The adjectives 坚强 and 顽强
The adjectives 坚强 и 顽强 have the same meaning, but differ slightly in usage.
The same meaning
The adjectives 坚强 
and 顽强 emphasize someone’s strong character.
and 顽强 emphasize someone’s strong character.Examples
他很顽强，没有向困难低过头
He was tenacious and never bowed to difficulties
tā hěn wánqiáng, méiyǒu xiàng kùnnan dīguò tóu
她是个坚强、有原则的女人
She is a strong and principled woman
tā shì ge jiānqiáng, yǒu yuánzé de nǚrén
Other meanings of 顽强
顽强 is used when referring to will and actions.
Pay attention
坚强 cannot be used to describe actions or will.
Examples
他们顽强拼搏，终于赢得了第一名
They fought hard and finally won first place
tāmen wánqiáng pīnbó, zhōngyú yíngdé le dìyī míng
尽管有病，他仍顽强地坚持工作
Despite his illness, he persevered with his work
jǐnguǎn yǒu bìng, tā réng wánqiáng de jiānchí gōngzuò
In some cases, 顽强 has a negative connotation meaning "stubborn" and "indomitable".
Pay attention
坚强 doesn't have a negative connotation.
Examples
他们会顽强抵抗，因为他们不想回家
They will persist because they don't want to go home
tāmen huì wánqiáng dǐkàng, yīnwèi tāmen bù xiǎng huí jiā
Other meanings of 坚强
坚强 can also be used as the verb "to strengthen".
Pay attention
顽强 cannot be used as a verb.
Examples
丰富自己的知识，坚强自己的信心
Enrich your knowledge and build your confidence
fēngfù zìjǐ de zhīshi, jiānqiáng zìjǐ de xìnxīn