Designing High Performance Safety Belts

Safety belt is a type of protective device designed to protect a person, animal, or object from injury or damage. Fall from height is a primitive hazard for a worker who is working at height. The local safety regulations and laws are forced to provide suitable working platform, safe access and proper fencing to dangerous places [1-4]. The use of safety belts is the only and best option when it is impracticable to provide above mentioned safety measures at work place. It is usually attached between a stationary and non-stationary object and is fabricated from rope, cable or webbing and locking hardware. Some safety belts are used in combination with a shock absorber, which is used to regulate deceleration when the end of the rope is reached. Safety belt and upper-body restraints that relax to permit comfort but tighten automatically during an impact are now common.


Introduction
Safety belt is a type of protective device designed to protect a person, animal, or object from injury or damage.Fall from height is a primitive hazard for a worker who is working at height.The local safety regulations and laws are forced to provide suitable working platform, safe access and proper fencing to dangerous places [1][2][3][4].The use of safety belts is the only and best option when it is impracticable to provide above mentioned safety measures at work place.It is usually attached between a stationary and non-stationary object and is fabricated from rope, cable or webbing and locking hardware.Some safety belts are used in combination with a shock absorber, which is used to regulate deceleration when the end of the rope is reached.Safety belt and upper-body restraints that relax to permit comfort but tighten automatically during an impact are now common.
Safety belt is a collective name for the different types of harnesses and belts like (i) Safety harness or full body harness; (ii) Semi-harness or chest harness; (iii) Rescue harness; (iv) Work positioning belt pole safety belt or lineman safety belt; (v) General purpose safety belt.Seat belt is the most well-known and important safety device.It is an energyabsorbing device that is designed to keep the load imposed on a victim's body during a crash down to survivable limits [5][6][7].Fundamentally, it is designed to provide non-recoverable extension to reduce the deceleration forces which the body encounters in a crash.Nonrecoverable extension is particularly important to prevent occupants from being pulled back into their seats and sustaining whiplash injuries immediately after an impact.To stop any more webbing from paying out after an accident, the automatic belt has a locking mechanism known as the inertia reel.
Technical textiles in automotive sector, where woven, knitted and nonwoven fabrics are used, makes up approximately 15% of the total manufactured technical textiles in the world.More than 50% of it is woven fabric because of their appropriate properties for this application [8,9].These fabrics are manufactured using synthetic material such as polyester, polyamide and polypropylene fibres due to special requirements and properties.The most important properties are: tenacity, elasticity, stability, inflammability, abrasion resistance, porosity, comfort and aesthetic appearance, colour fastness in order to meet ecological requirements etc.Moreover, some necessary properties are obtained by subsequent fabric treatments such as by coating a thin synthetic layer to achieve fabric inflammability and air impermeability [10,11].Safety belts are manufactured by narrow weaving and high tenacity, stability, the raw material composition is mostly polyester

Abstract
Safety belts are the life saving product for the persons working on high rise buildings, factories etc.The objective of this research work is to investigate the effect of various constructional variables on the properties and performance of safety belts.The samples were prepared using different denier of polyester filament yarn.Box-Behnken design of experiments with 3 factors and 3 levels has been used for the sample plan, the statistical analysis and the optimization.The results showed that the number of warp yarn is the most influencing parameter for strength and elongation of safety belts followed by the weft density and warp denier respectively.multifilament, a relatively high density of warp yarns and a relatively low density of weft yarns, twill weave is used in the weaving.Tensile strength and elongation are the crucial characteristics for the safety belts.
Breaking strength, elongation, resistance to abrasion, resistance to light, resistance to micro-organisms, resistance to temperature etc are some of the important properties of the safety belts [12,13].This research work is focused on improving the performance of safety belt by improving breaking strength and elongation.

Methodology Materials
In this research work, various important constructional parameters of the safety belts have been investigated for their effect of the tensile strength and elongation behavior of the safety belts.Polyester multifilament of different denier has been used to produce safety belt.Samples were prepared on the needle loom (Narrow Woven Fabric Manufacturing) of MODEL -KYANG -JYE (80/2).The details of the prepared samples were shown in the Table 1.Machine parameters are as under: • Number of Ribbon: 2

Methods
Strength and elongation testing: The samples were tested for the breaking strength and elongation at break following the standard test method [14] (BS2576).The samples were conditioned under standard laboratory conditions for 24 hours.ASTM D5035-06 (standard test method) is used for the measurement of breaking force and elongation of textile fabrics.The Breaking Strength of the fabric was determined using the breaking strength tester manufactured by Texcare Industries.Digital Tensile Testing Machine Parameters are as follows: • Measuring Unit : Kgf (Kilogram), N (Newton) Lbs (Pound) • Operating: Fully Automatic and Manual Both • Maximum Grip Separation : 1000mm Design of experiment: Box-Behnken statistical design with 3 factors, 3 levels and 13 runs (one centre point) was used for the optimization study.The independent and dependent variables are listed in Table 1.The polynomial equation generated by this experimental design (using Design-Expert 8.0.7.1) is as follows: Where Y i is the dependent variable; b 0 is the intercept; b 1 to b 33 are the regression coefficients; and A, B and C are the independent variable that was selected from the preliminary experiments.Box and Behnken design with measured responses are shown in Table 2.

Results and Discussion
Results obtained from testing of the samples were analysed and optimised using design expert software are presented in this section.

Effect of different variables on breaking strength of safety belts
Effect of different variables like number of warp ends, number of picks per inches and warp yarn count on the breaking strength of safety belts were studied, analysed and discussed in this section.The parameters in the ANOVA Table 3 clearly show the analysis and effect of different variables on the breaking strength of the safety belts.The model p-value depicts that the model is significant.

Effect of number of warp yarn on breaking strength of safety belts
Table 3 clearly shows that the number of warp yarns has a significant effect on the breaking strength of the safety belt.Breaking strength of safety belts increases with increase in the number of warp yarns.The relation is non-linear as depicted by the analysis of variance and the Figure 1.The increase in number of warp yarns increases the breaking strength in a non-linear manner i.e. the increase is not in straight line.The reason behind this is that the more number of warp yarn will have more load bearing capacity.The nonlinear relationship is unexpected in this case.It is mainly due to the interaction effect of other parameters of constructions.effect on the breaking strength of the safety belt.But the effect is relatively low as compared to the effect of number of yarns.Breaking strength of safety belts increases with increase in the denier of warp yarns.The relation is linear in this case as depicted by the analysis of variance and the Figure 2. The reason behind this is that the higher denier will have the more number of filaments in the warp direction and consequently will have more load bearing capacity.

Effect of weft density on breaking strength of safety belts
Table 3 depicts that the weft density also has insignificant effect on the breaking strength of the safety belt.However, the effect is relatively quite low as compared to the effect of warp denier.Breaking strength of safety belts increases with increase in the weft density.The relation is linear in this case as depicted by the analysis of variance and the Figure 3.It is mainly due to the higher weft density, which will have the better binding on the warps and consequently will have more load bearing capacity.The linear relationship is unexpected in this case.The reason behind this may be due to the interaction effect of other parameters of constructions.
Optimizing the dependent variable for maximum breaking strength of safety belts: Optimizing the independent variables for maximum breaking strength by using Box-Behnken design of experiments shows that the maximum breaking strength of safety belts can be achieved at maximum number of warp, weft density and warp denier.This behaviour is clearly shown in the perturbation plot in Figure 4.The contribution of the evaluated factor can also be seen in the Figure 4 which exhibits that the number of warp yarn is most important followed by the denier and the weft density respectively.

Effect of different variables on elongation at break of safety belts
Effect of different variables like number of warp ends, number of picks per inches and warp yarn count on the elongation at break of safety belts were studied, analysed and discussed in this section.The parameters in the ANOVA Table 4 clearly show the analysis and effect of different variables on the elongation at break of the safety belts.The model p-value depicts that the model is significant.effect on the elongation at break of the safety belt.The elongation at break of safety belts reduces with increase in the number of warp yarns.The relation is linear as depicted by the analysis of variance and the Figure 5.The reason behind this is that the more number of warp yarn will have more load bearing capacity hence low elongation.In this case, the interaction effect of other parameters of constructions is not significant to the second order.effect on the elongation at break of the safety belt.The elongation at break of safety belts reduces with increase in the number of warp yarns.The relation is linear as depicted by the analysis of variance and the Figure 6.The reason behind this is that the higher denier will have the more number of filaments in the warp direction and consequently will have more load bearing capacity and hence low elongation at break.Effect of warp denier is more pronounced at higher number of yarns.

Effect of weft density on elongation at break of safety belts
Table 4 clearly shows that the number of yarn has insignificant effect on the elongation at break of the safety belt.
The elongation at break of safety belts reduces with increase in the number of warp yarns.The relation is non-linear as depicted by the analysis of variance and the Figure 7. However the non-linearity is not significant.The reason behind this is that the higher weft density will have the better binding on the warps and consequently will have low elongation at break.

Optimizing the dependent variable for minimum elongation at break of safety belts:
Optimizing the independent variables for minimum elongation at break by using Box-Behnken design of experiments shows that the minimum elongation at break of safety belts can be achieved at maximum number of warp, weft density and warp denier.This behaviour is clearly shown in the perturbation plot in Figure 8.The contribution of the evaluated factor can also be seen in the Figure 8 which exhibits that the number of warp yarn is most important followed by the denier and the weft density respectively.

Conclusions
Safety belts produced with different fabric variable such as number of warp, warp denier and weft density.Statistical analysis of

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Motor :½ hp 1440RPM with Worm Reduction Gear Box Noise Less • Display Units : Load, Speed , Elongation • Traverse Speed: 300 mm/min • Calibration : Self Calibrated • Protection: Over Load, Over traverse up &amp; Down.• Auto Stop: At Test Finish.At Over Load, At Over Traverse • Report: Tensile Strength, Elongation.

Figure 1 :Figure 2 :
Figure 1: Effect of number of yarns and the picks per inches.

Volume 6 •Figure 5 :Figure 6 :
Figure 5: Effect of number of yarns and the picks per inches.

Table 1 :
Variables and their Levels in Box-Behnken Design.

Table 3
clearly shows that the warp denier also has a significant

Table 2 :
Box-Behnken experimental design with measured responses.

Table 3 :
Analysis of variance for response surface quadratic model for breaking strength of safety belts.

Table 4
clearly shows that the number of yarn has a significant

Table 4
clearly shows that the number of yarn has a significant

Table 4 :
Analysis of variance for response surface quadratic model for elongation at break of safety belts.