无法访问json值

I have a JSON array from ajax response but when I tried to access it field then it says undefined. here is my JSON

[{"material_name":1042,"qty_per_piece":"30","material_qty_req":150},{"material_name":1043,"qty_per_piece":"20","material_qty_req":100},{"material_name":1041,"qty_per_piece":"10","material_qty_req":50}]

what i am trying its following

for(var j = 0; j<material.length; j++){
  var matName = material.material_name[j];
  alert(matName);

when i tried through following it shows undefined

for(var j = 0; j<material.length; j++){
  var material_names = material[j].material_name;
   alert(material_names);

var material = [{"material_name":1042,"qty_per_piece":"30","material_qty_req":150},{"material_name":1043,"qty_per_piece":"20","material_qty_req":100},{"material_name":1041,"qty_per_piece":"10","material_qty_req":50}];

material.forEach(function(v,k){
    console.log(v.material_name);
});

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