Influence of matrix toughness and interfacial strength on the toughness of epoxy composites with ductile steel fabric reinforcement

In the last decades, several studies have been performed on polymers reinforced with steel cords or wires. However, the diameter of these steel reinforcements was still quite large (200 micron and more). Recently, stainless steel fibers were developed with a diameter down to 30 micron, which makes it possible to process steel fiber-reinforced composites in a similar way as carbon or glass fiber-reinforced composites. If a proper combination of the ductile steel fiber and a ductile polymer is chosen, a ductile composite should be achieved. This paper reports on the influence of the matrix toughness and the fiber/matrix adhesion strength on the ductility of the resulting steel fiber reinforced textile composite. Tensile tests have been combined with microscopic analysis to investigate the relation between the mechanical behavior and the observed damage morphology. It was found that distributed damage increases the toughness in a textile composite, because it softens the transversal structure that interlocks the ductile load-bearing yarns. This explains the counterintuitive observations regarding the influence of the matrix ductility and the fiber/matrix adhesion strength on the composite toughness. It was found that selecting a brittle epoxy matrix can lead to a ductile composite, because of the widely spread and dense cracking pattern that allows more strain to the ductile steel fibers. If the fiber-matrix adhesion is enhanced by introducing a silane coupling agent to the fiber surface, transversal cracks are prevented and the ductility of the composite drops drastically. These results for the textile composites are contrary to earlier findings on the UD and cross-ply counterparts

Mechanical properties and thermal conductivity of graphitic carbon nitride: A molecular dynamics study

Graphitic carbon nitride nanosheets are among 2D attractive materials due to presenting unusual physicochemical properties.Nevertheless, no adequate information exists about their mechanical and thermal properties. Therefore, we used classical molecular dynamics simulations to explore the thermal conductivity and mechanical response of two main structures of single-layer triazine-basedg-C3N4 films.By performing uniaxial tensile modeling, we found remarkable elastic modulus of 320 and 210 GPa, and tensile strength of 47 GPa and 30 GPa for two different structures of g-C3N4sheets. Using equilibrium molecular dynamics simulations, the thermal conductivity of free-standing g-C3N4 structures were also predicted to be around 7.6 W/mK and 3.5 W/mK. Our study suggests the g-C3N4films as exciting candidate for reinforcement of polymeric materials mechanical properties

Fatigue analysis-based numerical design of stamping tools made of cast iron

This work concerns stress and fatigue analysis of stamping tools made of cast iron with an essentially pearlitic matrix and containing foundry defects. Our approach consists at first, in coupling the stamping numerical processing simulations and structure analysis in order to improve the tool stiffness geometry for minimizing the stress state and optimizing their fatigue lifetime. The method consists in simulating the stamping process by considering the tool as a perfect rigid body. The estimated contact pressure is then used as boundary condition for FEM structure loading analysis of the tool. The result of this analysis is compared with the critical stress limit depending on the automotive model. The acceptance of this test allows calculating the fatigue lifetime of the critical zone by using the S–N curve of corresponding load ratio. If the prescribed tool life requirements are not satisfied, then the critical region of the tool is redesigned and the whole simulation procedures are reactivated. This method is applied for a cast iron EN-GJS-600-3. The stress-failure (S–N) curves for this material is determined at room temperature under push pull loading with different load ratios R0σmin/σmax0−2, R0−1 and R00.1. The effects of the foundry defects are determined by SEM observations of crack initiation sites. Their presence in tested specimens is associated with a reduction of fatigue lifetime by a factor of 2. However, the effect of the load ratio is more important

Interfacial fracture toughness of composite concrete beams

A test for measuring the interfacial fracture toughness of a bi-material interface, essentially for concrete overlaid pavements was developed. The measured interfacial fracture toughness of steel fibre-reinforced, roller-compacted, polymer modified concrete (SFR-RC-PMC) onto ordinary Portland cement concrete (OPCC) was found to be 52.0 J/m2 and 22.6 J/m2 for rough and smooth interfaces respectively. The experimental interfacial fracture toughness results can be suitable for the design of overlays on worn concrete pavements.In addition, the measured interfacial fracture toughness was used to predict the cracking trajectory of the composite beams under four-point bending (4 PB) tests. It was concluded that a single interfacial fracture parameter, the ERR (energy release rate) at interface, is an appropriate and sufficient parameter to assess the interfacial delamination performance of a composite beam under 4 PB flexure

Development of sputtered techniques for thrust chambers

Procedures for closing out coolant passages in regeneratively cooled thrust chambers by triode sputtering, using post and hollow Cu-0.15 percent Zr cathodes are described. The effects of aluminum composite filler materials, substrate preparation, sputter cleaning, substrate bias current density and system geometry on closeout layer bond strength and structure are evaluated. High strength closeout layers were sputtered over aluminum fillers. The tensile strength and microstructure of continuously sputtered Cu-0.15 percent Zr deposits were determined. These continuous sputtered deposits were as thick as 0.75 cm. Tensile strengths were consistently twice as great as the strength of the material in wrought form

Microfracture in high temperature metal matrix laminates

Computational simulation procedures are described to evaluate the composite microfracture behavior, establish the hierarchy/sequence of fracture modes, and the influence of compliant layers and partial debonding on composite properties and microfracture initiation. These procedures are based upon three-dimensional finite element analysis and composite micromechanics equations. Typical results for the effects of compliant layers and partial debonding, microfracture initiation, and propagation and the thermomechanical cyclic loading on a SiC/Ti15 composite system are presented and discussed. The results show that interfacial debonding follows fiber or matrix fracture, and the thermomechanical cyclic loading severely degrades the composite integrity

Elastic analysis of adhesion stresses for the design of a strengthening plate bonded to a beam

This paper presents methods for determining the elastic shear and peel stresses in an adhesive joint between a strengthening plate and a beam. Both closed-form and finite-difference solutions are given, allowing loading, temperature effects and plate prestrain to be considered in design. The method can be used to design strengthened beams with section properties that change along the beam (such as tapered plates), and can also be used to determine the sensitivity of an adhesive joint to bond defects. The results of some typical load cases and geometries are presented to illustrate the significance of adhesive stresses. (c) 2005 Elsevier Ltd. All rights reserved.</p&gt

Application of NDT thermographic imaging of aerospace structures

This work aims to address the effectiveness and challenges of Non-Destructive Testing (NDT) inspection and improve the detection of defects without causing damage to the material or operator. It focuses on two types of NDT methods; pulsed thermography and vibrothermography. The paper also explores the possibility of performing automated aerial inspection using an unmanned aerial vehicle (UAV) provided with a thermographic imaging system. The concept of active thermography is discussed for inspecting aircraft CFRP panels along with the proposal for performing aerial inspection using the UAV for real time inspection. Static NDT results and the further UAV research indicate that the UAV inspection approach could significantly reduce the inspection time, cost, and workload, whilst potentially increasing the probability of detection