The effect of disbond on the efficiency and durability of a composite patch repair in mode I and mixed mode considering different patch materials

In this paper, considering different parameters and various patch materials, the effect of disbond on the efficiency and durability of a composite patch repair is investigated in mode I and mixed-mode. One of the most important aspects of the composite patch repair is the bond strength. Repair patch disbond may occur at the patch edges or the crack site. At first, the effect of different parameters such as repair patch material and Young’s modulus and thickness of the adhesive on the efficiency and durability of the patch is investigated. Then, the effect of the disbond site on the stress intensity factor (patch efficiency) and adhesive stress (patch durability) is analyzed in both modes I and II. The results show that disbond at the crack site leads to a further reduction in patch efficiency compared to the patch edge disbond, but when separation occurs at the patch edge, the adhesive stress and the disbond growth rate are higher. Also, when 15% of the patch is separated in the crack site, for the longitudinal and transverse disbond modes, the mean KI is increased by 8 and 4%, respectively, compared to the state without disbond. Thus, the longitudinal disbond mode is more critical.

Curing monitoring of bonded composite patch at constant temperature with electromechanical impedance and system parameters evaluation approach

As one of cost-effective maintenance methods, bonded composite patch repair has been receiving more and more attention in the engineering community since past decades. However, realizing real-time monitoring for curing process of bonded repair patch is difficult for most current techniques. In our work, a method based on electromechanical impedance and system parameters evaluation for structural health monitoring issues was developed, which could implement the online monitoring throughout whole curing process. Compared with the dynamic thermomechanical analysis results, the experiment data matches well. It demonstrates that the proposed approach can effectively monitor the curing process of composite repair patch at a constant temperature of 120 °C. Hence, the presented approach in this paper is expected to be a novel, robust, and real-time monitoring method for structural maintenance with the composite patch.

Structural repair on a composite aircraft fuselage damaged by fire.

Composite materials have been used on aircraft for decades with tremendous benefits. Through the use of these advanced materials we have seen a great increase in the aircraft’s efficiency, while improving the strength of the aircraft. Unfortunately due to the complexity of this material, it has not been used in large structural components such as the fuselage until very recently. Because of this, there are still some unknown aspects of implementing this material which have not yet been researched. One example that demonstrates this is a large section of an aircraft’s composite fuselage structure which has sustained fire damage. The main difficulties here are the unknown extent of damage caused by the fire, the unproven repair methods, and the durability of the repair patch itself. This report outlines some of these challenges as well as offers two different repair methods that are then analyzed using CATIAs FEA suite.

Structural repair on a composite aircraft fuselage damaged by fire.

Composite materials have been used on aircraft for decades with tremendous benefits. Through the use of these advanced materials we have seen a great increase in the aircraft’s efficiency, while improving the strength of the aircraft. Unfortunately due to the complexity of this material, it has not been used in large structural components such as the fuselage until very recently. Because of this, there are still some unknown aspects of implementing this material which have not yet been researched. One example that demonstrates this is a large section of an aircraft’s composite fuselage structure which has sustained fire damage. The main difficulties here are the unknown extent of damage caused by the fire, the unproven repair methods, and the durability of the repair patch itself. This report outlines some of these challenges as well as offers two different repair methods that are then analyzed using CATIAs FEA suite.

Investigating the Effect of Stepped Scarf Repair Ratio in Repaired CFRP Laminates under Compressive Loading

In this work the effectiveness of stepped repairs to damaged fiber reinforced composite materials is investigated by using previously validated numerical models which were compared with tested repaired composite plates. Parametric studies were carried out in order to assess the scarf ratio (i.e., step length to ply thickness ratio) influence on ultimate forces, displacements, stresses and stiffnesses. FE models with repair scarf ratios varying from the value of 20 to the value 60 with a step increase of 10 were developed. The numerical models allowed a direct comparison of the influence that the scarf ratio had to the strength and stiffness restoration of the repaired composite structure. The study verifies that the restoration of the strength of a damaged laminate depends largely on the size of the repair patch. Generally, the bigger the size of a patch, the stronger the repaired structure is, up to a critical threshold size. To maximize the strength restoration, it is advised that the number of steps in each patch are no less than the number of plies on the base laminate.

Electromagnetic-mechanical repair patch of radar-absorbing structure with electroless nickel–plated glass fabric damaged by lightning strike

This paper presents an electromagnetic-mechanical repair patch (EMRP) to restore the mechanical and electromagnetic (EM) wave absorption performance of a radar-absorbing structure (RAS) damaged by lightning strike. Several researchers have primarily focused on ensuring high repair efficiency, particularly in terms of the primary load-bearing properties of repaired fiber-reinforced plastics. However, no study has proposed a practical repair approach that considers the multi-functionality of the radar-absorbing structure. The EMRP method can be used to repair lightning strike damage in a radar-absorbing structure with electroless nickel-plated glass fabric, considering the need to maintain structural integrity and electrical continuity to achieve a high repair efficiency. Damage due to an artificial lightning strike was assessed in terms of area and depth of the damage using image processing, ultrasonic C-scan, and micro X-ray inspection. The EM characteristics of one-dimensional return loss scanning and the echo radar-cross-section level were measured to verify the stealth performance of the repaired radar absorber in the X-band. In addition, the tensile test results demonstrated that the repaired radar absorber had a high recovery rate of 93% compared to the pristine radar absorber. The experimental results obtained in this study validate the use of the proposed EMRP method in repairing radar-absorbing structures.