Breakable.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class Breakable : MonoBehaviour
{
    public float mass = 50;
    public float impulseThreshold = 10000;

    Collider _collider;
    new Collider collider { get { if (!_collider) _collider = GetComponent<Collider>(); return _collider; } }

    bool isBroken;

    private void OnTriggerEnter(Collider col)
    {
        if (isBroken)
            return;

        var otherRb = col.attachedRigidbody;

        if (!otherRb)
            return;

        collider.isTrigger = false;

        // Since I don't have collision point info, I use rigidbody position. Not great, but it works..
        Vector3 relDir = (transform.position - otherRb.position).normalized;

        Debug.DrawRay(transform.position, relDir, Color.red, 4);

        // We need this to make sure a glancing blow doesn't break it
        float dot = Vector3.Dot(otherRb.velocity, relDir);

        float relImpulse = otherRb.mass * otherRb.velocity.magnitude * dot;

        if (relImpulse > impulseThreshold)
            Break();
        else
            StartCoroutine(TurnBackIntoTriggerCo());
    }

    void Break()
    {
        var rb = gameObject.AddComponent<Rigidbody>();
        rb.interpolation = RigidbodyInterpolation.Interpolate;
        rb.mass = mass;

        ElectricSpark.e.Spark(transform.position + Vector3.up * 0.3f);

        isBroken = true;
    }

    IEnumerator TurnBackIntoTriggerCo()
    {
        yield return null;
        yield return null;
        yield return null;

        collider.isTrigger = true;
    }
}