The Engineering Principles That Determine Equipment Reliability
In industrial systems, most failures are not caused by major components—
but by something much smaller:
👉 Fasteners
Bolts, nuts, and screws may seem simple, but they directly determine whether a system remains stable—or fails.
And here is the key reality:
👉 Most fastening failures are NOT caused by insufficient strength
They are caused by:
Improper preload
Incorrect installation
Poor understanding of engineering standards
To truly understand fasteners, we must move beyond individual components and adopt a system-level engineering perspective.
1. The True Nature of Bolted Connections
From an engineering standpoint, a bolted joint does not rely on the bolt itself to carry shear loads.
Instead, it works by:
👉 Generating preload force → Creating friction → Transmitting load
Key principle:
External loads are mainly carried by friction between contact surfaces
The bolt primarily experiences tensile stress, not shear
This is the fundamental assumption behind most engineering standards, including:
GB/T standards
ISO standards (ISO 898, ISO 4014, ISO 4032)
👉 If this assumption is violated, the connection becomes unstable.
2. Preload: The Most Critical Factor ⭐ MUST DO
Preload is not a random parameter—it must be carefully controlled.
A properly designed preload must ensure:
No slip under maximum load
Bolt remains within elastic range
Adequate fatigue life
⚠️ HIGH RISK:
Too low preload → joint loosening + fatigue failure
Too high preload → yielding or thread damage
💡 PRO TIP:
Fastener reliability is not about “tightening harder”—
it is about achieving and maintaining the correct preload.
3. Strength Grades: Not Always “Higher is Better”
Common bolt strength classes:
8.8 → General applications
10.9 → Higher load conditions
12.9 → High-strength applications
While higher grades allow higher stress:
👉 They also reduce ductility and fatigue tolerance
Key insight:
High strength ≠ high reliability
Wrong selection can accelerate failure
4. Fatigue Failure: The Real Enemy
According to ISO, DIN, and high-reliability industries:
👉 Most fastener failures are fatigue failures—not overload
Failure process:
Preload loss
Micro-slip between surfaces
Alternating stress on bolt
Crack initiation at thread root
Crack propagation → fracture
👉 This is why:
Reuse of critical bolts is restricted
Tightening procedures are strictly controlled
5. Material Selection: Match the Environment
Fastener materials must match operating conditions:
Carbon steel / alloy steel:
High strength
Good fatigue performance
Suitable for general environments
Stainless steel:
Excellent corrosion resistance
Lower strength compared to alloy steel
👉 Choosing the wrong material can:
❗ Reduce reliability under load
❗ Cause premature failure
6. Surface Treatment: More Than Corrosion Protection
Surface treatment affects not only corrosion resistance—but also:
👉 Friction coefficient
And friction directly affects:
👉 Preload accuracy
Example:
Dacromet coating
Stable friction coefficient
Better preload control
Widely used in high-strength applications
7. Anti-Loosening Design
The goal of anti-loosening is not just preventing rotation—
but maintaining preload stability over time.
Traditional methods (like spring washers) are no longer sufficient.
Modern solutions include:
Structural anti-rotation design
Friction stabilization
Controlled tightening processes
👉 Anti-loosening is a system design issue, not just a component issue.
8. Full Lifecycle Management
In industries such as:
Wind power
Rail transportation
Aerospace
Nuclear energy
Fasteners are treated as critical engineering elements.
Lifecycle control includes:
Design stage → load & fatigue calculation
Manufacturing stage → material & heat treatment
Assembly stage → controlled tightening
Operation stage → inspection & monitoring
Maintenance stage → replacement & traceability
👉 Fasteners are not consumables—they are lifecycle-managed components
🔚 Final Takeaway
The upper limit of equipment performance depends on design.
But the lower limit of reliability depends on:
👉 the quality of its connections
Fasteners may look simple, but they represent one of the most fundamental—and critical—engineering challenges.
👉 Respecting fasteners means respecting engineering principles.