13th International Symposium on Advanced Science and Technology in Experimental Mechanics

Study of Development of Underfloor Material that Reduces Risk ofFemur Fractures Due to Falls

Oct. 30-Nov. 2, 2018,
Kaohsiung City,Taiwan (ROC)- Investigation of Relationship Between Load on Femur and Hardness
and Thickness of Underfloor Materials -UNIVERSITYOFYAMANASHI

Takuya YAMASHITA, Yasumi ITO, Ryuichi YAMADA, Sonoka OKURA, Yoshiyuki KAGIYAMA and Tetsuya NEMOTO
University of Yamanashi
E-mail：g20tm026@yamanashi.ac.jp, yasumii@yamanashi.ac.jp

Results & DiscussionIntroduction

However, although it has been suggested that the effect of
the thickness of the underfloor material is effective infurther reducing the impact load, it has not been possible tomeasure the effect.
In this study, we prepared three types of flooring materials
with different hardness and varied their thickness toinvestigate the effect of the thickness of the underfloor
material on impact absorption. Based on the results, we
examined the effective design for fall fracture prevention
flooring material.

Others

The relationship between the maximum impact load and the underfloor thickness for each floor materials

Dementia

Fracture load

6.0
5.0
4.0
3.0
U-1

2.00 5 Without

Causes requiringlong-term care Stroke
Fracture･Fall
12.5 % Weakness• The reduction rate of the single layerof floor material is 5.37 [%].
• It is possible to reduce the load of
25.7~52.8 [%] by laminating the floorbase material.
• It is less than the elderly fracture load
(3440N) when using S + U-2 (7, 8mm).
• It is possible to reduce the risk offracture by using this flooring material.
• As the underfloor material thickness
increases, cushioning performance
improves and maximum impact loaddecreases.

7.0
Maximum impact load [kN]

The number of proximal femur fractures in Japan today is increasing every year, and 77.7% of
these injuries are caused by falls [1]. In 2019, the number of one to three causes of nursing careneeds among the elderly are diseases, while falls and fractures are the fourth, accounting for12.5% of the total [2].
Our research has shown that a laminated flooring material, which consists of a hard surface layerof floor covering material and a soft cushion layer of underfloor layer, can reduce the risk offracture by dispersing the impact that the bone receives during a fall, thereby reducing the impactload.

Underfloor

U-2

U-3

6
78
Underfloor thickness[mm]Shock absorption mechanism
Floor material single layer

Laminated flooring

It only disperses the impact over a wide areaand does not absorb the impact but
permeates it.

Surfacefloor material disperses the impact, andunderfloor material absorbs the impact, reducing
the maximum impact load.

Composition ratio of causes requiring long-term care

Materials & Methods
Surface layer
Underfloor layer
Structure of laminated flooring

The effect of spreading the impact of a fall over a wide area.
Underfloor layer
Absorbs dispersed impact and suppresses impact.

Relationship between underfloor material hardness and maximum impact load

Underfloor layer thickness 6 [mm]Underfloor layer thickness 7 [mm]Underfloor layer thickness 8 [mm]Cross section of the flooring used（Picture of S + U-1）

Underfloor layer thickness 6 [mm]Underfloor layer thickness 7 [mm]Underfloor layer thickness 8 [mm]Cross section of the flooring used（Picture of S + U-2）

Underfloor layer thickness 6 [mm]Underfloor layer thickness 7 [mm]Underfloor layer thickness 8 [mm]Cross section of the flooring used（Picture of S + U-3）
Details of floor materials

Variety

SymbolMaterial

Surface layer

SU-1
U-2
U-3

PVC+CaCO3
EVA

Underfloorlayer

Thickness[mm]
46, 7, 8PE

ASKER CHardness [-]235262

Area [mm2]Stress [MPa]

U-1

U-1
U-2
U-30

There is no significant increase in stress at aconstant gradient up to a strain of around 0.8.
U-2

0.5
Strain [-]1

U-1: Soft underfloor material
U-2, U-3: Hard underfloor material

It continues to rise with a constant gradient up to
the strain of 0.2, and reaches the "plateau region"
from the strain of 0.2 to 0.6. After that, the bubbles
are destroyed and the base metal is crushed.
U-3
It continues to rise with a constant gradient up to
the strain of 0.1, and reaches the "plateau region"
from the strain of 0.1 to 0.5. After that, the bubbles
are destroyed and the base metal is crushed.

Details of the impact testing machine that reproduces falls
Impactor

Accelerometer

Unit : mm

Pendulum arm
750
Axis of rotation
700
Fall height
Dummy skin Specimen

Loadcell

20Base300

050100
ASKER C Hardness [-]

6.0
5.0
4.0
3.0
2.0
1.0
0.0050100
ASKER C Hardness [-]Underfloor layer 8mm
6.0
5.0
4.0
3.0
2.0
1.0
0.0050100
ASKER C Hardness [-]Relationship between underfloor material hardness and maximum impact load shows themaximum impact load tends to decrease as the hardness increases. However, the maximum impact
load increases around the ASKER C hardness of 50. This suggests that it is suitable for the surface
material used in this experiment to increase the ASKER C hardness as much as possible when theASKER C hardness is 50 or less, and to decrease the ASKER C hardness when the ASKER Chardness is 50 or more. This tendency becomes more pronounced as the thickness of underfloor
material increases.

Conclusions(1)Compared with a single layer of flooring, the shock-absorbing effect of the underfloor inaddition to the shock-dispersing effect of the flooring material improved the shock-absorbing
performance of the laminated the surface layer and the underfloor layer.
(2)By increasing the thickness of the underfloor material, the impact load tended to decrease
regardless of the hardness of the underfloor material. The effect of increasing the underfloor
thickness was most pronounced for medium hard underfloors.
(3)When U-2 was used as the underfloor material, the fracture load of the elderly was less than
3440 [N] when the thickness was 7 or 8 [mm]. And the maximum impact load of U-3 was lower
than that of U-2 when the thickness was 8 [mm].

Acknowledgments
The authors would like to thank Mr. Ikeda and Mr.Tsukamoto of TOPPAN Inc. for advice on thisresearch.

• Can simulate the impact of a fall
• Implemented an impactor that simulates thehuman thighReferences• Uses dummy skin with cushioning performanceequivalent to human soft tissue [3]1. Hagino, H., Sakamoto, K., Harada, A., Nakamura, T., Mutoh, Y., Mori, S., Endo, N., Nakano, T., Itoi, E., Kita, K., Yamamoto,N., Aoyagi, K. and Yamazaki, K. for the Committee on Osteoporosis of The Japanese Orthopaedic Association.: Nationwide
one-decade survey of hip fractures in Japan, ORTHOPAEDIC SCIENCE, 150-6 (2010), 735-745.

• Impact load of 6500N can be applied under theconditions of impactor drop height of 50cm andhuman skin gel of 20mm

Comparison of experimental conditions and falls from a standing position

Impact load [N]Impact velocity [m/s]

6.0
5.0
4.0
3.0
2.0
1.0
0.0

Underfloor layer 7mm

100000Stress-strain compression curves of underfloor layer
1.4
1.2
1.00.8
0.6
0.4
0.2
0.0

Maximum impact load [kN]

Underfloor layer 6mm

Maximum impact load [kN]

Surface layer

Maximum impact load [kN]

Flooring conditions

Pendulum tester
6560±78
3.0

Fall from standing
5600 [4]3.0 [5]

2. Ministry of Health, Labour and Welfare.: Summary Report of Comprehensive Survey of Living Conditions (2019).
3. T. Fukuoka, Y. Ito, K. Shinmura, T. Matsubara, Y. Kagiyama, R. Yamada, T. Nemoto.: Proposal of New Dummy Skin forEvaluating Fracture by Dynamic Force (in Japanese), Jornal of JSEM, 19-3 (2019), 57-62.
4. S. N. Robinovitch, W. C. Hayes, T.A. McMahon.: Prediction of Femoral Impact Forces in Falls on the Hip, Journal ofBiomechanical Engineering, 113-4 (1991), 366-374.
5. Fabio Feldman, Stephen N. Robinovitch.: Reducing hip fracture risk during sideways falls: Evidence in young adults of theprotective effects of impact to the hands and stepping, Journal of Biomechanics, 40-12 (2007), 2612-2618.