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1

Współczynnik ścinania w warstwowych płytach z tektury falistej

Garbowski Tomasz, Graczyk Julia

Przegląd Papierniczy

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2025

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R. 81, nr 12

686--690

PL

Płyty warstwowe z rdzeniem pofalowanym stanowią istotną grupę lekkich konstrukcji stosowanych w opakowaniach, przegrodach budowlanych, konstrukcjach transportowych oraz panelach inżynierskich. Odpowiedź mechaniczna takich układów w dużej mierze zależy od geometrii periodycznego rdzenia, która determinuje podatność na ścinanie poprzeczne, a tym samym efektywną sztywność postaciową płyty. Podczas gdy klasyczne współczynniki korekcyjne ścinania są dobrze znane w rdzeniach płaskich, brak jest ujednoliconej formuły analitycznej dla rdzeni pofalowanych o dowolnym kształcie. W niniejszej pracy przedstawiono zwartą formułę matematyczną umożliwiającą wyznaczenie współczynnika korekcyjnego ścinania ks dla płyt warstwowych z periodycznym rdzeniem pofalowanym o różnych kształtach, takich jak: fala sinusoidalna, trapezowa, półkolista, elipsoidalna i trójkątna. Podstawą analizy jest zasada równoważności energii odkształcenia postaciowego przekroju rzeczywistego i jego odpowiednika w teorii Timoshenki. Pole naprężeń stycznych rekonstruowane jest na podstawie ogólnego opisu geometrycznego profilu fali i całkowane w obrębie jednej komórki periodycznej. Zaproponowana metoda pokazuje, w jaki sposób kształt pofalowania wpływa bezpośrednio na mechanizm przenoszenia ścinania poprzez rozkład szerokości efektywnej oraz moment statyczny. Bez wchodzenia w zagadnienia optymalizacji, czy szczegółowej walidacji numerycznej, praca koncentruje się na strukturze matematycznej współczynnika ks oraz jego wrażliwości geometrycznej. Uzyskane zależności stanowią przejrzyste narzędzie do analiz porównawczych oraz projektowania nowych rdzeni w płytach warstwowych, takich jak tektura falista.

EN

Sandwich plates with corrugated cores represent an important class of lightweight structural systems used in packaging, building envelopes, transport structures and engineered panels. The mechanical response of such systems is strongly influenced by the geometry of the periodic core, which governs transverse shear deformation and, consequently, the effective shear stiffness of the plate. While classical shear correction factors are well established for flat sandwich cores, no unified analytical framework exists for corrugated cores of arbitrary shape. This short contribution presents a concise mathematical formulation for the evaluation of the shear correction factor ks in sandwich plates with periodic corrugated cores of various geometries, including sinusoidal, trapezoidal, semicircular, elliptical and triangular waveforms. The formulation is based on energetic equivalence between the true cross-sectional shear strain energy and the corresponding Timoshenko plate idealization. The shear-stress field is reconstructed using a generalized geometric description of the corrugation profile and integrated over one periodic cell. The proposed framework highlights how the corrugation shape directly influences the shear-transfer mechanism through the first moment of area and the effective material width distribution. Without focusing on numerical optimization or detailed finite element validation, the paper emphasizes the mathematical structure of ks and its geometric sensitivity. The derived expressions provide compact analytical insight into the role of corrugation shape and may serve as a transparent tool for preliminary design and comparative studies of new cores in corrugated bords.

2

Response of sandwich structures with novel TPMS cores under cyclic uniaxial compression

Vasile Alexandru, Coropeţchi Iulian Constantin, Indreş Andrei Ioan, Constantinescu Dan Mihai, Sorohan Ştefan, Apostol Dragoş Alexandru

Journal of Theoretical and Applied Mechanics

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2025

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Vol. 63 nr 3

535--543

EN

This paper focuses on the compressive behavior of nine triply periodic minimal surface (TPMS) structures and one stochastic geometry, designed through an implicit modeling approach and fabricated using a stereolithography (SLA) technique. The compressive response is analyzed, with two topologies outperforming the well-known gyroid, in terms of rigidity and yield strength. Low cyclic testing at two strain levels highlights the good repeatability and stability of the proposed topologies, while comparing the specimens from an energy absorption performance and residual deformation perspective. The stochastic geometry exhibited the worst recovery rates, even though it had the second-best energy absorption capabilities for the single compression testing.

3

Examination of energy damping behavior of fiberglass reinforced sandwich structures with extruded polystyrene core material

Yavuz Ibrahim, Şenol Barış, Şimşir Ercan

Bulletin of the Polish Academy of Sciences. Technical Sciences

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2025

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Vol. 73, nr 3

art. no. e153430

EN

Composite materials are defined as new materials formed by combining two or more materials that do not mix, leveraging the best properties of each constituent. Composite materials are used in important industrial sectors such as aerospace and automotive due to their superior properties. In this study, XPS (extruded polystyrene) polymer foam was utilized as the core material. Glass fibers were combined with resin in a total of eight and twelve layers and applied to both the top and bottom of the core structure. Production involved both manual laying and vacuum bagging methods. Two types of glass fiber, weighing 200 g/m2 and 300 g/m2 , were employed. After production, the composites were cut to standardized dimensions, followed by three-point bending and low-speed impact tests. Impact experiments were conducted with a constant energy of 50 J. Results showed that the 200 g/m2 glass fiber composites experienced perforation in the eight-layer samples and rebound in the twelve-layer samples. Although greater deformation was observed in the impact tests of the 300 g/m2 glass fiber composites in the eight-layer samples compared to the twelve-layer samples, a rebound occurred in both. In three-point bending tests, the bending strength increased as the number of layers increased, and at the same number of layers, composites with 300 g/m2 properties showed higher strength than 200 g/m2 composites.

4

Failure analysis of hybrid sandwich structures with different cladding materials

Rogala Michał, Kaczyński Roman, Gajewski Jakub, Gawdzińska Katarzyna

Advances in Science and Technology. Research Journal

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2025

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Vol. 19, no. 7

56--69

EN

The dynamic development of the automotive and aviation industry has resulted in the continuous improvement of sandwich structures. These structures are lightweight and strong due to the application of lightweight materials as their core. The structure finds particular application in automotive or aerospace vehicles, which are focused on minimizing the weight of the structure, which translates into operating costs. The use of sandwich structures carries risks due to cladding debonding. The present study is intended to analyze the failure mechanism of structures based on aluminum foam with three types of cladding: aluminum sheet, carbon fiber plate and linen fiber plate. The structures were subjected to three-point bending during which the ability to transfer mechanical stress was observed, as well as the failure mechanism resulting from failure of the adhesive bond, core or cladding. Studies conducted revealed a significant contribution from the porous core. The tests showed similar load transfer and mechanical energy absorption capacities for the analyzed samples. The flax composite exhibited the lowest capacity, where destruction occurred from approximately 800N for the analyzed sample geometry. Despite similar load-carrying capacity, different types of structural failure were recorded, such as delamination, cladding debonding and metal foam pore cracking detailed in the paper.

5

Elastic buckling of a rectangular sandwich plate with an individual functionally graded core

Magnucki Krzysztof, Magnucka-Blandzi Ewa, Sowiński Krzysztof

Journal of Theoretical and Applied Mechanics

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2024

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Vol. 62 nr 1

171--185

EN

This paper is devoted to a thin-walled sandwich plate with an individual functionally graded core. The nonlinear shear deformation theory of a straight normal line is applied. A system of three differential equations of equilibrium of this plate is obtained, based on the principle of stationary potential energy, which is reduced to two differential equations and solved analytically. The critical load of the rectangular sandwich plate is determined. A detailed analytical study is carried out for selected exemplary plates. Moreover, a numerical FEM model of this plate is developed. The results of these calculations are compared with each other.

6

Investigation of the influence of debonding shapes and debonding locations on vibration behavior of sandwich structure

Demircioğlu Ufuk, Çakır Mutlu Tarık

Composites Theory and Practice

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2024

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R. 24, nr 1

39--48

EN

Sandwich structures are employed in many different fields including automobile, marine, and aircraft structures. However, debonding may take place at the core-face sheet interface, reducing the stiffness of the structure. Debonding may occur for a variety of reasons, including initial manufacturing faults, changes in service loads, tool drops, and foreign object impacts. It is critical to comprehend how debonding zones impact the vibration of sandwich structures because decreases in the natural frequencies (NF) could lead to a structure vibrating at resonance and lead to structural failure. This paper investigates the influence of debonding shapes and debonding locations on the free-vibration behavior of sandwich structures. Different sandwich structures that have varied debonding shapes at various locations are modeled using COMSOL MULTIPHYSICS. Debonding is modeled by using the CZM model. Validation studies were performed to validate the current study. After the validation study, free vibration analysis of all the sandwich structures was performed and the first six NF were obtained from the simulations. The results show the influence of the debonding shapes and debonding locations on the NF of the sandwich structures. From the results, it was observed that both the debonding shapes and debonding locations significantly change the NF of the sandwich structures. The debonding shapes cause a reduction and an increase depending on the debonding location. It was also revealed that both debonding shapes and debonding locations have a significant effect on the vibration behavior of sandwich structures. Using this method, the debonding shape and location, delamination shape, and location can be predicted using machine learning algorithms. This study includes free vibration analysis of sandwich structures with different debonding shapes and locations, and the results show that natural frequencies change depending on the debonding shapes and locations. This information can be implemented in machine learning for use in the field of damage detection and utilized to predict the shape and location of delamination in sandwich structures.

7

Buckling and free flexural vibration of an asymmetric sandwich beam with a functionally graded core

Magnucki K., Magnucka-Blandzi E., Sowiński K.

Archives of Mechanics

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2024

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Vol. 76, nr 4

335--355

EN

This paper is devoted to an asymmetrical sandwich beam with a functionally graded core with three different variants of boundary conditions. An analytical model of this beam, considering individual nonlinear shear deformation theory, is developed. Based on Hamilton’s principle, two differential equations of motion for this beam are obtained. These equations are solved analytically, and as a consequence, the critical forces and basic natural frequencies for each beam support variant are determined. Detailed calculations are carried out for selected exemplary beam structures, and their results are compared with numerical FEM analysis.

8

Vibration analysis of asymmetric sandwich rotating FG porous discs coated with agglomerated nanocomposite facesheets

Jazi Farnoosh Rasooli, Amir Saeed, Arshid Ehsan

Archives of Civil and Mechanical Engineering

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2024

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Vol. 24, no. 4

art. 201, 1--20

EN

The present research conducts free vibration analysis of annular rotating discs made from functionally graded porous materials, and nanocomposite reinforced carbon nanotubes face sheets. Pores distribution in the porous core is considered based on three different patterns, namely Nonsymmetric, Symmetric, and Monotonous ones across the thickness, and also, carbo nanotube dispersion in the face sheets is investigated randomly by considering their agglomeration effect. Kinematic relations of the mentioned structure regarding the shear deformation effects and based on the first-order theory are described, and then, variations of strain and kinetic energies by considering rotation via the calculus variation method are calculated. To extract the governing motion equations and associated boundary conditions, Hamilton's principle is employed, and then they are solved with the aid of the generalized differential quadrature method. After ensuring the correctness of the results obtained from the scripted code by comparing them in the simpler state with the previous research, the effect of different parameters such as pores’ distribution patterns, carbon nanotubes dispersion patterns and their agglomeration, core and face sheets thickness, and other parameters on the natural frequencies of the structure is investigated. Considering the obtained results, it can be found that increasing the porosity leads to a slight increment in the natural frequencies, generally, and increasing the carbon nanotubes’ mass fraction leads to significant enhancement in them. The outcomes of this study can be used in different industries, such as aerospace, military, and marine industries.

9

Numerical Study of the Energy Absorption Performance of 3D Printed Sandwich Structures

Estrada Quirino, Zubrzycki Jarosław, Reynoso-Jardón Elva, Szwedowicz Dariusz, Rodriguez-Mendez Alejandro, Marchewka Magdalena, Vergara-Vazquez Julio, Bastarrachea Aztlán, Silva Jesús M.

Advances in Science and Technology. Research Journal

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2023

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Vol. 17, no. 5

153--162

EN

Nowadays, Fused Deposition Modeling (FDM) is a powerful tool for manufacturing complex components, due to its customizability, low cost, accessibility, and fast prototyping time. It is an alternative for creating thin-walled structures, as it allows for novel designs. This article focuses on the design and numerical evaluation of 3D printed sandwich structures for energy absorption applications. For this purpose, five structures of Acrylonitrile Butadiene Styrene (ABS) were designed. To ensure optimal performance, the 3D printing parameters were optimized based on the corresponding literature. The structures had cores based on polygonal and cell arrangements. The effects of cross-section and mass on energy absorption were analyzed, and parameters such as energy absorption, peak load, mean force, and crush force efficiency (CFE) were determined during the study. The structures were assessed by out-of-plane compression tests. The numerical analysis was executed using Abaqus finite element software. Results showed that the energy absorption performance is primarily determined by the geometry and density of the structures. The best performance was found for a circular cellular structure, with a CFE of 0.884.

10

Testing the attenuation capabilities of ballistic shields made using 3D printing

Wierzbicka Karolina, Paszula Józef, Gieleta Roman, Komorek Zenon

Materiały Wysokoenergetyczne

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2022

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T. 14

58--75

EN

The paper describes a study of the blast wave energy absorption capabilities of sandwich ballistic shields. A comparative study of multilayer structures containing cores with different elementary cell shapes in their structure was performed. Energy-absorbing layers of different types of polymers were made. Tests of static and dynamic properties of the ballistic shield layers were carried out. The attenuation capabilities of these shields were determined by measuring the force acting on the base substrate of the shield.

PL

W pracy zaprojektowano i wykonano osłony balistyczne typu sandwich oraz przeprowadzono badania zdolności absorbowania energii fali podmuchowej. Przeprowadzono porównawcze badania struktur wielowarstwowych zawierających w swojej strukturze rdzenie o różnych kształtach komórek elementarnych. W badaniach przygotowano warstwy wykonane z różnych typów materiałów. Przeprowadzono badania właściwości statycznych i dynamicznych zaprojektowanych warstw osłon balistycznych. Zdolność tłumiącą wytypowanych osłon określano poprzez pomiar siły działającej na podstawę osłony.

11

Free vibration and buckling analyses of FG porous sandwich curved microbeams in thermal environment under magnetic field based on modified couple stress theory

Arshid Ehsan, Arshid Hossein, Amir Saeed, Mousavi S. Behnam

Archives of Civil and Mechanical Engineering

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2021

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Vol. 21, no. 1

89--111

EN

Porous sandwich structures include different numbers of layers and are capable of demonstrating higher values of strength to weight ratio in comparison with traditional sandwich structures. Free vibration and mechanical buckling responses of a three-layered curved microbeam was investigated under the Lorentz magnetic load in the current study. A viscoelastic substrate was considered and the effect of the thermal environment on its mechanical properties was assessed. The core was composed of the functionally graded porous materials whose properties changed across the thickness based on some given functions. The face sheets were FG-carbon nanotube-reinforced composites and the influence of the placement of CNTs was evaluated on the behavior of the faces. Using the extended rule of mixture, their effective properties were determined. Modified couple stress theory was used to predict the results in the micro-dimension. While the governing equations were derived based on the higher order shear deformation theory and energy method, and mathematically solved via Navier’s method. The results were validated with the previously published works, considering the effects of various parameters. As comprehensively explained in the results section, natural frequencies and critical buckling loads were reduced by enhancing the central opening angle. Moreover, an increase in the porosity coefficient declined the mentioned values, but increasing the CNTs content showed the opposite effect. The outcomes of this study may help in the design and manufacturing of various equipment using such smart structures, making high stiffness to weight ratios more accessible.

12

Change of the thermal properties of footwear packages by using of different polymer-based materials

Serweta Wioleta, Wójcik Justyna, Szałek Beata, Matusiak Małgorzata

Inżynieria Materiałowa

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2020

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Vol. 41, nr 2

14--19

EN

In this paper authors focused on the thermal properties of polymer materials used as footwear linings. The research concerned on the two types textiles: with two-dimensional and spacer structures. The monitoring of thermal conductivity property through the upper footwear materials is very important in order to create the qualitative and quantitative evaluation of them and make the recommendations to use of them in a footwear applications. In the next step of research, the two-layered packages were created and then the previously mentioned properties were measured. The optimal packages due to the thermal resistance and absorption were found based also on the other hygienic measures, like water vapour permeability and absorption.

PL

Zbadano właściwości przewodnictwa cieplnego polimerowych materiałów obuwniczych płaskich i przestrzennych. Materiały te są powszechnie stosowane w roli wyściółek i podszewek. Monitorowanie zjawiska przewodnictwa cieplnego materiałów cholewkowych jest bardzo ważnym czynni- kiem w ocenie jakościowej i ilościowej materiałów rekomendowanych do wykorzystania w produkcji cholewek. W kolejnym etapie na bazie wcześniej zbadanych materiałów pojedynczych utworzono pakiety dwuwarstwowe i wytypowano te, które w najbardziej optymalny sposób zabezpieczały stopę przed utratą ciepła, a jednocześnie pozwalały na zachowanie bardzo dobrych właściwości higienicznych pod kątem absorpcji i przepuszczalności pary wodnej.

13

Mechanical performances of metal-polymer sandwich structures with 3D-printed lattice cores subjected to bending load

Liu Zhaobing, Chen Hantang, Xing Shuaiqi

Archives of Civil and Mechanical Engineering

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2020

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Vol. 20, no. 3

368--384

EN

In this article, we propose a new class of metal-polymer architected sandwich structures that exhibit different mechanical behaviors. These lightweight sandwich structures have been made of aluminum face sheets and 3D-printed lattice cores with 2D (Bi-grid, Tri-grid, Quadri-grid and Kagome-grid) and 3D (face-centered cubic-like and body-centered cubic-like) topologies. Finite element simulation and experimental tests were carried out to evaluate mechanical performances of the proposed sandwich structures under quasi-static three-point bending load. Specifically, the damage-tolerant capability, energy absorption and failure mechanisms of these sandwich structures were investigated and evaluated through a combination of analytical, numerical and experimental methods. It is found that sandwich structures with 3D face and body-centered cubic-like cores can provide more excellent flexural stiffness, strength and energy absorption performance. These enhanced mechanical features could be further explained by a so-called ‘Stress Propagation’ mechanism through finite element analysis (FEA) that can facilitate sandwich structures with 3D cores, especially body-centered cubic-like one, to transfer bending loads from central lattice units across neighboring ones more efficiently than 2D cores. Furthermore, core cracking is the main failure mode for the proposed sandwich structures, which is primarily caused and dominated by bending-induced tensile stress followed by shear stress. It is worth mentioning that our findings provide new insights into the design of novel lightweight sandwich composites with tailored mechanical properties, which can benefit a wide variety of high-performance applications.

14

Numerical simulations of sandwich structures under lateral compression

Estrada Quirino, Szwedowicz Dariusz, Vergara Julio C., Solis José, Paredes Miguel A., Wiebe Lara, Silva Jesús M.

Applied Computer Science

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2019

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Vol. 15, no. 2

31--41

EN

The current paper analyzes the effect of the cross-section on the energy absorption capabilities of sandwich structures under compressive loads. For this purpose, several cross-section including triangular, square, hexagonal and circular shapes were analyzed using Abaqus software. According to the results the hexagonal shape is the most favorable cross-section to increase the crashworthiness performance of the structures up to 700% of CFE with respect to the square arrangement.

15

Transient forced vibration response analysis of heterogeneous sandwich circular plates under viscoelastic boundary support

Alipour M. M.

Archives of Civil and Mechanical Engineering

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2018

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Vol. 18, no. 1

12--31

EN

For the first time the transient bending analysis of a sandwich plate with viscoelastic boundary support is investigated in this study. Viscoelastic support consists of two sets of translational springs and dashpots connected in parallel along the in-plane and transverse directions. The sandwich plate is fabricated from heterogeneous face sheets where the material properties of each face sheets are assumed to be varied continuously in the radial direction according to a power-law function. Variations of the material properties of each face sheets are monitored by eight distinct inhomogeneity parameters. Therefore, the solution procedure may be used for a wide range of the practical problems. In order to investigate the effects of viscoelastic edge supports on the transient response of sandwich plate a wide range of the stiffness and damping coefficients of the edge supports in the in-plane and transverse directions are applied. Results of sandwich plates with the classical edge conditions as some special cases of the elastic/viscoelastic supports are compared with those extracted from the ABAQUS software based on the 3D theory of elasticity. The comparisons show that even for relatively complicated cases, there is a good agreement between the results.

16

Composite GFRP u-shaped footbridge

Chróścielewski J., Miśkiewicz M., Pyrzowski Ł., Wilde K.

Polish Maritime Research

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2017

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S 1

25--31

EN

The paper presents proposals for the use of glass fiber reinforced polymer composites for the construction of engineering objects, known and commonly used in the shipbuilding industry. An example of a pedestrian footbridge was used in this case, which, despite the considerable thickness of the structural material, was made using infusion technology in one production cycle. The designed and produced footbridge span is durable, dynamically resistant, incombustible, easy to install and maintain, resistant to weather conditions and also aesthetically interesting. For footbridge production environmentally friendly PET foam core may be used. It may come from recycling of used plastic packages and which is produced with less energy consumption process and much less CO2 emission. The load bearing part of the structure (skin) is made of polymer laminate reinforced with glass fabrics (GFRP).

17

Characterization of quasi-static behavior of honeycomb core sandwich structures

Katunin A., John M., Joszko K., Kajzer A.

Modelowanie Inżynierskie

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2014

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T. 22, nr 53

78--84

EN

Honeycomb core sandwich composite structures gained their popularity in aircraft, aerospace, automotive and naval industries mainly due to their superior flexural stiffness and very low mass, which cause that their application in engineering constructions becomes very attractive. Since they contain core and face sheets made of different materials with different properties their behavior under quasi-static loading is highly nonlinear and the forcedisplacement response contains characteristic zones caused by various mechanical phenomena. The characterization of such behavior under tensile and bending loading as well as characterization of failure mechanisms accompanied with quasi-static loading is the main goal of this paper. Obtained experimental results and their analysis allow for better understanding of occurred phenomena in such structures, which can be helpful during modeling of elements made of such sandwich composites as well as prediction of their behavior under various loading conditions.

PL

Kompozyty przekładkowe z rdzeniem o strukturze plastra miodu zyskały swoją popularność w przemyśle lotniczym, kosmicznym, samochodowym oraz okrętowym głównie dzięki swojej wyjątkowej sztywności oraz bardzo niskiej masie, co spowodowało że ich wykorzystanie w konstrukcjach inżynierskich stało się bardzo atrakcyjne. Biorąc pod uwagę fakt, że rdzeń i okładziny wykonane są z różnych materiałów o różnych właściwościach zachowanie tych struktur pod wpływem obciążeń quasi-statycznych jest wysoce nieliniowe, a odpowiedź siła-przemieszczenie zawiera charakterystyczne obszary spowodowane różnymi zjawiskami mechanicznymi. Charakteryzacja takiego zachowania podczas obciążeń rozciągających i zginających oraz mechanizmów zniszczenia towarzyszących obciążeniom quasi-statycznym jest głównym celem tej pracy. Otrzymane wyniki eksperymentalne i ich analiza pozwalają na lepsze zrozumienie zachodzących zjawisk w takich strukturach, co może być przydatne przy modelowaniu elementów wykonanych z kompozytów przekładkowych, jak również predykcji ich zachowania przy różnych warunkach obciążenia.

18

Influence of longitudinal edge profiling in sandwich panels on interpretation of experimental results

Chuda-Kowalska M.

Prace Naukowe Instytutu Matematyki i Informatyki Politechniki Częstochowskiej

|

2012

|

Vol. 11, nr 4

19-27

EN

Panels with a polyurethane foam core and thin metal facings are considered. Behaviour of these structures depends strongly on the shear rigidity. The recommended methods of identification of the Kirchhoff modulus of the core material GC give different results depending on the used sample. The FEM analysis are performed and the effects of longitudinal edge profiling are presented and discussed.

19

Poliuretanowo-stalowe konstrukcje sandwiczowe typu SIP

Datta J., Surawska E., Witkiewicz W.

Przemysł Chemiczny

|

2008

|

T. 87, nr 11

1115-1117

20

Experimental support for numerical simulations of energy absorbing structures

Ochelski S., Gotowicki P.

Journal of KONES

|

2008

|

Vol. 15, No. 1

183-217

EN

This paper presents experimental investigations of mechanical properties of materials used in the absorbing energy structures. Numerous experimental investigations are essential to develop a reliable numerical model of composite structures absorbing the impact energy. This model should correctly describe the dissipation of kinetic impact energy in the progressive crush process. Mechanical properties of composite materials like elastic modulus, strength, failure strains with influence of anisotropic properties are obtained experimentally. Different strength hypotheses are used for fibrous composites. The investigations on the complex stress state allow determining which of these theories describes the composite best. It was proved that both the matrix type and the structure of the composite have a very large influence on the SEA (Specific Energy Absorption), in particular on their crack propagation resistance. The dependence between the energy absorbed by a single energy absorbing element and a fragment of the structure absorbing the impact energy was discussed. Friction forces play the important role in the progressive crush of composites and they should be taken into account in developing a valid numerical model. Some authors state that the friction forces absorb 40% of the impact energy. The influence of failure strain rates on the absorbing energy capability, which is not clearly defined in the literature about composite structures, was also discussed.