Composites have been used in various industries such as aerospace, automotive and infrastructure structures and recently in oil and gas industries. These materials have low weight and high specific strength and have high corrosion resistance for long periods, which increases their durability and efficiency and, as a result, their high reliability. In recent years, steel pipelines play a vital role due to the increasing demand for energy in the world. Many of these pipelines have been used for many years, and in these years, they have been corroded under factors such as high-temperature changes, high pressure, and chemical wear and need to be repaired or replaced. In the world, billions of dollars are spent annually to repair corroded or damaged steel pipes. A large amount of these costs are related to the old methods used in which the damaged part of the pipe is removed and replaced by a new piece of metal. This operation requires stopping the transfer operation, which causes the loss of a significant amount of possible income. In the last five years, several reports have been presented about the use of composite multilayers for the repair of pipelines, which shows the rapid growth of the use of this method in the pipeline industry.
In recent years, the use of natural fibers as a reinforcement or filler in the construction of composites has attracted the attention of many researchers and different sectors of the industry. Compared to other competing reinforcements such as glass fibers and mineral fillers, these fibers have many advantages, such as being environmentally friendly, lower density, higher strength, and specific modulus, and easy to modify the fiber surface, and they are also widely available. These fibers are cheaper than synthetic fibers and can replace synthetic fibers in many applications where it is preferable to save on the resistance properties of the product. The fact that natural fibers are renewable plays an important role in the use of these materials in the future, and the increasing interest of consumers to buy environmentally friendly products has increased the need for industries to use natural materials. Therefore, there is a wide range of materials that can be used as fillers and reinforcements in the construction of composites, which can be wood particles and fibers, animal-based fibers, agricultural waste particles and fibers (linen fibers, hemp, bamboo, straw, and stubble, rice bran, etc.) were divided. Therefore, the comparative investigation of composite properties obtained from materials with different shapes (fibers or particles) can be considered one of the most important research activities to increase the added value of products and reduce costs. Humans have been using natural fibers for many years to make various parts. The use of straw in mud walls, bamboo fibers in the construction of boats, goat wool and horse tail hair together with flowers in the construction of ovens, and palm fibers in the construction of boats and shelters are different examples of the use of natural fibers in the construction of various products that mankind has developed throughout history. They have benefited. Even today, researchers’ serious attention to the use of natural fibers in the manufacture of advanced composite parts shows the importance of this category of fibers.
Today, sandwich panels are used in air structures, military industry, rail transportation, ships, building construction, wind turbine blades, and the like. Structures made of two strong shells separated by a light core are sandwich structures. As the thickness of the structure increases, without a significant increase in weight, the ratio of bending strength to its weight increases dramatically. The material core is usually made of light materials such as foam or three-dimensional structures. Shells are also mainly made of light metals or layered composites. Fiber-reinforced layered composites are lightweight materials that have significant mechanical properties. Therefore, in recent years, researchers have focused on the design of materials and different patterns of cores of sandwich panels with composite tops. Layered composite materials reinforced with synthetic fibers such as carbon, glass, and Kevlar have been proposed as the most suitable material for a wide range of industrial applications. For example, these materials are widely used in aerospace industry structures, ship hulls in marine engineering, micro-electromechanical systems, and also reinforcing parts of concrete structures.