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This chapter describes the execution phase of the project and how the methods and conclusions from the pre-study were implemented.
Evaluation of Y1
The Y1 concept was evaluated together with rescue workers from SAR and SSRS.
Workshop with SAR
The workshop was held at Brinellvägen 85, Stockholm, KTH on 18 February. The workshop started with a quick summary about the Y1 helmet and the project goal for the thesis work. Both users had the chance to try and further inspect the Y1 helmet and during that time discuss anything that came to mind. Some of the key feedback that was received throughout the workshop was:
• Possible to fit different types of goggles
• Create a flush camera mount (Prevent the winch from attaching to the camera)
• A camera mount that can fit all
• Easy to push on and off with thick gloves
• Possible to integrate the snorkel
• A semi-integrated position light, with changeable cover for different light colours
• a bit long at the back, ends to close to the neck.
• Be sure to have the gravitational point on the centre of the helmet
See Appendix H for complete Y1 evaluation/ feedback.
Workshop with SSRS
An interview was carried out with SSRS members Mats Ryde, Thore Hagman and Fredrik Falkman, who had been involved in developing, selecting and evaluating safety equipment for SSRS. The purpose of the interview was to get a better understanding of the work involved in rescue operations and what they demand of their equipment, focusing on head protection. The interview took place on 6 March at SSRS headquarters on Talattagatan 24, Västra Frölunda, Gothenburg.
Figure 22. At SSRS headquarters with Fredrik Falkman and Mats Ryde, to the right.
The Y1 concept developed in the MF2061 project was presented and used as reference for the interview and discussions. The interview led to the following insights regarding head protection and their expectations:
• The weight is the most important performance criteria. The base helmet must weigh no more than 400-600 grams.
• Durable and designed for multiple impacts rather than singular high impact scenarios. The outer shell should be made of a material that would allow making holes for mounting components.
• SSRS prefers modular design over integrated features – loose one function and you need to dispose of the helmet. Mounts needed for position light, communication, and visor. The position light must be mounted on the top so that it is visible from all sides. Would like to have a visor that can be mounted in mid position, acting as a sun screen. It is exhausting for the eyes to constantly have to re-focus when looking through a visor covered in water droplets.
• User friendliness is of essence when performing volunteer work. It should take no longer than two hours to clean the helmet after each mission from saltwater and dirt. No special training should be required to use the helmet to its fullest potential. All functions, buttons etc., need to be self explanatory and accessible even with thick neoprene gloves.
• Larger sizes needed. 62cm in circumference is often the largest available size. Since the head never stops growing it would be great with a 63-64cm size.
SSRS also presented a communication system that they had co-developed with Peltor, named the Rescue kit, as seen in Figure 23. The system is fully submersible in saltwater, according to IP-68 standard, and features two helmet mounted speakers and a microphone. The transmitter is separately mounted on the chest of the user to minimize the total weight of the helmet.
Figure 23. Peltor Rescue-kit, speaker and microphone.
SWOT-analysis of Y1
Every strength, weakness, opportunity and threat of the Y1 helmet was added into a S.W.O.T.
chart, for further development of the new R1 helmet. See Table 6.
Before the ideation process could start, a design requirement list was created of needs, demands and X-factor. An X-factor is referred to as an innovative feature that would place the product ahead of the competition. The design requirement list was carried over from the previous project MF2061, the PAS 028 guidelines and the Y1 evaluation conducted in this thesis project. For the complete design requirement list, see Appendix I. The bullet list below is an extract from the complete design requirement list:
• Balanced weight
• Ergonomic fit, suitable for people with bigger head sizes
• Prevent wires from interfering with components on the helmet
• Possible to fit desired components, such as lights, camera, eye protection and intercom-system
• Being able to interchange components
• Withstand multiple impacts
• Optimized for marine application
• There must be room on the front of the helmet for resting goggles or folding up a visor.
• The placement of the ventilation holes that are used for mounting components need to be carefully considered.
• Components such as cameras and working lights need to be positioned in a similar angle as the field of view.
• The position light needs to be placed making it visible 360 degrees and from above
• PAS-028 standard states that the helmet must not have sharp edges or shapes extruding more than 5mm.
• The mounting points should look indistinguishable when no components are attached.
Additional required and desired functions for eye protection:
• Protect the user from harsh wind and water
• See clearer during bad weather
• Misdirect water and debris from head
• Good optics quality material
• Piecewise adjustment (step by step)
• Possible for the user to take it off easily or remove it from the eye of sight
• One-third visor, beneficial against sunlight
• Easy to clip on to the helmet
• Low weight
• Short so that it does not get in the way of snorkel or mouth protection
Interview with Mikael Swarén
Baering had started a relationship with Peak Innovation, a firm that helps new business with company relations. One of the new contacts was with Mid Sweden University. The test facility at Mid Sweden University specializes in testing special fabrics. A test rig for repeated impacts with slalom poles for POC. Björn Berggren and Linus Wikström, from Baering, arranged a meeting with Mikael Swarén, from Mid Sweden University to talk about the rescue helmet project. Preparations was made before the interview with Swarén, some guideline questions where created. The key finding from the interview:
• SP, Technical research institute of Sweden, can perform testing according to PAS 028.
• Helmet impact scenarios should be analyzed to know if a stiff or more flexible material is needed. Consider how low and high impacts affect the shell.
• One-third visor would be beneficial against sunlight.
• A cut out near the ears so that water can run out during high water pressure, to prevent ear pressure from the water.
The complete questionnaire and Swaréns answers can be seen in Appendix J.
Inner liner thickness
To determine the thickness of the inner liner a simplified calculations was made. According to research papers the shell absorbs up to 30% of the total impact energy. There are also some papers that say that this value can differ up to 8,8% to 13,7 %, depending on shell construction.
The shell properties are excluded in this calculation to find the worst-case scenario for the foam. The impact velocity, given by PAS 028 is used to calculate the thickness. During an impact, the foam has a limit of how much energy it can absorb to prevent the foam to, “bottom out”, reach densification stage during impact. This means that the foam cannot be compressed more than 80% of its thickness(Shuaeib F. , Hamouda, Hamdan, Radin Umar, & M.S.J, 2002). According to PAS 028 the nominal impact energy for rigid mode method is 100J, the force on the helmeted head form shall not exceed 12,5kN. The equation according to Shaueib research paper to calculate , the stopping distance of the impact force, 1 × = (3) where the kinetic energy is the nominal impact energy, 100 J, putting the rest of the numerical values presented above in Eq. (3), will give Xmin=16mm, representing 80% of the liner thickness. This gives a nominal thickness of 19,2 mm.
The results from the competitor analysis was analysed regarding what type of materials used for the outer shell. The more popular materials were further researched, the composite materials were excluded as a single outer shell material due to the need of withstanding multiple impacts. CES EduPack was used as a tool to analyse each material. A material benchmark was conducted from the aspects of cost and shock absorption properties. A separate benchmark was conducted on composite material as a secondary material for added stiffness. See Appendix K for the materials chosen and relevant properties.
The thickness of the shell material is assumed to be 3-4 mm, similar to Manta SAR, Predator Full Cut and conducted research, this is still determined by performing penetration tests.
According to PAS 028, SAR and SSRS a requirement list for the outer shell could be created.
• Low material cost
• Low density
• Flexible shell material, to disperse impact force over a wider area without permanent deformation. High Yield strength and low enough young´s modulus and high elongation.
• Stiff enough to withstand penetration impacts. High young’s modulus and high hardness – Vickers value.
• High fracture toughness
• High fatigue strength
• High energy absorption property, impact strength.
• Low water absorption properties.
• Good UV properties
• Withstand extreme temperatures
• Good water resistance to salt/fresh water.
The requirements for inner liner are listed below:
• A liner high compressive strength
• Withstand multiple smaller impacts
• Not too rigid foam, soft touch against head
The evaluation method, Pugh’s matrix, was used for choosing the most suited materials for further testing. The materials properties were gathered from CES EduPack and the mean value was calculated for each property to ease the comparison. The criteria’s for each grading can be done by using one alternative as a reference, the normality value. The reference alternative will have the total score of zero. In this case, ABS plastic was chosen as the reference, due to the majority of helmets researched uses ABS. Due to ABS plastics poor UV protection and low hardness-Vickers value, a negative score was given on those categories. The ABS plastic also has good water properties and low material cost and therefore given a positive score in those categories. The material properties were graded better, worse or equal to the reference material. A positive score (+) was given when the material was better, neutral score (0) when equal and a negative score (-) when worse than the reference material. The manufacturing cost was assumed to be for 1000 helmets and therefore making injection moulding a high cost per unit. The rest of the thermoplastic materials were assumed to be manufactured through thermoforming. The upper limit for highest young’s modulus was set to 12 GPa and elongation at 100%.
According to the Pugh’s matrix, the thermoplastics with best scores were Polycarbonate, PC, with a total of 4 and PC/ABS at the second place with the score of 3. See Appendix L for complete material benchmark.
Material sample droptest
To further benchmark the chosen materials as base for selecting the appropriate density, a simple drop test was constructed to test different material combinations for the outer shell and liner, suggested by Mikael Swaren. The test was also performed to better understand the compression behaviour of the liner material, EPP, together with a hard shell.
If the density is too low, the densification zone is reached and a very high force is obtained before the energy has been displaced. But if the density is too high the force exceeds the critical value before energy has been absorbed. Therefore when conducting the sample tests, both the acceleration and the duration of the impact is analysed and evaluated. Eq. (1) is used with Eq.(3) to calculate the failure threshold for the drop test when the drop height is 1 meter and the weight is 1 kg together assuming that the kinetic energy is equal to the potential energy gives us Eq. (4) and (5).
With a maximum compression of 16 mm, , will give a failure threshold of 1,22 kN.
Two shell materials and three EPP densities were tested, resulting in6 test samples in total. The Table 7defines each material.ABS was excluded from the testing due to enough data already available from the research conducted. The inner liner densities and densities were chosen based on the inner liner calculations and research gathered.
A simple test mechanism was constructed, see Figure 24.
The load cell is placed under the materials and the weight is fixed to a wire that guides the fall. The weight falls on to the material where the load cell measures the acceleration. See Figure 25 for the test fixture. A material fixture was created to hold the material sample in place but also guide the force perpendicular to the measuring surface of the load cell to prevent shearing forces. The shearing forces can affect the result that the load cell registers which can result in a higher peak force.
Table of contents :
2.1 ITERATIVE DESIGN PROCESS
2.2 PROJECT PLANNING METHODS
2.2.1 Project plan
2.3 INFORMATION RETRIEVAL
2.4 COMPETITOR ANALYSIS
2.5 MATERIAL ANALYSIS
2.6 SEMI-STRUCTURED INTERVIEWS
2.7 IDEATION WORKSHOP
2.8 FOCUS GROUP
2.9.3 Speed sketching
2.9.4 Exploratory sketching
2.10.3 Clay model
2.10.5 Physical prototype
3 FRAME OF REFERENCE
3.1 PROJECT PLAN
3.2 USER GROUPS
3.3.1 Head sizes
3.4 ESSENTIAL HELMET COMPONENTS
3.4.1 Outer shell
3.4.2 Inner liner
3.4.3 Comfort liner
3.4.5 Retention system
3.5 EXTERNAL COMPONENTS
3.5.2 Eye protection
3.6.1 Helmet standards
126.96.36.199 PAS 028
188.8.131.52 Testing according to PAS 028
3.6.2 Component standards
3.7 COMPETITOR ANALYSIS
3.7.1 Main competitors
184.108.40.206 Manta Hi-Viz SAR Multi-Role Helmet
220.127.116.11 OPS-core FAST
3.8.1 Outer shell
18.104.22.168 Composite shell
3.8.2 Inner liner
3.8.3 Inner liner and shell combination
3.9.1 Injection moulding
22.214.171.124 Vacuum forming
126.96.36.199 Pressure forming
188.8.131.52 Design recommendations
3.9.3 Expanded foam moulding
3.10 ASSEMBLY METHODS
3.10.1 Spray Adhesive
184.108.40.206 Double-sided adhesive
220.127.116.11 Two component glue
3.10.3 External components
18.104.22.168 ACH-ARC rail
22.214.171.124 Picatinny Mount
126.96.36.199 Commercial mounts
4.1 EVALUATION OF Y1
4.1.1 Workshop with SAR
4.1.2 Workshop with SSRS
4.1.3 SWOT-analysis of Y1
4.2 DESIGN REQUIREMENTS
4.2.1 Interview with Mikael Swarén
4.2.2 Inner liner thickness
4.3 MATERIAL ANALYSIS
4.3.1 Material requirements
4.3.3 Material sample droptest
4.4 CONCEPT GENERATION
4.4.3 Speed sketching
4.4.4 Exploratory sketching
4.4.5 Feedback from HOWL design studio
4.5 FURTHER DEVELOPMENT
4.5.1 Refined sketching
4.5.2 Mount concepts
4.6.1 Clay models
4.6.2 Digital prototypes
188.8.131.52 Function – carrier of systems
184.108.40.206 Materials and manufacturing
4.7 CONCEPT EVALUATION
4.7.5 Concept evaluation
4.8 FURTHER REFINEMENT
4.8.1 Mount concept
220.127.116.11 Flush ACH-ARC rail
18.104.22.168 Picatinny snap mount
22.214.171.124 Flexi snap mount
126.96.36.199 Mount Evaluation
4.10 PRODUCTION R1 HELMET
188.8.131.52 Manufacturing process
184.108.40.206 Injection moulding
5.1 R1 – RESCUE ONE HELMET
5.2 HELMET COMPONENTS
5.2.1 Outer shell
5.2.2 Inner liner
5.2.3 Ear covers and chin strap
5.2.4 Communication system
5.2.5 Retention system
5.2.6 Mount concept
5.2.7 Half integrated top light
5.2.8 Eye shield
5.2.9 Visor concept
5.3 PHYSICAL PROTOTYPE
5.3.1 Outer shell
220.127.116.11 Vacuum forming
5.3.5 Estimated cost calculation
5.4.1 Testing at MIPS
6 DISCUSSION AND CONCLUSIONS
6.2 Y1 EVALUATION
6.3 USER CENTRED DESIGN
6.4 MATERIAL CHOICE
6.6 PHYSICAL TESTING
6.7 FINAL RESULT
7 RECOMMENDATIONS AND FUTURE WORK
7.1 POTENTIAL MANUFACTURERS
7.2 MOUNT TESTING
7.3 INITIAL EVALUATION
7.4 FURTHER TESTING
7.5 FIELD TESTING
7.6 REFINE DESIGN
7.7 FINAL EVALUATION
7.8 CERTIFICATION AND MANUFACTURING
APPENDIX A – PROJECT PLAN
APPENDIX B – GANTT-SCHEME
APPENDIX C – FOLKSAM HELMET TEST RESULTS
APPENDIX D – STANDARD EVALUATION
APPENDIX E – TEST METHOD DESCRIPTION
APPENDIX F – COMPETITOR ANALYSIS
APPENDIX G – JENS ARPRO, SUGGESTED ADHESIVES
APPENDIX H – WORKSHOP SAR, Y1 EVALUATION
APPENDIX I – DESIGN GUIDELINE
APPENDIX J – INTERVIEW MIKAEL SWAREN
APPENDIX K – MATERIAL PROPERTIES
APPENDIX L – MATERIAL BENCHMARK
APPENDIX M – UNDERLAY
APPENDIX N – HOWL MEETING
APPENDIX O – SAR CONCEPT EVALUATION
APPENDIX P – HOWL CONCEPT EVALUATION
APPENDIX Q – COMPANIES CONTACTED
APPENDIX R – THERMOFORMING GUIDE
APPENDIX S – MIPS TEST PLAN
APPENDIX T – MIPS TEST RESULTS