Many plastic welds are used all the time on perspex without cracking , it depends on the perspex and the plastic weld formula all are different.
Some perspex is extruded some cast , but usually with a polished or smooth laser cut edge there are no problems with a good plastic weld usually its due to scratched rough cut or poor quality cheap acrylic,
I have never had cracking with our Poly-Weld on extruded or cast acrylics it is made for use on perspex as well as many other plastics but it could always happen with poor grade acrylics.. but... i have never seen it in tests or model building, we always have bits of perspex and other acrylics welded with it on display at shows.
Any plastic weld with acetone or mek in it should be avoided on perspex some sell them as plastic weld or mix in to reduce cost or posting weight as mek and acetone are lighter and cheaper than things used in industrial grade perspex welds.
Using a water free canopy type glue would give a clearer and better bond than silicone as silicone tends to be slightly cloudy and tend to yellow with age. Odourless cyano would also be suitable as it would not fog.
Standard superglues can also...if too much is put on...cause micro cracks to form on a lot of clear plastics but it is very rare and only with a non polished edge.
