Elastic leak of a seal

An elastomeric seal may leak by elastic deformation without any material damage. We describe elastic leak using a theoretical model, and watch a seal deform and leak using a transparent experimental setup. The elastomer seals the fluid by forming contact with surroundinghardmaterials. As the fluid pressure increases, the contact stress also increases but not as much. When the fluid pressure surpasses the contact stress, the elastomer and the hard materials lose contact in some region, forming a leaking path. The critical fluid pressure for elastic leak depends on the geometry and constraint of the seal, but is insensitive to the rate at which the fluid is injected. Our study points to the significance of elastic deformation in modes of failure that also involve material damage. © 2014 Elsevier Ltd. All rights reserved. Seals are ubiquitous. Familiar examples are those in plumbing joints, drinking bottles, and pressure cookers. Engines require seals to enable gas-tight, reciprocating motion of pistons in cylinders [1]. Hydraulic fracture requires seals to isolate fluids in gaps between pipes and boreholes [2–5]. Seals, along with tires and bearings, are among the most significant applications of elastomers [6]. Seals are inexpensive, but their failure can be costly. The explosion of the space shuttle Challenger, for example, was traced to the failure of O-rings [7]. The softness of an elastomer is essential to both the function and failure of a seal. The elastomer seals a fluid in a gap between mating parts made of hard materials. The softness enables the seal to deform easily, adapting to unpredictable variations in its working environment, such as the height of the gap, the misalignment of the mating parts, the roughness of their surfaces, and changes in temperature. With this adaptation, neither the seal nor ∗ Corresponding author. E-mail address: [email protected] (Z. Suo). 1 These authors contributed equally to this work. http://dx.doi.org/10.1016/j.eml.2014.10.001 2352-4316/© 2014 Elsevier Ltd. All rights reserved. the mating parts need to be designed with high precision, which could be costly or impossible. The softness of the elastomer, however, also makes the seal prone to failure. The fluid pressure can cause the seal to deform and damage, leading to leak [1,8]. Here we study a particular mode of failure, elastic leak. An elastomer seals a fluid by forming contact with surrounding hard materials. As the fluid pressure increases, the contact stress also increases but not asmuch.When the fluid pressure surpasses the contact stress in some part of the contact region, the seal and the hardmaterials lose contact in this region, forming a leaking pathwhich eventually penetrates through the whole contact region. This mode of failure is entirely due to elastic deformation: the seal leaks without any material damage. We construct a transparent experimental setup to watch the seal deform and leak, and compare experimental observations to theoretical predictions.We find that the critical fluid pressure for elastic leak depends on the geometry and constraint of the seal, but is insensitive to the rate at which the fluid is injected. Whereas seals have been studied as boundary-value problems of elasticity (e.g., [9–11]), how the solutions of elasticity relate to the leak of seals is poorly understood. In Q. Liu et al. / Extreme Mechanics Letters 1 (2014) 54–61 55 (a) Precompress. (b) Seal. (c) Escape. (d) Leak.