipment. A crashworthiness design can be helpful to control the extent and position of crash impact damage, minimizing equipment losses. However, the wide use of composite materials has recently put the accent on the lack of data about the behavior of these structures under operative loads, such as the crash conditions. This paper presents the outcome of a set of tests carried out to achieve a controlled crush of UAV structures, and to maximize the Specific Energy Absorption. In this work, a small-scale experimental test able to characterize the energy absorption of a Carbon-fiber-reinforced polymer under compression was developed introducing self-supporting sinusoidal shape specimens, which avoid the need for complex anti-buckling devices. The specimens were produced with different auto-triggering configurations and fibers' continuity was interrupted in selected position and for different extent in order to investigate the Specific Energy Absorption of the weakened laminates. The auto-triggering configuration was able to control the position of the initial failure of the specimen without any decrease in safety performance. This new kind of very light crash absorber can be used in small UAV to reduce the crash loads in the avionic and payload bay. With reference to a small UAV designed and manufactured at University of Bologna, an optimization of the crash absorbers positions has been carried out in order to achieve the best results in terms of energy dissipation
Analysis of the Crushing Behavior of Flat Composite Plates Produced by Sheet Molding Compound
No full textSMC composites, comprising chopped fiber bundles within a matrix
material, offer the potential to create lightweight structures with high strength and
stiffness, serving as viable substitutes for heavier metal components. The complex
task of designing SMC composites with optimized performance characteristics is
compounded by their inherently localized anisotropic behavior and the presence of
various interacting forms of damage. Consequently, simulating the performance of
SMC in crash-worthy applications necessitates a comprehensive characterization
of the material’s mechanical properties through tailored experimental tests. In this
study, an experimental study has been conducted on a commercial SMC mate-
rial, with the primary objective of comprehensively comprehending its behavior
and deriving specific parameters essential for numerical simulations. Employing
ESI-VPS, the crashworthiness of flat components was simulated and successfully
achieved a favorable correlation between the obtained results and the experimental
data
Improving the crashworthiness of CFRP structures by rubbery nanofibrous interlayers
Full text linkCrashworthiness is the capability of a component to dissipate impact energy throughout its deformation and failure. Composite materials are used to produce crashworthy components to ensure vehicle safety, thanks to their ability to dissipate a high energy amount while maintaining a low weight. The present work investigates the integration of rubbery nanofibers within the laminate interlayers to enhance crush performance. Three different thicknesses (10, 20, and 40 μm) of nanofibrous mats made by nitrile butadiene rubber and polycaprolactone (NBR/PCL) blends were produced by single-needle electrospinning technique and integrated into the laminates during the hand-layup. Mechanical properties of the nano-modified laminates are compared to the reference configuration: the effect of the interlayers is evaluated by Double Cantilever Beam (DCB) and End-Notched Flexure (ENF) interlaminar fracture tests. At the same time, the specific crush energy absorption (SEA) is measured by the compression of self-supporting corrugated specimens. Results show that NBR/PCL nanofibers significantly increase the interlaminar fracture toughness (up to +254% for Mode I and +47% for Mode II), which ultimately helps to improve the total SEA up to +8.2%. The best SEA enhancement is achieved already with a 10 μm nanofibrous membrane while integrating the highest thickness mat has a detrimental effect
Material Characterization for Reliable Resin Transfer Molding Process Simulation
Full text linkResin transfer molding (RTM) technologies are widely used in automotive, marine, and aerospace applications. The need to evaluate the impact of design and production critical choices, also in terms of final costs, leads to the wider use of numerical simulation in the preliminary phase of component development. The main issue for accurate RTM analysis is the reliable characterization of the involved materials. The aim of this paper is to present a validated methodology for material characterization to be implemented and introduce data elaboration in the ESI PAM-RTM software. Experimental campaigns for reinforcement permeabilities and resin viscosity measurement are presented and discussed. Finally, the obtained data are implemented in the software and then compared to experimental results in order to validate the described methodology
Effetto di impatti sul comportamento crashworthiness di materiali compositi
Full text linkAttività sperimentale riguardante lo studio dei materiali compositi, nell’ambito della progettazione a crashworthiness, svolto, tramite test dei provini realizzati nell’attività di tirocinio, presso i laboratori didattici della Scuola di ingegneria e architettura, sede di Forlì.
Il lavoro di tesi, si è basato sulla valutazione dell’energia assorbita dai provini in materiale composito, tramite prove quasi-statiche; per questo tipo di prove sono stati utilizzati provini autostabilizzanti, rinforzati in fibra di carbonio e matrice in resina epossidica. Prima di procedere alla sperimentazione, sono stati studiati i risultati ottenuti da precedenti sperimentazioni eseguite da colleghi, per valutare quale fosse la configurazione migliore di provino, in termini di geometria, e trigger, che garantisse elevate energie di assorbimento.
Dopo una panoramica dei materiali compositi, con riferimento alle caratteristiche e proprietà, alle diverse tipologie che si possono avere in ambito industriale, è spiegato il concetto di crashworthiness, le varie tipologie di test di impatto e le varie tipologie di rottura alla quale può essere soggetto un provino. Si è di seguito descritto come è stata valutata la scelta del tipo di geometria e del trigger, che sarebbero stati utilizzati per la progettazione del provino, e si è accennato al processo di laminazione svolta presso i laboratori della Scuola per la fabbricazione del provino. Al termine della descrizione dei tester usati per la sperimentazione sono, infine, illustrati i risultati delle prove svolte, con successivi commenti
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