Deterministic Lock Lattice (DLL)

Technical Disclosure by Kevin Boykin 10/04/2025

Abstract

This concept outlines a mechanically tunable impact-protection structure that transitions from soft to rigid at a predetermined load. It combines two elements:
(1) a deterministic interlocking lattice that stiffens when its internal elastomer layer compresses past a preset gap, and
(2) a rebound-resistant laminate that prevents the structure from tearing apart during the rapid decompression phase that follows impact.
Unlike fluid-based or shear-thickening materials, this approach relies purely on geometry and layered cohesion to achieve a binary, resettable stiffness switch. The design can be fabricated with common additive or lamination processes and tuned by simple parameters—gap size, elastomer hardness, and rib geometry. Potential uses include wearable protection, electronics cases, helmets, and reusable shipping cushions.
This document records the principle for open use and further development.



1) Architecture (deterministic “lock”)

X (rigid): interleaved ribs or chevrons that form a shallow “V”.
Materials: PA12 (nylon), PETG, carbon-filled nylon, or thin aluminum ribs (0.3–1.0 mm).
O (compressible): elastomer wedges/pads that sit in the V-gaps between X ribs.
Materials: silicone (Shore A 20–50), TPU (Shore A 60–95), or micro-cellular PU foam (IFD tuned).
Key geometry
Pre-gap, g: clear distance between opposing X faces when O is unloaded (e.g., 0.2–1.2 mm).
O thickness, t0: elastomer height that crushes into the V (e.g., 2–6 mm).
Contact condition: lock occurs when Δ (compressive displacement) ≥ g, so X’s touch and create a rigid load path.
Intuition: under normal loads, O carries everything (soft). Under impact, O compresses quickly by g, letting X’s “kiss” and the lattice goes stiff.

2) How to pick the switch threshold (back-of-envelope)

You can aim the lock force F∗F^*F∗ by selecting O’s modulus and the gap ggg.

Let EOE_OEO​ = compressive (secant) modulus of O at your target strain rate
Let AAA = effective loaded area per unit cell
Approximate threshold force to close the gap:
F∗  ≈  EO  A  gt0F^* \;\approx\; E_O \; A \; \frac{g}{t_0}F∗≈EO​At0​g​

(Works well for first cuts; refine later with test data/DMA.)

Raise F∗F^*F∗ by: harder O (higher EOE_OEO​), bigger area AAA, larger gap ggg, or smaller t0t_0t0​.
Lower F∗F^*F∗ by: softer O, smaller AAA, smaller ggg, larger t0t_0t0​.

3) Tunable knobs (design table)

Knob Effect on Feel Effect on Switch
O durometer (Shore A +10) Firmer in hand Higher F∗F^*F∗, faster lock
Pre-gap g (+0.2 mm) No change at rest Higher F∗F^*F∗, more “crisp” lock
O thickness t0 (+1 mm) Softer at rest Lower F∗F^*F∗, longer stroke to lock
X rib angle (sharper V) More guided crush Cleaner, earlier X contact
X rib thickness (+0.2 mm) Slightly stiffer when locked Raises locked-state stiffness
Surface friction (textured X) N/A Reduces slip, increases locked stability

4) Build options (fast prototyping → production)

A. 3D-print sandwich (fastest)

Print X layers in PETG/nylon (0.6–1.0 mm ribs, 60–75° V).
Print O layer in TPU (Shore 85–95A) with rectilinear infill to tune compressibility.
Stack X/O/X with alignment pins; ultrasonically weld, adhesive bond (PU or silicone), or mechanical clips.
B. Molded elastomer in a rigid frame (cleaner, scalable)

Water-jet or stamp X ribs from aluminum or spring steel; spot-weld into a lattice frame.
Cast silicone (Shore A 30–40) into the V-wells using a simple 2-part mold; cure in place.
C. Fabric laminate (for wearables)

Laser-cut thin acetal/nylon X chevrons; stitch or RF-weld into pockets.
Fill pockets with cut O pads (silicone gel or PU foam); heat-laminate with TPU film.

5) Test plan (to quantify the “soft → lock”)

A. Quasi-static compression (define F∗F^*F∗)

Instron/UTM, platen compression of a 3×3 cell coupon.
Measure force–displacement; the knee where stiffness jumps is your lock point.
Vary rate (1, 10, 100 mm/min) to see any rate-dependence.
B. Impact/drop testing (prove real behavior)

ASTM D1596 (cushion curve) style drop on guided mass; accelerometer on the mass.
Compare peak g with and without pre-gap g; look for sharp g-reduction after lock.
Optional pendulum/Charpy-like strike for lateral impacts.
C. Dynamic Mechanical Analysis (DMA)

Temperature sweep (−10 °C → +40 °C) & frequency sweep (1–50 Hz).
Confirm O’s modulus stability and where the lock stays consistent.
D. Fatigue & recovery

1000 impact cycles at target energy; measure drift of F∗F^*F∗ and rebound time.
Inspect for delamination, O creep, X yielding.

6) Target numbers (a sensible first prototype)

Cell pitch: 10–15 mm; rib height: 3–5 mm; rib thickness: 0.6–0.8 mm
V angle: 60–70°; pre-gap g: 0.5 mm; O thickness t0: 3 mm
O material: silicone Shore A 35 (compressive modulus ≈ 1–2 MPa @ 10 s⁻¹)
With AAA ≈ 100 mm² per cell → F∗F^*F∗ per cell ≈ 17–33 N
9-cell coupon locks around 150–300 N quasi-stat (dial by g/durometer).

7) Failure modes to watch

O creep (permanent set): pick silicones with low compression set; consider micro-cell PU with skins.
Delamination: use surface prep (corona/plasma) or mechanical interlocks (through-holes) for O↔X bond.
X yielding: up-gauge ribs or switch to glass-/carbon-filled nylon.
Rate sensitivity: if O is too viscoelastic, you’ll see timing jitter—go slightly higher Shore or lower t0.

8) Where this shines

Protective wearables (knees, shoulders, gloves): supple in motion, rigid on hits.
Phone/laptop cases: soft in hand, rigid in drops.
Helmet liners & shin guards: controlled g-limit with crisp lock.
Shipping/packaging: reusable cushions that “set” under shock.

9) Why it’s novel

Prior art (STF/D3O/auxetics) achieves soft-to-stiff via chemistry or continuous geometry.
Proposal: a deterministic geometric interlock with a designed pre-gap that yields a binary, thresholded stiffness switch.
Emphasize: tunable F∗F^*F∗, resettable, scalable, low temp-dependence vs. fluids.



Copyright © 2025 Kevin Boykin. All Rights Reserved.

This document is published for record and informational purposes only. No part of this work may be reproduced, adapted, or used commercially without the express written consent of the author.







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