1.4 – Testing To Australian Standards

 BrushDestructor brushcutter blades has been subjected many hours trial and testing in the bush as well as being subjected to the following tests.


Australian Standards – AS3575-1995

 The aim of this test is to see how the

BrushDestructor Blade would fare when hit against a metal bar at full revs. 

Brushcutter Blade-Heavy duty BrushDestructor Blade tested to Australian Standards 3575 1995-Overview of test rig.

The scope of the test is to determine the strength of a metal blade when fitted to a brush cutter.

 
The principled of the test is for the brush cutter blade  to strike a 25mm diameter steel bar at 1 meter/second while running at maximum RPM to determine its resistance to breaking.
 
The standard states the the blade must not break or crack, but minor damage at the point of impact shall not be cause for failure.
 
Below is an overview of the test box, the walls expecting to catch any broken parts of the blade to estimate the impact by the damage to the custom wood sheeting. A very careful inspection of all walls after testing found no impact points, a future test will be carried out with corrugated cardboard attached to all four walls to see if pieces might penetrate the cardboard. 
 
Below is a new set of blades prior to testing.
BrushDestructor Heavy Duty blade test to Australian Standards 3575 1995 - Close up of steel bar & brush cutter blade
 
Close up of the 25mm steel bar showing damage after two impacts, some tips of teeth are visible embedded into the steel bar.
BrushDestructor Heavy Duty blade test as specified to Australian Standards 3575 1995 - Close up of steel bar after two impacts
 
Below is a close up of the blades after impact.
BrushDestructor Heavy Duty blade test as specified in Australian Standards 3575 1995 - Damaged blades after impact
Below are two sets of blades after testing; The first (left set) after impact with the bar at full revs and a strike velocity of 1m/s plus. This chipped the tips off each blade with each piece found found on the floor of the test rig within a 500mm radius of the steel bar suggesting that all of the energy was absorbed in the impact with the bar and that in this case the pieces posed no danger to properties or persons. The second test (right set) with newly turned over set of blades with several hours of use, after impact with bar at full revs and a strike velocity of 2m/s plus. Here you can see that the higher impact velocity resulted in impact on the first blade near the front of the blade, followed by impact a little higher up and then higher up again resulting in the bending of that blade. BrushDestructor Heavy Duty blade test as specified in Australian Standards 3575 1995 - Close up of two blade tests   Click to See Product Options And Prices    

The aim of this test is to check the strength of the blade around the pivot holes.

BrushDestructor brush cutter blade - Compromised BladeTest after 1 hour BrushDestructor’s flail blades have been subjected to many hours of hard use to see if a blade might fail about the pivot points. With no failures occurring after many hours of testing, a new set of blades was then compromising by 50% at the pivot points to see if and what it would take to cause failure. Below you can see how the three blades were compromised in three different ways. The test was carried out with the brush cutter running continuously at full revs for a whole hour. BrushDestructor brush cutter blade - Compromised blade test at 0 hours Below is a photo of the compromised blades after 1 hour of hard use, with no resulting failures.

BrushDestructor brush cutter blade - Compromised blade test at 1 hour
 
Below is a photo of the compromised blades after almost 2 hours; The tip of one blade broke off at 1 hour and 43 minutes while cutting through a 30mm gum sapling and as the tree was falling the cut line closed up wedging the blades resulting in the failure at the leading edge. The tip of the other blade broke off at 1 hour and 59 minutes when hitting an old hidden stump with some force. The third blade was used for another hour without failing. There were no failures at the pivot end of the flail blade. BrushDestructor brush cutter blade - Compromised blade test at 2 hour Click to See Product Options And Prices

The aim of this test is to check the fasteners to see if they could come loose

Below is a photo of test to check for two things; Firstly to see if a locknut might vibrate itself loose. This lock nut was wound on and off twenty times to compromise the nylon locking strip and then left un-tightened on a longer bolt to see if it might vibrate off. It did not rotate even one degree after two hours of hard use. Secondly to see if a bolt which was not locked in place with a lock nut, would vibrate itself loss and allow a blade to fly free. Again after two hours of hard use the bolt did not even slightly come lose, concluding that there is so much shear load on the bolt while running that there is no way it can vibrate loose while in use. BrushDestructor brush cutter blade - Test to see if nut and bolt will vibrate loose allowing blade to fly out becoming a hazard   Click to See Product Options And Prices

The aim of this test is to check by computer simulations, the stresses places on the hub and blades

Below are computer model images showing the stresses on the hub and blades at 15,000 rpm which is 50% above the general maximum rpm of most brush cutter heads.  Top view showing stress loads throughout the metal parts while spinning at 15,000rpm. Brushcutter Blade,ExtraHeavyDuty,BushDestructor-15000rpm-Results-Stress1-top.analysis Bottom view spinning at 15,000rpm. Brushcutter Blade,ExtraHeavyDuty,BushDestructor-15000rpm-Results-Stress1.analysis   Close up view of blade spinning at 15,000rpm. BrushDestructor,ExtraHeavyDuty,BushDestructor-15000rpm-Results-Stress1 blade only.analysis

Analysis of Brush cutter blade to an angular velocity of 15000 Rpm.

As can be seen in the analysis the brush cutter blade achieves an angular velocity of 15000 Rpm with a minimum factor of safety of 1.46. Under these conditions the stress is less than the maximum allowable stress for the stated Steel (1027 MPa or greater) within the blade structure.
 
The standard operating angular velocity for these blades is 10000 Rpm, as can be seen the blade is capable of achieving this with a factor of safety of 3.29.
Andy Wirth CSWP, BEng Mech.
 
It is not until just over 18000 Rpm that the yield stress of the material is exceeded.

Top view showing stress loads throughout the metal parts while spinning at 18,000rpm.

Brushcutter Blade,ExtraHeavyDuty,BushDestructor-18000rpm-Results-Stress1-top.analysis
 
 
Bottom view spinning at 18,000rpm.
 
Brushcutter Blade,ExtraHeavyDuty,BushDestructor-18000rpm-Results-Stress1.analysis
 
 
Top and Bottom view of Blade Bending tests.
 
Brushcutter Blade,ExtraHeavyDuty,BushDestructor-18000rpm-Results-Displacement1-top.analysis
Brushcutter Blade,ExtraHeavyDuty,BushDestructor-18000rpm-Results-Displacement1.analysis
 
 
 
Realtech SolutionsComputer Stress Analysis Carried by Realtech Solutions.

Andy Wirth CSWP, BEng Mech.

Phone     08  8557 7647    Mobile    0421  748 808

Web        http://www.realtechsolutions.net.au