Yes! You can crack a nut with a sledgehammer and it works very well.
I somehow managed to snap my nut crackers (either super human strength or they had corroded and become brittle) and the bag of in-shell hazelnuts sat intact looking like they wanted to be opened. I headed to my tool box and retrieved a mini sledgehammer.
You can see in the video above the large flat head of the sledgehammer on a flat concrete base worked really well. Only a tiny amount of force is needed and out of 20 or so only one nut got damaged, even then it was just into 3 large pieces that were still easy to eat. Far better than nutcrackers as you always risk squishing your fingers and have to line up each nut. Using a sledgehammer to crack a nut is far quicker, safer and can be done one handed. See the video above.
I will in the future always use the sledgehammer to open nuts – although it may get a bit chilly sat outside on the patio at Christmas so thankfully this method is quick.