A Contemporary Review on Knee Injuries and Protective Pads
497
2 Knee Pad Analysis
Most of the injuries occur due to impact forces, so the protective equipment is tested
using impact testing machines and strain gauge sensors. The pads made of different
materials and with different thicknesses are tested for shock absorption [15–17].
Sometime cadaver specimens are used to know the damage (impulse) in drop test
[17]. The force distribution of knee can be observed while kneeling. The kneepad of
hard polyethylene shell and soft foam material is tested and peak force is observed
using flexiforce sensor. The impact test and penetration test is used to identify the
strain energy at peak forces [6]. The polyurethane foam, LDPE foam, and viscoelastic
material are tested. The hard outer shell absorbs maximum energy and the foam
deforms easily to reduce the impact energy [18].
The penetration test on leg pads made of non-linear viscoelastic materials is tested
for different mass, velocity, and stiffness of the ball. The cannon uses pressurized air
to project the ball. The coefficient of restitution, peak force, deformation is observed.
The force transducer transfers output voltage which is used to obtain peak force.
Analysis based on recorded video of inbound velocity, outbound velocity, contact
time, and de-formation of the pad is observed for different impact velocities [19]. The
Image Pro Analyser software is used to identify the central impact and side-impact
which is used to obtain an equation based on deformation in terms of position of
inbound and penetration velocity.
3 Additive Manufactured Knee Pads
Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF) machines
are low-cost 3D printers that work on simple principle of extruding a thin filament of molten material through nozzle heated nozzle [20]. The most common
3D printing polymer materials are PolyLactic Acid (PLA), Acrylonitrile Butadiene
Styrene (ABS), Polyethylene Terephthalate (PETT), nylon, etc. The low cost and
ease of use material are PLA and the strongest one is ABS [21].
The additive manufactured (AM) method is used to create complex shapes,
lightweight geometries in less time and cost. The CAD model is prepared using lattice
structure. FDM is used to print the external rigid shell component with polypropylene material [20]. The internal foam is made using material 85% EVA and 15%
polyethylene. The shin pad and the commercial pads are tested under impact force.
It is observed that AM pads have a more constant stress slope, which implies a stiffer
pad.
The AM pads are evaluated in terms of their position, shape, area, thickness,
weight, flexibility, and ease of use. In general, polyester 51%, nylon 36%, and
polyurethane 13% are used. The commercial pads are not custom specific. AM pad is
prepared using a fused filament fabrication (FFF) method. The flexible thermoplastic
497
2 Knee Pad Analysis
Most of the injuries occur due to impact forces, so the protective equipment is tested
using impact testing machines and strain gauge sensors. The pads made of different
materials and with different thicknesses are tested for shock absorption [15–17].
Sometime cadaver specimens are used to know the damage (impulse) in drop test
[17]. The force distribution of knee can be observed while kneeling. The kneepad of
hard polyethylene shell and soft foam material is tested and peak force is observed
using flexiforce sensor. The impact test and penetration test is used to identify the
strain energy at peak forces [6]. The polyurethane foam, LDPE foam, and viscoelastic
material are tested. The hard outer shell absorbs maximum energy and the foam
deforms easily to reduce the impact energy [18].
The penetration test on leg pads made of non-linear viscoelastic materials is tested
for different mass, velocity, and stiffness of the ball. The cannon uses pressurized air
to project the ball. The coefficient of restitution, peak force, deformation is observed.
The force transducer transfers output voltage which is used to obtain peak force.
Analysis based on recorded video of inbound velocity, outbound velocity, contact
time, and de-formation of the pad is observed for different impact velocities [19]. The
Image Pro Analyser software is used to identify the central impact and side-impact
which is used to obtain an equation based on deformation in terms of position of
inbound and penetration velocity.
3 Additive Manufactured Knee Pads
Fused Deposition Modeling (FDM) or Fused Filament Fabrication (FFF) machines
are low-cost 3D printers that work on simple principle of extruding a thin filament of molten material through nozzle heated nozzle [20]. The most common
3D printing polymer materials are PolyLactic Acid (PLA), Acrylonitrile Butadiene
Styrene (ABS), Polyethylene Terephthalate (PETT), nylon, etc. The low cost and
ease of use material are PLA and the strongest one is ABS [21].
The additive manufactured (AM) method is used to create complex shapes,
lightweight geometries in less time and cost. The CAD model is prepared using lattice
structure. FDM is used to print the external rigid shell component with polypropylene material [20]. The internal foam is made using material 85% EVA and 15%
polyethylene. The shin pad and the commercial pads are tested under impact force.
It is observed that AM pads have a more constant stress slope, which implies a stiffer
pad.
The AM pads are evaluated in terms of their position, shape, area, thickness,
weight, flexibility, and ease of use. In general, polyester 51%, nylon 36%, and
polyurethane 13% are used. The commercial pads are not custom specific. AM pad is
prepared using a fused filament fabrication (FFF) method. The flexible thermoplastic