Numerical Analysis of the Bonded Composite Shape Effects under Thermal Loading in Aircraft Structures

The design of the optimal shape of patch with a good compromise between mechanical performances and manufacturing aspects can be sought in order to get the maximum structural safety-cost ratio. In this work an analysis has been conducted for development of a finite element methodology to circumvent the thermal effect problem in the bonded repair. Physical and geometrical parameters of the repair material were assumed to be variables, this method are based on two approaches: The first, have modified the patch shape by removing the two isosceles notches (h varied) for minimisation the heating size in the direction of loading. For the second step of the study, the same surface previously deduced are compensate in the other direction with varied the property module for the adhesive layer, for inducing a larger the area covering of crack tip and reduce the thermal stress. The values of thermal stresses obtained from the variation of these two parameters were found to be low compared to the obtained values for initial shape.

Stress–Strain Behaviour of Reparable Composite Panel with Step-Variable Thickness

There is an urgent problem of finding an economically viable method of maintenance and restoration of the bearing capacity of structures of various applications. Repair of structures with patches made of polymeric composite materials is one of the most promising repair technologies. However, an improper choice of parameters of the composite patch leads to unjustified increase in the structure mass and the cost of its further operation. These situations result from the lack of reliable methods for developing the repair process, which take into account the influence of the patch geometry and conditions for performance of repair works on the bearing capacity of the repaired structure. The mathematical model of the reparable composite shell–type panel taking into account inhomogeneity of transverse shear deformations at stepped variation of its thickness has been developed. In contrast to the classical theory of layered shells, the model allows simplifying a three-dimensional problem by setting of the displacement field on the layers’ interfaces and their linear interpolation over thickness of the panel, as well as considering the transverse shear deformations resulting from the strength, temperature, or shrinkage loading. According to results, the maximum rise in stresses in the case of a notched panel occurs in the weakened layer, and it is from this layer the failure of the structure will start. In the event of the patch, the panel surface opposite the reinforcement is the most loaded (i.e., susceptible to failure) surface. To confirm the reliability of the developed model, we compared the analytical calculations with the results of experimental and numerical studies of the deformed state of a panel of step–variable thickness by the method of holographic interferometry and modelling by the finite element method. Displacement fields available from experiments correspond to the predicted theoretical results. The resulting maximum error does not exceed 7%. The data obtained during numerical modelling allowed us to conclude that the accuracy of theoretical calculations is sufficient for engineering practice. Results of the work can be used to solve the practical problems such as determination of stress–strain behaviour of a damaged structure or structure after repair, specification of the permissible delamination dimensions, and defining of parameters of the bonded repair process.

Bonding Interface and Repairability of 3D-Printed Intraoral Splints: Shear Bond Strength to Current Polymers, with and without Ageing

This in-vitro study investigates the bonding interfaces reached by the conditioning of a splint material additively manufactured by digital light processing (AM base) as well as the shear bond strength (SBS) of resins bonded to these surfaces (repair material). Therefore, the AM base was either stored in dry for 12 h or wet environment for 14 days to simulate ageing by intraoral wear. The dry and wet group was bonded after physical and/or chemical conditioning to cylinders made from polymethylmethacrylate or four novel polymers allowing splint modifications. Blasted and methylmethacrylate (MMA)-conditioned Polymethylmethacrylate (PMMA) bonded to PMMA acted as the gold standard. The surface profiles revealed highest differences of Ra towards the gold standard in AM base conditioned with other than MMA after sandblasting. The adhesively bonded repair materials of the wet AM base were further aged in wet environment for 14 days. The SBS of the gold standard (25.2 MPa and 25.6 MPa) was only reached by PMMA bonded to blasted and MMA-conditioned AM base after dry (22.7 MPa) and non-conditioned after wet storage (23 MPa). Four repair materials failed to reach the threshold of 5 MPa after dry storage and three after wet storage, respectively. Non-conditioned AM base revealed the highest risk for adhesive fractures when using other resins than PMMA.

Towards a Robust Offshore Bonded Repair Strength Evaluation

Since the early 2000s, the number of Floating Production, Storage and Offloading (FPSO) units is increasing significantly. And so now, half of the fleet is over than 10 years old. As FPSO are mainly installed in tropical areas, with marine environment, high temperature and high humidity, corrosion is a permanent threat. Maintenance of steel structures become a challenge for oil major companies in offshore operation. Indeed, when allowable corrosion limit are reached, plates are to be repaired. However the current “crop and renew” technique implies a number of major issues for owners such as: “hot work”, i.e., welding; temporary structure weakening; necessity to empty, clean and vent oil tanks, leading to a long down time and an expensive solution. “Cold repair”, such as bonded repair, is an obvious solution, due to a short down-time and non-intrusively process. However, currently no standards or rules exist for this kind of repair and engineering faces problems as basic as strength qualification. To address the lack of knowledge on the strength assessment of bonded repair for primary structure, Bureau Veritas Marine & Offshore launched a Joint Industrial Project (JIP) named StrenghBond Offshore with oil companies, shipyards and suppliers. The main objectives of the JIP are to: Assess short term and fatigue strength of typical bonded repairs, Enrich knowledge of adhesive joints strength on typical offshore repairs cases, Enable a better evaluation of the margin between the actual strength of a repair and the design load, Validate the characterisation procedure for strength prediction of bonded assembly, Define a robust strength prediction method, Gather the collected experience in a industrially applicable guideline, Standardise qualification process for offshore composite bonded repairs. The project intends to provide a design approach for bonded reinforcement that is design orientated, accurate and recognized by the offshore industry.

A study on mechanical properties after bonded repair of sandwich composite materials

In this paper, an experimental study was conducted to determine the efficiency of repair methods for sandwich composites used as hull materials in leisure ships. The method was applied to external, scarf, and step patch repairs using an epoxy bond. The load was described in terms of the hogging and sagging moments applied to the hull by waves. Static and fatigue tests were performed to derive the recovery rate of repaired specimens. The experimental results indicated that the recovery rate of specimens with the scarf patch was the highest at 91.80% when the hogging moment was applied. However, the difference in the recovery rate between hogging and sagging moments was the lowest for specimens with the step patch, and the recovery rate was high at 89.96% and 85.15%, respectively.