Compression testing of foamed plastics and rubbers for use as orthotic shoe insoles

Abstract

Thirty-one materials have been tested in compression in order to generate the stress (force per unit of cross-sectional area) versus strain (deformation) behaviour, for the purpose of assessing the suitability of various foamed plastics and rubbers as shoe insole materials. It was found that the materials could be classified into three distinct categories (very stiff, moderately deformable and very deformable) according to the shape of the characteristic stress versus strain curve. The moderately deformable group has been selected as the most promising for clinical application.

Effect of Heating on the Mechanical Properties of Insole Materials

“…Sampling was performed from a preload of 10 kPa, simulating the pressure of putting the foot into the shoe, to the peak pressure (283 kPa). 4,5 Three unheated and three heated samples of each of the eight materials or combination of materials were tested, and each sample was tested five times. Three parameters were measured for each of the 48 tested samples: percent compression at maximum loads, strain under compressive load, and load transmission.…”

“…The two qualities are (1) the mechanical properties of the material as it deforms under applied loads and (2) force dissipation or the ratio of input versus output force (i.e., the proportion of force not transmitted to the plantar surface of the foot). 7 Previous studies have analyzed insole materials both by compressing the materials against a flat surface 4,5 and also in models of plantar bony prominences. 2,3 Because pain in sensate, or ulceration in insensate patients occurs under plantar bony prominences such as the metatarsal heads, it is common practice to create molding of the materials by first heating them.…”

Footwear Cushioning: Relating Objective and Subjective Measurements

“…However, static stiffness may not be a good measure for real-life situations involving human movement. Campbell, Newell, and McLure (1982) categorized materials based on compression characteristics using a modified ASTM-D 1667-76 procedure. The materials in that study were separated into three categories (very stiff, moderately deformable, and highly deformable) based on the shape of the stress-strain curves obtained from an Instron Universal Testing machine.…”

Novel Insole Material for Weight-Bearing Monitoring Medical Device to Be Used in Fractured Bone Clinic

“…Because of their investigations, all materials were divided into 3 categories: highly deformable, moderately deformable and very stiff (Table 2.1) according to the shape of their characteristic compression curve (Figure 2.1). Campbell et al (1982) Highly deformable materials (Category 3) undergo a rapid deformation that commonly referred to as "bottoming-out". Since these materials will not transfer a significant portion of the stress to adjacent regions of the foot, they have been judged to possess poor characteristics for use as an orthotic shoe insole material.…”