Why this c# program can not to auto die player

I want to make game of tank but I can not auto die player Ex. if three "Bullet" clash to the player, player was dead Where is wrong?

  using UnityEngine;
  using System.Collections;

  namespace StateMachineSample
  {
      public class PlayerController : MonoBehaviour
      {
          public Transform turret;
          public Transform muzzle;
          public GameObject bulletPrefab;

     private int maxLife = 3;
     private int life;

     private float force = 100f;
     private float maxSpeed = 30f;
     private float maxAngularVelocity = 360f;
     private float attackInterval = 0.8f;

     private int groundLayerMask;
     private float lastAttackTime;

     private void Start()
     {
         groundLayerMask = 1 << LayerMask.NameToLayer("Ground");
     }

     private void Update()
     {
         UpdateTank();
         UpdateTurret();
     }

     

     private void UpdateTank()
     {
         Vector3 velocity = GetComponent<Rigidbody>().velocity;

         life = maxLife;




         if (velocity.sqrMagnitude < 1f)
         {
             return;
         }

         Vector3 direction = new Vector3(velocity.x, 0f, velocity.z);

         Quaternion targetRotation = Quaternion.LookRotation(direction);
         transform.rotation = Quaternion.RotateTowards(transform.rotation, targetRotation, maxAngularVelocity * Time.deltaTime);
     }

     public void TakeDamage()
     {
         life--;
         if (life <= 0)
         {
             Destroy(gameObject);
         }
     }



     private void UpdateTurret()
     {

         life--;
         if (life <= 0)
         {
             Destroy(gameObject);
         }

         // マウス位置を狙う
         Ray ray = Camera.main.ScreenPointToRay(Input.mousePosition);
         RaycastHit hit;
         if (Physics.Raycast(ray, out hit, Mathf.Infinity, groundLayerMask))
         {
             turret.rotation = Quaternion.LookRotation(hit.point - turret.position);
         }

         
         

         // マウス左クリックで発射する
         if (Input.GetMouseButtonDown(0))
         {
             if (Time.time > lastAttackTime + attackInterval)
             {
                 Instantiate(bulletPrefab, muzzle.position, muzzle.rotation);
                 lastAttackTime = Time.time;
             }
         }
     }


     private void FixedUpdate()
     {
         float x = Input.GetAxisRaw("Horizontal");
         float z = Input.GetAxisRaw("Vertical");

         Vector3 direction = new Vector3(x, 0f, z).normalized;

         GetComponent<Rigidbody>().AddForce(direction * force);
         GetComponent<Rigidbody>().velocity = Vector3.ClampMagnitude(GetComponent<Rigidbody>().velocity, maxSpeed);
     }
 }

}