If a wife and a husband are unable to have a sexual relationship after one and half year of marriage, because the wife is shy or afraid of the act, what Islamic teachings apply to this bond? Does this sort of marital life stand? What help or advice you can provide to overcome her fear? Are there any prayers for strengthening this kind of weak relationship?Your advice will be a great help as this issue is heading towards Tallaq.

Praise be to Allah, the Lord of the Worlds; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.
Continuing the situation stated in your question for the period of one and half years is very rare and unusual. The husband and wife both of them might be responsible for this failure.
Anyway, the marriage contract is still legally binding and will continue unless by annulment of the marriage or divorce. There is no particular prayer for this problem, but we advise you of the following:
1. Both of you should seek Allah's Help to bless on you, relieve you from this hardship, help you to satisfy your desires and grant you good offspring. Supplicate this Dua' as much as possible. Allah Says (interpretation of meaning): {…"Our Lord! Bestow on us from our wives and our offspring who will be the comfort of our eyes, ….}[25:74].
2. We encourage you to become engrossed in supplicating Allah, reciting Qur'an, particularly the complete Surah Al-Baqarah every three days and your wife should pray. Sometimes this problem might go back to magic or Satan's temptation. The prayers and supplications weaken its effects.
3. There is no harm to ask a religious scholar to recite Qur'an on your wife without letting her be alone with him or uncovering herself.
4. There are many legal ways to remove this problem, sometimes a wife can not have sex with her husband even if she is interested in it. Sometimes the husband can not do it. For more details, please refer to Fatwas:
5. You should know there are many techniques one can use to stimulate his wife before having sexual relations. In your case, we encourage you to be kind, gentle, loving and caress her as much as you can till she is aroused sexually and desires to have relations. Sometimes approaching to this practice too directly, without tenderness may cause hatred or fear in a woman. Having sexual relations is a natural desire that one can not avoid.
6. Earlier Muslim scholars defined some solutions to stimulate a woman and arouse her for sex. They suggest to keep some kind of birds, especially a pair of pigeons or sparrows in the room of woman. When she observes their relations and how they practice love and foreplay before copulation, etc. this may arouse her sexual appetite.
Finally, we recommend you to be kind with your wife, deal with her patiently, and treat with her lovingly and try your best to solve her problem.
We ask Allah to bless you, protect you from evils and grand you pious offspring.

Allah knows best.