Most websites offering free downloads of this book are plagued with issues:
If you are a student in a recognized engineering college in India or abroad, your library likely subscribes to e-resources like:
RS Khurmi & N Khurmi Textbook of Strength of Materials - Amazon.in
S. Chand has digitized several books. Often, they provide or preview modes on Google Books. You can read upto 20% of the book for free. For the remaining 80%, you may need to purchase.