Shear failure of reinforced concrete, more properly called “diagonal tension failure” is one example. If a beam without properly designed shear reinforcement is overloaded to failure, shear col- lapse is likely to occur suddenly with no advance warning (brittle failure)

Creating this kind of condition in a beam is difficult as pure shear conditions prevail at points where you have bending moment zero and only shear force. It is difficult to visualise these condition except simple supports and points of inflection.

However a typical loading as shown in diagram attached will have pure shear conditions.

I agree with Pawan Bhattarai . If you want to insure that the failure is caused by shear in specific location, then simply you have to cast/design your tested beam without shear reinforcement (you can put stirrups up to half length of the beam and leave the other half without stirrups). in this case the shear failure will take place in the half without shear reinforcement stirrups.

If the beam is showing tension cracks in diagonal direction near to the support, then it indicates beam is failed in shear.

Thank you all for these precious answers! Pawan Bhattarai Om Prakash Chhangani Ahmed Mirghani Prashant Bansode