The water will expand as it freezes, exerting pressures on the inside walls of the beaker that could potentially cause it to fracture.
The Beaker’s Stability : The term stability is sometimes used in reference to balance (e.g. the balance of forces that prevent something from toppling over), but in this case it refers to structural stability, that is the ability of the beaker to hold together under stress.
Freezing water: We may be more familiar with liquids that expand when they evaporate into their gas phase and contract when they freeze into their solid phase. But water is different.
Water expands as it becomes a gas, but it also expands when it freezes into solid ice.
Another way of saying this is water molecules in a liquid phase are packed closer together than water molecules in ice or steam.
The densities of liquid water and ice are
Structural stability of solids containing freezing water The water in the beaker takes up a certain amount of space in liquid form, but it needs about 9% more space when it freezes into ice.
The water expands in all directions when it freezes. Imagining the water taking on the shape of a cylindrical beaker, a cylindrical shaped block of ice with circular cross-section would increase in length as well as circumference.
So the beaker would start to experience stress like a pair of tight jeans on a person who has gained weight and is almost 10% bigger than they used to be. Think of Bruce Banner bursting out of his pants as he transforms into the more massive Hulk.
The beaker will also experience increase pressure and break if it does not have sufficient fracture toughness or elasticity to constraint the expanding ice. This depends on the material properties of the beaker, i.e. whether the beaker is made of glass, plastic, etc.