Vol. 4, No. 1, January 2019
Abstract—The purpose of a shock absorber is to dampen the noise and vibrations from the application that it is used for. In the automotive industry, the purpose of a shock absorber is to reduce the noise created from the vehicle travelling and reduce the amount of vibrations that travel to the vehicle body in order to provide a smooth and comfortable ride [1]. In the aerospace industry, the purpose of shock absorbers is to reduce the impact on the fuselage created from take-off and landing.
For the marine industry, they are used to reduce the vibration caused by the engines in order to provide a smoother ride as well as reduce the amount of damage done to the body when the ship is docked or docking [2]. In structures, shock absorbers are used to minimize the damage to the building or bridge in order to keep the damages to a minimum during an earthquake [3]. In this paper the shock absorber application is applied in the aerospace industry; the automotive industry; the marine industry; and the structural industry.
Index Terms—Shock Absorber; Aerospace Industry;
Automotive Industry; Marine Industry; Structural Industry.
I. INTRODUCTION
There is a wide variety of application uses for shock absorbers and they come in a variety of shapes and sizes.
Because of their purpose and how they work, shock absorbers become an indispensible part of the system that they are used in. The energy that they create can be used to generate power for the particular system that they are used in [4]. Due to their application, not every shock absorber lasts the same amount of time. Some shock absorbers last longer than others. The type of material that the shocks are made of also affects their lifespan due to the fact that some materials are more durable than other. The application that they are used in also affects their life span. If a shock absorber on a car is used for rough terrain it will not last as long as a shock absorber that is used on a smooth surfaced road. Composite materials are a great way to reduce the weight of the shock absorbers, and increase the strength and lifespan [5]. The location, materials used, application and the type of shocks being used are all important points to consider as they will determine if the shocks will work or fail. There are several ways to make a shock absorber but the most popular ones are liquid extrusion [6] and hot bottom forming with is a very popular process in both the automotive industry and the aerospace industry [7]. Aside from being made from composite materials, most shock absorbers also have silicone base fluids as they tend to be less corrosive than other fluids and is capable of handling higher temperatures and pressure [8].
Published on January 18, 2019.
S. Spiteri is with the University of Bridgeport.
II. LOCATION
The location of a shock absorber is very important so that it can be effective in its application. A shock absorber is supposed to isolate the vibrations from one body to another in order to provide as smooth of a ride as possible [9].
A. Automotive
In the automotive industry, there are a few locations for shock absorbers based on the type of vehicle being evaluated. For a car, the locations for shock absorbers are behind the wheels to dampen the vibration from the road and underneath the engine to keep it attached to the car as well as keeping the engine from vibrating the whole vehicle.
Due to the location of these shocks, they are subject to higher stresses and tend to fail more often that the rest of the shocks [10]. On motorcycles there are two shocks on the front wheel and one spring supporting the back wheel. Since motorcycles are all about balance, it is important to keep balanced to help prevent the rider from falling when they go to make turns. On trucks shock absorbers have different functions. Depending on the size of the truck it might have more than the regular six shock absorbers. If the truck has a sleeping cabin in it, then it will have additional dampers to provide a smooth ride for the person in the sleeping section of the truck. Most trucks have spring shock absorbers in the front and air shock absorbers in the back wheels to account for the weight of the trailers. Trailers are also equipped with air type shock absorbers due to the heavy loads that they have to handle. The shock absorber is a vital part for a suspension system as it dampens the vibration that goes through the vehicle. According to ISO standard 2631-1, if the human body gets exposed to vibrations in the range of 0.5 Hz and 80 Hz for long periods of time, the risk of injury to the vertebrae in the lumbar region is tremendously high.
Eventually this type of damage can cause the nerves to stop functioning properly in that region [11].
B. Marine
In the marine industry, ships and boats use shock absorbers on their seats, steering wheels, engines and drive shafts. The shocks on the seats and steering wheel is mainly used on personal boats to absorb and dampen the impact as they tend to be more susceptible to the motion from waves due to their small size. Docks also have shock absorbers which help with the docking. Due to the nature of water and how ships are designed, it is not easy to stop over a short distance like cars. They require time and distance to stop, for that purpose when a boat is getting ready to dock, it starts to slow down and when it nears the dock, the shock absorbers absorb the impact and prevent the ship from hitting the solid concrete ground. This also prevents the ship from damaging itself, the dock and the crews both on and
Application of Shock Absorbers
Shaun Spiteri
Vol. 4, No. 1, January 2019
off the ship.
C. Aerospace
In the aerospace industry, the shock absorbers have a very important role and a complex design due to the force that they are subjected to. Each set of wheels on a jet aside from a lot of hydraulics, a jet also has one large shock absorber that acts as the main connection between the wheels and the airframe. For aircrafts, almost every part is made out of composite material as it is less likely to rust and is more durable than most any other metal. Due to the thermal shock that is experienced during take-off and landing, the shock absorbers are visually inspected for any cracks and deformation that might occur [12].
D. Structures
Most major structures in many countries are built with shock absorbers imbedded in the structure to prevent extensive damage to the structure itself and surrounding structures in case of earthquakes. Inland canals like the Panama Canal which provide a shortcut between one ocean and another have chambers that are separated by gates.
These chambers regulate the water level to allow the ship to go through, so they might raise the water level to allow a ship to go one direction and lower the water lever to allow it go in the opposite direction. These gates open to allow a ship to go through and close so that the water level could be raised or lowered depending what is happening at the time.
Depending on the how the gates work, whether they go up and down, or open and close, they require shock absorbers to absorb the impact so that they do not cause damage to themselves or their surrounding structures [13].
III. MATERIALS
There are many different types of materials that can be used for shock absorbers. Both internal and external materials can be changed. For the external, materials can be made out of rubber, aluminium, steel or a combination of composite materials. For the internal, shock absorbers can be either fluid filled, air filled or a combination of both depending on the application that they are being used for.
A. External Materials
Depending on the application for the shocks, a few different materials can be used. Aside from steel, other materials can be used are carbon steel and other variations of composite materials like fiber glass which reduce the overall weight and add strength to the body of the shock absorber. A new composite material that is becoming more popular is a form of aluminium composite materials due to it being light and extremely durable. Composite materials are becoming increasingly popular in both the automotive and the aerospace industries [14]. The leaf spring, has an elliptical shape and is composed of multiple bars of steel bolted to each other. The only way to add strength to it, would be to add more bars. Due to the elliptical shape, the leaf spring is very strong and durable, however it is also very heavy because it is usually made out of steel.
Composite materials can be used to lighten the weight as well as allow the spring to handle heavier loads [5], [15]. A material that is very popular in the aerospace industry due to
its strength and weight is titanium and titanium alloys.
Because of its structure and mechanical composition, titanium alloys can withstand very harsh environments [16]
B. Internal Materials
Different materials work better for different applications.
Fluids that can act as viscous dampers work great for high velocity shocks. These types of fluids can be split into two categories: Linear and Non-Linear Fluids. Linear fluids work great and have been used for a long time but Non- Linear fluids are starting to replace Linear fluids especially in high velocity applications due to better energy dissipation characteristics [17]. There are a few types of liquids that are used in shock absorbers but the most common type of fluid is the silicone fluid followed by oil because they are less corrosive than the rest of the fluids and have better damping ratio[8].
C. Failures
Failures on shock absorbers happen for a number of defects like manufacturing defects, no maintenance or even being used for applications that they were not designed to handle. Most failures happen at the weakest point of the shock which is the welded section where the support ring is attached to the tube that makes up the body of the shock absorber[18]. In the aerospace industry, a new concept for a crushable shock absorber is being tested for missions outside the Earth’s atmosphere. Due to its honeycomb design, when the platform touches the ground, the shock absorbers will crush just enough for the platform to touch the ground and stay level. This design will have less moving parts and is all a cheaper alternative to the traditional shock absorbing system for these types of platforms [19]
IV. APPLICATION
The main application of a shock absorber is to absorb the impact and dampen the vibrations that go through it [20].
For marine applications, the shock absorber is to absorb the keep the ship from hitting the concrete docks so that the cargo can be unloaded safely and prevent any damage to the ship, dock and the crew present at the time.
A. Automotive
Although the concept for hydraulic dampers came about in the early 20th century, it took a while for them to become popular [21]. In this industry the shock absorber can be used to generate power for the vehicle. For the shock absorber to generate power or electricity for the vehicle it would be best if a twin-tube design shocks are used. The fluid used in these designs would decrease and increase in pressure and create a larger damping force. This increased force also increases the amount of kinetic energy which can be stored for later use [22], [23].
B. Marine
Due to the vibration noise that ships and submarines produce, ship builders are starting to install dampers along the propeller-shafting system. Underwater vibration noise is a major problem for military ships and submarines that need to stay stealthy in order to go undetected for a long period of time. The dampers along the shaft work great not only for
Vol. 4, No. 1, January 2019 ships but also for boats and submarines. Because of the
cylindrical shape of the shaft, the dampers need to have multiple degrees of freedom in order to perform the function properly [24],[25].
C. Aerospace
In the aerospace industry, shock absorbers are used in the landing gear where the absorbers must dampen the shock and quickly dissipate the thermal energy created in order to execute a safe landing. Due to the heavy loads that the aircrafts and the helicopters carry, they experience high stress and strain on their landing gear. Because the back landing gear touches the ground first, the stresses seen tend to be higher than the front as they have to support the full weight of the aircraft or helicopter [26]. The landing gear of aircrafts and helicopters are very important for an aircraft in terms of landing, take-off and supporting the weight while on the ground. They are often the subject of failure which costs the company a lot of money in repairs and lawsuits [27],[28].
D. Structures
Civil engineers use multi degree of freedom shock absorbers to reduce the impact of earthquakes on the building infrastructure and reduce the amount of damage done. Because earthquakes can be very disastrous, the shock dampers need to be able to withstand vibrations from multiple angles and varying loads due to the fact that not every side of the building is supporting the same load. These types of absorbers tend to magnetic absorbers due to the nature of magnets. Magnets are able to handle larger loads for stationary objects [29].
Rubber shock absorbers can also be used but they are more effective on bridges and suspended highways as they provide a smoother ride for vehicles travelling on the road.
The rubber shocks can absorb the impact from colliding structures and reduce the amount of damage done. Thanks to the natural ability of rubber, it is able to under considerable compression deformation making it the most suitable for damping vibrations on a bridge that already experiences vibrations from multiple sources like vehicles and wind.
Having rubber shocks at certain intervals also helps with the expansion and contraction of the steel and cement in hot or cold weather [3].
V. TYPE
There are two major types of shock absorbers used for almost every application. One is the compression type of shocks while the other is the expansion type. Different types of applications require different types of shocks to perform the function along with varying sizes and shapes. Although compression and expansion shock absorbers perform differently and require different applications, their end result is the same.
A. Compression
The shock absorbers that are used on vehicles are compression type shock absorbers meaning that when a force is applied on them they compress. During compression they create a large amount of thermal energy. If used correctly, this thermal energy can be a great renewable
energy resource [30]. By using Faraday’s Law U=BI·v where U is the output of voltage, BI is the electromechanical coupling constant and v is the speed of the moving conductor, the energy created by the shock absorber can be used to provide more energy for the vehicle [31]. Another type of compression shock absorber is a rubber block used mainly on bridges to prevent excess damage to the structure during earthquakes. Since rubber has a high compression ratio, it is the ideal absorber for civil projects [32].
B. Expansion
Expansion type shock absorbers are used mainly to give leeway and dampen the impact from support ropes. It is used a lot in the marine industry where a personal sized boat would have an expansion shock absorber with the rope that is used to secure it to the dock. This provides a little bit of play in the rope so that the boat does not hit the docks during a storm. It also reduces the strain on the body of the boat when it is tied down because the shock would absorb the impact and prevent or reduce the amount of damage done to the boat itself.
VI. RESULTS AND DISCUSSION
The shock absorber acts as resistor and damper in order to provide a smoother transition of vibrations. It acts by absorbing the impact and vibrations so that they do not travel to the rest of the system [33]. Shock absorbers with fluids that have magnetic properties tend to me more resistant if the magnetic properties are high but if the magnetic properties are low then the resistance are lower [34].
Noise pollution is a major aspect of daily life which can harm the human body in more ways than one [35]. Vehicles create a lot of noise pollution as do ships and aircrafts.
Aircrafts and helicopters create a lot of noise due to the way that they are designed, unfortunately, the designs are slow to change due to the many components the engines have.
Airports in crowded areas have to close down for a certain amount of hours every night in order to reduce the noise pollution [36]. In an effort to reduce noise pollution, the FAA and the EASA are enforcing restrictions on the manufacturers to reduce the noise pollution. In the automotive industry, the suspension system is supposed to reduce the noise pollution created from the vibrations created by vehicle travelling on the road [37].
Due to the types of materials used, fatigue is bound to happen due to a combination of parameters. The mechanical response of the materials plays an important role in how fatigue will happen on the shock absorbing system. Fatigue starts with a slight deformation and slowly increases to a crack which then ends up allowing the material to crack [38].
Most modern shock absorbers use silicone based fluids as their dampers due to the fact they can be made into smaller bulk modules, are non-corrosive and have a higher operating range for both pressure and temperature [8]. Silicone based fluids are high popular in the aerospace industry and used in the landing gear for aircrafts also known as the oleo- pneumatic shock absorbers. These shocks have a combination of air and fluid which is used to dissipate the landing energy quickly and prevent high amount of
Vol. 4, No. 1, January 2019 vibrations from travelling to the fuselage especially when
landing can be a tedious job when there is a crosswind forcing the aircraft to go into unwanted positions [39],[40].
The shock absorbing system is a vital part for many applications especially in vehicles. According to ISO standard 2631-1, if the human body is exposed to vibrations between 0.5 Hz and 80 Hz for extended periods of time, the risk of injure to the vertebrae in the lumbar region is increased drastically. This can eventually cause the nerves to malfunction in that specific region. Since most people use some sort of vehicle for some period of time, having a good shock absorber can be the difference between feeling pain earlier on or not. A good shock absorbing system should minimize the vibrations cause from the vehicle travelling on the road [41].
VII. CONCLUSION
Shock absorbers have a really big impact on daily life especially when we travel. Shock absorbers provide a smooth ride when travelling by car, help prevent extensive damage to structures during earthquakes, help provide a smooth landing and takeoff, and prevent boats and ships from getting extensive damage when docked or docking.
Shocks come in varying sizes, shapes and are used for many applications. By absorbing the impact and vibrations from various applications, shock absorbers allow us to perform our daily tasks without too much harm to the body. Another way of shocks reducing the harm to the human body is by reducing the amount of noise vibration that is heard. Too much noise can rupture eardrums and cause internal damage.
Just like everything else, shock absorbers although very useful do not last forever and at some point, they will fail.
Different materials have different yielding points and different strengths as well as weaknesses. Depending on the application, shock absorbers can be either compression or tension style, made from different materials as well as have different types of fluids. Composite materials seem to be more popular as they are both lighter and stronger than the traditional method used. Silicone based fluids are also preferred over other materials due to the fluid being less corrosive and able to handle larger loads than other types of fluids.
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