from wood database
White ash
Specific Gravity (Basic, 12% MC): .55, .67
Janka Hardness: 1,320 lbf (5,870 N)
Modulus of Rupture: 15,000 lbf/in2 (103.5 MPa)
Elastic Modulus: 1,740,000 lbf/in2 (12.00 GPa)
Crushing Strength: 7,410 lbf/in2 (51.1 MPa)
Hard maple
Specific Gravity (Basic, 12% MC): .56, .71
Janka Hardness: 1,450 lbf (6,450 N)
Modulus of Rupture: 15,800 lbf/in2(109.0 MPa)
Elastic Modulus: 1,830,000 lbf/in2(12.62 GPa)
Crushing Strength: 7,830 lbf/in2 (54.0 MPa)
They dont seem terribly different by stats, But try it out I've seen some bowyers over in europe use ash as core lams for a good portion of their custom bows