تصلد انفعالي

التصلد الانفعالي بالإنگليزية: Strain Hardening or Work Hardening or Cold Work : هوتقوية المادة بزيادة كثافة انخلاع المادة.

في البلورات المعدنية، يحدث تشوه غير عكوس على المستوى المجهري يسمى الانخلاع، ينتج هذا الانخلاع عن تغير في حقول الإجهاد محليًا ضمن المادة يبلغ أوجه في إعادة تنظيم الشبكة البلورية نتيجة انتشار الانخلاع في الشبكة البلورية. يمكن إزالة الانخلاع عن طريق حمل درجة حرارة المعدن بعملية تسمى التخمير (Annealing). وبدون عملية التخمير تظل الانخلاعات مختزنة في المعدن، وتؤثر على بعضها البعض، فتكون كعائق يعترض طريق انتشار الانخلاعات في المعدن. يؤدي هذت إلى زيادة مقاومة الخضوع للمادة وانخفاض لمطيليتها.

زيادة الانخلاعات والتصلد الانفعالي

Figure 1: The yield stress of an ordered material has a half-root dependency on the number of dislocations present.

التقدير الكمي للتصلد الانفعالي

الجهد، ${\displaystyle \rho _{\perp$

{\displaystyle \tau =\tau _{0 +G\alpha b\rho _{\perp ^{1/2 \

where ${\displaystyle \alpha$

علاقات فرضية

There are two common mathematical descriptions of the work hardening phenomenon. Hollomon's equation is a power law relationship between the stress and the amount of plastic strain:

{\displaystyle \sigma =K\epsilon _{p ^{n \,\!

where σ is the stress, K is the strength index, ε_p is the plastic strain and n is the strain hardening index. Ludwik's equation is similar but includes the yield stress:

{\displaystyle \sigma =\sigma _{y +K\epsilon _{p ^{n \,\!

If a material has been subjected to prior deformation (at low temperature) then the yield stress will be increased by a factor depending on the amount of prior plastic strain ε₀:

{\displaystyle \sigma =\sigma _{y +K(\epsilon _{0 +\epsilon _{p )^{n \,\!

The constant K is structure dependent and is influenced by processing while n is a material property normally lying in the range 0.2–0.5. The strain hardening index can be described by:

{\displaystyle n={\frac {d\log(\sigma ) {d\log(\epsilon ) ={\frac {\epsilon {\sigma {\frac {d\sigma {d\epsilon \,\!

This equation can be evaluated from the slope of a log(σ) - log(ε) plot. Rearranging allows a determination of the rate of strain hardening at a given stress and strain:

{\displaystyle {\frac {d\sigma {d\epsilon =n{\frac {\sigma {\epsilon \,\!

العمليات

The following is a list of cold forming processes:

Squeezing
- Rolling
- Swaging
- Extrusion
- Forging
- Sizing
- Riveting
- Staking
- Coining
- Peening
- Burnishing
- Hubbing
- Thread rolling
Bending
- Angle bending
- Roll bending
- Draw and compression
- Roll forming
- Seaming
- Flanging
- Straightening
Shearing
- Slitting
- Blanking
- Piercing
- Lancing
- Perforating
- Notching
- Nibbling
- Shaving
- Trimming
- Cutoff
- Dinking
Drawing
- Tube drawing
- Wire drawing
- Spinning
- Embossing
- Stretch forming
- Sheet metal drawing
- Ironing
- Superplastic forming

المزايا والعيوب

المزايا:

No heating required
Better surface finish
Superior dimensional control
Better reproducibility and interchangeability
Directional properties can be imparted into the metal
Contamination problems are minimized

العيوب:

Greater forces are required
Heavier and more powerful equipment and stronger tooling are required
Metal is less ductile
Metal surfaces must be clean and scale-free
Intermediate anneals may be required to compensate for loss of ductility that accompanies strain hardening
The imparted directional properties may be detrimental
Undesirable residual stress may be produced