Thanks all for your answers.
After reading your comments, I am still not fully convinced

.
Up until reading your comments, I had no doubt that cervical penetration is an obvious fact for women. But your answers made me doubt, so I started researching deeper and here are some of the results I came up with.
First of all there are some medical methods that cervical penetration is the main point of it. some of them are :
Pap test or Pap smear
IUI
IUD
Hysteroscopy
Cervical dilation
None of these methods use anesthesia or anesthetic cream, specially the Pap test, and in most of them a discomfort or in worst case a
mild pain is expected. Here are some references :
Pap smears shouldn't hurt. If you're getting your first Pap, it may feel a little uncomfortable because it's a new sensation that your body isn't yet used to. People often say it feels like a small pinch, but everyone has a different threshold for pain.
Source :
Do Pap Smears Hurt? And 12 Other FAQs - Healthline
Some pictures and videos about Pap test and it's equipment :
Some Gifs and a video :
http://www.csmgraf.com/images/abstr/abstreichen_animated.gif
http://www.csmgraf.com/images/abstr/reinigen_animated.gif
Video
IUI :
IUI should not be painful, and most women don't experience much discomfort. The procedure takes about five to 10 minutes at the clinic, and does not require anesthesia or painkillers. That being said, it's not unusual to experience cramping or slight bleeding during or after the procedure
Source :
Is Intrauterine Insemination (IUI) Painful?
http://www.giftivf.com/imageuploads/pages/2019/01/29/iui.png
IUD :
Gynecologists insert a T-shaped device into the woman’s uterus (womb). This process is quick and not very painful. However, some
pain is inevitable, and
pain experience is different for every woman. It is normal to feel some discomfort when the opening of the womb (cervix) is stretched. For most women, this only lasts for a few seconds and may be felt as a sharp pain. The pain level during the insertion of an
intrauterine device (
IUD) is between 2/10 and 4/10 on the pain scale.
Source :
Is It Painful to Have an IUD Inserted?
Hysteroscopy
This seems to vary considerably between women. Some women feel no or only mild pain during a hysteroscopy, but for others the pain can be severe. If you find it too uncomfortable, tell the doctor or nurse. They can stop the procedure at any time.
It may not be necessary to use anaesthetic for the procedure, although
local anaesthetic (where medication is used to numb your cervix) is sometimes used.
General anaesthetic may be used if you're having treatment during the procedure or you would prefer to be asleep while it's carried out.
A hysteroscopy can take up to 30 minutes in total, although it may only last around 5 to 10 minutes if it's just being done to diagnose a condition or investigate symptoms.
Source :
Is a hysteroscopy painful?
Cervical dilators
This is most extreme insertion case I've encountered during my research.
Osmotic dilators are medical implements used to dilate the uterine
cervix by swelling as they absorb fluid from surrounding tissue.
Osmotic dilators may also be used to achieve cervical dilation prior to gynecology procedures, such as
hysteroscopy or
dilation and curettage of the non-pregnant uterus,
[8] although this is uncommon.
Over time, the osmotic dilator absorbs fluid and swells to 3-4 times the initial diameter.
[9] Most of the increase in size occurs within 6 hours after the dilator are placed in the cervix, though further expansion will continue over 12–24 hours.
Many women experience moderate to severe discomfort with osmotic dilator insertion. Providers use various methods to minimize this discomfort including paracervical block (PCB), non-steroidal anti-inflammatory medications (NSAIDs), anxiolytics and narcotics.
Osmotic dilators prior to expansion. Dilapan-S (left). Laminaria (right)
Osmotic dilators after soaking in water for 24 hours.
Dilapan-S (left). Laminaria (right).
This does not represent the amount of expansion that
will be occur when used in humans.
Other type of cervical dilator :
Coelution :
Based on precedent article, cervical penetration not only easily feasible, but also almost painless ( except for the cervix dilator, which has moderate to severe discomfort).
Beside of this research, there are women here that have sex with boar and confirm that boar's glans penis penetrated their cervix.
Also there is a guide which indicate cervical penetration is inevitable during sex with boars.
Guide To Woman And Boar Sex
Thanks for reading. I hope this has clarified this issue in some way.
Can't wait to hear your comments.