You can attach a SQL Server data file(.mdf) which has no log file(.ldf) associate with the data file.
Use the following SQL Query with the correct path of the data file.
CREATE DATABASE MyDB
ON (FILENAME = ‘C:\Program Files\Microsoft SQL Server\MSSQL10_50.MSSQLSERVER\MSSQL\DATA\MyDB_Data.mdf’) — change the drive and file path
FOR ATTACH_REBUILD_LOG ;