Formability is an essential material property that needs to be considered when selecting materials for hot stamping applications. Due to the difficulties of achieving rapid cooling before deformation and the failure of lubricant systems, however, it is challenging to use conventional Nakajima and Marciniak tests to evaluate the formability of materials under hot stamping conditions. Recently, biaxial test methods have shown great potential to overcome this challenge. In this paper, recent developments of the biaxial test methods for formability evaluation are reviewed, including testing machines, specimen designs, specimen heating methods, testing procedures, and limit strain determination methods. Compared to the Nakajima or the Marciniak tests, the biaxial test method can provide better simulation for hot stamping conditions and it can be a promising method for evaluating the formability of sheet metals under hot stamping conditions. However, more developments such as the standardisation of the specimen designs and the limit strain determination methods, are still needed for the wide use of the biaxial test method.

Introduction We report a case of unilateral mydriasis following microvascular decompression for hemifacial spasm complicated by pneumocephalus through the operative incision. Case report A 50-year-old gentleman with a past medical history of hypertension presented with a left hemifacial spasm. He received left-side microvascular decompression under general anaesthesia. After operation, the patient's right pupil was found to be markedly dilated (6 mm), with diminishing direct or consensual light reflex. The left pupil was 2 mm and also nonreactive to light. Emergent head CT revealed pneumocephalus and no intracranial haemorrhage or any other abnormalities. We concluded that the right oculomotor must have been distorted by pneumocephalus. The patient was extubated in the operation room. The right pupil returned to normality within the next 6 h. Postoperative course was uneventful other than insomnia in the first 24 h. Conclusion We think that pneumocephalus leads to brainstem shift and distorted the right oculomotor nerve. Unilateral mydriasis is alarming after neurosurgery and must be interpreted with caution.