A Study on Adhesive Strength of Co-Cured CFRP- Metal Multi-Material Joints and Joint Failure Detection Using Electrical Resistance Measurement

A study on bond strength of multi-material CFRP-Metal bonded joints and joint failure detection using electrical resistance measurement. A study on the bond strength of multi-material CFRP-Metal co-cured joints and joint failure detection using electrical resistance. A study on the bond strength of multi-material CFRP-Metal joints and the detection of joint failure.

A study on the bond strength of multi-material CFRP-Metal co-cured joints and joint failure. This has led to the concept of "multi-material design", in which hetero-joints between composites and metals have become an important issue. Although joining many materials using the co-curing method results in a lower bond strength than glue-bonded joints, this method can reduce the curing time since both the adhesive cure and the CFRP proceed simultaneously and enables health monitoring of nodes in real time using elec. resistance measurement because the carbon fiber directly contacts the metal surface, both of which are electrically conductive.

Electrical resistance was increased when the contact area between carbon fiber and metal surface was reduced, so it can monitor the fault detection at the multi-material connections. Based on the experimental results, it is feasible to monitor failures in multi-material connections between CFRPs and conductive metals in real time by measuring the change in resistance.

Introduction

The disadvantages of this method are the poor surface finish of the welded points and the development of high loads during the joining process. Among them, the connection using glue does not cause deterioration of the joint due to heat, because the temperature of the connection is not high, and it is possible to achieve high joint stiffness due to the face joint and ensure the hermeticity of the joint, but requires additional time for hardening. Some methods of joining many materials; (a) Bubble-induced plasticity in LAMP from [2], (b) SPR body and support plate shape [3], (c) Schematic arrangements illustrating thin-plate FSW [6], (d) MC procedure [10] and (e) Schematic of ultrasonic welding [11].

Therefore, joint structural health monitoring (SHM) studies are being conducted for driver safety. In this work, the fatigue strength was increased by 12.8% by mixing 2% of carbon nanotubes into the epoxy adhesive, and the fracture of the joint was diagnosed through the change in electrical resistance. In this research, we studied failure detection of multi-material joints through electrical resistance monitoring without adversely affecting or adding an additional step to the existing manufacturing process.

Figure 1. Several methods of the multi-material joining; (a) Plastic induced by bubble in LAMP from [2], (b) SPR body and supporting plate shape [3], (c) Schematic arrangements illustrating FSW in thin plate [6], (d) MC procedure [10] and (e

Literature Review

Structural Health Monitoring of CFRPs
Joining Method for CFRPs
Stress and Bending Moment Analysis of Single-Lap Shear
Surface Treatment for Metal
Detection of Joint Failures

He measured the resistance by the method of probes 2 and 4 and compared the piezoresistance and contact resistance of the composite. The special feature of this paper is to take into account the interlaminar behavior of the piezo-resistive material. 41, 42] focused on the numerical structural analysis of UD CFRPs and the change in electrical resistance. 1 (b) shows the body of the SPR developed for the CFRP joint and the support metal to prevent the CFRP from peeling damage.

The joint plate, which is covered by the upper plate and the lower plate, expands under the lower plate by impact and expands radially while touching the bottom of the die. However, these are point joints that cause high stress concentrations, damage the composite and require access from both sides of the joint. However, adhesive bonding must consider the surface of all different materials and requires additional curing time of the adhesive after the composite has cured, which takes a lot of time.

6 (a) and (b) show the tensile and shear stresses in the out-of-plane direction of the single-layer joint on the first layer of the composite adhesive. The phenomenon of wetting of the adhesive and the surface of the base material greatly affects the adhesive strength, which requires an increase in the surface energy of the base material or a decrease in the surface tension of the adhesive. Common surface treatment procedures include cleaning to remove foreign matter and oil, polishing to remove oxide film, chemical treatment to improve affinity and foreign matter removal, and primer treatment to improve surface affinity by applying a primer.

Fiber optic sensors were used to measure the stiffness of the structure and applied to Brillouin Optical Time Domain Reflectometry (BOTDR). In this paper, he used this observation system to detect the unusual deformation of the adhesive bond of the mast-supporting hull and the bulkhead. 2 wt% of CNTs were added to the epoxy adhesive, which increased the fatigue strength by 12.8% and the damage of the joint was monitored by measuring the change in electrical resistance.

Fault detection of the joints; (a) Fiber optic sensing by BOTDR [47], (b) Schematic diagram of the adhesion fixture of CNTs mixed epoxy [20] and PWAS interaction with lambda modes from [48]; (c) Symmetric Lamb mode and (d) Antisymmetric Lamb mode.

Figure 4. (a) Fiber alignment during the tensile loading and (b) Positive piezo-resistivity during the tensile loading from [42]

Part 1 – Multi-Material Joining between CFRPs and Metals

Part Introduction
Experimental

Materials
Sample Preparation
Characterization

Results and Discussion

Adhesive Strength of Single-Lap Joints
Shear Strength of Steel Bushings
Atmospheric Plasma treatment
Surface Analysis

Summary

Schematic diagram of (a) dimension and (b) fabrication of VARTM of the joint-cured single-lap joints. In order to improve the adhesive strength of the hardened joints, the metal surface was subjected to atmospheric pressure plasma treatment. As the roughness of the surface increases, the adhesive strength becomes higher due to mechanical interlocking.

In addition, due to the change in the chemical composition of the metal surface, the bond strength with the resin becomes strong and the bond strength increases. In general, the adhesive strength of the conductive adhesive is stronger than that of the co-curing. Adhesion strength of the plasma-treated single joints; (a) CFRP-steel co-cured joints and (b) CFRP-aluminum single overlap co-cured joints.

The results show that the bond strength between steel bushing and CFRP is significantly stronger than that of single lap joints. Two measurement experiments were performed to analyze the cause of the increase in adhesive strength after plasma treatment. As a result, the plasma treatment increases the hydrophilicity of the metal surface, which leads to an intimate contact between the adhesive and the metal surface, thereby increasing the adhesive strength.

To measure the adhesive strength of the multi-material joint, we fabricated single-lap joints and CFRP inserts with co-curing jointed bundles. In general, single lap joints bonded with conductive glue have stronger adhesive strength than spliced joints. However, the adhesive strength of the co-cured multi-material joints was improved by plasma treatment.

Plasma treatment increases the hydrophilicity of the metal surface and facilitates the contact between the polyester resin and the metal surface, which helps to improve the adhesive strength. Through this experiment, it was confirmed that the adhesive strength of the multi-material joint by the co-curing is good. In particular, it was found that the bond strength between aluminum and CFRP bonded single surface joints after plasma treatment was improved by about 300%, and the bond strength of steel was also improved.

Figure 9. Schematic diagram of (a) dimension and (b) manufacturing of VARTM of the co-cured single-lap joints

Part 2 – Structural Health Monitoring of CFRP-Metal Junction

Part Introduction
Experimental

Materials
Sample Preparation
Characterization

Results and Discussion

Pre-Test and Single-Lap Joint Using 2-Probe Resistance Measurement
SHM of Single-Lap Joints Joined by Conductive Adhesive
SHM of Co-Cured Single-Lap Joints
Influence of Plasma Treatment on Resistance Change

Summary

2- and 4-probe methods were used to monitor the change in electrical resistance due to joint deformation during a single lap shear test. To analyze the cause of the electrical resistance change during the test, the fractured surfaces were measured with an optical microscope (Nikon model NV150N). First, a peel test was performed to check the fault detection of the connection using electrical resistance.

The load change and electrical resistance change of the single lap shear test are shown in Figure. This is due to the release of the carbon fiber layer, not due to the crack at the connection. Rate of change of force-resistance of the CFRP steel connections during the test, resistance measured by the 4-probe method.

The decrease in electrical resistance of steel-steel single-lap joints is related to the deformation of the joint. However, the resistance change in the conductive adhesive is too small to be measured in SHM of CFRP-steel single-cut joints. Force and resistance rate of change of the steel-steel connections during the test, resistance measured by 4-probe method.

Co-cured joints showed a significant change in electrical resistance due to the reduction in the contact area of the joined surfaces as the carbon fibers and metal come into direct contact. The force and resistance change rate of the CFRP-steel co-cured joints during the test, and cracks can be detected using resistance change. The force and resistance change rate of the CFRP-aluminum co-cured joints during the test, and cracks can be detected using resistance change.

Strength and resistance change rate of the CFRP-CFRP co-cured joints during the test. Therefore, the slope of the resistance change rate before fracture and the adhesive strength were compared to confirm how the plasma treatment affects the electrical resistance change in the joint. The change of the electrical resistance in the joint is caused by the area of adhesion.

Figure 24. Schematic of the 4-probe resistance measurement by DMM 2002.

Conclusions and Recommendations for Future Work

Conclusions

Future work

Design of a hole clamping process for joining dissimilar materials: Al6061-T4 alloy with DP780 steel, hot-pressed 22MnB5 steel and carbon fiber reinforced plastic. The effect of adhesive bonds between aluminum and composite prepreg on the mechanical properties of carbon fiber reinforced metal laminates. The production process of simultaneously cured single and double lap joints and evaluation of the load-bearing capacity of simultaneously cured joints.

Optimization of the simultaneous curing of two different composites with the aim of minimizing the residual curing stresses. Optimal design of the co-cured double overlap connection consisting of aluminum and carbon epoxy composite. Thrust and delamination of core saw drill while drilling carbon fiber reinforced plastics (CFRP).

Delamination monitoring of laminated composites subjected to low velocity impact using small diameter FBG sensors. In situ health monitoring of bonded composite repairs using a novel fiber Bragg grating sensor arrangement. Proceedings of the Royal Society of London A: Mathematical, Physical and Engineering Sciences; 1995: The Royal Society.

Self-sensing achieved in carbon-fiber-polymer-matrix structural composites using the interlaminar interface as a sensor. In-situ monitoring of damage in CFRP laminates using AC and DC measurements. Correlation between mechanical damage behavior and electrical resistance change in CFRP composites as a health monitoring sensor.

Tuned Lamb wave generation and detection with piezoelectric wafer active sensors for structural health monitoring.