So many people train with the misconception that doing hundreds of abdominal crunches or sit-ups is going to carve out their 6 pack.
Please stop doing this!
First and foremost the most crucial factor to making your abs visible is to get your nutrition under control, to ensure that your body fat is low enough.
Secondly you will get far better abdominal development by training them for power and explosiveness which will also assist you in improving performance.
Try performing a number of heavy deadlifts, power cleans or land mines and see if your your abs are feeling it the next day.
Alternatively add some resistance to the more typical abdominal exercises to make it challenging to complete 8 reps and I guarantee you will see far better development in your midsection.
Couple this up with a good nutrition plan and you will display a set of washboard abs before you know it.