International Journal of Trend in Research and Development, Volume 3(3), ISSN: 2394-9333

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Thermal and Failure Analysis of Industrial and

Cricket Helmets 1Aditya A. Deshmukh and

2D.V.Burande,

1U.G. Student,

2Professor,

1,2Department of Mechanical Engineering, Smt. Kashibai Navale College of Engineering, Pune, India

Abstract- The document specifies the requirements and testing

methods suitable to industrial and cricket helmets. The

important parameters considered during designing a helmet are

its shock absorption capacity and thermal comfort while

wearing it. The performance of a safety helmet involves the

shock-absorbing capacity of a striking object associated with a

deformation of the shell and cradle, as well as an increase in

the transferred force to the user's head. The protective helmets

used in cricket now-a-days offer sufficient protection to players

against impact. Discomfort due to heat is one of the cricket

player‟s main complaints when wearing the helmets.

Keywords: Helmet, Impact energy, Thermal comfort,

Ventilation

І. INTRODUCTION

Headgear is widely used in both occupation and leisure; it is

used as a fashionable accessory or as an optional/mandatory

means of protection. Primary review of thermal properties and

helmet comfort revealed the following similarities between

cricket and industrial helmets:

1. The two helmets should protect the wearer‟s head against

direct impact with an object;

2. Both workers and cricketers are exposed to extreme

environmental conditions for a long duration of time;

3. Most users find the existing helmets are heavy,

inadequately ventilated and uncomfortable;

4. Most international cricket games are played in

environments with low air velocity similar to low building

construction sites.

Here, for the failure test of industrial helmet we use a

methodology of testing shock absorption capacity. A helmet

placed on a head form is hit by a 5 kg hemispherical striker

freely falling from a height of 1 m. During the impact, the

value of the force acting on the head form beneath the helmet

is measured. According to the requirements, the maximum

value measured of that force must not exceed 5 KN. As a result,

the testing method involves a check on whether the safety of

helmet sufficiently reduces the transferred force to the user's

head during the impact of a moving object. In view of the

above, the question arises of how the currently available

industrial safety helmets behave during impacts exerted with

higher energy.

For the thermal analysis of cricket helmets, the main aim of

this was to study the thermal properties of selected, cricket

helmets, which are widely used in international cricket games

in order to develop knowledge and understanding of the

thermal behaviour of cricket helmets. Also, the newly acquired

knowledge can be applied in future to improve thermal comfort

of cricketers. This research aimed at quantifying

1. The net heat transfer,

2. The average temperature under the helmet,

3. Average radiant heat with the help of thermal imaging.

The readings acquired were then used to describe the

thermal properties of the helmets at normal conditions for low

to moderate intensity activity games, where the ambient

temperature was found to be 23 ⁰C and relative humidity was

around 65%. The radiation, convection and total heat

transferred between the helmeted head form and the

surrounding environment, under steady-state conditions, were

calculated. It is found that insight into the thermal distribution

of the helmeted head form will allow design improvement of

cricket helmets and this can lead to an improvement in thermal

comfort.

ІІ. TESTING OF INDUSTRIAL HELMET

A. Testing method

Due to the impact exerted by a moving object, also occurs the

deformation of the shell and cradle of the helmet. For the

impacts to the highest point of the shell and directed vertically

downwards the most significant deformation occurs within the

area of height X (Fig. 1). Due to the deformation of helmet

elements, absorption of the impact of the striking object is

observed, also an increase in the force transferred to the head

form is seen. So to find the value of the energy absorbed by the

helmet when hit by a moving object generating a force of F = 5

kN, the following equation was used (1)

E5=0∫∆x5

F (∆x) d∆x (1)

B. Experimental Setup

The setup for testing the industrial safety helmets mainly

consist of test object, falling weight, monitoring system with

sensors. The setup is shown in fig. 1

Figure 1: Setup for energy absorption of industrial safety helmets [2]

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1 – Monolithic base, 2 –slide ways, 3–4 – trolley, 5 – hoist, 6 –

electromagnetic latch, 7 – striker, 8 – button for striker disengagement, 9 –

head form, 10 – test helmet, 11 – force transducer, 12 – amplifier, 13 –

analog filter, 14 – digital oscilloscope, 15 – high speed camera, 16 –

computer, 17 – device for measuring striker speed, 18 – laser diode, and 19

– marker on striker.

In the figure shown above, (1) is the monolithic base

on which the head form is placed. This base not only supports

the stand of the system but also absorbs the shocks generated

during the testing of the helmet. Vertical stand (2) has a trolley

(4) which slides on the vertical bars of the stand on this trolley,

a striker (7) is attached.

Initially the trolley is locked magnetically by an

electromagnetic latch (6), its vertical position is set by another

trolley (3). This helps in gaining the desired kinetic energy for

the striker. The position of this latch is varied using the push

buttons (8) and it is also used to release the latch.

The test helmet is positioned on the head form. The

stand is fitted with electronic system for measuring the

transferred force to the head form, which is achieved by a

transducer (11) at the base. The axis of this transducer

coincides with the axis of the striker. The transducer is

connected to the display unit using an amplifier and filter

circuit. The digital oscilloscope (14), records the time course of

the force acting on the transducer (12). The second measuring

system has a high speed digital camera (15), which records the

displacement of the marker (19) attached to the striker surface

(7) during the impact. The camera (15) is coupled with a

computer (16), used for programming the desired mode for the

camera, saving the images recorded by the camera, and to

process them after they are saved. The camera is such

positioned that the laser diode (18), the test helmet, and the

striker (7) are in its line of sight at the moment of contact. The

system measures the striker speed for the last 20 mm of its

drop prior to impact on the helmet and simultaneously

generates signals for the data recording by the oscilloscope (14)

and switching on the laser diode (18). In this way the data

recorded by the oscilloscope and by the camera (the

displacement of the striker) is achieved in synchronous with

each other. The industrial test helmet used is shown in fig. 2

Figure 2: Section of an industrial safety helmet 1–shell, 2–cradle, X–

distance between the internal surface of shell and cradle, and F–force acting

during an impact. [2]

C. Test Results

The test was carried out at three different

temperatures -30, 20, 50. The height of the striker was so

adjusted that the force acting on the head form would not

exceed 5kN. The damages caused to the helmet at three

temperatures are very less that is there no perceptible damage

was caused.

The F vs. ∆x characteristics which were obtained for

the above test is as follows in the fig. 3

Figure 3: Sample F(∆x) characteristics of helmet based on test results obtained

by conditioning at 30⁰ C, +20⁰ C, and +50 ⁰C. [2]

D. Summary of the test results

During the test, the value of impulse recorded was about

10KN for the helmet. The steep increase in the graph for all

three temperatures shows that the contact of internal surface of

shell and cradle has occurred that means all the force has

transferred to the user's head. In this case the helmet broke at

the connecting junctions of the cradle to the shell.

Due to increase in conditioning temperature, the

capability of the helmet to absorb the energy was reduced.

Material softening occurred due to increased temperature

which was found to affect both, the shell and the cradle. Due to

this the contact of internal surface of shell and cradle took

place at lower force values.

ІІІ. TESING OF CRICKET HELMETS

A. Experimental setup

The set-up used in this study consists of a slim rectangular

flat plate and a timber plank, on which the aluminium manikin

head form was securely mounted (Fig. 4).

Figure 4: Experimental set-up. [1]

Two insulated pipes were fitted to the head form. One of the

two pipes was connected to the water boiler and another pipe

was connected to a water pump through which used water was

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removed from the head form and again supplied to the water

boiler that mean the head form, water boiler and the pump are

in closed loop. An infrared camera which is used to capture the

thermal images of the head form was installed in front of the

head form to capture its images.

For the first hour of the test, the warm water was

continuously fed to the head form so that the steady state was

achieved. The temperature on the surface of the head form was

maintained within the range of 34.9 ± 0.1⁰C so that it matches

the actual skin temperature. To measure the rise in head form

temperature total 8 k-type thermocouples with an accuracy of

±1.5⁰C or ±0.25⁰C were used which were located to the right

side of the head form as shown in the fig. 5.

Figure 5: Thermocouple sampling zones. [1]

Total five types of helmets were selected for the study.

B. Helmet Details:

Following helmets were used for the study (Fig. 6):

Figure 6: Details of helmets used in the study [1]

1. The „NXT‟ helmet contains two layers of shell: the inner

layer has linear cuts (length 20 mm) from front to back,

to increase the airflow through the helmet; the layer

above is dotted with small 96 round holes (diameter 5

mm, approximate total surface area of the ventilation

holes is 1884 mm^2) which allows airflow through the

outer layer and allows final dissipation of heat to the

environment.

2. The „Elite‟ helmet is made of a polypropylene moulded

shell, has four radial openings across the shell, and a

small, cross shaped opening at the crown. (Total surface

area of the ventilation opening is 3460 mm^2.)

3. The „Premiere‟ helmet is prepared using a high-impact

injection-moulded shell, which has three circular holes

(diameter 13 mm) surrounding the crown area to

facilitate ventilation. (Total surface area of the

ventilation opening is 950 mm^2.)

4. The „Masuri‟ helmet is made using a strong carbon-fibre

reinforced shell, has two circular holes (diameter 11

mm) on each side of the crown to facilitate ventilation.

(Total surface area of the ventilation holes is 190

mm^2.)

5. The „Ultimate‟ helmet includes three circular vents

(diameter 16 mm, total surface area of the holes is 600

mm^2) located at the front and both sides of this carbon-

fibre reinforced polymer shell.

C. Results

1. Thermal distribution

The heat exchange between each helmet was depicted by using

a graph shown in fig. 7

Figure 7: Temperature measurements on Al. head form [1]

(1) Phase 1 (0-2 min): temperature of head form without

helmet.

(2) Phase 2 (2.0-30 min‟s): temperature of head form with

helmet properly fastened and steady state attained.

(3) Phase 3 (30-45 min‟s): temperature of head form after the

helmet was removed.

It can be clearly seen from the graph that once the helmets

were put on then the temperatures started to increase beneath

the helmet for about 8 min‟s, then during the test periods they

remained stable. The recorded temperatures increased by an

average of 1.4°C for all the helmet types.

The highest temperature increase was found at the

Location 8 where on average, the temperature increased by 1.7

± 0.1°C, followed by Position 7 were the temperature increased

by about 1.4 ± 0.1°C. The temperatures at the forehead area i.e.

position 3 incremented by 1.2 ± 0.2°C. The average

temperature increment at position 4 was 0.5 ± 0.1°C and was

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least than the other locations. The recorded temperature measurements showed differences among the various types of

helmet.

2. Thermal imaging:

The infrared camera used showed us the images of the surface

temperatures on the helmets tested. Repeatability of surface temperature was determined and the standard deviation of the

temperature measurement was 0.22°C. The obtained results are

shown in the fig. 8

Figure 8: (left) Thermal images at the start of 2-30 min phase,

(right) thermal images after 30 min. [1]

Thermal imaging showed temperature variations on the surface

areas for the same helmet, depending on the design and

construction of ventilation holes of the helmet, where heat

tended to radiate through the vents; the mean temperatures near

the ventilation holes were approximately 1-2°C higher than

surface areas that are 50-70 mm away from the holes.

Figure 9: Mean values for heat transfer for the helmets. [1]

The values for the heat transfer for all five helmets is shown

below with the help of a bar chart (fig. 9)

The formula used for the total heat transfer is given by,

q = qconv + qrad

q = h.A(Tsk – Tsur) + ε.A.σ(T4

sk – T4Hei) (2)

Where, qconv (W) is the convection heat transfer given by

Newton‟s law of cooling and qrad (W) is the radiation emitted

from a surface at a thermodynamic temperature given by the

Stefan-Boltzmann law. Tsk (K) is the surface temperature of

head form, THei (K) is the mean radiant temperature of the

helmets, Tsur (K) is the temperature of surrounding A is the

surface area of the head form (estimated to be 0.069 m2),

σ =

Stefan-Boltzmann constant = 5.67 * 10

-8 Wm

-2K

-4, and ε =

emissivity of the head form (determined as 0.98).

D. Design suggestions:

For the obtained results, temperatures in the parietal and the

frontal regions were higher by about 1.5°C. This was probably

because most of the test helmets did not have ventilation holes

at these regions. Following are the suggestions to improve the

ventilation.

1. Inserting circular vents:

It is believed that the general thermal comfort of the helmet

can be improved by increasing round ventilation holes at the

parietal and forehead zones to allow cooing air to circulate

through the helmet as shown in fig.10. As cricket is mostly

played between 11 and 5 pm, when the sun is high in the sky,

larger ventilation holes could cause more heat gain from the

hot sun through radiant heat.

Figure 10: Circular ventilation holes to improve heat transfer according to

hotspots (highlighted in black dots). [1]

2. Inserting grooves:

Several parallel grooves with several vents in each groove

could be added to provide space or channels for air to flow.

Ventilations holes or slots are need in a minimum of three

positions: in the front and rear of the helmet for air to flow in

or out of the helmet, and on the top of the helmet to take

advantage of the convective mode of heat transfer, in which

warm air rises and is replaced by cooler air that flows into the

helmet via rear and front vents as shown in fig. 11

Figure 11: Parallel grooves to improve airflow according to hotspots

(highlighted in black dots) [1]

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3. Insert additional pads:

Additional pads may be added to the inside surface of the

helmet which will allow more customization to ensure a snug

fit, while creating a gap or space between the helmet and the

wearer‟s head in improve ventilation. Comfort foam of 12-16

mm thickness provided along the circumference sides of the

helmet only, but not on the top as shown in fig. 12.

Figure 12. Additional pads to create air gap and space to improve

ventilation.[1]

4. Insert suspension straps:

The suspention straps are positioned perpendicular to each

other so that they intersect crown of the head. These increase

air gap and to promote airflow between helmet shell and head,

thus increasing the potential for heat dissipation from the head

as shown in fig. 13

Figure 13: Suspension straps to increase air gap and to promote airflow. [1]

CONCLUSION

The article gives detailed experimental study of failure test of

industrial safety helmet and heat transfer and its influence on

the thermal comfort in cricket helmet. The following

conclusions can be drawn from this study:

1. Failure test of industrial safety helmets: With increasing

temperature the capability of the helmets to absorb impact

energy decreased. This was mainly due to softening of both the

shell and the cradle materials. This phenomenon actually

reflects the actual conditions of use at worksites. These effects

can be reduced if helmet shells and cradles are produced using

materials whose mechanical characteristics do not dependent

on temperature. The deterioration of the mechanical strength of

helmet elements, such as attachments connecting the shell to

the cradle, can also be responsible for reduced capability to

absorb impact energy. Strength deterioration, breaking of

elements, occurs mostly at low temperatures.

2. Thermal analysis of cricket helmets: The total heat

transfer from the head form to the surrounding environment

decreased, on average by 15%, after putting on a cricket helmet;

hence, the helmets resists the heat dissipation from the head.

Experimental results confirmed that the helmets cause head

temperature to rise by 1.5 ± 0.1°C around the frontal and

parietal regions, which can cause discomfort. Thermal imaging

results showed that the helmets tended to radiate heat through

the side rim and ventilation outlets depending on their design

and construction.

i. By inserting circular vents at the parietal and forehead

zones to allow cooing air to circulate through the

helmet.

ii. By inserting four grooves from front to the rear of the

helmet with two centrally located and the remaining

two on each side.

iii. By inserting additional pads throughout the

circumference of the helmet.

iv. By inserting suspension straps fastened respectively at

the opposite ends of the circular ring-shaped head strap

and intersecting each other at the crown of the head.

Acknowledgment

I am very thankful to those who have helped me in completing

this study. I am also thankful to the authors of the references I

have referred, as their work has greatly helped and influenced

me. I am extremely grateful to these authors.

I am also thankful to Prof. D.V. Burande for his

support and guidance.

References

[1] Toh Yen Pang, Aleksandar Subic, Monir Takla, “A

comparative experimental study of the thermal properties

of cricket helmets,” International Journal of Industrial

Ergonomics, vol. 43 (2013) 161-169, January 2013.

[2] Krzysztof Baszczynski, “The effect of temperature on the

capability of industrial safety helmets to absorb impact

energy.” Engineering Failure Analysis, vol. 46 (2014) 1–

8, July 2014.

[3] Cornelis P. Bogerd, Jean-Marie Aerts, Simon Annaheim,

Peter Brode, Guido de Bruyne, Andreas D. Flouris, Kalev

kuklane, Tiago Sotto Mayor, Rene M. Rossi, “Areview

on ergonomics of headgear: Thermal effects,”

International Journal of Industrial Ergonomics, vol. 45,

pp 1-12, November 2014