Epoxy Interlayer Research Articles

The effect of temperature on the strength of epoxy adhesive joints under Brazilian testing

The paper reports the results of Brazilian tests on aluminum alloy specimens with an epoxy interlayer. ED-20 epoxy resin cured by polyamidepolyamine and diethylenetriamine is used as the interlayer. The stress state is varied by altering the tilt angle of the adhesion plane to the applied load in the range between 0 and 20 degrees. The experiments were performed at −50, +25, and +50°, and this corresponds to the range of climatic temperatures on the Eurasian continent. The experiments show that the composition of the curing agent affects differently the strength of the joints, depending on temperature and the angle between the action of the loading force and the adhesion plane.

Microscopic testing of carbon fiber laminates with shape memory epoxy interlayer

For the first time, microscopic testing has been performed on shape memory polymer composites (SMPCs) which were manufactured by commercial materials already used in aerospace. Results from micro-tests have been compared with those from conventional memory-recovery cycling on macro-scale. Two shape memory polymer composite (SMPC) laminates were fabricated with different shape memory (SM) interlayer: one in the form of an uncured epoxy powder and the other in the form of a thin epoxy foam. The latter, in particular has been studied to evaluate lightweight and stiff sandwich structures with SM properties. The assessment of the manufacturing process by a hot press moulding technique was assessed through micro scale analysis using SEM and MicroCT analysis. DMA analyses were carried out to understand the interaction mechanisms between raw constituents. A Vickers micro-indentation examination before and after heating was able to assess the shape recovery behaviour at the micro-scale level. A nano-instrumental indentation was used to characterise the shape memory response under different loads at elevated temperatures. Whilst an instrumented thermo-mechanical test allowed to investigate the shape memory behaviour at macro-scale level. Results allow identifying the recovery mechanisms at the micro-scale which are responsible for the shape memory performances at the macro-scale. The higher recovery ability of the SM foam is confirmed in comparison with bulk interlayers.

Fabrication and impact output voltage characteristics of carbon fiber reinforced polymer composites with lead-free piezoelectric nano-particles

Wearable Internet of Things (IoT) devices for sports require an innovative design of a self-powered technology that is able to wirelessly transmit and receive the signal (force, ambient condition) forms a body wearing item, relying upon the vibration/impact energy harvesting materials that possess lightweight but excellent resistance to intense exercise. In this study, piezoelectric hybrid carbon fiber reinforced polymer (CFRP) composite laminates are developed by embedding potassium sodium niobate (KNN) nano-particle filled epoxy interlayer, and the composite samples are successfully polarized. The output voltage of the samples due to impact load is then measured. The results show that a voltage higher than 50 mV is generated. Our work represents an important step forward in the development of piezoelectric CFRP composite materials for energy harvesting applications and opens the door for further development of lightweight, robust and efficient energy harvesting sport equipment.

Generalised fracture mechanics approach to the interfacial failure analysis of a bonded steel-concrete joint

Steel-concrete joints are often made by welded shear studs. However, this connection reduces the fatigue strength, especially in situations where locally concentrated loads occur with a large number of load cycles e.g. in bridge decks. In this paper the shear bond strength between steel and ultrahigh performance concrete (UHPC) without welded mechanical shear connectors is evaluated through push-out tests and a generalized fracture mechanics approach based on analytical and finite element analyses. The connection is achieved by an epoxy adhesive layer gritted with granules. In the tests, specimens made with various manners of preparation of the epoxy interlayer are tested experimentally. Numerical-analytical 2D and 3D modelling of a steel-concrete connection is performed without and with the epoxy interlayer. The model of a bi-material notch with various geometrical and material properties is used to simulate various singular stress concentrators that can be responsible for failure initiation. Thus conditions of crack initiation can be predicted from knowledge of the standard mechanical and fracture-mechanics properties of particular materials. Results of the fracture-mechanics studies are compared with each other and with experimental results. On the basis of the comparison, the 2D simulation of the steel-concrete connection without the epoxy interlayer is shown to be suitable for the estimation of failure conditions.

Study of imperfect bonding effects on sound transmission loss through functionally graded laminated sandwich cylindrical shells

Effects of imperfect bonding on sound transmission across a double-walled cylinder with FGM-core are studied by using the three-dimensional theory of elasticity. Aluminum and zirconia are inner and outer shells respectively, whereas the FGM-core is sandwiched between these layers. A very thin adhesive epoxy interlayer was applied in order to bond the adjacent layers. The imperfect bonding (adhesive epoxy interlayer) is modeled by a linear spring model. Infinite values of stiffness of linear spring reveal that there are no interfaces between the adjacent layers. However, the interface tractions do not exist and the layers are completely deboned from each other due to zero values of these parameters. The linear spring model is incorporated into the global transfer matrix with the aid of suitable transfer matrices. The proposed model is used to calculate the effects of imperfect bonding on TL of multi-layered cylinder which excited by an external plane wave. The obtained results are compared with those of other researches recently published in the literature. Excellent agreement is observed for high stiffness of adhesive bond. The results have also illustrated the fact that the existence of imperfect interfaces leads to the enhancement of the TL of sandwich cylindrical shell. Moreover, low stiffness of interlaminar adhesive bonding has more positive effect on the TL enhancement, particularly in high frequency range. Finally, it can be concluded that at high frequencies the spring layer model with low stiffness cannot transmit the waves because of more fluctuations.

Properties of Fiber Reinforced High Performance Cement Based Overlays for Orthotropic Bridge Decks

An increasing number of steel orthotropic bridge deck require repair due to fatigue cracking. For the rib to deckplate joint, a possible solution is to reinforce the fatigue prone deck plate by replacing the asphalt wearing surface with a reinforced high strength concrete overlay. However, this process has been proven very difficult to execute and consequently has some issues regarding durability. This paper reports on high performance fiber reinforced cement based overlay solutions with gritted epoxy interlayer for a typical orthotropic deck with inadequate plate dimensions. Material characterization of three mix designs includes determination of compressive and tensile strength, and post crack behavior by CMOD registration from 3PBT. Furthermore, the steel-concrete composite action in the positive and negative bending moment zone is investigated experimentally. The test results give insight into the concrete behavior, the steel-epoxy-concrete interaction, and are used as input for a 3D finite element model of the reinforced deck under fatigue loading. The results indicate that fiber reinforced cement based overlay solutions may be a viable option for orthotropic decks with inadequate deck plate thicknesses

The Influence of the Epoxy Interlayer on the Assessment of Failure Conditions of Push-Out Test Specimens

Connection between steel and concrete parts is frequently required in constructions where the steel-concrete joints are often realized by welded shear studs. In order to avoid stress concentrations, corrosion proneness, and other negative consequences of the welding process, steel-concrete connection without welded mechanical shear connectors is sought nowadays. Connection can be realized via an epoxy adhesive layer and gritted with granules. In the paper, the assessment of the push-out test configuration was performed from the generalized fracture mechanics point of view. The numerical-analytical modelling of a steel-concrete connection is performed without and with the epoxy interlayer, while 2D and 3D modelling is used. Thus conditions of crack initiation can be predicted from knowledge of the standard mechanical and fracture-mechanics properties of particular materials. The model of a bi-material notch with various geometry, and material properties is used to simulate various singular stress concentrators that can be responsible for failure initiation. Various manners of preparation of the epoxy interlayer are tested experimentally. Results of the fracture-mechanics studies are compared with each other and with experimental results. On the basis of the comparison, the 2D simulation of the steel-concrete connection without the epoxy interlayer is shown to be suitable for the estimation of failure conditions.

Substrate and material transfer effects on the surface chemistry and texture of diamond‐like carbon deposited by plasma‐enhanced chemical vapour deposition

Diamond‐like carbon (DLC), a thin amorphous carbon film, has many uses in tribological systems. Exploiting alternative substrates and interlayers can enable the control of the hardness and modulus of the multilayer system and improve wear or friction properties. We used XPS and atomic force microscopy to examine DLC that had been concurrently coated on an epoxy interlayer and a steel substrate by plasma‐enhanced chemical vapour deposition. sp2/sp3 ratios were calculated both by the deconvolution of the XPS C1s line and by the analysis of the C KLL Auger spectrum. Altering the substrate causes changes in the carbon bonding configuration, evident with the same trend through both analysis methods, although with differing absolute values, related to hydrogen and oxygen content. There is significant variation in the microscale surface texture, exhibited by both average roughness values and size and uniformity of surface asperities. This suggests that alteration to the film surface structure is a factor to be considered in addition to interface adhesion, hardness and elastic modulus in investigating substrates and interlayers for tribological coatings. Examination of a DLC film separately produced on a steel substrate, in comparison with that produced concurrently with a DLC coating on epoxy, shows the possibility of effects on the chemistry of the film through transfer of material from adjacent samples within the plasma deposition, related to heating, outgassing or sputtering processes. The possibility of such contamination has implications in coating parameter design and coating of multiple samples with plasma‐enhanced chemical vapour deposition. Copyright © 2012 John Wiley & Sons, Ltd.

Modes I and II interlaminar fracture toughness and fatigue delamination of CF/epoxy laminates with self-same epoxy interleaf

Interlaminar fracture toughness and delamination fatigue crack growth behavior were investigated for carbon fiber (CF)/epoxy laminates with the self-same epoxy interleaf. The matrix epoxy with a thickness of 50 μm was chosen as the interleaf material in order to clarify the effect of resin-rich layer thickness on the delamination fatigue crack growth behavior. Tests under mode I loading were carried out using double cantilever beam specimens. For tests under mode II loading, three-point end notched flexure specimens were used for interlaminar fracture toughness tests, while four-point end notched flexure specimens were used for delamination fatigue tests. The mode I properties (interlaminar fracture toughness and delamination fatigue threshold) of these epoxy-interleaved CFRP laminates were almost identical to those of the laminates without interleaf (base CFRP laminates). The effect of epoxy interleaf was completely different under mode II loading. The mode II interlaminar fracture toughness for the epoxy-interleaved laminates was 1.6 (initial value) and 3.4 (propagation value) times higher than that for the base CFRP laminates. The mode II delamination fatigue threshold of the epoxy-interleaved laminates was 2–2.3 times higher than those of the base CFRP laminates. While the toughness of the interleaf is the key factor under mode I, the thickness of interlayer is the key factor under mode II. The difference in the effect of the self-same epoxy interlayer on the interlaminar fracture properties under modes I and II loadings was discussed on the bases of the fractographic observations and mechanism considerations.

Deformation in Concrete with External CFRP Sheet Reinforcement

A detailed experimental investigation of local and global deformations of tensile-loaded, cracked, rectangular, concrete prisms reinforced with externally bonded carbon fiber reinforced polymer (CFRP) sheets was carried out. High and low modulus sheets were applied using three different thicknesses of epoxy interlayer between the sheet and concrete. It was found that the stiffness of the CFRP sheet had a dominant effect on global tension stiffening, whereas interlayer thickness had a dominant effect on local load transfer and damage formation. Thicker interlayers transferred load into through-cracked concrete over longer transfer zones, thereby increasing the spacing of subsequent cracks in the concrete. The combined effect on global stiffness of changes in transfer zones and crack spacing due to interlayer thickness was negligible. Increasing the stiffness of the CFRP sheet resulted in considerably increased global tension stiffening. Full field strain measurements by moire ´ interferometry revealed detailed information about local load transfer in the CFRP sheet, epoxy interlayer, and concrete in the vicinity of cracks.

1-1-3 Piezocomposite for hydrophone transducer

Abstract A piezocomposite structure was prepared in a 1-1-3 configuration by casting a soft epoxy interlayer between PZT rods and a stiff polymer preform matrix to maximize the hydrostatic sensitivity of 1–3 type PZT polymer hydrophone transducers. By minimizing the adverse contribution of the lateral components of the hydrostatic pressure, a figure of merit of 7,200 (10−15 m2/N) was obtained in an ambient atmosphere. By encapsulating the composite with cover plates, a stable pressure dependence (up to 14 MPa) of the hydrostatic voltage and charge coefficients was obtained. In addition, the interface configuration between the composite and cover plate was modified to provide pressure amplification proportional to the reciprocal of the volume fraction of the PZT rods in the composite. As a result the modified interface structure in 1-1-3 composite transducer gave significantly increased piezoelectric coefficients, and the figure of merit at 2MPa hydrostatic pressure was enhanced to more than 22,000 (10−15 ...