Behaviour of a speargun with a novel muzzle

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Abstract

The paper presents the results of a numerical and experimental investigation performed on a barrelof a speargun equipped with two kinds of muzzle. In particular, a standard muzzle for speargun (having anelastic propulsion) has been compared with an innovative one called ‘roller’. This new muzzle is equipped withtwo rollers and special bands. The rubber bands, fixed at the lower side of the barrel, run through the rollersand are engaged in suitable seats of the shaft. These bands are, therefore, longer than the traditional ones and,consequently, with equal force applied by the diver, the roller speargun has a longer range. Thanks to theparticular geometry of the new muzzle, one of the front constraints of the elastic bands is moved to the lowerpart of the barrel or the handle.As a consequence, the scheme of the loads applied on the speargun remarkably changes passing from a standardmuzzle to a roller one. All that has a great influence on the level of deformation of the barrel and, consequently,on the accuracy of the shot. Because of the low velocity of the spear (if compared with the firearms), in fact, theaccuracy of the shoot if strongly influenced by the barrel bending due to the forces applied by means of theelastic bands.In this paper it is experimentally evaluated the bending of the barrel equipped both with the innovative muzzleand with the traditional one in order to compare their performances.The experimental analysis of the barrel was performed by electrical strain gauges suitably located at the sectionwith the highest values of the strains. In order to find the barrel section with the highest strain values where tolocate the strain gauges, a preliminary numerical FEM analysis has been performed.The loads and constraints scheme has been evaluated both for the standard and the new muzzle. In particular,the forces due to the elastic bands, their application points and directions have been experimentally obtained.To speed up the process of numerical simulation, without invalidating the results reliability, simplified FEMmodels have been used. In particular, a very accurate model of the barrel has been shaped, whereas the modelsof the muzzles and the handle have been simplified. The forces due to the elastic bands, experimentallyobtained, have been applied on the FEM models. The maps of the maximum and minimum principal strainshave allowed to find the area with the highest strain values, placed in rear part of the barrel (near the handle).The strain values experimentally measured on the speargun have been very similar to the ones calculated bymeans of the numerical simulations. That demonstrates the developed FEM models are very reliable and canben used to predict the performances of the speragun under different loads conditions.The speargun with the new roller muzzle shows very lower strain values if compared with the ones measured inthe standard one. Nevertheless, considering the two spearguns have different elastic bands setup, it has beenthought the comparison of their performances should be made hypothesizing the same maximum force appliedduring the speargun charge. This condition, moreover, could be really obtained by changing the kind of the elastic bands in the speargun with the roller muzzle. For this reason, during the results analysis phase, the strainvalues measured on the roller speargun have been ‘normalized’ by increasing them of a value equal to the ratioof the maximum forces due to the rubber bands.The data post processing has allowed to evaluate the forces and the bending moments on the barrels with thestandard
Lingua originaleEnglish
pagine (da-a)132-142
Numero di pagine11
RivistaFRATTURA E INTEGRITÀ STRUTTURALE
Volume26
Stato di pubblicazionePublished - 2013

All Science Journal Classification (ASJC) codes

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