This paper looks like a good place to start (it has references to quite a lot of other relevant papers):

Tensile strength and toughness of partially sintered ceramics using discrete element simulations, Jauffrès, D., Liu, X., Martin, C.L, Engineering Fracture Mechanics

Volume 103, May 2013, Pages 132-140

The fracture behavior of highly porous ceramics is simulated using the discrete element method. Spherical particles model the powder used to obtain the partially sintered ceramic material. Three-dimensional representative volume elements of porous microstructures made of several tens of thousands of particles were first generated by numerical sintering. Elastic force-displacement laws model the solid bonds formed between particles during sintering. A realistic fracture criterion, based on the local stress intensity factor associated with the bond between two particles, is also introduced. The simulation of tensile tests allows the assessment of the effective strength of these microstructures as a function of the residual porosity. Furthermore, the introduction of a pre-crack in a sample subjected to a remote tensile stress allows the critical stress intensity factor to be calculated. Porous electrodes for electrochemical applications represent an important application field for these ceramics. Those discrete element simulations should be an effective tool for optimizing their microstructure at the micron length scale.

Two highly cited papers from reliable research groups on sintered alumina (there doesn't seem to be anything specifically on zirconia):

Journal of the American Ceramic Society

Volume 77, Issue 8, August 1994, Pages 2113-2117

Mechanical properties of partially dense alumina produced from powder compacts Lam, David C.C., Lange, Fred F., Evans, Anthony G.

The elastic modulus (E), the critical strain energy release rate (Gc), and the flexural strength (σ) have been determined for two partially dense alumina bodies produced from the same powder but with different initial densities. The mechanical properties were measured for specimens fabricated at four different relative densities. The measured elastic modulus, critical strain energy release rate, and a calculated critical stress intensity factor (Kc) were observed to be linearly related to (ρ-ρ0)/(1-ρ0), where ρ is the current relative density and ρ0 is the initial relative density of the powder compact. With the observed linear relations for E, Gc (or Kc), and the assumption that the crack length responsible for failure was present in the initial powder compact and shrunk in proportion to the relative density change, a Griffith equation was constructed to estimate the strength at any relative density. This relation was in good agreement with measurements.

Journal of the European Ceramic Society

Volume 15, Issue 8, 1995, Pages 769-775

Mechanical properties of a partially sintered alumina

Hardy, D., Green, D.J.

An experimental investigation was performed to understand the mechanical properties of alumina with moderate amounts of porosity (∼ 20-40%). Young's modulus, strength and fracture toughness showed similar behavior as a function of the degree of sintering. For low sintering temperatures (

OK, there's this:

Effect of agglomeration on mechanical properties of porous zirconia fabricated by partial sintering

By: Deng, ZY; Yang, JF; Beppu, Y; et al.

JOURNAL OF THE AMERICAN CERAMIC SOCIETY Volume: 85 Issue: 8 Pages: 1961-1965 Published: AUG 2002

Porous ZrO2 ceramics were fabricated by compacting a fine ZrO2 powder, followed by pressureless sintering. Two unidirectional pressures of 30 and 75 MPa were used to prepare the green compacts. The strength and the fracture toughness of porous ZrO2 specimens sintered from the compacts prepared by 75 MPa were substantially higher than those by 30 MPa, especially for the specimens with low porosity. However, the corresponding Young's moduli were identical. This caused the strain to failure of these porous bodies to increase significantly with increasing compaction pressure. Microstructural analyses showed that a number of voids and small flaws existed in the green compacts prepared by the lower pressure, due to the agglomeration of fine ZrO2 grains. It was revealed that the ZrO2 agglomeration resulted in a localized nonuniform shrinkage and degraded the mechanical properties of porous ZrO2 ceramics.

Thanks Steve. I found the two reference materials (i.e. Mechanical properties of a partially sintered alumina and Effect of agglomeration on mechanical properties of porous zirconia fabricated by partial sintering) very informative.