The shock absorption property

Transcription

1 The shock absorption property Standard & Biomechanics Juan V. Durá Institute of Biomechanics of Valencia

2 The Institute of Biomechanics of Valencia (IBV) IBV is a Research and Development (R&D) centre. Its objective is the promotion and practice of scientific research, technological development, technical assessment and training of qualified personnel. Created in 1976, it is sponsored both by the Institute for Medium and Small Industries of Valencia (IMPIVA) and the Polytechnic of Valencia (UPV). In 1994 it became a Non Profit Association constituted by public and private entities interested in the development of Biomechanics in service of the social, industrial and economic interests in our environment.

3 "The science of mechanics is the noblest and above all others the most useful, seeing that by means of it all animated bodies which have movements perform all their action." Leonardo da Vinci ( ) Biomechanics is mechanics applied to biology. Biomechanics seeks to understand the mechanics of living systems. The motivation for research in this area comes from the realization that biology can no more be understood without biomechanics than an airplane can without aerodynamics. For an airplane, mechanics enables us to design its structure and predict its performance. For an organism, biomechanics helps us to understand its normal function, predict changes due to alterations, and propose methods of artificial intervention.. Y.C. Fung

4 Fields of Research: Groups and Sections ORTHOPAEDIC BIOMECHANICS analyses the pathologies which affect the human body in order to generate solutions. Sections Technical Aids Orthopaedic Implants OCCUPATIONAL BIOMECHANICS analyses the mechanical relationship between the human body and interacting elements Sections Furniture Ergonomics of the workplace SPORTS BIOMECHANICS studies sports practice to improve performance and the design of gear and materials Sections Footwear Gear and materials TECHNOLOGY APPLICATIONS develops laboratory and measurement equipment for applied biomechanical research

5 The biomechanics of sports surfaces Shock absorption: Deformation. Size of the deformation area (areaelasticity). Rigidity. Energy. Friction.

6 Deformation Stability problems. Foot fixation. AREA ELASTICA PUNTO ELASTICA

7 Impact: force peak, high force applied in a short time period. Shock absorption

8 Impact protection To eliminate high frequencies. To reduce forces. NOT DAMPED IMPACT DAMPED IMPACT

9 The impact transmission VERTICAL FORCE FZ1 TIBIAL ACCELERATION TFZ1 TFZ2 TIME CABEZA (MODELO AXIAL) (25 Hz) OJOS (30-80 Hz) HOMBRO (4-5 Hz) PULMONES BRAZO (16-30 Hz) RAQUIS (MODELO AXIAL) (10-12 Hz) MANO ( Hz) CAJA TORACICA (60 Hz) MANO - BRAZO ABDOMEN (4-8 Hz) PIERNAS (2-20 Hz) TAT1 TAT2 TIME SENTADO HEAD ACCELERATION TAC TIME DE PIE

10 Accelerometers: impacts. Biomechanical tests

11 Biomechanical tests: analysis of movement Video: joint angles, velocities. Force platforms: forces over the surface.

12 Biomechanical tests: pressure

13 Viscoelastic behaviour Force Force Deformation Dissipated energy Time Deformation

14 Viscoelastic behaviour Will change with: Impact velocity. Force Maximum force. Dissipated energy Deformation

15 Viscoelastic behaviour The sportsmen are able to protect themselves if the impact lasts less than 30 milliseconds. Most of the materials are more rigid when the impacts are faster. The shock absorption must be tested with fast impacts.

16 Mechanical tests Different mechanical testing devices and parameters have been used. But there are doubts about their capability for measuring the effect in athletes. - Drop tests. - Artificial athletes.

17 Protection against falls: head injuries. Drop tests

18 Artificial Athlete

19 Artificial Athlete

20 Shock Absorption 600Kg IMPACT FORCE ON CONCRETE 300Kg IMPACT FORCE ON SPORTS SURFACES Force Reduction = 100* 1- Force on sports surface Force on concrete

21 Standard vertical deformation Max. Force 1500N Stv Max. Deformation = 1500 * Max. Force StV Max. Deformation

22 Disadvantages of Artificial athlete Force Force reduction is not enough to explain the shock absorption. Energy is also related with shock absorption. Dissipated energy Deformation

23 IBV test for shock absorbing materials VISCOELASTIC MODEL σ = σ 0 (w) sin(wt) ε = ε0(w) sin(wt (w)) Dynamic Rigidity G = σ ε Loss tangent 0 0 (w) (w) tan( (w))

24 Example MATERIAL RF % A. PVC 6mm thick 19% B. C. Synthetic rubber 13mm thick Synthetic rubber 6.5mm thick 37% 20%

25 RIGIDITY (KN/m) Rigidity 80,000 70,000 A 60,000 50,000 40,000 30,000 20,000 10,000 0 B C -10,000

26 Loss tangent LOSS TANGENT B 0.80 A 0.60 C

27 Protection vs. Performance Is it possible to protect the athletes and to improve their performance? Is there an ideal sport surface?

28 Protection vs. Performance Biomechanics has proven the possibility of finding an optimal solution.

29 Problem: multisport surface Running: Forefoot impact Heel impact Long jump High jump Triple Jump Basketball Body weight

30 Advantages of Artificial athlete Simulation of fast impacts, the most dangerous for the athletes. The same machine is used for laboratory tests and on site tests. Reproducibility: ±2. Force reduction is related with the shock absorption.

31 Thanks for your attention