Aajm Ton Peijs

Hybrid composites based on polyethylene and carbon fibres Part 3: Impact resistant structural composites through damage management

Damage tolerance and impact resistance have become key parameters for composite materials in structural applications. In this paper a toughening concept for structural composites based on the hybridization of carbon fibres with high performance polyethylene (HP-PE) fibres is presented. Impact behaviour of hybrid HP-PE/carbon laminates was studied using a falling weight impact test. The effect of the addition of HP-PE fibres as well as the effect of the adhesion level of these fibres on the impact resistance of hybrid HP-PE/carbon structures was investigated. Hybridization results in structural composites exhibiting a significantly better resistance to impact damage than all-carbon laminates due to a change in energy absorption mode. After hybridization more energy is stored in the HP-PE component and consequently less energy is available for damage in the structural carbon component, resulting in a reduction in impact damage and improved post-impact properties.

Hybrid composites based on polyethylene and carbon fibres Part 2: influence of composition and adhesion level of polyethylene fibres on mechanical properties

Abstract Combining high performance polyethylene (HP-PE) and carbon fibres as reinforcing elements in so-called hybrid composite structures results in a unique class of structural materials possessing high damping and impact resistance. Mechanical properties of unidirectional HP-PE/carbon-epoxy hybrids have been studied, emphasizing basic mechanical characterization such as tensile, compressive and shear strength, initial as well as long-term modulus, vibrational damping and impact response. This paper describes the influence of overall composition and adhesion level of the HP-PE fibres on the mechanical properties of such hybrids.

Continuous-glass-fibre-reinforced polypropylene composites : I. Influence of maleic-anhydride-modified polypropylene on mechanical properties

This study investigates the influence of maleicanhydride-modified polypropylene (m-PP) on monotonic mechanical properties of continuous-glass-fibre-reinforced polypropylene (PP) composites. Maleicanhydride-modified polypropylene was added to the PP homopolymer to improve the adhesion between the matrix and the glass fibre. Three-point bending tests were performed on 0° and 90° unidirectional glass-fibre/PP laminates with various weight fractions of m-PP in the PP matrix. These tests showed an increase in both longitudinal and transverse flexural strength up to 10 wt% m-PP, whereas at higher weight fractions of m-PP a decrease in flexural strength was observed. No significant influence of m-PP on composite stiffness was observed. Additional mechanical tests on unidirectional glass/PP composites with 0 wt% and 10 wt% m-PP showed only a small increase in fibre-dominated properties such as longitudinal tensile strength and strain, whereas composite properties that are governed by the interphase, such as transverse, shear and compressive strength, showed significant increases as a result of matrix modification and an enhanced interaction between the glass fibres and the PP matrix.

Hybrid composites based on polyethylene and carbon fibres. Part 6: Tensile and fatigue behaviour

Abstract The tensile and fatigue behaviour of unidirectional carbon-high-performance polyethylene/epoxy hybrid composites has been studied, including the effect of hybrid design and surface treatment of the high-performance polyethylene ( hp-pe ) fibres. Results indicated that the tensile behaviour of carbon- hp-pe hybrids in both monotonic and fatigue testing can be interpreted, adopting the conventional ‘constant strain’ model for hybrid composites. Deviations from this constant strain model, so-called hybrid effects, were observed in monotonic tensile testing for those hybrid systems with the highest degree of fibre dispersion, incorporating either untreated or treated hp-pe fibres, whereas only the latter displayed synergistic fatigue performance. Hybrid effects under tensile loading conditions were in reasonable agreement with calculations accounting for statistical effects and stress concentrations as determined by finite element analyses.

A micromechanical approach to the viscoelasticity of unidirectional hybrid composites

Abstract Combination of the well-known rule of mixtures and the classical theory of linear viscoelasticity leads to a stress/strain relation that effectively predicts the viscoelastic behaviour of hybrid composites in uniaxial extension. From this theory, it is shown that the rule of mixtures does not apply directly to the dynamic quantities Ed and tan δ, whereas it can be used directly to correlate the storage and loss moduli of the composite to the properties of its components. The stress/strain relation is experimentally verified under isothermal conditions for a unidirectional, hybrid polyethylene-aramid/epoxy system both in constant strain rate and dynamic forced vibration experiments. The micromechanical model leads to numerical predictions which are in good agreement with experimental data on composite materials in various compositions.

Hybrid composites based on polyethylene and carbon fibres : Part 5: Energy absorption under quasi-static crash conditions

The crush performance of tubes from epoxy resin composite with intermingled high-performance polyethylene (I) fiber-carbon fiber hybrid with a const. fiber orientation, was studied. The sp. crush stress, being the sustained crush stress divided by the tube d., was used for sp. energy absorption comparison between 2 hybrid composites contg. 55 and 77% I fibers. The overall results showed that the post-crush structural integrity of carbon fiber-epoxy resin composite tubes can be improved significantly by hybridization with I fibers. However, no hybrid effect was obsd. with respect to sp. energy absorption due to a linear redn. in crush load with increasing amt. of I fibers.

Impact resistant and damage tolerant hybrid composite structures based on carbon and polyethylene fibers

Damage tolerance and structural performance are two essential requirements for a composite material Combining high-performance polyethylene (HP- PE) fibres and carbon fibres in a hybrid composite structure results in a new type of material with respect to impact-strength-stiffness since both fibres are to some extent complementary in properties. In this paper a toughening concept based on hybridization of carbon fibres with HP-PE fibres in an epoxy matrix is presented. Impact behaviour of hybrid laminates was studied using dart-impact tests and falling weight impact tests. Investigations focused on the effect of stacking sequence, fibre ratio and adhesion level of HP-PE fibres to optimize the impact performance of hybrid laminates.

Hybrid Composites Based on Polyethylene/Carbon Fibres

The mechanical properties of high-performance polyethylene (HP-PE) and carbon fibres are to some extent complimentary with respect to toughness, compressive strength and long term properties.

Influence of the interface on the performance of polyethylene fiber reinforced composites

This study investigates the effect of fibre surface treatment on the performance of polyethylene fibre reinforced composites. Polyethylene/epoxy composites have been studied, emphasizing basic mechanical properties such as tensile, compressive, flexural and interlaminar shear strength as well as fatigue and impact behaviour. Results showed that impact properties are strongly reduced with improved adhesion, whereas with respect to structural behaviour, properties are dominated by the anisotropy of the fibre rather than by the interface.

Influence of the interface on the longitudinal tensile strength of polyethylene fiber-reinforced composites

Statistical models are well known to describe the mechanics of failure of unidirectional composites in longitudinal tensile loading. In all the models previously developed it is assumed that the fibres are perfectly bonded to the matrix, but for polyethylene fibre reinforced composites this assumption is unrealistic. The model proposed in this paper takes into account the effect of the interfacial bond strength and consequently leads to better predictions of the strength of PE fibre reinforced composites.