Shock and vibration are ubiquitous in the world around us, but how do we tell the difference between the two? Although closely related, shock and vibration are fundamentally different forces that affect everyday life and industry. However, these forces generally do not pose a problem unless there is excessive shock and vibration. What is their main difference? How do you design solutions to potential problems?
All your questions about Shock and Vibration are answered in today’s guide, read on to find out more.
1. What are vibration and shock?
Vibration is a mechanical phenomenon that oscillates around a point of equilibrium. Oscillations can be periodic or random. Vibration may be part of the function of a device, such as violin strings. Alternatively, this could indicate an alignment or operation imperfection, such as a motor bearing. A vibrating table provides periodic, usually sinusoidal, vibration.
A sinusoidal sweep reveals the resonant frequency, which means the vibration-induced displacement is maximized. The resonant frequency should be well above any vibration loads the product may experience. The random vibrations normally induced in a HALT chamber excite all frequencies simultaneously. Both sinusoidal and random vibrations can occur in the product environment.
A shock is a pulse applied to a system. It’s a sudden acceleration. Drops, kicks, slams, or explosions are examples of shocks. The impulse is short, so the change in velocity, and acceleration can be quite large. To describe a shock pulse, use peak acceleration, duration, and pulse shape (half-sine, triangle, etc.). The unit g represents the multiple of the acceleration due to gravity and is a vector.
Shock loading is one way to induce vibrations within a system.
2. What is the difference between shock and vibration?
Although related in some cases, shock and vibration are both uniquely defined and resolved in the real world. Shock is a transient condition where the balance of a system is disrupted by a sudden applied force. In contrast, vibrations are periodic or random oscillating forces occurring near a point of equilibrium.
For example, when we strike a stationary object with a hammer, the resulting impact disrupts the balance of the object. Also, vibrations when plucking a guitar string. The string vibrates visibly, oscillating in waves. While different in nature, vibration is often present when the shock is also a factor. Let’s go back to the hammer example. When the hammer strikes an object, it transmits fast, powerful vibrations throughout the system, further damaging the object beyond the point of impact.
However, distinguishing between shock and vibration is critical when designing solutions for your product to mitigate these forces where needed.
3. Vibration can be divided into three types
Free vibration occurs when the system is activated, such as hitting a drum, and then allowed to vibrate freely. The shape and material of the drum will determine the sound produced. The different sounds are caused by different drums having different natural frequencies. The impacting surface or structure of a product tends to vibrate at its natural frequency.
Forced vibration is a time-varying load, displacement, or velocity imposed on a system. Disturbances can be periodic, steady state, transient or random in nature. An example of forced vibration might be your phone moving across the table (and onto the floor) when the vibrator feature alerts you of a phone call.
A poorly tuned vehicle motor can cause the entire vehicle to shake (coarsely) at idle. Damped vibration occurs when the energy of a vibrating system is dissipated through friction or some form of resistance. A vibrating system without damping may oscillate for a long time, whereas a damped system may quickly return to its equilibrium position.
4. Vibration and shock hazards
Almost any moving object needs to overcome variable frictional loads or uneven surfaces, creating vibrations within the system. The generation of vibration and shock may cause the following problems in your product.
- Fatigue damage
- Mechanical hardening
- Mechanical wear
- Loose fasteners
- Hydraulic or pneumatic leaks
- Connector separation
- Unwanted noise
5. What is vibration isolation?
When vibrational forces are present and disturb surrounding people, places, or equipment, there are solutions to mitigate transmission. Vibration isolation is achieved when an isolator is placed between the vibrating unit and its bracket, reducing the transmission of vibrational forces. The vibration isolation system allows the inertia of the equipment to be counteracted, thereby reducing the vibrational movement transmitted to the support.
6. How to achieve impact control?
As you might imagine, shock control is not the same as vibration isolation in practice. In order to reduce vibration, the transmitted power applied to the object is greatly reduced, thereby reducing the impact and transmission of vibration on the entire body.
Shock control is achieved when an isolator is placed between the shock/shock-generating unit and its support. This material receives and absorbs most of the kinetic energy and then releases/dissipates it in the form of heat over a longer period of time. Without some sort of material to absorb the impact, the kinetic energy transmits enormous momentum to the environment.
7. What characteristics should an isolator have?
In shock and vibration applications, isolators are critical to developing solutions that reduce the transmission of these forces. For vibration, the ideal isolator remains resilient throughout the lifetime of its installation, which means it must be reliable, strong, and flexible.
In addition, an ideal vibration isolator should have the ability to withstand the static weight of the device and the unbalanced dynamic force. Ideally, the natural frequency of the isolator should be lower than the interference frequency of the interfering unit. However, in some cases, an isolator with a higher natural frequency is better suited for the application.
8. Isolators for shock control
The ideal shock isolator must be capable of storing energy to handle harsh conditions. This means that the isolator must have sufficient deflection capability and stiffness to withstand the intensity and frequency of shocks. Additionally, the isolator must reform or “recover” shape before the next shock event to maintain ideal isolation and device operation.
Any item cannot avoid shock or vibration during transportation. Therefore, it is very necessary to carry out shock and vibration tests on your products. If you want to know more about this test system, please feel free to contact Linkotest.