Alexei Volkov
A plastic hinge is a deformation of a section of a beam where plastic bending occurs. In structural engineering beam theory, it refers to the deformation of a part of a beam where plastic bending happens. It is designed to allow for flexibility and rotational movement without causing permanent deformation or failure of the part. In earthquake engineering, it is a type of energy damping device that allows plastic rotation or deformation of an otherwise rigid column connection. Plastic hinges are commonly used in electronic device enclosures, automotive components, and flip-top containers due to their flexibility, durability, and cost-effectiveness. They are also lightweight, corrosion-resistant, and non-conductive, making them suitable for electrical applications.
Characteristics and Values of a Plastic Hinge
| Characteristics | Values |
|---|---|
| Definition | Deformation of a section of a beam where plastic bending occurs |
| Function | Allows structures to displace without collapsing; acts as a "structural fuse" |
| Use Cases | Bridges, tall buildings, flip-top containers, electronic devices, automotive components, furniture, medical equipment, toys, kitchen appliances |
| Benefits | Lightweight, corrosion-resistant, flexible, cost-effective, safe (non-conductive), durable |
| Repair | Can be repaired through adhesive bonding, plastic welding, reinforcing with additional material, or metal pins; may need replacement |
| Analysis | Elastoplastic analysis can be performed using the hinge-by-hinge concept |
| Moment Redistribution | Depends on structure and loading conditions; may require moment capacity of hogging region to be twice that of sagging region |
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What You'll Learn
Plastic hinges in structural engineering
In structural engineering beam theory, a plastic hinge is a deformation of a beam section where plastic bending occurs. It is a type of energy damping device that allows plastic rotation or deformation of an otherwise rigid column connection. This is particularly useful in earthquake engineering.
Plastic hinges are designed to allow structures to withstand high loads without total collapse. For instance, in the event of an earthquake, a column with a plastic hinge will displace but not collapse. This is known as moment release energy, which reduces the total load that needs to be resisted to a manageable amount. While this prevents total collapse, it does mean that major repairs will be needed after the structure has been displaced. This philosophy is known as progressive failure, where damage is allowed but total structural failure is prevented.
Plastic hinges are typically used in large-scale structures such as bridges and tall buildings, rather than small-scale structures. In these large structures, the hinge method is usually incorporated into the beams rather than the columns. When a section of a beam experiences a fully plastic stress, a plastic hinge is formed, and this hinge has no additional moment resistance. As the load on a structure increases, the formation of plastic hinges changes the restraint characteristics, resulting in a redistribution of internal forces. This causes other sections of the structure to reach their full strength and develop plastic hinges, which can lead to a collapse mechanism.
The distribution of plastic hinges can be observed in structures damaged by earthquakes, where the hinge points are typically located at the beam ends. Analyses have shown that it is accurate to consider beams as rigid-plastic, with plasticity confined to plastic hinges at points. This assumption is sufficient for limit-state analysis, but finite element formulations can also account for the spread of plasticity along hinge lengths. By inserting a plastic hinge at a plastic limit load, a kinematic mechanism is formed, permitting unbounded displacement, which can lead to a controlled collapse.
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Plastic hinges as an energy damping device
In structural engineering beam theory, a plastic hinge is the deformation of a section of a beam where plastic bending occurs. Plastic hinges are used as energy damping devices in earthquake engineering to allow plastic rotation or deformation of otherwise rigid column connections. They are designed to fail safely and prevent catastrophic failure. This is known as the philosophy of progressive failure, where damage is allowed but total collapse is prevented.
Plastic hinges are particularly important in the design of bridges and tall buildings. In these structures, the hinge method is incorporated into the beams to manage lateral loads. By designing a plastic hinge into the column, it can displace beyond its normal range without collapsing. This additional displacement is known as moment release energy, which reduces the total load that needs to be resisted to a manageable amount.
The use of plastic hinges in structures allows for continuous analysis through the hinge-by-hinge concept. By inserting a plastic hinge at any section reaching its plastic moment, the structure becomes increasingly flexible until its stiffness is reduced, leading to imminent collapse. This flexibility enables the distribution of plastic hinges in beams, columns, and supports, with hinge points typically appearing at the beam ends.
Plastic hinges also play a role in the finite element nonlinear analysis of structures using tools like SAP2000. By studying the distribution of plastic hinges when a structure is damaged in an earthquake, engineers can understand the formation of plastic hinges and the resulting flexibility. This knowledge helps in designing structures that can withstand seismic events with reduced load case damping to prevent double-counting of energy dissipation.
The concept of plastic hinges is integral to the design of energy damping devices in earthquake engineering and structural engineering. By allowing controlled deformation, plastic hinges prevent total collapse and enable the safe management of loads in bridges and tall buildings.
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Plastic hinges in injection moulding
In structural engineering beam theory, a plastic hinge is a deformation of a beam section where plastic bending occurs. It is a type of energy damping device that allows plastic rotation of an otherwise rigid column connection. This concept is used in earthquake engineering to prevent total collapse.
Plastic hinges are also used in injection moulding to provide flexibility and rotational movement. They are designed with specific geometry and dimensions, including thin sections or living hinges, to enable bending or pivoting without permanent deformation. This is achieved through the inherent elasticity and flexibility of certain plastic materials, such as polypropylene and polyethylene, which can endure repeated cycles of bending or flexing.
Injection-moulded plastic hinges offer enhanced safety due to their non-conductive properties, making them suitable for electrical and electronic applications. They are commonly used in flip-top containers, electronic device enclosures, and automotive components, providing smooth and reliable movement.
Designing plastic hinges requires careful consideration of material selection and thickness. The plastic must be thin enough for flexibility but thick enough to withstand hundreds or thousands of movements without tearing or fracturing. Polyethylene and polypropylene are ideal choices due to their high melt flow, tensile strength, and ability to handle thickness changes during the moulding process.
Overall, plastic hinges in injection moulding offer enhanced versatility, durability, and cost-effectiveness by reducing the number of assembly components and manufacturing costs.
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Plastic hinges in electronic devices
Plastic hinges are an essential component in various applications, including electronic devices and structural engineering. In the context of electronic devices, plastic hinges offer several advantages that make them a popular choice for manufacturers and consumers alike.
One of the key benefits of plastic hinges in electronic devices is their corrosion resistance. Unlike metal hinges, plastic hinges do not rust or degrade over time, ensuring a longer lifespan and reducing maintenance concerns. This is especially important for devices that may be exposed to moisture or varying environmental conditions.
Plastic hinges also offer enhanced flexibility. They can endure repeated cycles of opening and closing without losing their structural integrity. This makes them ideal for devices with moving parts, such as laptop screens or flip phones, where hinges need to withstand frequent use without failure.
The versatility of plastic hinges is another advantage. Plastic can be molded into complex shapes, allowing manufacturers to create customized hinge designs that meet specific application requirements. This versatility also extends to the types of devices plastic hinges can be used in, ranging from small gadgets to larger equipment.
Safety is another critical factor in electronic devices, and plastic hinges offer a distinct advantage in this area. Plastic is non-conductive, reducing the risk of electrical hazards. This makes plastic hinges well-suited for use in electrical and electronic applications, where they can enhance user safety and help prevent accidents.
Additionally, plastic hinges are cost-effective. They are typically more affordable than metal hinges, making them a financially viable option for mass production. This cost-efficiency, coupled with their durability and versatility, contributes to their popularity in the manufacturing industry.
In summary, plastic hinges in electronic devices offer a combination of corrosion resistance, flexibility, versatility, enhanced safety, and cost-effectiveness. These advantages make them a preferred choice for manufacturers and consumers, ensuring both functionality and reliability in a wide range of electronic products.
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Plastic hinges in automotive components
In structural engineering beam theory, a plastic hinge is the deformation of a beam section where plastic bending occurs. It is a type of energy damping device that allows plastic rotation in an otherwise rigid column connection.
In the context of automotive components, single and multi-joint hinges are used at various points in a vehicle. These hinges are typically fitted with metal-rolled bearings with a PTFE coating. However, to achieve a low-backlash system, these bearings need to be recalibrated, which can be a laborious process.
On the other hand, all-plastic bushings can be used as an alternative. These bushings calibrate themselves through the effect of heat during the e-coating process, resulting in a low-backlash bearing even with a coarse sheet metal bore. Plastic hinges in automotive components offer several advantages:
- Corrosion resistance: Plastic hinges are corrosion-resistant, eliminating concerns about rust or degradation over time.
- Flexibility: Plastic hinges provide excellent flexibility, enabling repetitive opening and closing without losing structural integrity.
- Cost-effectiveness: Plastic hinges are cost-effective, making them a suitable choice for mass production.
- Safety: They are non-conductive, reducing the risk of electrical hazards and making them safer for electrical and electronic applications.
- Customization: Plastic hinges can be molded into complex shapes, allowing versatile and customized designs to meet specific automotive requirements.
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Frequently asked questions
A plastic hinge is a deformation of a beam where plastic bending occurs, allowing free rotation without resistance to the moment.
Plastic hinges are used in structures like bridges and tall buildings to prevent total collapse during earthquakes or other load-bearing events. They act as a "structural fuse," allowing for controlled failure and reducing the total load that needs to be resisted.
A plastic hinge enables large rotations at a constant plastic moment, increasing the structure's flexibility until it reaches imminent collapse. This helps in redistributing moments and analysing the structure's behaviour.
Plastic hinges offer lightweight, corrosion-resistant, and cost-effective alternatives to metal hinges. They provide excellent flexibility, durability, and versatility in design, making them ideal for electronic devices, automotive components, and packaging.
Plastic hinges are designed with specific geometry and dimensions, incorporating thin sections or "living hinges" to enable rotational movement without permanent deformation. Repairs can be made using adhesive bonding, plastic welding, or reinforcing with additional material or metal pins.
