Shock loading is a concern in spring design. It occurs when a sudden force impacts the spring. Engineers need to understand how to design a spring that can manage these shock loads. Consider a vehicle's suspension system spring. An unsuitable spring can affect stability during sudden movements and potentially risk safety. This article covers essential topics like measuring the static spring load from shock force, understanding fatigue due to repeated shocks, and the potential benefits of a spring-damper combination. Knowing these elements can help engineers predict how a system reacts to sudden and heavy loading, supporting better design choices.
How to Determine Static Spring Load from a Shock Force
The first step in calculating the static load on a spring from a shock force is identifying the magnitude and duration of the shock force. This value can be obtained from empirical testing methods, such as drop tests. Alternatively, it can be derived from simulation data or historical operational data from similar applications.
To convert the shock force into a static load that the spring will endure, its best to look at the energy exchange from the part the spring supports that is exerted into the spring. These steps are outlined below:
- Determine the final velocity: Typically, a shock force will be described similar to "18g for 75ms". Assuming 0 starting velocity, you can use the kinematic equation v=v0+at to determine that the ending velocity will be 18*9.81*.075 = 13.2m/s.
- Determine the kinetic energy of the supported part: A part with a mass of 10kg, with the speed above will have a kinetic energy 1/2*m*v^2, or 1/2*10*13.2^2 = 877J
- Determine the Spring Displacement: The potential energy of a spring is equal to 1/2*k*x^2. Given you would know your spring constant, you can then back calculate your total displacement (x).
- Determine the Spring Load: You can simply use the Spring Force equation, F=k*x, to determine what your spring force is.
Keep in mind that this assumes the load is fully through the springs axis, and that the spring absorbs 100% of the shock energy. In many cases, this energy is also absorbed by a damper.
If you're looking to pick out a spring that fits your shock absorbing application, consider using the CoilsDB Spring Calculator . The calculator is built specifically to help you iterate on the best values for stiffness, stroke, and other factors of your choosing that may not yet be concrete as your design your shock absorber.
For selecting the right spring for shock loading, the key is to find the correct balance between stiffness and flexibility. For instance, in a scenario where delicate equipment is exposed to high-frequency shocks, a spring with a medium-to-low spring constant may effectively handle frequent, small shocks without significant deformation. However, in cases where sturdier equipment is subjected to infrequent, intense shocks, a spring with a high spring constant may be more appropriate. This type of spring can withstand large shocks without significant deformation. Hence, the choice of the spring constant, and consequently the static spring load, should take into account the specific shock characteristics and the equipment requirements.
Fatigue Considerations from Repeated Shock
Repeated shock loading may cause shock fatigue, which affects the lifespan and functionality of a spring, calling for certain design considerations.
The use of a material with notable fatigue strength may counter shock fatigue. Common choices include high-carbon steel or chrome silicon due to their fatigue strength. An example would be a spring in the suspension system of an off-road vehicle which encounters uneven terrains often. The use of such materials may prolong the spring's functional duration.
Implementing surface finishing strategies into the design could enhance fatigue resistance. Shot peening, a surface treatment strategy, raises the compressive residual stress on the surface of the spring, thereby enhancing the fatigue strength. This strategy is used in high-performance automobile racing, where severe shock loads are common, to enhance spring longevity.
Taking into account the effects of environmental conditions on the fatigue lifespan of a spring is beneficial in its design process. Environmental conditions such as temperature and humidity could alter the fatigue capacity of a spring. For instance, a spring in a high operating temperature setting such as an engine compartment may exhibit different fatigue behavior compared to a spring in a more temperate setting.
Therefore, addressing shock fatigue in spring design involves an integrated approach - utilizing material with superior fatigue strength, incorporating relevant surface treatment processes, and recognizing the effects of the environment on spring fatigue. This approach aims for consistent performance of the spring under shock loading conditions.
Combine with a Damper
In a spring system designed for shock absorption, an engineering solution often used involves pairing a spring with a damper to form what is known as a spring-damper system. This combination serves to manage two key elements of energy: absorption and dissemination. Here's how it works. The spring's role is to take on kinetic energy and then release it. The damper, in contrast, serves the function of distributing the absorbed energy, thus diminishing the effect of shock loads. Take a vehicle's suspension system for a real-world example. When shocks are created by road irregularities, they are initially taken on by the springs. After that, the dampers disseminate this energy over time, resulting in fewer residual vibrations.
When selecting a damper for a spring-damper system, a common choice is the hydraulic damper due to its advantageous damping behavior. This damper's damping coefficient - a variable determined by the viscosity of the damper's fluid and the size of its orifice - can be adjusted to regulate energy dissipation. However, the damping effect is not static and can be influenced by factors such as changes in temperature and the damper' s age. For instance, when the temperature rises, the hydraulic fluid's viscosity decreases, which can potentially decrease the effectiveness of the damping. To keep the damper working effectively, regular checks and servicing are recommended. Taking these considerations into account during the design process can help decrease the force of shocks, prolong the life of the system, and maintain safe operation.
In closing, designing a spring for shock loading involves a comprehensive grasp of shock force. The repeated shocks' fatigue effects should be evaluated during the design phase. Integrating a damper helps improve shock absorption, thus reinforcing the resilience of the system. Conducting actual testing of the designed spring is a necessary procedure to validate the design. This step allows for an assessment of the spring's capability to bear shock loads and its behavior under continual shocks.