Auxetic Backpack Straps for Pressure Relief and Breathability
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Solution Overview
Problem
Conventional backpack shoulder straps experience a contraction under load, concentrating pressure at the user's shoulders and promoting sweat stagnation due to limited auxetic effect and lack of breathability, with elastic rebound causing discomfort during transportation.
Innovation Solution
The shoulder straps incorporate a core of elastic expanded plastic material with a lattice of through openings and a partially porous or net-shaped sheath, connected by fastening means, to enhance auxetic properties and breathability, while the waist belt uses similar auxetic structures for secure fit and comfort.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional shoulder straps are used, then the structure is simple and easy to manufacture, but the straps contract under load causing pressure concentration and discomfort
Solution Approach 1:
The patent changes the fundamental parameter of the material structure by introducing an auxetic structure with negative Poisson's ratio. This causes the material to expand laterally when stretched longitudinally, opposite to conventional materials. The core uses expanded plastic material with a specific lattice of through-openings that enables this auxetic behavior, transforming how the strap responds to load and thereby improving comfort by distributing pressure rather than concentrating it.
Solution Approach 2:
The shoulder strap employs a composite structure consisting of an inner core made of auxetic expanded plastic material and an outer covering sheath made of fabric or synthetic material. This composite design combines the pressure-distributing auxetic effect of the core with the protective and aesthetic properties of the covering, resolving the contradiction between comfort improvement and structural simplicity.
2Ease of operation
If conventional fabric covering is used, then the material is simple and waterproof, but it forms a barrier that promotes sweat concentration and stagnation
Solution Approach 1:
The patent specifies that the outer covering sheath should be porous or net-shaped rather than solid fabric. This porous structure allows air circulation and sweat evaporation through the strap, directly addressing the sweat stagnation problem. The covering may be made of mesh material or fabric with permeable properties, enabling moisture to pass through while maintaining the structural integrity and waterproof outer layer where needed.
3Ease of operation
If the padding core is free inside the covering sheath, then the structure is simple, but elastic rebound causes Yo-Yo effect and discomfort during transportation
Solution Approach 1:
The patent implements preliminary connection between the auxetic core and the outer covering sheath at the ends and at intermediate points along the length of the strap. This pre-established connection prevents the core from moving independently within the sheath during use, eliminating the elastic rebound and Yo-Yo effect that would occur with an unconnected core. The connection is made through stitching, adhesive, or other fastening methods that secure the core in place while allowing it to maintain its auxetic functionality.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design reduces shoulder and waist pressure concentration, enhances breathability, and minimizes elastic rebound, providing increased comfort and sweat evaporation, especially under heavy loads.
Implementation Method 1
Auxetic structures are structures having a negative Poisson's ratio (or transverse expansion coefficient). While conventional structures subjected to tension along one direction contract in the direction transverse to that of the stress, auxetic structures subjected to tension dilate in the direction transverse to that of the applied traction force.
Implementation Method 2
said core and sheath being connected by mutual fastening means at least at one intermediate zone of their longitudinal extension in order to keep them fast with each other and to limit the longitudinal expansion and contraction of the core with respect to the sheath
Data Source
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AI summary
A backpack includes a hollow body (12) for containing objects, from which a harness (14) extends for connecting it to a user, which includes a pair of elongated shoulder straps (16) with auxetic properties, the opposite longitudinal ends of which are fixed to the hollow body (12). The shoulder straps (16) comprise a core (18) of substantially elastic expanded plastic material in which a lattice of through openings (20) is formed, consisting of hollow cells of a predetermined shape with a plurality of corners. The core (18) is inserted into a covering sheath (22) at least partially porous or net-shaped, having a reduced elasticity compared to that of the core (18), the core (18) and the sheath (22) being connected by mutual fixing means (24) at an intermediate zone thereof to keep them fast with each other and to limit the longitudinal expansion and contraction of the core (18) with respect to the sheath (22). The backpack (10) also includes a waist belt (26) having auxetic properties similar to those of the shoulder straps (16).